notes

unixtoolbox.xhtml (160332B)

---

    Unix Toolbox
 
    This document is a collection of Unix/Linux/BSD commands and tasks which
    are useful for IT work or for advanced users. This is a practical guide
    with concise explanations, however the reader is supposed to know what
    s/he is doing.
 
    Unix Toolbox revision 14.5
    The latest version of this document can be found at
    http://cb.vu/unixtoolbox.xhtml. Replace .xhtml on the link with .pdf for
    the PDF version and with .book.pdf for the booklet version. On a duplex
    printer the booklet will create a small book ready to bind. This XHTML
    page can be converted into a nice PDF document with a CSS3 compliant
    application (see the script example). See also the about page.
    Error reports and comments are most welcome - c@cb.vu Colin Barschel.
 
    © Colin Barschel 2007-2016. Some rights reserved under Creative Commons.
 
     1. System
     2. Processes
     3. File System
     4. Network
     5. SSH SCP
     6. VPN with SSH
     7. RSYNC
     8. SUDO
     9. Encrypt Files
    10. Encrypt Partitions
    11. SSL Certificates
    12. CVS
    13. SVN
    14. Useful Commands
    15. Install Software
    16. Convert Media
    17. Printing
    18. Databases
    19. Disk Quota
    20. Shells
    21. Scripting
    22. Programming
    23. Online Help
 
    white black
 
 System
 
    Hardware | Statistics | Users | Limits | Runlevels | root password |
    Compile kernel | Repair grub | Misc
    Running kernel and system information
 # uname -a                           # Get the kernel version (and BSD version)
 # lsb_release -a                     # Full release info of any LSB distribution
 # cat /etc/SuSE-release              # Get SuSE version
 # cat /etc/debian_version            # Get Debian version
 
    Use /etc/DISTR-release with DISTR= lsb (Ubuntu), redhat, gentoo,
    mandrake, sun (Solaris), and so on. See also /etc/issue.
 # uptime                             # Show how long the system has been running
 + load
 # hostname                           # system's host name
 # hostname -i                        # Display the IP address of the host. (Linux
  only)
 # man hier                           # Description of the file system hierarchy
 # last reboot                        # Show system reboot history
 
 Hardware Informations
 
    Kernel detected hardware
 # dmesg                              # Detected hardware and boot messages
 # lsdev                              # information about installed hardware
 # dd if=/dev/mem bs=1k skip=768 count=256 2>/dev/null | strings -n 8 # Read BIOS
 
 Linux
 
 # cat /proc/cpuinfo                  # CPU model
 # cat /proc/meminfo                  # Hardware memory
 # grep MemTotal /proc/meminfo        # Display the physical memory
 # watch -n1 'cat /proc/interrupts'   # Watch changeable interrupts continuously
 # free -m                            # Used and free memory (-m for MB)
 # cat /proc/devices                  # Configured devices
 # lspci -tv                          # Show PCI devices
 # lsusb -tv                          # Show USB devices
 # lshal                              # Show a list of all devices with their prop
 erties
 # dmidecode                          # Show DMI/SMBIOS: hw info from the BIOS
 
 FreeBSD
 
 # sysctl hw.model                    # CPU model
 # sysctl hw                          # Gives a lot of hardware information
 # sysctl hw.ncpu                     # number of active CPUs installed
 # sysctl vm                          # Memory usage
 # sysctl hw.realmem                  # Hardware memory
 # sysctl -a | grep mem               # Kernel memory settings and info
 # sysctl dev                         # Configured devices
 # pciconf -l -cv                     # Show PCI devices
 # usbdevs -v                         # Show USB devices
 # atacontrol list                    # Show ATA devices
 # camcontrol devlist -v              # Show SCSI devices
 
 Load, statistics and messages
 
    The following commands are useful to find out what is going on on the
    system.
 # top                                # display and update the top cpu processes
 # mpstat 1                           # display processors related statistics
 # vmstat 2                           # display virtual memory statistics
 # iostat 2                           # display I/O statistics (2 s intervals)
 # systat -vmstat 1                   # BSD summary of system statistics (1 s inte
 rvals)
 # systat -tcp 1                      # BSD tcp connections (try also -ip)
 # systat -netstat 1                  # BSD active network connections
 # systat -ifstat 1                   # BSD network traffic through active interfa
 ces
 # systat -iostat 1                   # BSD CPU and and disk throughput
 # ipcs -a                            # information on System V interprocess
 # tail -n 500 /var/log/messages      # Last 500 kernel/syslog messages
 # tail /var/log/warn                 # System warnings messages see syslog.conf
 
 Users
 
 # id                                 # Show the active user id with login and gro
 up
 # last                               # Show last logins on the system
 # who                                # Show who is logged on the system
 # groupadd admin                     # Add group "admin" and user colin (Linux/So
 laris)
 # useradd -c "Colin Barschel" -g admin -m colin
 # usermod -a -G <group> <user>       # Add existing user to group (Debian)
 # groupmod -A <user> <group>         # Add existing user to group (SuSE)
 # userdel colin                      # Delete user colin (Linux/Solaris)
 # adduser joe                        # FreeBSD add user joe (interactive)
 # rmuser joe                         # FreeBSD delete user joe (interactive)
 # pw groupadd admin                  # Use pw on FreeBSD
 # pw groupmod admin -m newmember     # Add a new member to a group
 # pw useradd colin -c "Colin Barschel" -g admin -m -s /bin/tcsh
 # pw userdel colin; pw groupdel admin
 
    Encrypted passwords are stored in /etc/shadow for Linux and Solaris and
    /etc/master.passwd on FreeBSD. If the master.passwd is modified manually
    (say to delete a password), run # pwd_mkdb -p master.passwd to rebuild
    the database.
    To temporarily prevent logins system wide (for all users but root) use
    nologin. The message in nologin will be displayed (might not work with
    ssh pre-shared keys).
 # echo "Sorry no login now" > /etc/nologin       # (Linux)
 # echo "Sorry no login now" > /var/run/nologin   # (FreeBSD)
 
 Limits
 
    Some application require higher limits on open files and sockets (like a
    proxy web server, database). The default limits are usually too low.
 
 Linux
 
 Per shell/script
 
    The shell limits are governed by ulimit. The status is checked with
    ulimit -a. For example to change the open files limit from 1024 to 10240
    do:
 # ulimit -n 10240                    # This is only valid within the shell
 
    The ulimit command can be used in a script to change the limits for the
    script only.
 
 Per user/process
 
    Login users and applications can be configured in
    /etc/security/limits.conf. For example:
 # cat /etc/security/limits.conf
 *   hard    nproc   250              # Limit user processes
 asterisk hard nofile 409600          # Limit application open files
 
 System wide
 
    Kernel limits are set with sysctl. Permanent limits are set in
    /etc/sysctl.conf.
 # sysctl -a                          # View all system limits
 # sysctl fs.file-max                 # View max open files limit
 # sysctl fs.file-max=102400          # Change max open files limit
 # echo "1024 50000" > /proc/sys/net/ipv4/ip_local_port_range  # port range
 # cat /etc/sysctl.conf
 fs.file-max=102400                   # Permanent entry in sysctl.conf
 # cat /proc/sys/fs/file-nr           # How many file descriptors are in use
 
 FreeBSD
 
 Per shell/script
 
    Use the command limits in csh or tcsh or as in Linux, use ulimit in an
    sh or bash shell.
 
 Per user/process
 
    The default limits on login are set in /etc/login.conf. An unlimited
    value is still limited by the system maximal value.
 
 System wide
 
    Kernel limits are also set with sysctl. Permanent limits are set in
    /etc/sysctl.conf or /boot/loader.conf. The syntax is the same as Linux
    but the keys are different.
 # sysctl -a                          # View all system limits
 # sysctl kern.maxfiles=XXXX          # maximum number of file descriptors
 kern.ipc.nmbclusters=32768           # Permanent entry in /etc/sysctl.conf
 kern.maxfiles=65536                  # Typical values for Squid
 kern.maxfilesperproc=32768
 kern.ipc.somaxconn=8192              # TCP queue. Better for apache/sendmail
 # sysctl kern.openfiles              # How many file descriptors are in use
 # sysctl kern.ipc.numopensockets     # How many open sockets are in use
 # sysctl net.inet.ip.portrange.last=50000 # Default is 1024-5000
 # netstat -m                         # network memory buffers statistics
 
    See The FreeBSD handbook Chapter
    11http://www.freebsd.org/handbook/configtuning-kernel-limits.html for
    details. And also FreeBSD performance
    tuninghttp://serverfault.com/questions/64356/freebsd-performance-tuning-
    sysctls-loader-conf-kernel
 
 Solaris
 
    The following values in /etc/system will increase the maximum file
    descriptors per proc:
 set rlim_fd_max = 4096               # Hard limit on file descriptors for a singl
 e proc
 set rlim_fd_cur = 1024               # Soft limit on file descriptors for a singl
 e proc
 
 Runlevels
 
 Linux
 
    Once booted, the kernel starts init which then starts rc which starts
    all scripts belonging to a runlevel. The scripts are stored in
    /etc/init.d and are linked into /etc/rc.d/rcN.d with N the runlevel
    number.
    The default runlevel is configured in /etc/inittab. It is usually 3 or
    5:
 # grep default: /etc/inittab
 id:3:initdefault:
 
    The actual runlevel can be changed with init. For example to go from 3
    to 5:
 # init 5                             # Enters runlevel 5
      * 0       Shutdown and halt
      * 1       Single-User mode (also S)
      * 2       Multi-user without network
      * 3       Multi-user with network
      * 5       Multi-user with X
      * 6       Reboot
 
    Use chkconfig to configure the programs that will be started at boot in
    a runlevel.
 # chkconfig --list                   # List all init scripts
 # chkconfig --list sshd              # Report the status of sshd
 # chkconfig sshd --level 35 on       # Configure sshd for levels 3 and 5
 # chkconfig sshd off                 # Disable sshd for all runlevels
 
    Debian and Debian based distributions like Ubuntu or Knoppix use the
    command update-rc.d to manage the runlevels scripts. Default is to start
    in 2,3,4 and 5 and shutdown in 0,1 and 6.
 # update-rc.d sshd defaults          # Activate sshd with the default runlevels
 # update-rc.d sshd start 20 2 3 4 5 . stop 20 0 1 6 .  # With explicit arguments
 # update-rc.d -f sshd remove         # Disable sshd for all runlevels
 # shutdown -h now (or # poweroff)    # Shutdown and halt the system
 
 FreeBSD
 
    The BSD boot approach is different from the SysV, there are no
    runlevels. The final boot state (single user, with or without X) is
    configured in /etc/ttys. All OS scripts are located in /etc/rc.d/ and in
    /usr/local/etc/rc.d/ for third-party applications. The activation of the
    service is configured in /etc/rc.conf and /etc/rc.conf.local. The
    default behavior is configured in /etc/defaults/rc.conf. The scripts
    responds at least to start|stop|status.
 # /etc/rc.d/sshd status
 sshd is running as pid 552.
 # shutdown now                       # Go into single-user mode
 # exit                               # Go back to multi-user mode
 # shutdown -p now                    # Shutdown and halt the system
 # shutdown -r now                    # Reboot
 
    The process init can also be used to reach one of the following states
    level. For example # init 6 for reboot.
      * 0       Halt and turn the power off (signal USR2)
      * 1       Go to single-user mode (signal TERM)
      * 6       Reboot the machine (signal INT)
      * c       Block further logins (signal TSTP)
      * q       Rescan the ttys(5) file (signal HUP)
 
 Windows
 
    Start and stop a service with either the service name or "service
    description" (shown in the Services Control Panel) as follows:
 net stop WSearch
 net start WSearch                    # start search service
 net stop "Windows Search"
 net start "Windows Search"           # same as above using descr.
 
 Reset root password
 
 Linux method 1
 
    At the boot loader (lilo or grub), enter the following boot option:
 init=/bin/sh
 
    The kernel will mount the root partition and init will start the bourne
    shell instead of rc and then a runlevel. Use the command passwd at the
    prompt to change the password and then reboot. Forget the single user
    mode as you need the password for that.
    If, after booting, the root partition is mounted read only, remount it
    rw:
 # mount -o remount,rw /
 # passwd                             # or delete the root password (/etc/shadow)
 # sync; mount -o remount,ro /        # sync before to remount read only
 # reboot
 
 FreeBSD method 1
 
    On FreeBSD, boot in single user mode, remount / rw and use passwd. You
    can select the single user mode on the boot menu (option 4) which is
    displayed for 10 seconds at startup. The single user mode will give you
    a root shell on the / partition.
 # mount -u /; mount -a               # will mount / rw
 # passwd
 # reboot
 
 Unixes and FreeBSD and Linux method 2
 
    Other Unixes might not let you go away with the simple init trick. The
    solution is to mount the root partition from an other OS (like a rescue
    CD) and change the password on the disk.
      * Boot a live CD or installation CD into a rescue mode which will give
        you a shell.
      * Find the root partition with fdisk e.g. fdisk /dev/sda
      * Mount it and use chroot:
 
 # mount -o rw /dev/ad4s3a /mnt
 # chroot /mnt                        # chroot into /mnt
 # passwd
 # reboot
 
 Kernel modules
 
 Linux
 
 # lsmod                              # List all modules loaded in the kernel
 # modprobe isdn                      # To load a module (here isdn)
 
 FreeBSD
 
 # kldstat                            # List all modules loaded in the kernel
 # kldload crypto                     # To load a module (here crypto)
 
 Compile Kernel
 
 Linux
 
 # cd /usr/src/linux
 # make mrproper                      # Clean everything, including config files
 # make oldconfig                     # Reuse the old .config if existent
 # make menuconfig                    # or xconfig (Qt) or gconfig (GTK)
 # make                               # Create a compressed kernel image
 # make modules                       # Compile the modules
 # make modules_install               # Install the modules
 # make install                       # Install the kernel
 # reboot
 
 FreeBSD
 
    Optionally update the source tree (in /usr/src) with csup (as of FreeBSD
    6.2 or later):
 # csup <supfile>
 
    I use the following supfile:
 *default host=cvsup5.FreeBSD.org  # www.freebsd.org/handbook/cvsup.html#CVSUP-MIR
 RORS
 *default prefix=/usr
 *default base=/var/db
 *default release=cvs delete tag=RELENG_7
 src-all
 
    To modify and rebuild the kernel, copy the generic configuration file to
    a new name and edit it as needed (you can also edit the file GENERIC
    directly). To restart the build after an interruption, add the option
    NO_CLEAN=YES to the make command to avoid cleaning the objects already
    build.
 # cd /usr/src/sys/i386/conf/
 # cp GENERIC MYKERNEL
 # cd /usr/src
 # make buildkernel KERNCONF=MYKERNEL
 # make installkernel KERNCONF=MYKERNEL
 
    To rebuild the full OS:
 # make buildworld                    # Build the full OS but not the kernel
 # make buildkernel                   # Use KERNCONF as above if appropriate
 # make installkernel
 # reboot
 # mergemaster -p                     # Compares only files known to be essential
 # make installworld
 # mergemaster -i -U                  # Update all configurations and other files
 # reboot
 
    For small changes in the source you can use NO_CLEAN=yes to avoid
    rebuilding the whole tree.
 # make buildworld NO_CLEAN=yes       # Don't delete the old objects
 # make buildkernel KERNCONF=MYKERNEL NO_CLEAN=yes
 
 Repair grub
 
    So you broke grub? Boot from a live cd, [find your linux partition under
    /dev and use fdisk to find the linux partion] mount the linux partition,
    add /proc and /dev and use grub-install /dev/xyz. Suppose linux lies on
    /dev/sda6:
 # mount /dev/sda6 /mnt               # mount the linux partition on /mnt
 # mount --bind /proc /mnt/proc       # mount the proc subsystem into /mnt
 # mount --bind /dev /mnt/dev         # mount the devices into /mnt
 # chroot /mnt                        # change root to the linux partition
 # grub-install /dev/sda              # reinstall grub with your old settings
 
 Misc
 
    Disable OSX virtual memory (repeat with load to re-enable). Faster
    system, but a little risky.
 # sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.dynamic_pager.
 plist
 # sleep 3600; pmset sleepnow           # go to standby in one hour (OSX)
 # defaults write -g com.apple.mouse.scaling -float 8
                                      # OSX mouse acceleration (use -1 to reverse)
 
 Processes
 
    Listing | Priority | Background/Foreground | Top | Kill
 
 Listing and PIDs
 
    Each process has a unique number, the PID. A list of all running process
    is retrieved with ps.
 # ps -auxefw                         # Extensive list of all running process
 
    However more typical usage is with a pipe or with pgrep (for OS X
    install proctools from MacPorts):
 # ps axww | grep cron
   586  ??  Is     0:01.48 /usr/sbin/cron -s
 # ps axjf                            # All processes in a tree format (Linux)
 # ps aux | grep 'ss[h]'              # Find all ssh pids without the grep pid
 # pgrep -l sshd                      # Find the PIDs of processes by (part of) na
 me
 # echo $$                            # The PID of your shell
 # fuser -va 22/tcp                   # List processes using port 22 (Linux)
 # pmap PID                           # Memory map of process (hunt memory leaks)
 (Linux)
 # fuser -va /home                    # List processes accessing the /home partiti
 on
 # strace df                          # Trace system calls and signals
 # truss df                           # same as above on FreeBSD/Solaris/Unixware
 
 Priority
 
    Change the priority of a running process with renice. Negative numbers
    have a higher priority, the lowest is -20 and "nice" have a positive
    value.
 # renice -5 586                      # Stronger priority
 586: old priority 0, new priority -5
 
    Start the process with a defined priority with nice. Positive is "nice"
    or weak, negative is strong scheduling priority. Make sure you know if
    /usr/bin/nice or the shell built-in is used (check with # which nice).
 # nice -n -5 top                     # Stronger priority (/usr/bin/nice)
 # nice -n 5 top                      # Weaker priority (/usr/bin/nice)
 # nice +5 top                        # tcsh builtin nice (same as above!)
 
    While nice changes the CPU scheduler, an other useful command ionice
    will schedule the disk IO. This is very useful for intensive IO
    application (e.g. compiling). You can select a class (idle - best effort
    - real time), the man page is short and well explained.
 # ionice c3 -p123                    # set idle class for pid 123 (Linux only)
 # ionice -c2 -n0 firefox             # Run firefox with best effort and high prio
 rity
 # ionice -c3 -p$$                    # Set the actual shell to idle priority
 
    The last command is very useful to compile (or debug) a large project.
    Every command launched from this shell will have a lover priority. $$ is
    your shell pid (try echo $$).
    FreeBSD uses idprio/rtprio (0 = max priority, 31 = most idle):
 # idprio 31 make                     # compile in the lowest priority
 # idprio 31 -1234                    # set PID 1234 with lowest priority
 # idprio -t -1234                    # -t removes any real time/idle priority
 
 Background/Foreground
 
    When started from a shell, processes can be brought in the background
    and back to the foreground with [Ctrl]-[Z] (^Z), bg and fg. List the
    processes with jobs. When needed detach from the terminal with disown.
 # ping cb.vu > ping.log
 ^Z                                   # ping is suspended (stopped) with [Ctrl]-[Z
 ]
 # bg                                 # put in background and continues running
 # jobs -l                            # List processes in background
 [1]  - 36232 Running                       ping cb.vu > ping.log
 [2]  + 36233 Suspended (tty output)        top
 # fg %2                              # Bring process 2 back in foreground
 
 # make                               # start a long compile job but need to leave
  the terminal
 ^Z                                   # suspended (stopped) with [Ctrl]-[Z]
 # bg                                 # put in background and continues running
 # disown -h %1                       # detatch process from terminal, won't be ki
 lled at logout
 
    No straight forward way to re-attach the process to a new terminal, try
    reptyr (Linux).
    Use nohup to start a process which has to keep running when the shell is
    closed (immune to hangups).
 # nohup ping -i 60 > ping.log &
 
 Top
 
    The program top displays running information of processes. See also the
    program htop from htop.sourceforge.net (a more powerful version of top)
    which runs on Linux and FreeBSD (ports/sysutils/htop/). While top is
    running press the key h for a help overview. Useful keys are:
      * u [user name] To display only the processes belonging to the user.
        Use + or blank to see all users
      * k [pid] Kill the process with pid.
      * 1 To display all processors statistics (Linux only)
      * R Toggle normal/reverse sort.
 
 Signals/Kill
 
    Terminate or send a signal with kill or killall.
 # ping -i 60 cb.vu > ping.log &
 [1] 4712
 # kill -s TERM 4712                  # same as kill -15 4712
 # killall -1 httpd                   # Kill HUP processes by exact name
 # pkill -9 http                      # Kill TERM processes by (part of) name
 # pkill -TERM -u www                 # Kill TERM processes owned by www
 # fuser -k -TERM -m /home            # Kill every process accessing /home (to umo
 unt)
 
    Important signals are:
      * 1       HUP (hang up)
      * 2       INT (interrupt)
      * 3       QUIT (quit)
      * 9       KILL (non-catchable, non-ignorable kill)
      * 15     TERM (software termination signal)
 
 File System
 
    Disk info | Boot | Disk usage | Opened files | Mount/remount | Mount SMB
    | Mount image | Burn ISO | Create image | Memory disk | Disk performance
 
 Permissions
 
    Change permission and ownership with chmod and chown. The default umask
    can be changed for all users in /etc/profile for Linux or
    /etc/login.conf for FreeBSD. The default umask is usually 022. The umask
    is subtracted from 777, thus umask 022 results in a permission 0f 755.
 1 --x execute                        # Mode 764 = exec/read/write | read/write |
 read
 2 -w- write                          # For:       |--  Owner  --|   |- Group-|
 |Oth|
 4 r-- read
   ugo=a                              u=user, g=group, o=others, a=everyone
 
 # chmod [OPTION] MODE[,MODE] FILE    # MODE is of the form [ugoa]*([-+=]([rwxXst]
 ))
 # chmod 640 /var/log/maillog         # Restrict the log -rw-r-----
 # chmod u=rw,g=r,o= /var/log/maillog # Same as above
 # chmod -R o-r /home/*               # Recursive remove other readable for all us
 ers
 # chmod u+s /path/to/prog            # Set SUID bit on executable (know what you
 do!)
 # find / -perm -u+s -print           # Find all programs with the SUID bit
 # chown user:group /path/to/file     # Change the user and group ownership of a f
 ile
 # chgrp group /path/to/file          # Change the group ownership of a file
 # chmod 640 `find ./ -type f -print` # Change permissions to 640 for all files
 # chmod 751 `find ./ -type d -print` # Change permissions to 751 for all director
 ies
 
 Disk information
 
 # diskinfo -v /dev/ad2               # information about disk (sector/size) FreeB
 SD
 # hdparm -I /dev/sda                 # information about the IDE/ATA disk (Linux)
 # fdisk /dev/ad2                     # Display and manipulate the partition table
 # smartctl -a /dev/ad2               # Display the disk SMART info
 
 Boot
 
 FreeBSD
 
    To boot an old kernel if the new kernel doesn't boot, stop the boot at
    during the count down.
 # unload
 # load kernel.old
 # boot
 
 System mount points/Disk usage
 
 # mount | column -t                  # Show mounted file-systems on the system
 # df                                 # display free disk space and mounted device
 s
 # cat /proc/partitions               # Show all registered partitions (Linux)
 
 Disk usage
 
 # du -sh *                           # Directory sizes as listing
 # du -csh                            # Total directory size of the current direct
 ory
 # du -ks * | sort -n -r              # Sort everything by size in kilobytes
 # ls -lSr                            # Show files, biggest last
 
 Who has which files opened
 
    This is useful to find out which file is blocking a partition which has
    to be unmounted and gives a typical error of:
 # umount /home/
 umount: unmount of /home             # umount impossible because a file is lockin
 g home
    failed: Device busy
 
 FreeBSD and most Unixes
 
 # fstat -f /home                     # for a mount point
 # fstat -p PID                       # for an application with PID
 # fstat -u user                      # for a user name
 
    Find opened log file (or other opened files), say for Xorg:
 # ps ax | grep Xorg | awk '{print $1}'
 1252
 # fstat -p 1252
 USER     CMD          PID   FD MOUNT      INUM MODE         SZ|DV R/W
 root     Xorg        1252 root /             2 drwxr-xr-x     512  r
 root     Xorg        1252 text /usr     216016 -rws--x--x  1679848 r
 root     Xorg        1252    0 /var     212042 -rw-r--r--   56987  w
 
    The file with inum 212042 is the only file in /var:
 # find -x /var -inum 212042
 /var/log/Xorg.0.log
 
 Linux
 
    Find opened files on a mount point with fuser or lsof:
 # fuser -m /home                     # List processes accessing /home
 # lsof /home
 COMMAND   PID    USER   FD   TYPE DEVICE    SIZE     NODE NAME
 tcsh    29029 eedcoba  cwd    DIR   0,18   12288  1048587 /home/eedcoba (guam:/ho
 me)
 lsof    29140 eedcoba  cwd    DIR   0,18   12288  1048587 /home/eedcoba (guam:/ho
 me)
 
    About an application:
 ps ax | grep Xorg | awk '{print $1}'
 3324
 # lsof -p 3324
 COMMAND   PID    USER   FD   TYPE DEVICE    SIZE    NODE NAME
 Xorg    3324 root    0w   REG        8,6   56296      12492 /var/log/Xorg.0.log
 
    About a single file:
 # lsof /var/log/Xorg.0.log
 COMMAND  PID USER   FD   TYPE DEVICE  SIZE  NODE NAME
 Xorg    3324 root    0w   REG    8,6 56296 12492 /var/log/Xorg.0.log
 
 Mount/remount a file system
 
    For example the cdrom. If listed in /etc/fstab:
 # mount /cdrom
 
    Or find the device in /dev/ or with dmesg
 
 FreeBSD
 
 # mount -v -t cd9660 /dev/cd0c /mnt  # cdrom
 # mount_cd9660 /dev/wcd0c /cdrom     # other method
 # mount -v -t msdos /dev/fd0c /mnt   # floppy
 
    Entry in /etc/fstab:
 # Device                Mountpoint      FStype  Options         Dump    Pass#
 /dev/acd0               /cdrom          cd9660  ro,noauto       0       0
 
    To let users do it:
 # sysctl vfs.usermount=1  # Or insert the line "vfs.usermount=1" in /etc/sysctl.c
 onf
 
 Linux
 
 # mount -t auto /dev/cdrom /mnt/cdrom   # typical cdrom mount command
 # mount /dev/hdc -t iso9660 -r /cdrom   # typical IDE
 # mount /dev/scd0 -t iso9660 -r /cdrom  # typical SCSI cdrom
 # mount /dev/sdc0 -t ntfs-3g /windows   # typical SCSI
 
    Entry in /etc/fstab:
 /dev/cdrom   /media/cdrom  subfs noauto,fs=cdfss,ro,procuid,nosuid,nodev,exec 0 0
 
 Mount a FreeBSD partition with Linux
 
    Find the partition number containing with fdisk, this is usually the
    root partition, but it could be an other BSD slice too. If the FreeBSD
    has many slices, they are the one not listed in the fdisk table, but
    visible in /dev/sda* or /dev/hda*.
 # fdisk /dev/sda                     # Find the FreeBSD partition
 /dev/sda3   *        5357        7905    20474842+  a5  FreeBSD
 # mount -t ufs -o ufstype=ufs2,ro /dev/sda3 /mnt
 /dev/sda10 = /tmp; /dev/sda11 /usr   # The other slices
 
 Remount
 
    Remount a device without unmounting it. Necessary for fsck for example
 # mount -o remount,ro /              # Linux
 # mount -o ro -u /                   # FreeBSD
 
    Copy the raw data from a cdrom into an iso image (default 512 blocksize
    might cause problems):
 # dd if=/dev/cd0c of=file.iso bs=2048
 
 Virtualbox
 
    Allow a share on the host:
 # VBoxManage sharedfolder add "GuestName" --name "share" --hostpath "C:\hostshare
 "
 
    Mount share on guest (linux, FreeBSD)
 # sudo mount -t vboxsf share /home/vboxshare # -o uid=1000,gid=1000 (as appropria
 te)
 share /home/colin/share vboxsf defaults,uid=colin 0 0 # fstab entry
 
 OSX
 
 # diskutil list                      # List the partitions of a disk
 # diskutil unmountDisk /dev/disk1    # Unmount an entire disk (all volumes)
 # chflags hidden ~/Documents/folder  # Hide folder (reverse with unhidden)
 
 Add swap on-the-fly
 
    Suppose you need more swap (right now), say a 2GB file /swap2gb (Linux
    only).
 # dd if=/dev/zero of=/swap2gb bs=1024k count=2000
 # mkswap /swap2gb                    # create the swap area
 # swapon /swap2gb                    # activate the swap. It now in use
 # swapoff /swap2gb                   # when done deactivate the swap
 # rm /swap2gb
 
 Mount an SMB share
 
    Suppose we want to access the SMB share myshare on the computer
    smbserver, the address as typed on a Windows PC is \\smbserver\myshare\.
    We mount on /mnt/smbshare. Warning> cifs wants an IP or DNS name, not a
    Windows name.
 
 Linux/OSX
 
 # smbclient -U user -I 192.168.16.229 -L //smbshare/    # List the shares
 # mount -t smbfs -o username=winuser //smbserver/myshare /mnt/smbshare
 # mount -t cifs -o username=winuser,password=winpwd //192.168.16.229/myshare /mnt
 /share
 
    Mount Samba share through ssh tunnel
 # ssh -C -f -N -p 20022 -L 445:127.0.0.1:445 me@server  # connect on 20022, tunne
 l 445
 # mount -t smbfs //colin@localhost/colin ~/mnt
 # mount_smbfs //colin:mypassword@127.0.0.1/private /Volumes/private # I use this
 on OSX + ssh
 
    Additionally with the package mount.cifs it is possible to store the
    credentials in a file, for example /home/user/.smb:
 username=winuser
 password=winpwd
 
    And mount as follow:
 # mount -t cifs -o credentials=/home/user/.smb //192.168.16.229/myshare /mnt/smbs
 hare
 
 FreeBSD
 
    Use -I to give the IP (or DNS name); smbserver is the Windows name.
 # smbutil view -I 192.168.16.229 //winuser@smbserver    # List the shares
 # mount_smbfs -I 192.168.16.229 //winuser@smbserver/myshare /mnt/smbshare
 
 Mount an image
 
 # hdiutil mount image.iso                               # OS X
 
 Linux loop-back
 
 # mount -t iso9660 -o loop file.iso /mnt                # Mount a CD image
 # mount -t ext3 -o loop file.img /mnt                   # Mount an image with ext
 3 fs
 
 FreeBSD
 
    With memory device (do # kldload md.ko if necessary):
 # mdconfig -a -t vnode -f file.iso -u 0
 # mount -t cd9660 /dev/md0 /mnt
 # umount /mnt; mdconfig -d -u 0                         # Cleanup the md device
 
    Or with virtual node:
 # vnconfig /dev/vn0c file.iso; mount -t cd9660 /dev/vn0c /mnt
 # umount /mnt; vnconfig -u /dev/vn0c                    # Cleanup the vn device
 
 Solaris and FreeBSD
 
    with loop-back file interface or lofi:
 # lofiadm -a file.iso
 # mount -F hsfs -o ro /dev/lofi/1 /mnt
 # umount /mnt; lofiadm -d /dev/lofi/1                   # Cleanup the lofi device
 
 Create and burn an ISO image
 
    This will copy the cd or DVD sector for sector. Without conv=notrunc,
    the image will be smaller if there is less content on the cd. See below
    and the dd examples.
 # dd if=/dev/hdc of=/tmp/mycd.iso bs=2048 conv=notrunc
 
    Use mkisofs to create a CD/DVD image from files in a directory. To
    overcome the file names restrictions: -r enables the Rock Ridge
    extensions common to UNIX systems, -J enables Joliet extensions used by
    Microsoft systems. -L allows ISO9660 filenames to begin with a period.
 # mkisofs -J -L -r -V TITLE -o imagefile.iso /path/to/dir
 # hdiutil makehybrid -iso -joliet -o dir.iso dir/       # OS X
 
    On FreeBSD, mkisofs is found in the ports in sysutils/cdrtools.
 
 Burn a CD/DVD ISO image
 
 FreeBSD
 
    FreeBSD does not enable DMA on ATAPI drives by default. DMA is enabled
    with the sysctl command and the arguments below, or with
    /boot/loader.conf with the following entries:
 hw.ata.ata_dma="1"
 hw.ata.atapi_dma="1"
 
    Use burncd with an ATAPI device (burncd is part of the base system) and
    cdrecord (in sysutils/cdrtools) with a SCSI drive.
 # burncd -f /dev/acd0 data imagefile.iso fixate      # For ATAPI drive
 # cdrecord -scanbus                  # To find the burner device (like 1,0,0)
 # cdrecord dev=1,0,0 imagefile.iso
 
 Linux
 
    Also use cdrecord with Linux as described above. Additionally it is
    possible to use the native ATAPI interface which is found with:
 # cdrecord dev=ATAPI -scanbus
 
    And burn the CD/DVD as above.
 
 dvd+rw-tools
 
    The dvd+rw-tools package (FreeBSD: ports/sysutils/dvd+rw-tools) can do
    it all and includes growisofs to burn CDs or DVDs. The examples refer to
    the dvd device as /dev/dvd which could be a symlink to /dev/scd0
    (typical scsi on Linux) or /dev/cd0 (typical FreeBSD) or /dev/rcd0c
    (typical NetBSD/OpenBSD character SCSI) or /dev/rdsk/c0t1d0s2 (Solaris
    example of a character SCSI/ATAPI CD-ROM device). There is a nice
    documentation with examples on the FreeBSD handbook chapter
    18.7http://www.freebsd.org/handbook/creating-dvds.html.
                        # -dvd-compat closes the disk
 # growisofs -dvd-compat -Z /dev/dvd=imagefile.iso     # Burn existing iso image
 # growisofs -dvd-compat -Z /dev/dvd -J -R /p/to/data  # Burn directly
 
 Convert a Nero .nrg file to .iso
 
    Nero simply adds a 300Kb header to a normal iso image. This can be
    trimmed with dd.
 # dd bs=1k if=imagefile.nrg of=imagefile.iso skip=300
 
 Convert a bin/cue image to .iso
 
    The little bchunk programhttp://freshmeat.net/projects/bchunk/ can do
    this. It is in the FreeBSD ports in sysutils/bchunk.
 # bchunk imagefile.bin imagefile.cue imagefile.iso
 
 Create a file based image
 
    For example a partition of 1GB using the file /usr/vdisk.img. Here we
    use the vnode 0, but it could also be 1.
 
 FreeBSD
 
 # dd if=/dev/random of=/usr/vdisk.img bs=1K count=1M
 # mdconfig -a -t vnode -f /usr/vdisk.img -u 0         # Creates device /dev/md1
 # bsdlabel -w /dev/md0
 # newfs /dev/md0c
 # mount /dev/md0c /mnt
 # umount /mnt; mdconfig -d -u 0; rm /usr/vdisk.img    # Cleanup the md device
 
    The file based image can be automatically mounted during boot with an
    entry in /etc/rc.conf and /etc/fstab. Test your setup with #
    /etc/rc.d/mdconfig start (first delete the md0 device with # mdconfig -d
    -u 0).
    Note however that this automatic setup will only work if the file image
    is NOT on the root partition. The reason is that the /etc/rc.d/mdconfig
    script is executed very early during boot and the root partition is
    still read-only. Images located outside the root partition will be
    mounted later with the script /etc/rc.d/mdconfig2.
    /boot/loader.conf:
 md_load="YES"
 
    /etc/rc.conf:
 # mdconfig_md0="-t vnode -f /usr/vdisk.img"          # /usr is not on the root pa
 rtition
 
    /etc/fstab: (The 0 0 at the end is important, it tell fsck to ignore
    this device, as is does not exist yet)
 /dev/md0                /usr/vdisk      ufs     rw              0       0
 
    It is also possible to increase the size of the image afterward, say for
    example 300 MB larger.
 # umount /mnt; mdconfig -d -u 0
 # dd if=/dev/zero bs=1m count=300 >> /usr/vdisk.img
 # mdconfig -a -t vnode -f /usr/vdisk.img -u 0
 # growfs /dev/md0
 # mount /dev/md0c /mnt                                # File partition is now 300
  MB larger
 
 Linux
 
 # dd if=/dev/zero of=/usr/vdisk.img bs=1024k count=1024
 # mkfs.ext3 /usr/vdisk.img
 # mount -o loop /usr/vdisk.img /mnt
 # umount /mnt; rm /usr/vdisk.img                      # Cleanup
 
 Linux with losetup
 
    /dev/zero is much faster than urandom, but less secure for encryption.
 # dd if=/dev/urandom of=/usr/vdisk.img bs=1024k count=1024
 # losetup /dev/loop0 /usr/vdisk.img                   # Creates and associates /d
 ev/loop0
 # mkfs.ext3 /dev/loop0
 # mount /dev/loop0 /mnt
 # losetup -a                                          # Check used loops
 # umount /mnt
 # losetup -d /dev/loop0                               # Detach
 # rm /usr/vdisk.img
 
 Create a memory file system
 
    A memory based file system is very fast for heavy IO application. How to
    create a 64 MB partition mounted on /memdisk:
 
 FreeBSD
 
 # mount_mfs -o rw -s 64M md /memdisk
 # umount /memdisk; mdconfig -d -u 0                   # Cleanup the md device
 md     /memdisk     mfs     rw,-s64M    0   0         # /etc/fstab entry
 
 Linux
 
 # mount -t tmpfs -osize=64m tmpfs /memdisk
 
 Disk performance
 
    Read and write a 1 GB file on partition ad4s3c (/home)
 # time dd if=/dev/ad4s3c of=/dev/null bs=1024k count=1000
 # time dd if=/dev/zero bs=1024k count=1000 of=/home/1Gb.file
 # hdparm -tT /dev/hda      # Linux only
 
 Network
 
    Routing | Additional IP | Change MAC | Ports | Firewall | IP Forward |
    NAT | DNS | DHCP | Traffic | QoS | NIS | Netcat
 
 Debugging (See also Traffic analysis)
 
 Linux
 
 # ethtool eth0              # Show the ethernet status (replaces mii-diag)
 # ethtool -s eth0 speed 100 duplex full # Force 100Mbit Full duplex
 # ethtool -s eth0 autoneg off # Disable auto negotiation
 # ethtool -p eth1           # Blink the ethernet led - very useful when supported
 # ip link show              # Display all interfaces on Linux (similar to ifconfi
 g)
 # ip link set eth0 up       # Bring device up (or down). Same as "ifconfig eth0 u
 p"
 # ip addr show              # Display all IP addresses on Linux (similar to ifcon
 fig)
 # ip neigh show             # Similar to arp -a
 
 Other OSes
 
 # ifconfig fxp0             # Check the "media" field on FreeBSD
 # arp -a                    # Check the router (or host) ARP entry (all OS)
 # ping cb.vu                # The first thing to try...
 # traceroute cb.vu          # Print the route path to destination
 # ifconfig fxp0 media 100baseTX mediaopt full-duplex # 100Mbit full duplex (FreeB
 SD)
 # netstat -s                # System-wide statistics for each network protocol
 
    Additional commands which are not always installed per default but easy
    to find:
 # arping 192.168.16.254     # Ping on ethernet layer
 # tcptraceroute -f 5 cb.vu  # uses tcp instead of icmp to trace through firewalls
 
 Routing
 
 Print routing table
 
 # route -n                  # Linux or use "ip route"
 # netstat -rn               # Linux, BSD and UNIX
 # route print               # Windows
 
 Add and delete a route
 
 FreeBSD
 
 # route add 212.117.0.0/16 192.168.1.1
 # route delete 212.117.0.0/16
 # route add default 192.168.1.1
 
    Add the route permanently in /etc/rc.conf
 static_routes="myroute"
 route_myroute="-net 212.117.0.0/16 192.168.1.1"
 
 OS X
 
 # sudo route -n add 192.168.0.0/27 192.168.0.62         # add a route
 # netstat -nr                                           # routing table
 
 Linux
 
 # route add -net 192.168.20.0 netmask 255.255.255.0 gw 192.168.16.254
 # ip route add 192.168.20.0/24 via 192.168.16.254       # same as above with ip r
 oute
 # route add -net 192.168.20.0 netmask 255.255.255.0 dev eth0
 # route add default gw 192.168.51.254
 # ip route add default via 192.168.51.254 dev eth0      # same as above with ip r
 oute
 # route delete -net 192.168.20.0 netmask 255.255.255.0
 
 Solaris
 
 # route add -net 192.168.20.0 -netmask 255.255.255.0 192.168.16.254
 # route add default 192.168.51.254 1                    # 1 = hops to the next ga
 teway
 # route change default 192.168.50.254 1
 
    Permanent entries are set in entry in /etc/defaultrouter.
 
 Windows
 
 # Route add 192.168.50.0 mask 255.255.255.0 192.168.51.253
 # Route add 0.0.0.0 mask 0.0.0.0 192.168.51.254
 
    Use add -p to make the route persistent.
 
 Configure additional IP addresses
 
 Linux
 
 # ifconfig eth0 192.168.50.254 netmask 255.255.255.0       # First IP
 # ifconfig eth0:0 192.168.51.254 netmask 255.255.255.0     # Second IP
 # ip addr add 192.168.50.254/24 dev eth0                   # Equivalent ip comman
 ds
 # ip link set dev eth0 up                                  # Activate eth0 networ
 k interface
 # ip addr add 192.168.51.254/24 dev eth0 label eth0:1
 # ip link ls dev eth0                                      # Get info on eth0
 # ip addr del 1.2.3.4/32 dev eth0                          # Remove an IP
 # ip addr flush dev eth0                                   # Remove all addresses
 
 FreeBSD
 
 # ifconfig fxp0 inet 192.168.50.254/24                     # First IP
 # ifconfig fxp0 alias 192.168.51.254 netmask 255.255.255.0 # Second IP
 # ifconfig fxp0 -alias 192.168.51.254                      # Remove second IP ali
 as
 
    Permanent entries in /etc/rc.conf
 ifconfig_fxp0="inet 192.168.50.254  netmask 255.255.255.0"
 ifconfig_fxp0_alias0="192.168.51.254 netmask 255.255.255.0"
 
 OS X
 
 # sudo ifconfig en3 10.10.10.201/24                        # First IP
 # ifconfig en3 delete 10.10.10.201                         # Delete IP
 # sudo ifconfig en1 down ; sudo ifconfig en1 up
 # ipconfig getifaddr en1                                   # current IP address
 
 Solaris
 
    Check the settings with ifconfig -a
 # ifconfig hme0 plumb                                      # Enable the network c
 ard
 # ifconfig hme0 192.168.50.254 netmask 255.255.255.0 up    # First IP
 # ifconfig hme0:1 192.168.51.254 netmask 255.255.255.0 up  # Second IP
 
 Change MAC address
 
    Normally you have to bring the interface down before the change. Don't
    tell me why you want to change the MAC address...
 # ifconfig eth0 down
 # ifconfig eth0 hw ether 00:01:02:03:04:05      # Linux
 # ifconfig fxp0 link 00:01:02:03:04:05          # FreeBSD
 # ifconfig hme0 ether 00:01:02:03:04:05         # Solaris
 # sudo ifconfig en0 ether 00:01:02:03:04:05     # OS X Tiger, Snow Leopard LAN*
 # sudo ifconfig en0 lladdr 00:01:02:03:04:05    # OS X Leopard
 
    *Typical wireless interface is en1 and needs do disassociate from any
    network first (osxdaily howto).
 # echo "alias airport='/System/Library/PrivateFrameworks/Apple80211.framework/Ver
 sions/Current/Resources/airport'"\
 >> ~/.bash_profile         # or symlink to /usr/sbin
 # airport -z               # Disassociate from wireless networks
 # airport -I               # Get info from wireless network
 
    Many tools exist for Windows. For example
    etherchangehttp://ntsecurity.nu/toolbox/etherchange. Or look for "Mac
    Makeup", "smac".
 
 Ports in use
 
    Listening open ports:
 # netstat -an | grep LISTEN
 # lsof -i                  # Linux list all Internet connections
 # socklist                 # Linux display list of open sockets
 # sockstat -4              # FreeBSD application listing
 # netstat -anp --udp --tcp | grep LISTEN        # Linux
 # netstat -tup             # List active connections to/from system (Linux)
 # netstat -tupl            # List listening ports from system (Linux)
 # netstat -ano             # Windows
 
 Firewall
 
    Check if a firewall is running (typical configuration only):
 
 Linux
 
 # iptables -L -n -v                  # For status
 Open the iptables firewall
 # iptables -P INPUT       ACCEPT     # Open everything
 # iptables -P FORWARD     ACCEPT
 # iptables -P OUTPUT      ACCEPT
 # iptables -Z                        # Zero the packet and byte counters in all c
 hains
 # iptables -F                        # Flush all chains
 # iptables -X                        # Delete all chains
 
 FreeBSD
 
 # ipfw show                          # For status
 # ipfw list 65535 # if answer is "65535 deny ip from any to any" the fw is disabl
 ed
 # sysctl net.inet.ip.fw.enable=0     # Disable
 # sysctl net.inet.ip.fw.enable=1     # Enable
 
 IP Forward for routing
 
 Linux
 
    Check and then enable IP forward with:
 # cat /proc/sys/net/ipv4/ip_forward  # Check IP forward 0=off, 1=on
 # echo 1 > /proc/sys/net/ipv4/ip_forward
 
    or edit /etc/sysctl.conf with:
 net.ipv4.ip_forward = 1
 
 FreeBSD
 
    Check and enable with:
 # sysctl net.inet.ip.forwarding      # Check IP forward 0=off, 1=on
 # sysctl net.inet.ip.forwarding=1
 # sysctl net.inet.ip.fastforwarding=1   # For dedicated router or firewall
 Permanent with entry in /etc/rc.conf:
 gateway_enable="YES"                 # Set to YES if this host will be a gateway.
 
 Solaris
 
 # ndd -set /dev/ip ip_forwarding 1   # Set IP forward 0=off, 1=on
 
 NAT Network Address Translation
 
 Linux
 
 # iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE  # to activate NAT
 # iptables -t nat -A PREROUTING -p tcp -d 78.31.70.238 --dport 20022 -j DNAT \
 --to 192.168.16.44:22           # Port forward 20022 to internal IP port ssh
 # iptables -t nat -A PREROUTING -p tcp -d 78.31.70.238 --dport 993:995 -j DNAT \
 --to 192.168.16.254:993-995     # Port forward of range 993-995
 # ip route flush cache
 # iptables -L -t nat            # Check NAT status
 
    Delete the port forward with -D instead of -A. The program
    netstat-nathttp://tweegy.nl/projects/netstat-nat is very useful to track
    connections (it uses /proc/net/ip_conntrack or /proc/net/nf_conntrack).
 # netstat-nat -n                # show all connections with IPs
 
 FreeBSD
 
 # natd -s -m -u -dynamic -f /etc/natd.conf -n fxp0
 Or edit /etc/rc.conf with:
 firewall_enable="YES"           # Set to YES to enable firewall functionality
 firewall_type="open"            # Firewall type (see /etc/rc.firewall)
 natd_enable="YES"               # Enable natd (if firewall_enable == YES).
 natd_interface="tun0"           # Public interface or IP address to use.
 natd_flags="-s -m -u -dynamic -f /etc/natd.conf"
 
    Port forward with:
 # cat /etc/natd.conf
 same_ports yes
 use_sockets yes
 unregistered_only
 # redirect_port tcp insideIP:2300-2399 3300-3399  # port range
 redirect_port udp 192.168.51.103:7777 7777
 
 DNS
 
    On Unix the DNS entries are valid for all interfaces and are stored in
    /etc/resolv.conf. The domain to which the host belongs is also stored in
    this file. A minimal configuration is:
 nameserver 78.31.70.238
 search sleepyowl.net intern.lab
 domain sleepyowl.net
 
    Check the system domain name with:
 # hostname -d                        # Same as dnsdomainname
 
 Windows
 
    On Windows the DNS are configured per interface. To display the
    configured DNS and to flush the DNS cache use:
 # ipconfig /?                        # Display help
 # ipconfig /all                      # See all information including DNS
 
 Flush DNS
 
    Flush the OS DNS cache, some application using their own cache (e.g.
    Firefox) and will be unaffected.
 # /etc/init.d/nscd restart           # Restart nscd if used - Linux/BSD/Solaris
 # lookupd -flushcache                # OS X Tiger
 # dscacheutil -flushcache            # OS X Leopard and newer
 # ipconfig /flushdns                 # Windows
 
 Forward queries
 
    Dig is you friend to test the DNS settings. For example the public DNS
    server 213.133.105.2 ns.second-ns.de can be used for testing. See from
    which server the client receives the answer (simplified answer).
 # dig sleepyowl.net
 sleepyowl.net.          600     IN      A       78.31.70.238
 ;; SERVER: 192.168.51.254#53(192.168.51.254)
 
    The router 192.168.51.254 answered and the response is the A entry. Any
    entry can be queried and the DNS server can be selected with @:
 # dig MX google.com
 # dig @127.0.0.1 NS sun.com          # To test the local server
 # dig @204.97.212.10 NS MX heise.de  # Query an external server
 # dig AXFR @ns1.xname.org cb.vu      # Get the full zone (zone transfer)
 
    The program host is also powerful.
 # host -t MX cb.vu                   # Get the mail MX entry
 # host -t NS -T sun.com              # Get the NS record over a TCP connection
 # host -a sleepyowl.net              # Get everything
 
 Reverse queries
 
    Find the name belonging to an IP address (in-addr.arpa.). This can be
    done with dig, host and nslookup:
 # dig -x 78.31.70.238
 # host 78.31.70.238
 # nslookup 78.31.70.238
 
 /etc/hosts
 
    Single hosts can be configured in the file /etc/hosts instead of running
    named locally to resolve the hostname queries. The format is simple, for
    example:
 78.31.70.238   sleepyowl.net   sleepyowl
 
    The priority between hosts and a dns query, that is the name resolution
    order, can be configured in /etc/nsswitch.conf AND /etc/host.conf. The
    file also exists on Windows, it is usually in:
 C:\WINDOWS\SYSTEM32\DRIVERS\ETC
 
 DHCP
 
 Linux
 
    Some distributions (SuSE) use dhcpcd as client. The default interface is
    eth0.
 # dhcpcd -n eth0           # Trigger a renew (does not always work)
 # dhcpcd -k eth0           # release and shutdown
 
    The lease with the full information is stored in:
 /var/lib/dhcpcd/dhcpcd-eth0.info
 
 FreeBSD
 
    FreeBSD (and Debian) uses dhclient. To configure an interface (for
    example bge0) run:
 # dhclient bge0
 
    The lease with the full information is stored in:
 /var/db/dhclient.leases.bge0
 
    Use
 /etc/dhclient.conf
 
    to prepend options or force different options:
 # cat /etc/dhclient.conf
 interface "rl0" {
     prepend domain-name-servers 127.0.0.1;
     default domain-name "sleepyowl.net";
     supersede domain-name "sleepyowl.net";
 }
 
 Windows
 
    The dhcp lease can be renewed with ipconfig:
 # ipconfig /renew          # renew all adapters
 # ipconfig /renew LAN      # renew the adapter named "LAN"
 # ipconfig /release WLAN   # release the adapter named "WLAN"
 
    Yes it is a good idea to rename you adapter with simple names!
 
 Traffic analysis
 
    Bmonhttp://people.suug.ch/~tgr/bmon/ is a small console bandwidth
    monitor and can display the flow on different interfaces.
 
 Sniff with tcpdump
 
 # tcpdump -nl -i bge0 not port ssh and src \(192.168.16.121 or 192.168.16.54\)
 # tcpdump -n -i eth1 net 192.168.16.121           # select to/from a single IP
 # tcpdump -n -i eth1 net 192.168.16.0/24          # select traffic to/from a netw
 ork
 # tcpdump -l > dump && tail -f dump               # Buffered output
 # tcpdump -i rl0 -w traffic.rl0                   # Write traffic headers in bina
 ry file
 # tcpdump -i rl0 -s 0 -w traffic.rl0              # Write traffic + payload in bi
 nary file
 # tcpdump -r traffic.rl0                          # Read from file (also for ethe
 real
 # tcpdump port 80                                 # The two classic commands
 # tcpdump host google.com
 # tcpdump -i eth0 -X port \(110 or 143\)          # Check if pop or imap is secur
 e
 # tcpdump -n -i eth0 icmp                         # Only catch pings
 # tcpdump -i eth0 -s 0 -A port 80 | grep GET      # -s 0 for full packet -A for A
 SCII
 
    Additional important options:
      * -A     Print each packets in clear text (without header)
      * -X     Print packets in hex and ASCII
      * -l     Make stdout line buffered
      * -D     Print all interfaces available
 
    On Windows use windump from www.winpcap.org. Use windump -D to list the
    interfaces.
 
 Scan with nmap
 
    Nmaphttp://insecure.org/nmap/ is a port scanner with OS detection, it is
    usually installed on most distributions and is also available for
    Windows. If you don't scan your servers, hackers do it for you...
 # nmap cb.vu               # scans all reserved TCP ports on the host
 # nmap -sP 192.168.16.0/24 # Find out which IP are used and by which host on 0/24
 # nmap -sS -sV -O cb.vu    # Do a stealth SYN scan with version and OS detection
 PORT      STATE  SERVICE             VERSION
 22/tcp    open   ssh                 OpenSSH 3.8.1p1 FreeBSD-20060930 (protocol 2
 .0)
 25/tcp    open   smtp                Sendmail smtpd 8.13.6/8.13.6
 80/tcp    open   http                Apache httpd 2.0.59 ((FreeBSD) DAV/2 PHP/4.
 [...]
 Running: FreeBSD 5.X
 Uptime 33.120 days (since Fri Aug 31 11:41:04 2007)
 
    Other non standard but useful tools are hping (www.hping.org) an IP
    packet assembler/analyzer and fping (fping.sourceforge.net). fping can
    check multiple hosts in a round-robin fashion.
 
 Traffic control (QoS)
 
    Traffic control manages the queuing, policing, scheduling, and other
    traffic parameters for a network. The following examples are simple
    practical uses of the Linux and FreeBSD capabilities to better use the
    available bandwidth.
 
 Limit upload
 
    DSL or cable modems have a long queue to improve the upload throughput.
    However filling the queue with a fast device (e.g. ethernet) will
    dramatically decrease the interactivity. It is therefore useful to limit
    the device upload rate to match the physical capacity of the modem, this
    should greatly improve the interactivity. Set to about 90% of the modem
    maximal (cable) speed.
 
 Linux
 
    For a 512 Kbit upload modem.
 # tc qdisc add dev eth0 root tbf rate 480kbit latency 50ms burst 1540
 # tc -s qdisc ls dev eth0                         # Status
 # tc qdisc del dev eth0 root                      # Delete the queue
 # tc qdisc change dev eth0 root tbf rate 220kbit latency 50ms burst 1540
 
 FreeBSD
 
    FreeBSD uses the dummynet traffic shaper which is configured with ipfw.
    Pipes are used to set limits the bandwidth in units of
    [K|M]{bit/s|Byte/s}, 0 means unlimited bandwidth. Using the same pipe
    number will reconfigure it. For example limit the upload bandwidth to
    500 Kbit.
 # kldload dummynet                                # load the module if necessary
 # ipfw pipe 1 config bw 500Kbit/s                 # create a pipe with limited ba
 ndwidth
 # ipfw add pipe 1 ip from me to any               # divert the full upload into t
 he pipe
 
 Quality of service
 
 Linux
 
    Priority queuing with tc to optimize VoIP. See the full example on
    voip-info.org or www.howtoforge.com. Suppose VoIP uses udp on ports
    10000:11024 and device eth0 (could also be ppp0 or so). The following
    commands define the QoS to three queues and force the VoIP traffic to
    queue 1 with QoS 0x1e (all bits set). The default traffic flows into
    queue 3 and QoS Minimize-Delay flows into queue 2.
 # tc qdisc add dev eth0 root handle 1: prio priomap 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1
  0
 # tc qdisc add dev eth0 parent 1:1 handle 10: sfq
 # tc qdisc add dev eth0 parent 1:2 handle 20: sfq
 # tc qdisc add dev eth0 parent 1:3 handle 30: sfq
 # tc filter add dev eth0 protocol ip parent 1: prio 1 u32 \
   match ip dport 10000 0x3C00 flowid 1:1          # use server port range
   match ip dst 123.23.0.1 flowid 1:1              # or/and use server IP
 
    Status and remove with
 # tc -s qdisc ls dev eth0                         # queue status
 # tc qdisc del dev eth0 root                      # delete all QoS
 
 Calculate port range and mask
 
    The tc filter defines the port range with port and mask which you have
    to calculate. Find the 2^N ending of the port range, deduce the range
    and convert to HEX. This is your mask. Example for 10000 -> 11024, the
    range is 1024.
 # 2^13 (8192) < 10000 < 2^14 (16384)              # ending is 2^14 = 16384
 # echo "obase=16;(2^14)-1024" | bc                # mask is 0x3C00
 
 FreeBSD
 
    The max link bandwidth is 500Kbit/s and we define 3 queues with priority
    100:10:1 for VoIP:ssh:all the rest.
 # ipfw pipe 1 config bw 500Kbit/s
 # ipfw queue 1 config pipe 1 weight 100
 # ipfw queue 2 config pipe 1 weight 10
 # ipfw queue 3 config pipe 1 weight 1
 # ipfw add 10 queue 1 proto udp dst-port 10000-11024
 # ipfw add 11 queue 1 proto udp dst-ip 123.23.0.1 # or/and use server IP
 # ipfw add 20 queue 2 dsp-port ssh
 # ipfw add 30 queue 3 from me to any              # all the rest
 
    Status and remove with
 # ipfw list                                       # rules status
 # ipfw pipe list                                  # pipe status
 # ipfw flush                                      # deletes all rules but default
 
 NIS Debugging
 
    Some commands which should work on a well configured NIS client:
 # ypwhich                  # get the connected NIS server name
 # domainname               # The NIS domain name as configured
 # ypcat group              # should display the group from the NIS server
 # cd /var/yp && make       # Rebuild the yp database
 # rpcinfo -p servername    # Report RPC services of the server
 
    Is ypbind running?
 # ps auxww | grep ypbind
 /usr/sbin/ypbind -s -m -S servername1,servername2       # FreeBSD
 /usr/sbin/ypbind           # Linux
 # yppoll passwd.byname
 Map passwd.byname has order number 1190635041. Mon Sep 24 13:57:21 2007
 The master server is servername.domain.net.
 
 Linux
 
 # cat /etc/yp.conf
 ypserver servername
 domain domain.net broadcast
 
 Netcat
 
    Netcathttp://netcat.sourceforge.net (nc) is better known as the "network
    Swiss Army Knife", it can manipulate, create or read/write TCP/IP
    connections. Here some useful examples, there are many more on the net,
    for example
    g-loaded.eu[...]http://www.g-loaded.eu/2006/11/06/netcat-a-couple-of-use
    ful-examples and
    herehttp://www.terminally-incoherent.com/blog/2007/08/07/few-useful-netc
    at-tricks.
    You might need to use the command netcat instead of nc. Also see the
    similar command socat.
 
 File transfer
 
    Copy a large folder over a raw tcp connection. The transfer is very
    quick (no protocol overhead) and you don't need to mess up with NFS or
    SMB or FTP or so, simply make the file available on the server, and get
    it from the client. Here 192.168.1.1 is the server IP address.
 server# tar -cf - -C VIDEO_TS . | nc -l -p 4444         # Serve tar folder on por
 t 4444
 client# nc 192.168.1.1 4444 | tar xpf - -C VIDEO_TS     # Pull the file on port 4
 444
 server# cat largefile | nc -l 5678                      # Server a single file
 client# nc 192.168.1.1 5678 > largefile                 # Pull the single file
 server# dd if=/dev/da0 | nc -l 4444                     # Server partition image
 client# nc 192.168.1.1 4444 | dd of=/dev/da0            # Pull partition to clone
 client# nc 192.168.1.1 4444 | dd of=da0.img             # Pull partition to file
 
 Other hacks
 
    Specially here, you must know what you are doing.
 
 Remote shell
 
    Option -e only on the Windows version? Or use nc 1.10.
 # nc -lp 4444 -e /bin/bash                        # Provide a remote shell (serve
 r backdoor)
 # nc -lp 4444 -e cmd.exe                          # remote shell for Windows
 
 Emergency web server
 
    Serve a single file on port 80 in a loop.
 # while true; do nc -l -p 80 < unixtoolbox.xhtml; done
 
 Chat
 
    Alice and Bob can chat over a simple TCP socket. The text is transferred
    with the enter key.
 alice# nc -lp 4444
 bob  # nc 192.168.1.1 4444
 
 SSH SCP
 
    Public key | Fingerprint | SCP | Tunneling | SSHFS
    See other tricks 25 ssh cmdhttp://blog.urfix.com/25-ssh-commands-tricks/
 
 Public key authentication
 
    Connect to a host without password using public key authentication. The
    idea is to append your public key to the authorized_keys2 file on the
    remote host. For this example let's connect host-client to host-server,
    the key is generated on the client. With cygwin you might have to create
    your home directoy and the .ssh directory with # mkdir -p
    /home/USER/.ssh
      * Use ssh-keygen to generate a key pair. ~/.ssh/id_dsa is the private
        key, ~/.ssh/id_dsa.pub is the public key.
      * Copy only the public key to the server and append it to the file
        ~/.ssh/authorized_keys2 on your home on the server.
 
 # ssh-keygen -t dsa -N ''
 # cat ~/.ssh/id_dsa.pub | ssh you@host-server "cat - >> ~/.ssh/authorized_keys2"
 
 Using the Windows client from ssh.com
 
    The non commercial version of the ssh.com client can be downloaded the
    main ftp site: ftp.ssh.com/pub/ssh/. Keys generated by the ssh.com
    client need to be converted for the OpenSSH server. This can be done
    with the ssh-keygen command.
      * Create a key pair with the ssh.com client: Settings - User
        Authentication - Generate New....
      * I use Key type DSA; key length 2048.
      * Copy the public key generated by the ssh.com client to the server
        into the ~/.ssh folder.
      * The keys are in C:\Documents and Settings\%USERNAME%\Application
        Data\SSH\UserKeys.
      * Use the ssh-keygen command on the server to convert the key:
 # cd ~/.ssh
 # ssh-keygen -i -f keyfilename.pub >> authorized_keys2
 
    Notice: We used a DSA key, RSA is also possible. The key is not
    protected by a password.
 
 Using putty for Windows
 
    Puttyhttp://www.chiark.greenend.org.uk/~sgtatham/putty/download.html is
    a simple and free ssh client for Windows.
      * Create a key pair with the puTTYgen program.
      * Save the public and private keys (for example into C:\Documents and
        Settings\%USERNAME%\.ssh).
      * Copy the public key to the server into the ~/.ssh folder:
 # scp .ssh/puttykey.pub root@192.168.51.254:.ssh/
      * Use the ssh-keygen command on the server to convert the key for
        OpenSSH:
 # cd ~/.ssh
 # ssh-keygen -i -f puttykey.pub >> authorized_keys2
 
      * Point the private key location in the putty settings: Connection -
        SSH - Auth
 
 Check fingerprint
 
    At the first login, ssh will ask if the unknown host with the
    fingerprint has to be stored in the known hosts. To avoid a
    man-in-the-middle attack the administrator of the server can send you
    the server fingerprint which is then compared on the first login. Use
    ssh-keygen -l to get the fingerprint (on the server):
 # ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key.pub      # For RSA key
 2048 61:33:be:9b:ae:6c:36:31:fd:83:98:b7:99:2d:9f:cd /etc/ssh/ssh_host_rsa_key.pu
 b
 # ssh-keygen -l -f /etc/ssh/ssh_host_dsa_key.pub      # For DSA key (default)
 2048 14:4a:aa:d9:73:25:46:6d:0a:48:35:c7:f4:16:d4:ee /etc/ssh/ssh_host_dsa_key.pu
 b
 
    Now the client connecting to this server can verify that he is
    connecting to the right server:
 # ssh linda
 The authenticity of host 'linda (192.168.16.54)' can't be established.
 DSA key fingerprint is 14:4a:aa:d9:73:25:46:6d:0a:48:35:c7:f4:16:d4:ee.
 Are you sure you want to continue connecting (yes/no)? yes
 
 Secure file transfer
 
    Some simple commands:
 # scp file.txt host-two:/tmp
 # scp joe@host-two:/www/*.html /www/tmp
 # scp -r joe@host-two:/www /www/tmp
 # scp -P 20022 cb@cb.vu:unixtoolbox.xhtml .           # connect on port 20022
 
    In Konqueror or Midnight Commander it is possible to access a remote
    file system with the address fish://user@gate. However the
    implementation is very slow.
    Furthermore it is possible to mount a remote folder with sshfs a file
    system client based on SCP. See fuse
    sshfshttp://fuse.sourceforge.net/sshfs.html.
 ssh_exchange_identification: Connection closed by remote host
 
    With this error try the following on the server:
 echo 'SSHD: ALL' >> /etc/hosts.allow
 /etc/init.d/sshd restart
 
 Tunneling
 
    SSH tunneling allows to forward or reverse forward a port over the SSH
    connection, thus securing the traffic and accessing ports which would
    otherwise be blocked. This only works with TCP. The general nomenclature
    for forward and reverse is (see also ssh and NAT example):
 # ssh -L localport:desthost:destport user@gate  # desthost as seen from the gate
 # ssh -R destport:desthost:localport user@gate  # forwards your localport to dest
 ination
     # desthost:localport as seen from the client initiating the tunnel
 # ssh -X user@gate   # To force X forwarding
 
    This will connect to gate and forward the local port to the host
    desthost:destport. Note desthost is the destination host as seen by the
    gate, so if the connection is to the gate, then desthost is localhost.
    More than one port forward is possible.
 
 Direct forward on the gate
 
    Let say we want to access the CVS (port 2401) and http (port 80) which
    are running on the gate. This is the simplest example, desthost is thus
    localhost, and we use the port 8080 locally instead of 80 so we don't
    need to be root. Once the ssh session is open, both services are
    accessible on the local ports.
 # ssh -L 2401:localhost:2401 -L 8080:localhost:80 user@gate
 
 Netbios and remote desktop forward to a second server
 
    Let say a Windows smb server is behind the gate and is not running ssh.
    We need access to the smb share and also remote desktop to the server.
 # ssh -L 139:smbserver:139 -L 3388:smbserver:3389 user@gate
 
    The smb share can now be accessed with \\127.0.0.1\, but only if the
    local share is disabled, because the local share is listening on port
    139.
    It is possible to keep the local share enabled, for this we need to
    create a new virtual device with a new IP address for the tunnel, the
    smb share will be connected over this address. Furthermore the local RDP
    is already listening on 3389, so we choose 3388. For this example let's
    use a virtual IP of 10.1.1.1.
      * With putty use Source port=10.1.1.1:139. It is possible to create
        multiple loop devices and tunnel. On Windows 2000, only putty worked
        for me. On Windows Vista also forward the port 445 in addition to
        the port 139. Also on Vista the patch KB942624 prevents the port 445
        to be forwarded, so I had to uninstall this path in Vista.
      * With the ssh.com client, disable "Allow local connections only".
        Since ssh.com will bind to all addresses, only a single share can be
        connected.
 
    Now create the loopback interface with IP 10.1.1.1:
      * # System->Control Panel->Add Hardware # Yes, Hardware is already
        connected # Add a new hardware device (at bottom).
      * # Install the hardware that I manually select # Network adapters #
        Microsoft , Microsoft Loopback Adapter.
      * Configure the IP address of the fake device to 10.1.1.1 mask
        255.255.255.0, no gateway.
      * advanced->WINS, Enable LMHosts Lookup; Disable NetBIOS over TCP/IP.
      * # Enable Client for Microsoft Networks. # Disable File and Printer
        Sharing for Microsoft Networks.
 
    I HAD to reboot for this to work. Now connect to the smb share with
    \\10.1.1.1 and remote desktop to 10.1.1.1:3388.
 
 Debug
 
    If it is not working:
      * Are the ports forwarded: netstat -an? Look at 0.0.0.0:139 or
        10.1.1.1:139
      * Does telnet 10.1.1.1 139 connect?
      * You need the checkbox "Local ports accept connections from other
        hosts".
      * Is "File and Printer Sharing for Microsoft Networks" disabled on the
        loopback interface?
 
 Connect two clients behind NAT
 
    Suppose two clients are behind a NAT gateway and client cliadmin has to
    connect to client cliuser (the destination), both can login to the gate
    with ssh and are running Linux with sshd. You don't need root access
    anywhere as long as the ports on gate are above 1024. We use 2022 on
    gate. Also since the gate is used locally, the option GatewayPorts is
    not necessary.
    On client cliuser (from destination to gate):
 # ssh -R 2022:localhost:22 user@gate            # forwards client 22 to gate:2022
 
    On client cliadmin (from host to gate):
 # ssh -L 3022:localhost:2022 admin@gate         # forwards client 3022 to gate:20
 22
 
    Now the admin can connect directly to the client cliuser with:
 # ssh -p 3022 admin@localhost                   # local:3022 -> gate:2022 -> clie
 nt:22
 
 Connect to VNC behind NAT
 
    Suppose a Windows client with VNC listening on port 5900 has to be
    accessed from behind NAT. On client cliwin to gate:
 # ssh -R 15900:localhost:5900 user@gate
 
    On client cliadmin (from host to gate):
 # ssh -L 5900:localhost:15900 admin@gate
 
    Now the admin can connect directly to the client VNC with:
 # vncconnect -display :0 localhost
 
 Dig a multi-hop ssh tunnel
 
    Suppose you can not reach a server directly with ssh, but only via
    multiple intermediate hosts (for example because of routing issues).
    Sometimes it is still necessary to get a direct client - server
    connection, for example to copy files with scp, or forward other ports
    like smb or vnc. One way to do this is to chain tunnels together to
    forward a port to the server along the hops. This "carrier" port only
    reaches its final destination on the last connection to the server.
    Suppose we want to forward the ssh port from a client to a server over
    two hops. Once the tunnel is build, it is possible to connect to the
    server directly from the client (and also add an other port forward).
 
 Create tunnel in one shell
 
    client -> host1 -> host2 -> server and dig tunnel 5678
 client># ssh -L5678:localhost:5678 host1        # 5678 is an arbitrary port for t
 he tunnel
 host_1># ssh -L5678:localhost:5678 host2        # chain 5678 from host1 to host2
 host_2># ssh -L5678:localhost:22 server         # end the tunnel on port 22 on th
 e server
 
 Use tunnel with an other shell
 
    client -> server using tunnel 5678
 # ssh -p 5678 localhost                         # connect directly from client to
   server
 # scp -P 5678 myfile localhost:/tmp/            # or copy a file directly using t
 he tunnel
 # rsync -e 'ssh -p 5678' myfile localhost:/tmp/ # or rsync a file directly to the
  server
 
 Autoconnect and keep alive script
 
    I use variations of the following script to keep a machine reacheable
    over a reverse ssh tunnel. The connection is automatically rebuilt if
    closed. You can add multiple -L or -R tunnels on one line.
 #!/bin/sh
 COMMAND="ssh -N -f -g -R 3022:localhost:22 colin@cb.vu"
 pgrep -f -x "$COMMAND" > /dev/null 2>&1 || $COMMAND
 exit 0
 
 1 * * * * colin /home/colin/port_forward.sh     # crontab entry (here hourly)
 
 sshfs
 
    Mount a filesystem with ssh.
 # sshfs cb@cb.vu:/ /Users/barschel/cbvu -oauto_cache,reconnect,defer_permissions
 \
     ,noappledouble,negative_vncache,volname=cbvu
 
    Or via a two hops tunnel
 # ssh -Y -A -t -L20022:127.0.0.1:20022 cbarsche@lbgw ssh -Y -A -t -L20022:127.0.0
 .1:22 rootbgv@bgvctrl
 # sshfs -p 20022 cb@cb.vu:/ /Users/barschel/cbvu -oauto_cache,reconnect,defer_per
 missions \
     ,noappledouble,negative_vncache,volname=cbvu
 
 VPN with SSH
 
    As of version 4.3, OpenSSH can use the tun/tap device to encrypt a
    tunnel. This is very similar to other TLS based VPN solutions like
    OpenVPN. One advantage with SSH is that there is no need to install and
    configure additional software. Additionally the tunnel uses the SSH
    authentication like pre shared keys. The drawback is that the
    encapsulation is done over TCP which might result in poor performance on
    a slow link. Also the tunnel is relying on a single (fragile) TCP
    connection. This technique is very useful for a quick IP based VPN
    setup. There is no limitation as with the single TCP port forward, all
    layer 3/4 protocols like ICMP, TCP/UDP, etc. are forwarded over the VPN.
    In any case, the following options are needed in the sshd_conf file:
 PermitRootLogin yes
 PermitTunnel yes
 
 Single P2P connection
 
    Here we are connecting two hosts, hclient and hserver with a peer to
    peer tunnel. The connection is started from hclient to hserver and is
    done as root. The tunnel end points are 10.0.1.1 (server) and 10.0.1.2
    (client) and we create a device tun5 (this could also be an other
    number). The procedure is very simple:
      * Connect with SSH using the tunnel option -w
      * Configure the IP addresses of the tunnel. Once on the server and
        once on the client.
 
 Connect to the server
 
    Connection started on the client and commands are executed on the
    server.
 
 Server is on Linux
 
 cli># ssh -w5:5 root@hserver
 srv># ifconfig tun5 10.0.1.1 netmask 255.255.255.252   # Executed on the server s
 hell
 
 Server is on FreeBSD
 
 cli># ssh -w5:5 root@hserver
 srv># ifconfig tun5 10.0.1.1 10.0.1.2                  # Executed on the server s
 hell
 
 Configure the client
 
    Commands executed on the client:
 cli># ifconfig tun5 10.0.1.2 netmask 255.255.255.252   # Client is on Linux
 cli># ifconfig tun5 10.0.1.2 10.0.1.1                  # Client is on FreeBSD
 
    The two hosts are now connected and can transparently communicate with
    any layer 3/4 protocol using the tunnel IP addresses.
 
 Connect two networks
 
    In addition to the p2p setup above, it is more useful to connect two
    private networks with an SSH VPN using two gates. Suppose for the
    example, netA is 192.168.51.0/24 and netB 192.168.16.0/24. The procedure
    is similar as above, we only need to add the routing. NAT must be
    activated on the private interface only if the gates are not the same as
    the default gateway of their network.
    192.168.51.0/24 (netA)|gateA <-> gateB|192.168.16.0/24 (netB)
      * Connect with SSH using the tunnel option -w.
      * Configure the IP addresses of the tunnel. Once on the server and
        once on the client.
      * Add the routing for the two networks.
      * If necessary, activate NAT on the private interface of the gate.
 
    The setup is started from gateA in netA.
 
 Connect from gateA to gateB
 
    Connection is started from gateA and commands are executed on gateB.
 
 gateB is on Linux
 
 gateA># ssh -w5:5 root@gateB
 gateB># ifconfig tun5 10.0.1.1 netmask 255.255.255.252 # Executed on the gateB sh
 ell
 gateB># route add -net 192.168.51.0 netmask 255.255.255.0 dev tun5
 gateB># echo 1 > /proc/sys/net/ipv4/ip_forward        # Only needed if not defaul
 t gw
 gateB># iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
 
 gateB is on FreeBSD
 
 gateA># ssh -w5:5 root@gateB                          # Creates the tun5 devices
 gateB># ifconfig tun5 10.0.1.1 10.0.1.2               # Executed on the gateB she
 ll
 gateB># route add 192.168.51.0/24 10.0.1.2
 gateB># sysctl net.inet.ip.forwarding=1               # Only needed if not defaul
 t gw
 gateB># natd -s -m -u -dynamic -n fxp0                # see NAT
 gateA># sysctl net.inet.ip.fw.enable=1
 
 Configure gateA
 
    Commands executed on gateA:
 
 gateA is on Linux
 
 gateA># ifconfig tun5 10.0.1.2 netmask 255.255.255.252
 gateA># route add -net 192.168.16.0 netmask 255.255.255.0 dev tun5
 gateA># echo 1 > /proc/sys/net/ipv4/ip_forward
 gateA># iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
 
 gateA is on FreeBSD
 
 gateA># ifconfig tun5 10.0.1.2 10.0.1.1
 gateA># route add 192.168.16.0/24 10.0.1.2
 gateA># sysctl net.inet.ip.forwarding=1
 gateA># natd -s -m -u -dynamic -n fxp0                # see NAT
 gateA># sysctl net.inet.ip.fw.enable=1
 
    The two private networks are now transparently connected via the SSH
    VPN. The IP forward and NAT settings are only necessary if the gates are
    not the default gateways. In this case the clients would not know where
    to forward the response, and nat must be activated.
 
 RSYNC
 
    Rsync can almost completely replace cp and scp, furthermore interrupted
    transfers are efficiently restarted. A trailing slash (and the absence
    thereof) has different meanings, the man page is good... Here some
    examples:
    Copy the directories with full content:
 # rsync -a /home/colin/ /backup/colin/                # "archive" mode. e.g keep
 the same
 # rsync -a /var/ /var_bak/
 # rsync -aR --delete-during /home/user/ /backup/      # use relative (see below)
 # /opt/local/bin/rsync -azv --iconv=UTF-8-MAC,UTF-8 ~/Music/flac/ me@server:/dst/
                            # convert filenames OSX UTF8 to Windows UTF8
 
    Same as before but over the network and with compression. Rsync uses SSH
    for the transport per default and will use the ssh key if they are set.
    Use ":" as with SCP. A typical remote copy:
 # rsync -axSRzv /home/user/ user@server:/backup/user/ # Copy to remote
 # rsync -a 'user@server:My\ Documents' My\ Documents  # Quote AND escape spaces f
 or the remote shell
 
    Exclude any directory tmp within /home/user/ and keep the relative
    folders hierarchy, that is the remote directory will have the structure
    /backup/home/user/. This is typically used for backups.
 # rsync -azR --exclude=tmp/ /home/user/ user@server:/backup/
 
    Use port 20022 for the ssh connection:
 # rsync -az -e 'ssh -p 20022' /home/colin/ user@server:/backup/colin/
 
    Using the rsync daemon (used with "::") is much faster, but not
    encrypted over ssh. The location of /backup is defined by the
    configuration in /etc/rsyncd.conf. The variable RSYNC_PASSWORD can be
    set to avoid the need to enter the password manually.
 # rsync -axSRz /home/ ruser@hostname::rmodule/backup/
 # rsync -axSRz ruser@hostname::rmodule/backup/ /home/    # To copy back
 
    Some important options:
      * -a, --archive       archive mode; same as -rlptgoD (no -H)
      * -r, --recursive       recurse into directories
      * -R, --relative       use relative path names
      * -H, --hard-links       preserve hard links
      * -S, --sparse       handle sparse files efficiently
      * -x, --one-file-system       don't cross file system boundaries
      * --exclude=PATTERN       exclude files matching PATTERN
      * --delete-during       receiver deletes during xfer, not before
      * --delete-after       receiver deletes after transfer, not before
 
 Rsync on Windows
 
    Rsync is available for Windows through cygwin or as stand-alone packaged
    in cwrsynchttp://sourceforge.net/projects/sereds. This is very
    convenient for automated backups. Install one of them (not both) and add
    the path to the Windows system variables: # Control Panel -> System ->
    tab Advanced, button Environment Variables. Edit the "Path" system
    variable and add the full path to the installed rsync, e.g. C:\Program
    Files\cwRsync\bin or C:\cygwin\bin. This way the commands rsync and ssh
    are available in a Windows command shell.
 
 Public key authentication
 
    Rsync is automatically tunneled over SSH and thus uses the SSH
    authentication on the server. Automatic backups have to avoid a user
    interaction, for this the SSH public key authentication can be used and
    the rsync command will run without a password.
    All the following commands are executed within a Windows console. In a
    console (Start -> Run -> cmd) create and upload the key as described in
    SSH, change "user" and "server" as appropriate. If the file
    authorized_keys2 does not exist yet, simply copy id_dsa.pub to
    authorized_keys2 and upload it.
 # ssh-keygen -t dsa -N ''                   # Creates a public and a private key
 # rsync user@server:.ssh/authorized_keys2 . # Copy the file locally from the serv
 er
 # cat id_dsa.pub >> authorized_keys2        # Or use an editor to add the key
 # rsync authorized_keys2 user@server:.ssh/  # Copy the file back to the server
 # del authorized_keys2                      # Remove the local copy
 
    Now test it with (in one line):
 rsync -rv "/cygdrive/c/Documents and Settings/%USERNAME%/My Documents/" \
 'user@server:My\ Documents/'
 
 Automatic backup
 
    Use a batch file to automate the backup and add the file in the
    scheduled tasks (Programs -> Accessories -> System Tools -> Scheduled
    Tasks). For example create the file backup.bat and replace user@server.
 @ECHO OFF
 REM rsync the directory My Documents
 SETLOCAL
 SET CWRSYNCHOME=C:\PROGRAM FILES\CWRSYNC
 SET CYGWIN=nontsec
 SET CWOLDPATH=%PATH%
 REM uncomment the next line when using cygwin
 SET PATH=%CWRSYNCHOME%\BIN;%PATH%
 echo Press Control-C to abort
 rsync -av "/cygdrive/c/Documents and Settings/%USERNAME%/My Documents/" \
 'user@server:My\ Documents/'
 pause
 
 SUDO
 
    Sudo is a standard way to give users some administrative rights without
    giving out the root password. Sudo is very useful in a multi user
    environment with a mix of server and workstations. Simply call the
    command with sudo:
 # sudo /etc/init.d/dhcpd restart            # Run the rc script as root
 # sudo -u sysadmin whoami                   # Run cmd as an other user
 
 Configuration
 
    Sudo is configured in /etc/sudoers and must only be edited with visudo.
    The basic syntax is (the lists are comma separated):
 user hosts = (runas) commands          # In /etc/sudoers
      * users one or more users or %group (like %wheel) to gain the rights
      * hosts list of hosts (or ALL)
      * runas list of users (or ALL) that the command rule can be run as. It
        is enclosed in ( )!
      * commands list of commands (or ALL) that will be run as root or as
        (runas)
 
    Additionally those keywords can be defined as alias, they are called
    User_Alias, Host_Alias, Runas_Alias and Cmnd_Alias. This is useful for
    larger setups. Here a sudoers example:
 # cat /etc/sudoers
 # Host aliases are subnets or hostnames.
 Host_Alias   DMZ     = 212.118.81.40/28
 Host_Alias   DESKTOP = work1, work2
 
 # User aliases are a list of users which can have the same rights
 User_Alias   ADMINS  = colin, luca, admin
 User_Alias   DEVEL   = joe, jack, julia
 Runas_Alias  DBA     = oracle,pgsql
 
 # Command aliases define the full path of a list of commands
 Cmnd_Alias   SYSTEM  = /sbin/reboot,/usr/bin/kill,/sbin/halt,/sbin/shutdown,/etc/
 init.d/
 Cmnd_Alias   PW      = /usr/bin/passwd [A-z]*, !/usr/bin/passwd root # Not root p
 wd!
 Cmnd_Alias   DEBUG   = /usr/sbin/tcpdump,/usr/bin/wireshark,/usr/bin/nmap
 
 # The actual rules
 root,ADMINS  ALL     = (ALL) NOPASSWD: ALL    # ADMINS can do anything w/o a pass
 word.
 DEVEL        DESKTOP = (ALL) NOPASSWD: ALL    # Developers have full right on des
 ktops
 DEVEL        DMZ     = (ALL) NOPASSWD: DEBUG  # Developers can debug the DMZ serv
 ers.
 
 # User sysadmin can mess around in the DMZ servers with some commands.
 sysadmin     DMZ     = (ALL) NOPASSWD: SYSTEM,PW,DEBUG
 sysadmin     ALL,!DMZ = (ALL) NOPASSWD: ALL   # Can do anything outside the DMZ.
 %dba         ALL     = (DBA) ALL              # Group dba can run as database use
 r.
 
 # anyone can mount/unmount a cd-rom on the desktop machines
 ALL          DESKTOP = NOPASSWD: /sbin/mount /cdrom,/sbin/umount /cdrom
 
 Encrypt Files
 
 OpenSSL
 
 A single file
 
    Encrypt and decrypt:
 # openssl aes-128-cbc -salt -in file -out file.aes
 # openssl aes-128-cbc -d -salt -in file.aes -out file
 
    Note that the file can of course be a tar archive.
 
 tar and encrypt a whole directory
 
 # tar -cf - directory | openssl aes-128-cbc -salt -out directory.tar.aes      # E
 ncrypt
 # openssl aes-128-cbc -d -salt -in directory.tar.aes | tar -x -f -            # D
 ecrypt
 
 tar zip and encrypt a whole directory
 
 # tar -zcf - directory | openssl aes-128-cbc -salt -out directory.tar.gz.aes  # E
 ncrypt
 # openssl aes-128-cbc -d -salt -in directory.tar.gz.aes | tar -xz -f -        # D
 ecrypt
 
      * Use -k mysecretpassword after aes-128-cbc to avoid the interactive
        password request. However note that this is highly insecure.
      * Use aes-256-cbc instead of aes-128-cbc to get even stronger
        encryption. This uses also more CPU.
 
 GPG
 
    GnuPG is well known to encrypt and sign emails or any data. Furthermore
    gpg and also provides an advanced key management system. This section
    only covers files encryption, not email usage, signing or the
    Web-Of-Trust.
    The simplest encryption is with a symmetric cipher. In this case the
    file is encrypted with a password and anyone who knows the password can
    decrypt it, thus the keys are not needed. Gpg adds an extention ".gpg"
    to the encrypted file names.
 # gpg -c file                        # Encrypt file with password
 # gpg file.gpg                       # Decrypt file (optionally -o otherfile)
 
 Using keys
 
    For more details see GPG Quick
    Starthttp://www.madboa.com/geek/gpg-quickstart and GPG/PGP
    Basicshttp://aplawrence.com/Basics/gpg.html and the gnupg
    documentationhttp://gnupg.org/documentation among others.
    The private and public keys are the heart of asymmetric cryptography.
    What is important to remember:
      * Your public key is used by others to encrypt files that only you as
        the receiver can decrypt (not even the one who encrypted the file
        can decrypt it). The public key is thus meant to be distributed.
      * Your private key is encrypted with your passphrase and is used to
        decrypt files which were encrypted with your public key. The private
        key must be kept secure. Also if the key or passphrase is lost, so
        are all the files encrypted with your public key.
      * The key files are called keyrings as they can contain more than one
        key.
 
    First generate a key pair. The defaults are fine, however you will have
    to enter at least your full name and email and optionally a comment. The
    comment is useful to create more than one key with the same name and
    email. Also you should use a "passphrase", not a simple password.
 # gpg --gen-key                      # This can take a long time
 
    The keys are stored in ~/.gnupg/ on Unix, on Windows they are typically
    stored in
    C:/Documents and Settings/%USERNAME%/Application Data/gnupg/.
 ~/.gnupg/pubring.gpg                 # Contains your public keys and all others i
 mported
 ~/.gnupg/secring.gpg                 # Can contain more than one private key
 
    Short reminder on most used options:
      * -e encrypt data
      * -d decrypt data
      * -r NAME encrypt for recipient NAME (or 'Full Name' or
        'email@domain')
      * -a create ascii armored output of a key
      * -o use as output file
 
    The examples use 'Your Name' and 'Alice' as the keys are referred to by
    the email or full name or partial name. For example I can use 'Colin' or
    'c@cb.vu' for my key [Colin Barschel (cb.vu) <c@cb.vu>].
 
 Encrypt for personal use only
 
    No need to export/import any key for this. You have both already.
 # gpg -e -r 'Your Name' file                  # Encrypt with your public key
 # gpg -o file -d file.gpg                     # Decrypt. Use -o or it goes to std
 out
 
 Encrypt - Decrypt with keys
 
    First you need to export your public key for someone else to use it. And
    you need to import the public say from Alice to encrypt a file for her.
    You can either handle the keys in simple ascii files or use a public key
    server.
    For example Alice export her public key and you import it, you can then
    encrypt a file for her. That is only Alice will be able to decrypt it.
 # gpg -a -o alicekey.asc --export 'Alice'     # Alice exported her key in ascii f
 ile.
 # gpg --send-keys --keyserver subkeys.pgp.net KEYID   # Alice put her key on a se
 rver.
 # gpg --import alicekey.asc                   # You import her key into your pubr
 ing.
 # gpg --search-keys --keyserver subkeys.pgp.net 'Alice' # or get her key from a s
 erver.
 
    Once the keys are imported it is very easy to encrypt or decrypt a file:
 # gpg -e -r 'Alice' file                      # Encrypt the file for Alice.
 # gpg -d file.gpg -o file                     # Decrypt a file encrypted by Alice
  for you.
 
 Key administration
 
 # gpg --list-keys                             # list public keys and see the KEYI
 DS
     The KEYID follows the '/' e.g. for: pub   1024D/D12B77CE the KEYID is D12B77C
 E
 # gpg --gen-revoke 'Your Name'                # generate revocation certificate
 # gpg --list-secret-keys                      # list private keys
 # gpg --delete-keys NAME                      # delete a public key from local ke
 y ring
 # gpg --delete-secret-key NAME                # delete a secret key from local ke
 y ring
 # gpg --fingerprint KEYID                     # Show the fingerprint of the key
 # gpg --edit-key KEYID                        # Edit key (e.g sign or add/del ema
 il)
 
 Encrypt Partitions
 
    Linux with LUKS | Linux dm-crypt only | FreeBSD GELI | FBSD pwd only |
    OS X image
    There are (many) other alternative methods to encrypt disks, I only show
    here the methods I know and use. Keep in mind that the security is only
    good as long the OS has not been tempered with. An intruder could easily
    record the password from the keyboard events. Furthermore the data is
    freely accessible when the partition is attached and will not prevent an
    intruder to have access to it in this state.
 
 Linux
 
    Those instructions use the Linux dm-crypt (device-mapper) facility
    available on the 2.6 kernel. In this example, lets encrypt the partition
    /dev/sdc1, it could be however any other partition or disk, or USB or a
    file based partition created with losetup. In this case we would use
    /dev/loop0. See file image partition. The device mapper uses labels to
    identify a partition. We use sdc1 in this example, but it could be any
    string.
 
 dm-crypt with LUKS
 
    LUKS with dm-crypt has better encryption and makes it possible to have
    multiple passphrase for the same partition or to change the password
    easily. To test if LUKS is available, simply type # cryptsetup --help,
    if nothing about LUKS shows up, use the instructions below Without LUKS.
    First create a partition if necessary: fdisk /dev/sdc.
 
 Create encrypted partition
 
 # dd if=/dev/urandom of=/dev/sdc1          # Optional. For paranoids only (takes
 days)
 # cryptsetup -y luksFormat /dev/sdc1       # This destroys any data on sdc1
 # cryptsetup luksOpen /dev/sdc1 sdc1
 # mkfs.ext3 /dev/mapper/sdc1               # create ext3 file system
 # mount -t ext3 /dev/mapper/sdc1 /mnt
 # umount /mnt
 # cryptsetup luksClose sdc1                # Detach the encrypted partition
 
 Attach
 
 # cryptsetup luksOpen /dev/sdc1 sdc1
 # mount -t ext3 /dev/mapper/sdc1 /mnt
 
 Detach
 
 # umount /mnt
 # cryptsetup luksClose sdc1
 
 dm-crypt without LUKS
 
 # cryptsetup -y create sdc1 /dev/sdc1      # or any other partition like /dev/loo
 p0
 # dmsetup ls                               # check it, will display: sdc1 (254, 0
 )
 # mkfs.ext3 /dev/mapper/sdc1               # This is done only the first time!
 # mount -t ext3 /dev/mapper/sdc1 /mnt
 # umount /mnt/
 # cryptsetup remove sdc1                   # Detach the encrypted partition
 
    Do exactly the same (without the mkfs part!) to re-attach the partition.
    If the password is not correct, the mount command will fail. In this
    case simply remove the map sdc1 (cryptsetup remove sdc1) and create it
    again.
 
 FreeBSD
 
    The two popular FreeBSD disk encryption modules are gbde and geli. I now
    use geli because it is faster and also uses the crypto device for
    hardware acceleration. See The FreeBSD handbook Chapter
    18.6http://www.freebsd.org/handbook/disks-encrypting.html for all the
    details. The geli module must be loaded or compiled into the kernel:
 options GEOM_ELI
 device crypto                                       # or as module:
 # echo 'geom_eli_load="YES"' >> /boot/loader.conf   # or do: kldload geom_eli
 
 Use password and key
 
    I use those settings for a typical disk encryption, it uses a passphrase
    AND a key to encrypt the master key. That is you need both the password
    and the generated key /root/ad1.key to attach the partition. The master
    key is stored inside the partition and is not visible. See below for
    typical USB or file based image.
 
 Create encrypted partition
 
 # dd if=/dev/random of=/root/ad1.key bs=64 count=1  # this key encrypts the mater
  key
 # geli init -s 4096 -K /root/ad1.key /dev/ad1       # -s 8192 is also OK for disk
 s
 # geli attach -k /root/ad1.key /dev/ad1             # DO make a backup of /root/a
 d1.key
 # dd if=/dev/random of=/dev/ad1.eli bs=1m           # Optional and takes a long t
 ime
 # newfs /dev/ad1.eli                                # Create file system
 # mount /dev/ad1.eli /mnt
 
 Attach
 
 # geli attach -k /root/ad1.key /dev/ad1
 # fsck -ny -t ffs /dev/ad1.eli                      # In doubt check the file sys
 tem
 # mount /dev/ad1.eli /mnt
 
 Detach
 
    The detach procedure is done automatically on shutdown.
 # umount /mnt
 # geli detach /dev/ad1.eli
 
 /etc/fstab
 
    The encrypted partition can be configured to be mounted with /etc/fstab.
    The password will be prompted when booting. The following settings are
    required for this example:
 # grep geli /etc/rc.conf
 geli_devices="ad1"
 geli_ad1_flags="-k /root/ad1.key"
 # grep geli /etc/fstab
 /dev/ad1.eli         /home/private              ufs             rw      0       0
 
 Use password only
 
    It is more convenient to encrypt a USB stick or file based image with a
    passphrase only and no key. In this case it is not necessary to carry
    the additional key file around. The procedure is very much the same as
    above, simply without the key file. Let's encrypt a file based image
    /cryptedfile of 1 GB.
 # dd if=/dev/zero of=/cryptedfile bs=1M count=1000  # 1 GB file
 # mdconfig -at vnode -f /cryptedfile
 # geli init /dev/md0                                # encrypts with password only
 # geli attach /dev/md0
 # newfs -U -m 0 /dev/md0.eli
 # mount /dev/md0.eli /mnt
 # umount /dev/md0.eli
 # geli detach md0.eli
 
    It is now possible to mount this image on an other system with the
    password only.
 # mdconfig -at vnode -f /cryptedfile
 # geli attach /dev/md0
 # mount /dev/md0.eli /mnt
 
 OS X Encrypted Disk Image
 
    Don't know by command line only. See OS X Encrypted Disk
    Imagehttps://wiki.thayer.dartmouth.edu/display/computing/Creating+a+Mac+
    OS+X+Encrypted+Disk+Image and Apple
    supporthttp://support.apple.com/kb/ht1578
 
 SSL Certificates
 
    So called SSL/TLS certificates are cryptographic public key certificates
    and are composed of a public and a private key. The certificates are
    used to authenticate the endpoints and encrypt the data. They are used
    for example on a web server (https) or mail server (imaps).
 
 Procedure
 
      * We need a certificate authority to sign our certificate. This step
        is usually provided by a vendor like Thawte, Verisign, etc., however
        we can also create our own.
      * Create a certificate signing request. This request is like an
        unsigned certificate (the public part) and already contains all
        necessary information. The certificate request is normally sent to
        the authority vendor for signing. This step also creates the private
        key on the local machine.
      * Sign the certificate with the certificate authority.
      * If necessary join the certificate and the key in a single file to be
        used by the application (web server, mail server etc.).
 
 Configure OpenSSL
 
    We use /usr/local/certs as directory for this example check or edit
    /etc/ssl/openssl.cnf accordingly to your settings so you know where the
    files will be created. Here are the relevant part of openssl.cnf:
 [ CA_default ]
 dir             = /usr/local/certs/CA       # Where everything is kept
 certs           = $dir/certs                # Where the issued certs are kept
 crl_dir         = $dir/crl                  # Where the issued crl are kept
 database        = $dir/index.txt            # database index file.
 
    Make sure the directories exist or create them
 # mkdir -p /usr/local/certs/CA
 # cd /usr/local/certs/CA
 # mkdir certs crl newcerts private
 # echo "01" > serial                        # Only if serial does not exist
 # touch index.txt
 
    If you intend to get a signed certificate from a vendor, you only need a
    certificate signing request (CSR). This CSR will then be signed by the
    vendor for a limited time (e.g. 1 year).
 
 Create a certificate authority
 
    If you do not have a certificate authority from a vendor, you'll have to
    create your own. This step is not necessary if one intend to use a
    vendor to sign the request. To make a certificate authority (CA):
 # openssl req -new -x509 -days 730 -config /etc/ssl/openssl.cnf \
 -keyout CA/private/cakey.pem -out CA/cacert.pem
 
 Create a certificate signing request
 
    To make a new certificate (for mail server or web server for example),
    first create a request certificate with its private key. If your
    application do not support encrypted private key (for example UW-IMAP
    does not), then disable encryption with -nodes.
 # openssl req -new -keyout newkey.pem -out newreq.pem \
 -config /etc/ssl/openssl.cnf
 # openssl req -nodes -new -keyout newkey.pem -out newreq.pem \
 -config /etc/ssl/openssl.cnf                # No encryption for the key
 
    Keep this created CSR (newreq.pem) as it can be signed again at the next
    renewal, the signature onlt will limit the validity of the certificate.
    This process also created the private key newkey.pem.
 
 Sign the certificate
 
    The certificate request has to be signed by the CA to be valid, this
    step is usually done by the vendor. Note: replace "servername" with the
    name of your server in the next commands.
 # cat newreq.pem newkey.pem > new.pem
 # openssl ca -policy policy_anything -out servernamecert.pem \
 -config /etc/ssl/openssl.cnf -infiles new.pem
 # mv newkey.pem servernamekey.pem
 
    Now servernamekey.pem is the private key and servernamecert.pem is the
    server certificate.
 
 Create united certificate
 
    The IMAP server wants to have both private key and server certificate in
    the same file. And in general, this is also easier to handle, but the
    file has to be kept securely!. Apache also can deal with it well. Create
    a file servername.pem containing both the certificate and key.
      * Open the private key (servernamekey.pem) with a text editor and copy
        the private key into the "servername.pem" file.
      * Do the same with the server certificate (servernamecert.pem).
 
    The final servername.pem file should look like this:
 -----BEGIN RSA PRIVATE KEY-----
 MIICXQIBAAKBgQDutWy+o/XZ/[...]qK5LqQgT3c9dU6fcR+WuSs6aejdEDDqBRQ
 -----END RSA PRIVATE KEY-----
 -----BEGIN CERTIFICATE-----
 MIIERzCCA7CgAwIBAgIBBDANB[...]iG9w0BAQQFADCBxTELMAkGA1UEBhMCREUx
 -----END CERTIFICATE-----
 
    What we have now in the directory /usr/local/certs/:
      * CA/private/cakey.pem (CA server private key)
      * CA/cacert.pem (CA server public key)
      * certs/servernamekey.pem (server private key)
      * certs/servernamecert.pem (server signed certificate)
      * certs/servername.pem (server certificate with private key)
 
    Keep the private key secure!
 
 View certificate information
 
    To view the certificate information simply do:
 # openssl x509 -text -in servernamecert.pem      # View the certificate info
 # openssl req -noout -text -in server.csr        # View the request info
 # openssl s_client -connect cb.vu:443            # Check a web server certificate
 
 CVS
 
    Server setup | CVS test | SSH tunneling | CVS usage
 
 Server setup
 
 Initiate the CVS
 
    Decide where the main repository will rest and create a root cvs. For
    example /usr/local/cvs (as root):
 # mkdir -p /usr/local/cvs
 # setenv CVSROOT /usr/local/cvs      # Set CVSROOT to the new location (local)
 # cvs init                           # Creates all internal CVS config files
 # cd /root
 # cvs checkout CVSROOT               # Checkout the config files to modify them
 # cd CVSROOT
 edit config ( fine as it is)
 # cvs commit config
 cat >> writers                       # Create a writers file (optionally also rea
 ders)
 colin
 ^D                                   # Use [Control][D] to quit the edit
 # cvs add writers                    # Add the file writers into the repository
 # cvs edit checkoutlist
 # cat >> checkoutlist
 writers
 ^D                                   # Use [Control][D] to quit the edit
 # cvs commit                         # Commit all the configuration changes
 
    Add a readers file if you want to differentiate read and write
    permissions Note: Do not (ever) edit files directly into the main cvs,
    but rather checkout the file, modify it and check it in. We did this
    with the file writers to define the write access.
    There are three popular ways to access the CVS at this point. The first
    two don't need any further configuration. See the examples on CVSROOT
    below for how to use them:
      * Direct local access to the file system. The user(s) need sufficient
        file permission to access the CS directly and there is no further
        authentication in addition to the OS login. However this is only
        useful if the repository is local.
      * Remote access with ssh with the ext protocol. Any use with an ssh
        shell account and read/write permissions on the CVS server can
        access the CVS directly with ext over ssh without any additional
        tunnel. There is no server process running on the CVS for this to
        work. The ssh login does the authentication.
      * Remote access with pserver (default port: 2401/tcp). This is the
        preferred use for larger user base as the users are authenticated by
        the CVS pserver with a dedicated password database, there is
        therefore no need for local users accounts. This setup is explained
        below.
 
 Network setup with inetd
 
    The CVS can be run locally only if a network access is not needed. For a
    remote access, the daemon inetd can start the pserver with the following
    line in /etc/inetd.conf (/etc/xinetd.d/cvs on SuSE):
 cvspserver      stream  tcp  nowait  cvs  /usr/bin/cvs  cvs \
 --allow-root=/usr/local/cvs pserver
 
    It is a good idea to block the cvs port from the Internet with the
    firewall and use an ssh tunnel to access the repository remotely.
 
 Separate authentication
 
    It is possible to have cvs users which are not part of the OS (no local
    users). This is actually probably wanted too from the security point of
    view. Simply add a file named passwd (in the CVSROOT directory)
    containing the users login and password in the crypt format. This is can
    be done with the apache htpasswd tool.
    Note: This passwd file is the only file which has to be edited directly
    in the CVSROOT directory. Also it won't be checked out. More info with
    htpasswd --help
 # htpasswd -cb passwd user1 password1  # -c creates the file
 # htpasswd -b passwd user2 password2
 
    Now add :cvs at the end of each line to tell the cvs server to change
    the user to cvs (or whatever your cvs server is running under). It looks
    like this:
 # cat passwd
 user1:xsFjhU22u8Fuo:cvs
 user2:vnefJOsnnvToM:cvs
 
 Test it
 
    Test the login as normal user (for example here me)
 # cvs -d :pserver:colin@192.168.50.254:/usr/local/cvs login
 Logging in to :pserver:colin@192.168.50.254:2401/usr/local/cvs
 CVS password:
 
 
 CVSROOT variable
 
    This is an environment variable used to specify the location of the
    repository we're doing operations on. For local use, it can be just set
    to the directory of the repository. For use over the network, the
    transport protocol must be specified. Set the CVSROOT variable with
    setenv CVSROOT string on a csh, tcsh shell, or with export
    CVSROOT=string on a sh, bash shell.
 # setenv CVSROOT :pserver:<username>@<host>:/cvsdirectory
 For example:
 # setenv CVSROOT /usr/local/cvs                               # Used locally only
 # setenv CVSROOT :local:/usr/local/cvs                        # Same as above
 # setenv CVSROOT :ext:user@cvsserver:/usr/local/cvs           # Direct access wit
 h SSH
 # setenv CVS_RSH ssh                                          # for the ext acces
 s
 # setenv CVSROOT :pserver:user@cvsserver.254:/usr/local/cvs   # network with pser
 ver
 
    When the login succeeded one can import a new project into the
    repository: cd into your project root directory
 cvs import <module name> <vendor tag> <initial tag>
 cvs -d :pserver:colin@192.168.50.254:/usr/local/cvs import MyProject MyCompany ST
 ART
 
    Where MyProject is the name of the new project in the repository (used
    later to checkout). Cvs will import the current directory content into
    the new project.
    To checkout:
 # cvs -d :pserver:colin@192.168.50.254:/usr/local/cvs checkout MyProject
 or
 # setenv CVSROOT :pserver:colin@192.168.50.254:/usr/local/cvs
 # cvs checkout MyProject
 
 SSH tunneling for CVS
 
    We need 2 shells for this. On the first shell we connect to the cvs
    server with ssh and port-forward the cvs connection. On the second shell
    we use the cvs normally as if it where running locally.
    on shell 1:
 # ssh -L2401:localhost:2401 colin@cvs_server   # Connect directly to the CVS serv
 er. Or:
 # ssh -L2401:cvs_server:2401 colin@gateway     # Use a gateway to reach the CVS
 
    on shell 2:
 # setenv CVSROOT :pserver:colin@localhost:/usr/local/cvs
 # cvs login
 Logging in to :pserver:colin@localhost:2401/usr/local/cvs
 CVS password:
 # cvs checkout MyProject/src
 
 CVS commands and usage
 
 Import
 
    The import command is used to add a whole directory, it must be run from
    within the directory to be imported. Say the directory /devel/ contains
    all files and subdirectories to be imported. The directory name on the
    CVS (the module) will be called "myapp".
 # cvs import [options] directory-name vendor-tag release-tag
 # cd /devel                          # Must be inside the project to import it
 # cvs import myapp Company R1_0      # Release tag can be anything in one word
 
    After a while a new directory "/devel/tools/" was added and it has to be
    imported too.
 # cd /devel/tools
 # cvs import myapp/tools Company R1_0
 
 Checkout update add commit
 
 # cvs co myapp/tools                 # Will only checkout the directory tools
 # cvs co -r R1_1 myapp               # Checkout myapp at release R1_1 (is sticky)
 # cvs -q -d update -P                # A typical CVS update
 # cvs update -A                      # Reset any sticky tag (or date, option)
 # cvs add newfile                    # Add a new file
 # cvs add -kb newfile                # Add a new binary file
 # cvs commit file1 file2             # Commit the two files only
 # cvs commit -m "message"            # Commit all changes done with a message
 
 Create a patch
 
    It is best to create and apply a patch from the working development
    directory related to the project, or from within the source directory.
 # cd /devel/project
 # diff -Naur olddir newdir > patchfile # Create a patch from a directory or a fil
 e
 # diff -Naur oldfile newfile > patchfile
 
 Apply a patch
 
    Sometimes it is necessary to strip a directory level from the patch,
    depending how it was created. In case of difficulties, simply look at
    the first lines of the patch and try -p0, -p1 or -p2.
 # cd /devel/project
 # patch --dry-run -p0 < patchfile    # Test the path without applying it
 # patch -p0 < patchfile
 # patch -p1 < patchfile              # strip off the 1st level from the path
 
 SVN
 
    Server setup | SVN+SSH | SVN over http | SVN usage
    Subversion (SVN)http://subversion.tigris.org/ is a version control
    system designed to be the successor of CVS (Concurrent Versions System).
    The concept is similar to CVS, but many shortcomings where improved. See
    also the SVN bookhttp://svnbook.red-bean.com/en/1.4/.
 
 Server setup
 
    The initiation of the repository is fairly simple (here for example
    /home/svn/ must exist):
 # svnadmin create --fs-type fsfs /home/svn/project1
 
    Now the access to the repository is made possible with:
      * file:// Direct file system access with the svn client with. This
        requires local permissions on the file system.
      * svn:// or svn+ssh:// Remote access with the svnserve server (also
        over SSH). This requires local permissions on the file system
        (default port: 2690/tcp).
      * http:// Remote access with webdav using apache. No local users are
        necessary for this method.
 
    Using the local file system, it is now possible to import and then check
    out an existing project. Unlike with CVS it is not necessary to cd into
    the project directory, simply give the full path:
 # svn import /project1/ file:///home/svn/project1/trunk -m 'Initial import'
 # svn checkout file:///home/svn/project1
 
    The new directory "trunk" is only a convention, this is not required.
 
 Remote access with ssh
 
    No special setup is required to access the repository via ssh, simply
    replace file:// with svn+ssh/hostname. For example:
 # svn checkout svn+ssh://hostname/home/svn/project1
 
    As with the local file access, every user needs an ssh access to the
    server (with a local account) and also read/write access. This method
    might be suitable for a small group. All users could belong to a
    subversion group which owns the repository, for example:
 # groupadd subversion
 # groupmod -A user1 subversion
 # chown -R root:subversion /home/svn
 # chmod -R 770 /home/svn
 
 Remote access with http (apache)
 
    Remote access over http (https) is the only good solution for a larger
    user group. This method uses the apache authentication, not the local
    accounts. This is a typical but small apache configuration:
 LoadModule dav_module         modules/mod_dav.so
 LoadModule dav_svn_module     modules/mod_dav_svn.so
 LoadModule authz_svn_module   modules/mod_authz_svn.so    # Only for access contr
 ol
 
 <Location /svn>
   DAV svn
   # any "/svn/foo" URL will map to a repository /home/svn/foo
   SVNParentPath /home/svn
   AuthType Basic
   AuthName "Subversion repository"
   AuthzSVNAccessFile /etc/apache2/svn.acl
   AuthUserFile /etc/apache2/svn-passwd
   Require valid-user
 </Location>
 
    The apache server needs full access to the repository:
 # chown -R www:www /home/svn
 
    Create a user with htpasswd2:
 # htpasswd -c /etc/svn-passwd user1  # -c creates the file
 
 Access control svn.acl example
 
 # Default it read access. "* =" would be default no access
 [/]
 * = r
 [groups]
 project1-developers = joe, jack, jane
 # Give write access to the developers
 [project1:]
 @project1-developers = rw
 
 SVN commands and usage
 
    See also the Subversion Quick Reference
    Cardhttp://www.cs.put.poznan.pl/csobaniec/Papers/svn-refcard.pdf.
    Tortoise SVNhttp://tortoisesvn.tigris.org is a nice Windows interface.
 
 Import
 
    A new project, that is a directory with some files, is imported into the
    repository with the import command. Import is also used to add a
    directory with its content to an existing project.
 # svn help import                                # Get help for any command
     # Add a new directory (with content) into the src dir on project1
 # svn import /project1/newdir http://host.url/svn/project1/trunk/src -m 'add newd
 ir'
 
 Typical SVN commands
 
 # svn co http://host.url/svn/project1/trunk      # Checkout the most recent versi
 on
     # Tags and branches are created by copying
 # svn mkdir http://host.url/svn/project1/tags/   # Create the tags directory
 # svn copy -m "Tag rc1 rel." http://host.url/svn/project1/trunk \
                              http://host.url/svn/project1/tags/1.0rc1
 # svn status [--verbose]                         # Check files status into workin
 g dir
 # svn add src/file.h src/file.cpp                # Add two files
 # svn commit -m 'Added new class file'           # Commit the changes with a mess
 age
 # svn ls http://host.url/svn/project1/tags/      # List all tags
 # svn move foo.c bar.c                           # Move (rename) files
 # svn delete some_old_file                       # Delete files
 
 Useful Commands
 
    less | vi | mail | tar | zip | dd | screen | find | Miscellaneous
 
 less
 
    The less command displays a text document on the console. It is present
    on most installation.
 # less unixtoolbox.xhtml
 
    Some important commands are (^N stands for [control]-[N]):
      * h H       good help on display
      * f ^F ^V SPACE       Forward one window (or N lines).
      * b ^B ESC-v       Backward one window (or N lines).
      * F       Forward forever; like "tail -f".
      * /pattern       Search forward for (N-th) matching line.
      * ?pattern       Search backward for (N-th) matching line.
      * n       Repeat previous search (for N-th occurrence).
      * N       Repeat previous search in reverse direction.
      * q       quit
 
 vi
 
    Vi is present on ANY Linux/Unix installation (not gentoo?) and it is
    therefore useful to know some basic commands. There are two modes:
    command mode and insertion mode. The commands mode is accessed with
    [ESC], the insertion mode with i. Use : help if you are lost.
    The editors nano and pico are usually available too and are easier
    (IMHO) to use.
 
 Quit
 
      * :w newfilename       save the file to newfilename
      * :wq or :x       save and quit
      * :q!       quit without saving
 
 Search and move
 
      * /string       Search forward for string
      * ?string       Search back for string
      * n       Search for next instance of string
      * N       Search for previous instance of string
      * {       Move a paragraph back
      * }       Move a paragraph forward
      * 1G       Move to the first line of the file
      * nG       Move to the n th line of the file
      * G       Move to the last line of the file
      * :%s/OLD/NEW/g       Search and replace every occurrence
 
 Delete copy paste text
 
      * dd (dw)       Cut current line (word)
      * D       Cut to the end of the line
      * x       Delete (cut) character
      * yy (yw)       Copy line (word) after cursor
      * P       Paste after cursor
      * u       Undo last modification
      * U       Undo all changes to current line
 
 mail
 
    The mail command is a basic application to read and send email, it is
    usually installed. To send an email simply type "mail user@domain". The
    first line is the subject, then the mail content. Terminate and send the
    email with a single dot (.) in a new line. Example:
 # mail c@cb.vu
 Subject: Your text is full of typos
 "For a moment, nothing happened. Then, after a second or so,
 nothing continued to happen."
 .
 EOT
 #
 
    This is also working with a pipe:
 # echo "This is the mail body" | mail c@cb.vu
 
    This is also a simple way to test the mail server.
 
 tar
 
    The command tar (tape archive) creates and extracts archives of file and
    directories. The archive .tar is uncompressed, a compressed archive has
    the extension .tgz or .tar.gz (zip) or .tbz (bzip2). Do not use absolute
    path when creating an archive, you probably want to unpack it somewhere
    else. Some typical commands are:
 
 Create
 
 # cd /
 # tar -cf home.tar home/        # archive the whole /home directory (c for create
 )
 # tar -czf home.tgz home/       # same with zip compression
 # tar -cjf home.tbz home/       # same with bzip2 compression
 
    Only include one (or two) directories from a tree, but keep the relative
    structure. For example archive /usr/local/etc and /usr/local/www and the
    first directory in the archive should be local/.
 # tar -C /usr -czf local.tgz local/etc local/www
 # tar -C /usr -xzf local.tgz    # To untar the local dir into /usr
 # cd /usr; tar -xzf local.tgz   # Is the same as above
 
 Extract
 
 # tar -tzf home.tgz             # look inside the archive without extracting (lis
 t)
 # tar -xf home.tar              # extract the archive here (x for extract)
 # tar -xzf home.tgz             # same with zip compression (-xjf for bzip2 compr
 ession)
                                 # remove leading path gallery2 and extract into g
 allery
 # tar --strip-components 1 -zxvf gallery2.tgz -C gallery/
 # tar -xjf home.tbz home/colin/file.txt    # Restore a single file
 # tar -xOf home.tbz home/colin/file.txt    # Print file to stdout (no extraction)
 
 More advanced
 
 # tar c dir/ | gzip | ssh user@remote 'dd of=dir.tgz' # arch dir/ and store remot
 ely.
 # tar cvf - `find . -print` > backup.tar              # arch the current director
 y.
 # tar -cf - -C /etc . | tar xpf - -C /backup/etc      # Copy directories
 # tar -cf - -C /etc . | ssh user@remote tar xpf - -C /backup/etc      # Remote co
 py.
 # tar -czf home.tgz --exclude '*.o' --exclude 'tmp/' home/
 
 zip/unzip
 
    Zip files can be easier to share with Windows.
 # zip -r fileName.zip /path/to/dir                    # zip dir into file fileNam
 e.zip
 # unzip fileName.zip                                  # uncompress zip file
 # unzip -l fileName.zip                               # list files inside archive
 # unzip -c fileName.zip fileinside.txt                # print one file to stdout
 (no extraction)
 # unzip fileName.zip fileinside.txt                   # extract one file only
 
 dd
 
    The program dd (disk dump or destroy disk or see the meaning of dd) is
    used to copy partitions and disks and for other copy tricks. Typical
    usage:
 # dd if=<source> of=<target> bs=<byte size> conv=<conversion>
 # kill -INFO PID                                      # View dd progress (FreeBSD
 , OSX)
 
    Important conv options:
      * notrunc       do not truncate the output file, all zeros will be
        written as zeros.
      * noerror       continue after read errors (e.g. bad blocks)
      * sync       pad every input block with Nulls to ibs-size
 
    The default byte size is 512 (one block). The MBR, where the partition
    table is located, is on the first block, the first 63 blocks of a disk
    are empty. Larger byte sizes are faster to copy but require also more
    memory.
 
 Backup and restore
 
 # dd if=/dev/hda of=/dev/hdc bs=16065b                # Copy disk to disk (same s
 ize)
 # dd if=/dev/sda7 of=/home/root.img bs=4096 conv=notrunc,noerror # Backup /
 # dd if=/home/root.img of=/dev/sda7 bs=4096 conv=notrunc,noerror # Restore /
 # dd bs=1M if=/dev/ad4s3e | gzip -c > ad4s3e.gz                  # Zip the backup
 # gunzip -dc ad4s3e.gz | dd of=/dev/ad0s3e bs=1M                 # Restore the zi
 p
 # dd bs=1M if=/dev/ad4s3e | gzip | ssh eedcoba@fry 'dd of=ad4s3e.gz' # also remot
 e
 # gunzip -dc ad4s3e.gz | ssh eedcoba@host 'dd of=/dev/ad0s3e bs=1M'
 # dd if=/dev/ad0 of=/dev/ad2 skip=1 seek=1 bs=4k conv=noerror    # Skip MBR
     # This is necessary if the destination (ad2) is smaller.
 # dd if=/vm/FreeBSD-8.2-RELEASE-amd64-memstick.img of=/dev/disk1 bs=10240 conv=sy
 nc
     # Copy FreeBSD image to USB memory stick
 
 Recover
 
    The command dd will read every single block of the partition. In case of
    problems it is better to use the option conv=sync,noerror so dd will
    skip the bad block and write zeros at the destination. Accordingly it is
    important to set the block size equal or smaller than the disk block
    size. A 1k size seems safe, set it with bs=1k. If a disk has bad sectors
    and the data should be recovered from a partition, create an image file
    with dd, mount the image and copy the content to a new disk. With the
    option noerror, dd will skip the bad sectors and write zeros instead,
    thus only the data contained in the bad sectors will be lost.
 # dd if=/dev/hda of=/dev/null bs=1m                   # Check for bad blocks
 # dd bs=1k if=/dev/hda1 conv=sync,noerror,notrunc | gzip | ssh \ # Send to remote
 root@fry 'dd of=hda1.gz bs=1k'
 # dd bs=1k if=/dev/hda1 conv=sync,noerror,notrunc of=hda1.img    # Store into an
 image
 # mount -o loop /hda1.img /mnt                        # Mount the image
 # rsync -ax /mnt/ /newdisk/                           # Copy on a new disk
 # dd if=/dev/hda of=/dev/hda                          # Refresh the magnetic stat
 e
   # The above is useful to refresh a disk. It is perfectly safe, but must be unmo
 unted.
 
 Delete
 
 # dd if=/dev/zero of=/dev/hdc                         # Delete full disk
 # dd if=/dev/urandom of=/dev/hdc                      # Delete full disk better
 # kill -USR1 PID                                      # View dd progress (Linux)
 # kill -INFO PID                                      # View dd progress (FreeBSD
 )
 
 MBR tricks
 
    The MBR contains the boot loader and the partition table and is 512
    bytes small. The first 446 are for the boot loader, the bytes 446 to 512
    are for the partition table.
 # dd if=/dev/sda of=/mbr_sda.bak bs=512 count=1       # Backup the full MBR
 # dd if=/dev/zero of=/dev/sda bs=512 count=1          # Delete MBR and partition
 table
 # dd if=/mbr_sda.bak of=/dev/sda bs=512 count=1       # Restore the full MBR
 # dd if=/mbr_sda.bak of=/dev/sda bs=446 count=1       # Restore only the boot loa
 der
 # dd if=/mbr_sda.bak of=/dev/sda bs=1 count=64 skip=446 seek=446 # Restore partit
 ion table
 
 screen
 
    Screen (a must have) has two main functionalities:
      * Run multiple terminal session within a single terminal.
      * A started program is decoupled from the real terminal and can thus
        run in the background. The real terminal can be closed and
        reattached later.
 
 Short start example
 
    start screen with:
 # screen
 
    Within the screen session we can start a long lasting program (like
    top).
 # top
 
    Now detach with Ctrl-a Ctrl-d. Reattach the terminal with:
 # screen -R -D
 
    In detail this means: If a session is running, then reattach. If
    necessary detach and logout remotely first. If it was not running create
    it and notify the user. Or:
 # screen -x
 
    Attach to a running screen in a multi display mode. The console is thus
    shared among multiple users. Very useful for team work/debug!
 
 Screen commands (within screen)
 
    All screen commands start with Ctrl-a.
      * Ctrl-a ? help and summary of functions
      * Ctrl-a c create an new window (terminal)
      * Ctrl-a Ctrl-n and Ctrl-a Ctrl-p to switch to the next or previous
        window in the list, by number.
      * Ctrl-a Ctrl-N where N is a number from 0 to 9, to switch to the
        corresponding window.
      * Ctrl-a " to get a navigable list of running windows
      * Ctrl-a a to clear a missed Ctrl-a
      * Ctrl-a Ctrl-d to disconnect and leave the session running in the
        background
      * Ctrl-a x lock the screen terminal with a password
      * Ctrl-a [ enter into scrollback mode, exit with esc.
        Use echo "defscrollback 5000" > ~/.screenrc to increase buffer
        (default is 100)
 
      * C-u Scrolls a half page up
      * C-b Scroll a full page up
      * C-d Scroll a half page down
      * C-f Scroll a full page down
      * / Search forward
      * ? Search backward
 
    Configuration in ~/.screenrc:
 defscrollback 100000                 # increase scrollback buffer (default is 100
 )
 termcapinfo xterm* ti@:te@           # avoid alternate text buffer to allow scrol
 ling
 
    The screen session is terminated when the program within the running
    terminal is closed and you logout from the terminal.
 
 Find
 
    Some important options:
      * -x (on BSD) -xdev (on Linux)       Stay on the same file system (dev
        in fstab).
      * -exec cmd {} \;       Execute the command and replace {} with the
        full path
      * -iname       Like -name but is case insensitive
      * -ls       Display information about the file (like ls -la)
      * -size n       n is +-n (k M G T P)
      * -cmin n       File's status was last changed n minutes ago.
 
 # find . -type f ! -perm -444        # Find files not readable by all
 # find . -type d ! -perm -111        # Find dirs not accessible by all
 # find /home/user/ -cmin 10 -print   # Files created or modified in the last 10 m
 in.
 # find . -name '*.[ch]' | xargs grep -E 'expr' # Search 'expr' in this dir and be
 low.
 # find / -name "*.core" | xargs rm   # Find core dumps and delete them (also try
 core.*)
 # find / -name "*.core" -print -exec rm {} \;  # Other syntax
       # Find images and create an archive, iname is not case sensitive. -r for ap
 pend
 # find . \( -iname "*.png" -o -iname "*.jpg" \) -print -exec tar -rf images.tar {
 } \;
 # find . -type f -name "*.txt" ! -name README.txt -print  # Exclude README.txt fi
 les
 # find /var/ -size +10M -exec ls -lh {} \;     # Find large files > 10 MB
 # find /var/ -size +10M -ls           # This is simpler
 # find . -size +10M -size -50M -print
 # find /usr/ports/ -name work -type d -print -exec rm -rf {} \;  # Clean the port
 s
       # Find files with SUID; those file are vulnerable and must be kept secure
 # find / -type f -user root -perm -4000 -exec ls -l {} \;
 # find flac/ -iname *.flac -print -size +500k -exec /Applications/Fluke.app/Conte
 nts/MacOS/Fluke {} \;
                                       # I use above to add flac files to iTunes o
 n OSX
 
    Be careful with xarg or exec as it might or might not honor quotings and
    can return wrong results when files or directories contain spaces. In
    doubt use "-print0 | xargs -0" instead of "| xargs". The option -print0
    must be the last in the find command. See this nice mini tutorial for
    findhttp://www.hccfl.edu/pollock/Unix/FindCmd.htm.
 # find . -type f | xargs ls -l       # Will not work with spaces in names
 # find . -type f -print0 | xargs -0 ls -l  # Will work with spaces in names
 # find . -type f -exec ls -l '{}' \; # Or use quotes '{}' with -exec
 
    Duplicate directory tree:
 # find . -type d -exec mkdir -p /tmp/new_dest/{} \;
 
 Miscellaneous
 
 # which command                      # Show full path name of command
 # time command                       # See how long a command takes to execute
 # time cat                           # Use time as stopwatch. Ctrl-c to stop
 # set | grep $USER                   # List the current environment
 # cal -3                             # Display a three month calendar
 # date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]
 # date 10022155                      # Set date and time
 # whatis grep                        # Display a short info on the command or wor
 d
 # whereis java                       # Search path and standard directories for w
 ord
 # setenv varname value               # Set env. variable varname to value (csh/tc
 sh)
 # export varname="value"             # set env. variable varname to value (sh/ksh
 /bash)
 # pwd                                # Print working directory
 # mkdir -p /path/to/dir              # no error if existing, make parent dirs as
 needed
 # mkdir -p project/{bin,src,obj,doc/{html,man,pdf},debug/some/more/dirs}
 # rmdir /path/to/dir                 # Remove directory
 # rm -rf /path/to/dir                # Remove directory and its content (force)
 # rm -- -badchar.txt                 # Remove file whitch starts with a dash (-)
 # cp -la /dir1 /dir2                 # Archive and hard link files instead of cop
 y
 # cp -lpR /dir1 /dir2                # Same for FreeBSD
 # cp unixtoolbox.xhtml{,.bak}        # Short way to copy the file with a new exte
 nsion
 # mv /dir1 /dir2                     # Rename a directory
 # ls -1                              # list one file per line
 # history | tail -50                 # Display the last 50 used commands
 # cd -                               # cd to previous ($OLDPWD) directory
 # /bin/ls| grep -v .py | xargs rm -r # pipe file names to rm with xargs
 
    Check file hashes with openssl. This is a nice alternative to the
    commands md5sum or sha1sum (FreeBSD uses md5 and sha1) which are not
    always installed.
 # openssl md5 file.tar.gz            # Generate an md5 checksum from file
 # openssl sha1 file.tar.gz           # Generate an sha1 checksum from file
 # openssl rmd160 file.tar.gz         # Generate a RIPEMD-160 checksum from file
 
 Install Software
 
    Usually the package manager uses the proxy variable for http/ftp
    requests. In .bashrc:
 export http_proxy=http://proxy_server:3128
 export ftp_proxy=http://proxy_server:3128
 
 List installed packages
 
 # rpm -qa                            # List installed packages (RH, SuSE, RPM bas
 ed)
 # dpkg -l                            # Debian, Ubuntu
 # pkg_info                           # FreeBSD list all installed packages
 # pkg_info -W smbd                   # FreeBSD show which package smbd belongs to
 # pkginfo                            # Solaris
 
    More on RPM:
 # rpm -ql package-name               # list the files for INSTALLED package
 # rpm -qlp package.rpm               # list the files inside package
 
 Add/remove software
 
    Front ends: yast2/yast for SuSE, redhat-config-packages for Red Hat.
 # rpm -i pkgname.rpm                 # install the package (RH, SuSE, RPM based)
 # rpm -e pkgname                     # Remove package
 
 SuSE zypper (see doc and cheet sheet)http://en.opensuse.org/SDB:Zypper_usage
 
 # zypper refresh                     # Refresh repositorie
 # zypper install vim                 # Install the package vim
 # zypper remove vim                  # Remove the package vim
 # zypper search vim                  # Search packages with vim
 # zypper update vim                  # Search packages with vim
 
 Debian
 
 # apt-get update                     # First update the package lists
 # apt-get install emacs              # Install the package emacs
 # dpkg --remove emacs                # Remove the package emacs
 # dpkg -S file                       # find what package a file belongs to
 
 Gentoo
 
    Gentoo uses emerge as the heart of its "Portage" package management
    system.
 # emerge --sync                      # First sync the local portage tree
 # emerge -u packagename              # Install or upgrade a package
 # emerge -C packagename              # Remove the package
 # revdep-rebuild                     # Repair dependencies
 
 Solaris
 
    The <cdrom> path is usually /cdrom/cdrom0.
 # pkgadd -d <cdrom>/Solaris_9/Product SUNWgtar
 # pkgadd -d SUNWgtar                 # Add downloaded package (bunzip2 first)
 # pkgrm SUNWgtar                     # Remove the package
 
 FreeBSD
 
 # pkg_add -r rsync                   # Fetch and install rsync.
 # pkg_delete /var/db/pkg/rsync-xx    # Delete the rsync package
 
    Set where the packages are fetched from with the PACKAGESITE variable.
    For example:
 # export PACKAGESITE=ftp://ftp.freebsd.org/pub/FreeBSD/ports/i386/packages/Latest
 /
 # or ftp://ftp.freebsd.org/pub/FreeBSD/ports/i386/packages-6-stable/Latest/
 
 FreeBSD portshttp://www.freebsd.org/handbook/ports.html
 
    The port tree /usr/ports/ is a collection of software ready to compile
    and install (see man ports). The ports are updated with the program
    portsnap.
 # portsnap fetch extract             # Create the tree when running the first tim
 e
 # portsnap fetch update              # Update the port tree
 # cd /usr/ports/net/rsync/           # Select the package to install
 # make install distclean             # Install and cleanup (also see man ports)
 # make package                       # Make a binary package of this port
 # pkgdb -F                           # Fix the package registry database
 # portsclean -C -DD                  # Clean workdir and distdir (part of portupg
 rade)
 
 OS X MacPortshttp://guide.macports.org/ (use sudo for all commands)
 
 # port selfupdate                    # Update the port tree (safe)
 # port installed                     # List installed ports
 # port deps apache2                  # List dependencies for this port
 # port search pgrep                  # Search for string
 # port install proctools             # Install this package
 # port variants ghostscript          # List variants of this port
 # port -v install ghostscript +no_x11# -no_x11 for negative value
 # port clean --all ghostscript       # Clean workdir of port
 # port upgrade ghostscript           # Upgrade this port
 # port uninstall ghostscript         # Uninstall this port
 # port -f uninstall installed        # Uninstall everything
 
 Library path
 
    Due to complex dependencies and runtime linking, programs are difficult
    to copy to an other system or distribution. However for small programs
    with little dependencies, the missing libraries can be copied over. The
    runtime libraries (and the missing one) are checked with ldd and managed
    with ldconfig.
 # ldd /usr/bin/rsync                 # List all needed runtime libraries
 # otool -L /usr/bin/rsync            # OS X equivalent to ldd
 # ldconfig -n /path/to/libs/         # Add a path to the shared libraries directo
 ries
 # ldconfig -m /path/to/libs/         # FreeBSD
 # LD_LIBRARY_PATH                    # The variable set the link library path
 
 Convert Media
 
    Sometimes one simply need to convert a video, audio file or document to
    another format.
 
 Text encoding
 
    Text encoding can get totally wrong, specially when the language
    requires special characters like àäç. The command iconv can convert from
    one encoding to an other.
 # iconv -f <from_encoding> -t <to_encoding> <input_file>
 # iconv -f ISO8859-1 -t UTF-8 -o file.input > file_utf8
 # iconv -l                           # List known coded character sets
 
    Without the -f option, iconv will use the local char-set, which is
    usually fine if the document displays well.
    Convert filenames from one encoding to another (not file content). Works
    also if only some files are already utf8
 # convmv -r -f utf8 --nfd -t utf8 --nfc /dir/* --notest
 
 Unix - DOS newlines
 
    Convert DOS (CR/LF) to Unix (LF) newlines and back within a Unix shell.
    See also dos2unix and unix2dos if you have them.
 # sed 's/.$//' dosfile.txt > unixfile.txt                  # DOS to UNIX
 # awk '{sub(/\r$/,"");print}' dosfile.txt > unixfile.txt   # DOS to UNIX
 # awk '{sub(/$/,"\r");print}' unixfile.txt > dosfile.txt   # UNIX to DOS
 
    Convert Unix to DOS newlines within a Windows environment. Use sed or
    awk from mingw or cygwin.
 # sed -n p unixfile.txt > dosfile.txt
 # awk 1 unixfile.txt > dosfile.txt   # UNIX to DOS (with a cygwin shell)
 
    Remove ^M mac newline and replace with unix new line. To get a ^M use
    CTL-V then CTL-M
 # tr '^M' '\n' < macfile.txt
 
 PDF images and concatenate PDF files
 
    Convert a PDF document with gs (GhostScript) to jpeg (or png) images for
    each page. Also much shorter with convert and mogrify (from ImageMagick
    or GraphicsMagick).
 # gs -dBATCH -dNOPAUSE -sDEVICE=jpeg -r150 -dTextAlphaBits=4 -dGraphicsAlphaBits=
 4 \
  -dMaxStripSize=8192 -sOutputFile=unixtoolbox_%d.jpg unixtoolbox.pdf
 # convert unixtoolbox.pdf unixtoolbox-%03d.png
 # convert *.jpeg images.pdf          # Create a simple PDF with all pictures
 # convert image000* -resample 120x120 -compress JPEG -quality 80 images.pdf
 # mogrify -format png *.ppm          # convert all ppm images to png format
 
    Ghostscript can also concatenate multiple pdf files into a single one.
    This only works well if the PDF files are "well behaved".
 # gs -q -sPAPERSIZE=a4 -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=all.pdf \
 file1.pdf file2.pdf ...              # On Windows use '#' instead of '='
 
    Create PDF file from images
 # convert 20140416-DSCF1915.jpg 20140416-DSCF1920.jpg all.pdf
 convert 20140416-DSCF1915.jpg 20140416-DSCF1920.jpg -resize 1240x1753 -units Pixe
 lsPerInch \
 -density 150x150 all.pdf             # force A4
 
    Extract images from pdf document using pdfimages from poppler or
    xpdfhttp://foolabs.com/xpdf/download.html
 # pdfimages document.pdf dst/        # extract all images and put in dst
 # yum install poppler-utils          # install poppler-utils if needed. or:
 # apt-get install poppler-utils
 
 Convert video
 
    Compress the Canon digicam video with an mpeg4 codec and repair the
    crappy sound.
 # mencoder -o videoout.avi -oac mp3lame -ovc lavc -srate 11025 \
 -channels 1 -af-adv force=1 -lameopts preset=medium -lavcopts \
 vcodec=msmpeg4v2:vbitrate=600 -mc 0 vidoein.AVI
 
    See sox for sound processing.
 
 Copy an audio cd
 
    The program cdparanoiahttp://xiph.org/paranoia/ can save the audio
    tracks (FreeBSD port in audio/cdparanoia/), oggenc can encode in Ogg
    Vorbis format, lame converts to mp3.
 # cdparanoia -B                      # Copy the tracks to wav files in current di
 r
 # lame -b 256 in.wav out.mp3         # Encode in mp3 256 kb/s
 # for i in *.wav; do lame -b 256 $i `basename $i .wav`.mp3; done
 # oggenc in.wav -b 256 out.ogg       # Encode in Ogg Vorbis 256 kb/s
 
 Printing
 
 Print with lpr
 
 # lpr unixtoolbox.ps                 # Print on default printer
 # export PRINTER=hp4600              # Change the default printer
 # lpr -Php4500 #2 unixtoolbox.ps     # Use printer hp4500 and print 2 copies
 # lpr -o Duplex=DuplexNoTumble ...   # Print duplex along the long side
 # lpr -o PageSize=A4,Duplex=DuplexNoTumble ...
 
 # lpq                                # Check the queue on default printer
 # lpq -l -Php4500                    # Queue on printer hp4500 with verbose
 # lprm -                             # Remove all users jobs on default printer
 # lprm -Php4500 3186                 # Remove job 3186. Find job nbr with lpq
 # lpc status                         # List all available printers
 # lpc status hp4500                  # Check if printer is online and queue lengt
 h
 
    Some devices are not postscript and will print garbage when fed with a
    pdf file. This might be solved with:
 # gs -dSAFER -dNOPAUSE -sDEVICE=deskjet -sOutputFile=\|lpr file.pdf
 
    Print to a PDF file even if the application does not support it. Use gs
    on the print command instead of lpr.
 # gs -q -sPAPERSIZE=a4 -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=/path/fil
 e.pdf
 
 Databases
 
 PostgreSQL
 
 Change root or a username password
 
 # psql -d template1 -U pgsql
 > alter user pgsql with password 'pgsql_password';  # Use username instead of "pg
 sql"
 
 Create user and database
 
    The commands createuser, dropuser, createdb and dropdb are convenient
    shortcuts equivalent to the SQL commands. The new user is bob with
    database bobdb ; use as root with pgsql the database super user:
 # createuser -U pgsql -P bob         # -P will ask for password
 # createdb -U pgsql -O bob bobdb     # new bobdb is owned by bob
 # dropdb bobdb                       # Delete database bobdb
 # dropuser bob                       # Delete user bob
 
    The general database authentication mechanism is configured in
    pg_hba.conf
 
 Grant remote access
 
    The file $PGSQL_DATA_D/postgresql.conf specifies the address to bind to.
    Typically listen_addresses = '*' for Postgres 8.x.
    The file $PGSQL_DATA_D/pg_hba.conf defines the access control. Examples:
 # TYPE  DATABASE    USER        IP-ADDRESS        IP-MASK          METHOD
 host    bobdb       bob        212.117.81.42     255.255.255.255   password
 host    all         all        0.0.0.0/0                           password
 
 Backup and restore
 
    The backups and restore are done with the user pgsql or postgres. Backup
    and restore a single database:
 # pg_dump --clean dbname > dbname_sql.dump
 # psql dbname < dbname_sql.dump
 
    Backup and restore all databases (including users):
 # pg_dumpall --clean > full.dump
 # psql -f full.dump postgres
 
    In this case the restore is started with the database postgres which is
    better when reloading an empty cluster.
 
 MySQL
 
 Change mysql root or username password
 
 Method 1
 
 # /etc/init.d/mysql stop
 or
 # killall mysqld
 # mysqld --skip-grant-tables
 # mysqladmin -u root password 'newpasswd'
 # /etc/init.d/mysql start
 
 Method 2
 
 # mysql -u root mysql
 mysql> UPDATE USER SET PASSWORD=PASSWORD("newpassword") where user='root';
 mysql> FLUSH PRIVILEGES;                           # Use username instead of "roo
 t"
 mysql> quit
 
 Create user and database (see MySQL
 dochttp://dev.mysql.com/doc/refman/5.1/en/adding-users.html)
 
 # mysql -u root mysql
 mysql> CREATE USER 'bob'@'localhost' IDENTIFIED BY 'pwd'; # create only a user
 mysql> CREATE DATABASE bobdb;
 mysql> GRANT ALL ON *.* TO 'bob'@'%' IDENTIFIED BY 'pwd'; # Use localhost instead
  of %
                                                    # to restrict the network acce
 ss
 mysql> DROP DATABASE bobdb;                        # Delete database
 mysql> DROP USER bob;                              # Delete user
 mysql> DELETE FROM mysql.user WHERE user='bob and host='hostname'; # Alt. command
 mysql> FLUSH PRIVILEGES;
 
 Grant remote access
 
    Remote access is typically permitted for a database, and not all
    databases. The file /etc/my.cnf contains the IP address to bind to. (On
    FreeBSD my.cnf not created per fedault, copy one .cnf file from
    /usr/local/share/mysql to /usr/local/etc/my.cnf) Typically comment the
    line bind-address = out.
 # mysql -u root mysql
 mysql> GRANT ALL ON bobdb.* TO bob@'xxx.xxx.xxx.xxx' IDENTIFIED BY 'PASSWORD';
 mysql> REVOKE GRANT OPTION ON foo.* FROM bar@'xxx.xxx.xxx.xxx';
 mysql> FLUSH PRIVILEGES;                  # Use 'hostname' or also '%' for full a
 ccess
 
 Backup and restore
 
    Backup and restore a single database:
 # mysqldump -u root -psecret --add-drop-database dbname > dbname_sql.dump
 # mysql -u root -psecret -D dbname < dbname_sql.dump
 
    Backup and restore all databases:
 # mysqldump -u root -psecret --add-drop-database --all-databases > full.dump
 # mysql -u root -psecret < full.dump
 
    Here is "secret" the mysql root password, there is no space after -p.
    When the -p option is used alone (w/o password), the password is asked
    at the command prompt.
 
 SQLite
 
    SQLitehttp://www.sqlite.org is a small powerful self-contained,
    serverless, zero-configuration SQL database.
 
 Dump and restore
 
    It can be useful to dump and restore an SQLite database. For example you
    can edit the dump file to change a column attribute or type and then
    restore the database. This is easier than messing with SQL commands. Use
    the command sqlite3 for a 3.x database.
 # sqlite database.db .dump > dump.sql              # dump
 # sqlite database.db < dump.sql                    # restore
 
 Convert 2.x to 3.x database
 
 sqlite database_v2.db .dump | sqlite3 database_v3.db
 
 Disk Quota
 
    A disk quota allows to limit the amount of disk space and/or the number
    of files a user or (or member of group) can use. The quotas are
    allocated on a per-file system basis and are enforced by the kernel.
 
 Linux setup
 
    The quota tools package usually needs to be installed, it contains the
    command line tools.
    Activate the user quota in the fstab and remount the partition. If the
    partition is busy, either all locked files must be closed, or the system
    must be rebooted. Add usrquota to the fstab mount options, for example:
 /dev/sda2     /home    reiserfs     rw,acl,user_xattr,usrquota 1 1
 # mount -o remount /home
 # mount                              # Check if usrquota is active, otherwise reb
 oot
 
    Initialize the quota.user file with quotacheck.
 # quotacheck -vum /home
 # chmod 644 /home/aquota.user        # To let the users check their own quota
 
    Activate the quota either with the provided script (e.g.
    /etc/init.d/quotad on SuSE) or with quotaon:
 quotaon -vu /home
 
    Check that the quota is active with:
 quota -v
 
 FreeBSD setup
 
    The quota tools are part of the base system, however the kernel needs
    the option quota. If it is not there, add it and recompile the kernel.
 options QUOTA
 
    As with Linux, add the quota to the fstab options (userquota, not
    usrquota):
 /dev/ad0s1d    /home    ufs     rw,noatime,userquota    2  2
 # mount /home                        # To remount the partition
 
    Enable disk quotas in /etc/rc.conf and start the quota.
 # grep quotas /etc/rc.conf
 enable_quotas="YES"                  # turn on quotas on startup (or NO).
 check_quotas="YES"                   # Check quotas on startup (or NO).
 # /etc/rc.d/quota start
 
 Assign quota limits
 
    The quotas are not limited per default (set to 0). The limits are set
    with edquota for single users. A quota can be also duplicated to many
    users. The file structure is different between the quota
    implementations, but the principle is the same: the values of blocks and
    inodes can be limited. Only change the values of soft and hard. If not
    specified, the blocks are 1k. The grace period is set with edquota -t.
    For example:
 # edquota -u colin
 
 Linux
 
 Disk quotas for user colin (uid 1007):
   Filesystem         blocks       soft       hard     inodes     soft     hard
   /dev/sda8            108       1000       2000          1        0        0
 
 FreeBSD
 
 Quotas for user colin:
 /home: kbytes in use: 504184, limits (soft = 700000, hard = 800000)
    inodes in use: 1792, limits (soft = 0, hard = 0)
 
 For many users
 
    The command edquota -p is used to duplicate a quota to other users. For
    example to duplicate a reference quota to all users:
 # edquota -p refuser `awk -F: '$3 > 499 {print $1}' /etc/passwd`
 # edquota -p refuser user1 user2     # Duplicate to 2 users
 
 Checks
 
    Users can check their quota by simply typing quota (the file quota.user
    must be readable). Root can check all quotas.
 # quota -u colin                     # Check quota for a user
 # repquota /home                     # Full report for the partition for all user
 s
 
 Shells
 
    Most Linux distributions use the bash shell while the BSDs use tcsh, the
    bourne shell is only used for scripts. Filters are very useful and can
    be piped:
      * grep   Pattern matching
      * sed   Search and Replace strings or characters
      * cut   Print specific columns from a marker
      * sort   Sort alphabetically or numerically
      * uniq   Remove duplicate lines from a file
 
    For example used all at once:
 # ifconfig | sed 's/  / /g' | cut -d" " -f1 | uniq | grep -E "[a-z0-9]+" | sort -
 r
 # ifconfig | sed '/.*inet addr:/!d;s///;s/ .*//'|sort -t. -k1,1n -k2,2n -k3,3n -k
 4,4n
 
    The first character in the sed pattern is a tab. To write a tab on the
    console, use ctrl-v ctrl-tab.
 
 bash
 
    Redirects and pipes for bash and sh:
 # cmd 1> file                         # Redirect stdout to file.
 # cmd 2> file                         # Redirect stderr to file.
 # cmd 1>> file                        # Redirect and append stdout to file.
 # cmd &> file                         # Redirect both stdout and stderr to file.
 # cmd >file 2>&1                      # Redirects stderr to stdout and then to fi
 le.
 # cmd1 | cmd2                         # pipe stdout to cmd2
 # cmd1 2>&1 | cmd2                    # pipe stdout and stderr to cmd2
 
    Modify your configuration in ~/.bashrc (it can also be ~/.bash_profile).
    The following entries are useful, reload with ". .bashrc". With cygwin
    use ~/.bash_profile; with rxvt past with shift + left-click.
 # in .bashrc
 bind '"\e[A"':history-search-backward # Use up and down arrow to search
 bind '"\e[B"':history-search-forward  # the history. Invaluable!
 set -o emacs                          # Set emacs mode in bash (see below)
 set bell-style visible                # Do not beep, inverse colors
     # Set a nice prompt like [user@host]/path/todir>
 PS1="\[\033[1;30m\][\[\033[1;34m\]\u\[\033[1;30m\]"
 PS1="$PS1@\[\033[0;33m\]\h\[\033[1;30m\]]\[\033[0;37m\]"
 PS1="$PS1\w\[\033[1;30m\]>\[\033[0m\]"
 
 # To check the currently active aliases, simply type alias
 alias  ls='ls -aF'                    # Append indicator (one of */=>@|)
 alias  ll='ls -aFls'                  # Listing
 alias  la='ls -all'
 alias ..='cd ..'
 alias ...='cd ../..'
 export HISTFILESIZE=5000              # Larger history
 export CLICOLOR=1                     # Use colors (if possible)
 export LSCOLORS=ExGxFxdxCxDxDxBxBxExEx
 
 tcsh
 
    Redirects and pipes for tcsh and csh (simple > and >> are the same as
    sh):
 # cmd >& file                         # Redirect both stdout and stderr to file.
 # cmd >>& file                        # Append both stdout and stderr to file.
 # cmd1 | cmd2                         # pipe stdout to cmd2
 # cmd1 |& cmd2                        # pipe stdout and stderr to cmd2
 
    The settings for csh/tcsh are set in ~/.cshrc, reload with "source
    .cshrc". Examples:
 # in .cshrc
 alias  ls      'ls -aF'
 alias  ll      'ls -aFls'
 alias  la      'ls -all'
 alias  ..      'cd ..'
 alias  ...     'cd ../..'
 set   prompt    = "%B%n%b@%B%m%b%/> " # like user@host/path/todir>
 set   history   =  5000
 set   savehist  = ( 6000 merge )
 set   autolist                        # Report possible completions with tab
 set   visiblebell                     # Do not beep, inverse colors
 
 # Bindkey and colors
 bindkey -e     Select Emacs bindings  # Use emacs keys to edit the command prompt
 bindkey -k up history-search-backward # Use up and down arrow to search
 bindkey -k down history-search-forward
 setenv CLICOLOR 1                     # Use colors (if possible)
 setenv LSCOLORS ExGxFxdxCxDxDxBxBxExEx
 
    The emacs mode enables to use the emacs keys shortcuts to modify the
    command prompt line. This is extremely useful (not only for emacs
    users). The most used commands are:
      * C-a       Move cursor to beginning of line
      * C-e       Move cursor to end of line
      * M-b       Move cursor back one word
      * M-f       Move cursor forward one word
      * M-d       Cut the next word
      * C-w       Cut the last word
      * C-u       Cut everything before the cursor
      * C-k       Cut everything after the cursor (rest of the line)
      * C-y       Paste the last thing to be cut (simply paste)
      * C-_       Undo
 
    Note: C- = hold control, M- = hold meta (which is usually the alt or
    escape key).
 
 Scripting
 
    Basics | Script example | awk | sed | Regular Expressions | useful
    commands
    The Bourne shell (/bin/sh) is present on all Unix installations and
    scripts written in this language are (quite) portable; man 1 sh is a
    good reference.
 
 Basics
 
 Variables and arguments
 
    Assign with variable=value and get content with $variable
 MESSAGE="Hello World"                        # Assign a string
 PI=3.1415                                    # Assign a decimal number
 N=8
 TWON=`expr $N * 2`                           # Arithmetic expression (only intege
 rs)
 TWON=$(($N * 2))                             # Other syntax
 TWOPI=`echo "$PI * 2" | bc -l`               # Use bc for floating point operatio
 ns
 ZERO=`echo "c($PI/4)-sqrt(2)/2" | bc -l`
 
    The command line arguments are
 $0, $1, $2, ...                              # $0 is the command itself
 $#                                           # The number of arguments
 $*                                           # All arguments (also $@)
 
 Special Variables
 
 $$                                           # The current process ID
 $?                                           # exit status of last command
   command
   if [ $? != 0 ]; then
     echo "command failed"
   fi
 mypath=`pwd`
 mypath=${mypath}/file.txt
 echo ${mypath##*/}                           # Display the filename only
 echo ${mypath%%.*}                           # Full path without extention
 foo=/tmp/my.dir/filename.tar.gz
 path = ${foo%/*}                             # Full path without extention
 var2=${var:=string}                          # Use var if set, otherwise use stri
 ng
                                              # assign string to var and then to v
 ar2.
 size=$(stat -c%s "$file")                    # get file size in bourne script
 filesize=${size:=-1}
 
 Constructs
 
 for file in `ls`
 do
     echo $file
 done
 
 count=0
 while [ $count -lt 5 ]; do
     echo $count
     sleep 1
     count=$(($count + 1))
 done
 
 myfunction() {
     find . -type f -name "*.$1" -print       # $1 is first argument of the functi
 on
 }
 myfunction "txt"
 
 Generate a file
 
 MYHOME=/home/colin
 cat > testhome.sh << _EOF
 # All of this goes into the file testhome.sh
 if [ -d "$MYHOME" ] ; then
     echo $MYHOME exists
 else
     echo $MYHOME does not exist
 fi
 _EOF
 sh testhome.sh
 
 Bourne script example
 
    As a small example, the script used to create a PDF booklet from this
    xhtml document:
 #!/bin/sh
 # This script creates a book in pdf format ready to print on a duplex printer
 if [ $# -ne 1 ]; then                        # Check the argument
   echo 1>&2 "Usage: $0 HtmlFile"
   exit 1                                     # non zero exit if error
 fi
 
 file=$1                                      # Assign the filename
 fname=${file%.*}                             # Get the name of the file only
 fext=${file#*.}                              # Get the extension of the file
 
 prince $file -o $fname.pdf                   # from www.princexml.com
 pdftops -paper A4 -noshrink $fname.pdf $fname.ps # create postscript booklet
 cat $fname.ps |psbook|psnup -Pa4 -2 |pstops -b "2:0,1U(21cm,29.7cm)" > $fname.boo
 k.ps
 
 ps2pdf13 -sPAPERSIZE=a4 -sAutoRotatePages=None $fname.book.ps $fname.book.pdf
                                              # use #a4 and #None on Windows!
 exit 0                                       # exit 0 means successful
 
 Some awk commands
 
    Awk is useful for field stripping, like cut in a more powerful way.
    Search this document for other examples. See for example gnulamp.com and
    one-liners for awk for some nice examples.
 awk '{ print $2, $1 }' file                  # Print and inverse first two column
 s
 awk '{printf("%5d : %s\n", NR,$0)}' file     # Add line number left aligned
 awk '{print FNR "\t" $0}' files              # Add line number right aligned
 awk NF test.txt                              # remove blank lines (same as grep '
 .')
 awk 'length > 80'                            # print line longer than 80 char)
 
 Some sed commands
 
    Here is the one liner gold
    minehttp://student.northpark.edu/pemente/sed/sed1line.txt. And a good
    introduction and tutorial to sedhttp://www.grymoire.com/Unix/Sed.html.
 sed 's/string1/string2/g'                    # Replace string1 with string2
 sed -i 's/wroong/wrong/g' *.txt              # Replace a recurring word with g
 sed 's/\(.*\)1/\12/g'                        # Modify anystring1 to anystring2
 sed '/<p>/,/<\/p>/d' t.xhtml                 # Delete lines that start with <p>
                                              # and end with </p>
 sed '/ *#/d; /^ *$/d'                        # Remove comments and blank lines
 sed 's/[ \t]*$//'                            # Remove trailing spaces (use tab as
  \t)
 sed 's/^[ \t]*//;s/[ \t]*$//'                # Remove leading and trailing spaces
 sed 's/[^*]/[&]/'                            # Enclose first char with [] top->[t
 ]op
 sed = file | sed 'N;s/\n/\t/' > file.num     # Number lines on a file
 
 Regular Expressions
 
    Some basic regular expression useful for sed too. See Basic Regex
    Syntaxhttp://www.regular-expressions.info/reference.html for a good
    primer.
 [\^$.|?*+()                          # special characters any other will match th
 emselves
 \                                    # escapes special characters and treat as li
 teral
 *                                    # repeat the previous item zero or more time
 s
 .                                    # single character except line break charact
 ers
 .*                                   # match zero or more characters
 ^                                    # match at the start of a line/string
 $                                    # match at the end of a line/string
 .$                                   # match a single character at the end of lin
 e/string
 ^ $                                  # match line with a single space
 ^[A-Z]                               # match any line beginning with any char fro
 m A to Z
 
 Some useful commands
 
    The following commands are useful to include in a script or as one
    liners.
 sort -t. -k1,1n -k2,2n -k3,3n -k4,4n         # Sort IPv4 ip addresses
 echo 'Test' | tr '[:lower:]' '[:upper:]'     # Case conversion
 echo foo.bar | cut -d . -f 1                 # Returns foo
 PID=$(ps | grep script.sh | grep bin | awk '{print $1}')    # PID of a running sc
 ript
 PID=$(ps axww | grep [p]ing | awk '{print $1}')             # PID of ping (w/o gr
 ep pid)
 IP=$(ifconfig $INTERFACE | sed '/.*inet addr:/!d;s///;s/ .*//')   # Linux
 IP=$(ifconfig $INTERFACE | sed '/.*inet /!d;s///;s/ .*//')        # FreeBSD
 if [ `diff file1 file2 | wc -l` != 0 ]; then [...] fi       # File changed?
 cat /etc/master.passwd | grep -v root | grep -v \*: | awk -F":" \ # Create http p
 asswd
 '{ printf("%s:%s\n", $1, $2) }' > /usr/local/etc/apache2/passwd
 
 testuser=$(cat /usr/local/etc/apache2/passwd | grep -v \    # Check user in passw
 d
 root | grep -v \*: | awk -F":" '{ printf("%s\n", $1) }' | grep ^user$)
 :(){ :|:& };:                                # bash fork bomb. Will kill your mac
 hine
 tail +2 file > file2                         # remove the first line from file
 
    I use this little trick to change the file extension for many files at
    once. For example from .cxx to .cpp. Test it first without the | sh at
    the end. You can also do this with the command rename if installed. Or
    with bash builtins.
 # ls *.cxx | awk -F. '{print "mv "$0" "$1".cpp"}' | sh
 # ls *.c | sed "s/.*/cp & &.$(date "+%Y%m%d")/" | sh # e.g. copy *.c to *.c.20080
 401
 # rename .cxx .cpp *.cxx                             # Rename all .cxx to cpp
 # for i in *.cxx; do mv $i ${i%%.cxx}.cpp; done      # with bash builtins
 
 Programming
 
 C basics
 
 strcpy(newstr,str)                        /* copy str to newstr */
 expr1 ? expr2 : expr3                     /* if (expr1) expr2 else expr3 */
 x = (y > z) ? y : z;                      /* if (y > z) x = y; else x = z; */
 int a[]={0,1,2};                          /* Initialized array (or a[3]={0,1,2};
 */
 int a[2][3]={{1,2,3},{4,5,6}};            /* Array of array of ints */
 int i = 12345;                            /* Convert in i to char str */
 char str[10];
 sprintf(str, "%d", i);
 
 C example
 
    A minimal c program simple.c:
 #include <stdio.h>
 main() {
     int number=42;
     printf("The answer is %i\n", number);
 }
 
    Compile with:
 # gcc simple.c -o simple
 # ./simple
 The answer is 42
 
 C++ basics
 
 *pointer                                  // Object pointed to by pointer
 &obj                                      // Address of object obj
 obj.x                                     // Member x of class obj (object obj)
 pobj->x                                   // Member x of class pointed to by pobj
                                           // (*pobj).x and pobj->x are the same
 
 C++ example
 
    As a slightly more realistic program in C++: a class in its own header
    (IPv4.h) and implementation (IPv4.cpp) and a program which uses the
    class functionality. The class converts an IP address in integer format
    to the known quad format.
 
 IPv4 class
 
 IPv4.h:
 
 #ifndef IPV4_H
 #define IPV4_H
 #include <string>
 
 namespace GenericUtils {                          // create a namespace
 class IPv4 {                                      // class definition
 public:
     IPv4(); ~IPv4();
     std::string IPint_to_IPquad(unsigned long ip);// member interface
 };
 } //namespace GenericUtils
 #endif // IPV4_H
 
 IPv4.cpp:
 
 #include "IPv4.h"
 #include <string>
 #include <sstream>
 using namespace std;                              // use the namespaces
 using namespace GenericUtils;
 
 IPv4::IPv4() {}                                   // default constructor/destruct
 or
 IPv4::~IPv4() {}
 string IPv4::IPint_to_IPquad(unsigned long ip) {  // member implementation
     ostringstream ipstr;                          // use a stringstream
     ipstr << ((ip &0xff000000) >> 24)             // Bitwise right shift
           << "." << ((ip &0x00ff0000) >> 16)
           << "." << ((ip &0x0000ff00) >> 8)
           << "." << ((ip &0x000000ff));
     return ipstr.str();
 }
 
 The program simplecpp.cpp
 
 #include "IPv4.h"
 #include <iostream>
 #include <string>
 using namespace std;
 int main (int argc, char* argv[]) {
     string ipstr;                                 // define variables
     unsigned long ipint = 1347861486;             // The IP in integer form
     GenericUtils::IPv4 iputils;                   // create an object of the clas
 s
     ipstr = iputils.IPint_to_IPquad(ipint);       // call the class member
     cout << ipint << " = " << ipstr << endl;      // print the result
 
     return 0;
 }
 
    Compile and execute with:
 # g++ -c IPv4.cpp simplecpp.cpp                # Compile in objects
 # g++ IPv4.o simplecpp.o -o simplecpp.exe      # Link the objects to final execut
 able
 # ./simplecpp.exe
 1347861486 = 80.86.187.238
 
    Use ldd to check which libraries are used by the executable and where
    they are located. Also used to check if a shared library is missing or
    if the executable is static.
 # ldd /sbin/ifconfig                           # list dynamic object dependencies
 # ar rcs staticlib.a *.o                       # create static archive
 # ar t staticlib.a                             # print the objects list from the
 archive
 # ar x /usr/lib/libc.a version.o               # extract an object file from the
 archive
 # nm version.o                                 # show function members provided b
 y object
 
 Simple Makefile
 
    The minimal Makefile for the multi-source program is shown below. The
    lines with instructions must begin with a tab! The back slash "\" can be
    used to cut long lines.
 CC = g++
 CFLAGS = -O
 OBJS = IPv4.o simplecpp.o
 
 simplecpp: ${OBJS}
         ${CC} -o simplecpp ${CFLAGS} ${OBJS}
 clean:
         rm -f ${TARGET} ${OBJS}
 
 Online Help
 
 Documentation
 
    Linux Documentation      en.tldp.org
    Linux Man Pages          www.linuxmanpages.com
    Linux commands directory www.oreillynet.com/linux/cmd
    Linux doc man howtos     linux.die.net
    FreeBSD Handbook         www.freebsd.org/handbook
    FreeBSD Man Pages        www.freebsd.org/cgi/man.cgi
    FreeBSD user wiki        www.freebsdwiki.net
    Solaris Man Pages        docs.sun.com/app/docs/coll/40.10
 
 Other Unix/Linux references
 
    Rosetta Stone for Unix bhami.com/rosetta.html (a Unix command
    translator)
    Unix guide cross reference unixguide.net/unixguide.shtml
    Linux commands line list www.linuxcmd.org
    Short Linux reference www.pixelbeat.org/cmdline.html
    Little command line goodies www.shell-fu.org
 
    That's all folks!
 
    This document: "Unix Toolbox revision 14.4" is licensed under a Creative
    Commons Licence [Attribution - Share Alike]. © Colin Barschel 2007-2012.
    Some rights reserved.