Unix Toolbox

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Revision: 11

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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.

The latest version of this document can be found at http://cb.vu/unixtoolbox.xhtml.


Running kernel and system information

# uname -a # Get the kernel version (and BSD version)

# 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.

# uptime # Show how long the system has been running + load

# hostname # system's host name

# hostname -i # Display the IP address of the host.

# man hier # Description of the file system hierarchy

# last reboot # Show system reboot history

1.1 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


# 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 properties

# dmidecode # Show DMI/SMBIOS: hw info from the BIOS


# sysctl hw.model # CPU model

# sysctl hw # Gives a lot of hardware information

# sysctl vm # Memory usage

# dmesg | grep "real mem" # 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

1.2 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 intervals)

# systat -tcp 1 # BSD tcp connections (try also -ip)

# systat -netstat 1 # BSD active network connections

# systat -ifstat 1 # BSD network traffic through active interfaces

# systat -iostat 1 # BSD CPU and and disk throughput

# tail -n 500 /var/log/messages # Last 500 kernel/syslog messages

# tail /var/log/warn # System warnings messages see syslog.conf

1.3 Users

# id # Show the active user id with login and group

# last # Show last logins on the system

# who # Show who is logged on the system

# groupadd admin # Add group "admin" and user colin (Linux/Solaris)

# useradd -c "Colin Barschel" -g admin -m colin

# 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.

# echo "Sorry no login now" > /etc/nologin # (Linux)

# echo "Sorry no login now" > /var/run/nologin # (FreeBSD)

1.4 Limits

Some application require higher limits on open files and sockets (like a proxy web server,database). The default limits are usually too low.


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

fs.file-max=102400 # Permanent entry in sysctl.conf

# cat /proc/sys/fs/file-nr # How many file descriptors are in use


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.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

See The FreeBSD handbook Chapter 111 for details.


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 single proc

set rlim_fd_cur = 1024 # Soft limit on file descriptors for a single proc

1.5 Runlevels


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


The actual runlevel (the list is shown below) 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


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)

1.6 Reset root password

Linux method 1

At the boot loader (lilo or grub), enter the following boot option:


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 and Linux method 2

FreeBSD won't 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

Alternatively on FreeBSD, boot in single user mode, remount / rw and use passwd.

# mount -u /; mount -a # will mount / rw

# passwd

# reboot

1.7 Kernel modules


# lsmod # List all modules loaded in the kernel

# modprobe isdn # To load a module (here isdn)


# kldstat # List all modules loaded in the kernel

# kldload crypto # To load a module (here crypto)

1.8 Compile Kernel


# cd /usr/src/linux

# make mrproper # Clean everything, including config files

# make oldconfig # Create a new config file from the current kernel

# 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


To modify and rebuild the kernel, copy the generic configuration file to a new name and edit it as needed. It is however also possible to edit the file GENERIC directly.

# cd /usr/src/sys/i386/conf/


# 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 # Update all configuration and other files

# reboot

For small changes in the source, sometimes the short version is enough:

# make kernel world # Compile and install both kernel and OS

# mergemaster

# reboot


2.1 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:

# ps axww | grep cron

586 ?? Is 0:01.48 /usr/sbin/cron -s

# pgrep -l sshd # Find the PIDs of processes by (part of) name

# fuser -va 22/tcp # List processes using port 22

# fuser -va /home # List processes accessing the /home partiton

# strace df # Trace system calls and signals

# truss df # same as above on FreeBSD/Solaris/Unixware

# history | tail -50 # Display the last 50 used commands

2.2 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!)

2.3 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. For example start two processes, bring them in the background, list the processes with jobs and bring one in the foreground.

# 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

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 &

2.4 Top

The program top displays running information of processes.

# top

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.

2.5 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 umount)

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)


3.1 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 umsak 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 users

# 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 file

# chgrp group /path/to/file # Change the group ownership of a file

3.2 Disk information

# diskinfo -v /dev/ad2 # information about disk (sector/size) FreeBSD

# 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

3.3 Boot


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

3.4 System mount points/Disk usage

# mount | column -t # Show mounted file-systems on the system

# df # display free disk space and mounted devices

# cat /proc/partitions # Show all registered partitions (Linux)

Disk usage

# du -sh * # Directory sizes as listing

# du -csh # Total directory size of the current directory

# du -ks * | sort -n -r # Sort everything by size in kilobytes

# ls -lSr # Show files, biggest last

3.5 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 locking 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}'


# fstat -p 1252


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



Find opened files on a mount point with fuser or lsof:

# fuser -m /home # List processes accessing /home

# lsof /home


tcsh 29029 eedcoba cwd DIR 0,18 12288 1048587 /home/eedcoba (guam:/home)

lsof 29140 eedcoba cwd DIR 0,18 12288 1048587 /home/eedcoba (guam:/home)

About an application:

ps ax | grep Xorg | awk '{print $1}'


# lsof -p 3324


Xorg 3324 root 0w REG 8,6 56296 12492 /var/log/Xorg.0.log

About a single file:

# lsof /var/log/Xorg.0.log


Xorg 3324 root 0w REG 8,6 56296 12492 /var/log/Xorg.0.log

3.6 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


# 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.conf


# mount -t auto /dev/cdrom /mnt/cdrom # typical cdrom mount command

# mount /dev/hdc -t iso9660 -r /cdrom # typical IDE

# mount /dev/sdc0 -t iso9660 -r /cdrom # 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 a device without unmounting it. Necessary for fsck for example

# mount -o remount,ro / # Linux

# mount -o ro / # FreeBSD

Copy the raw data from a cdrom into an iso image:

# dd if=/dev/cd0c of=file.iso

3.7 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.


# smbclient -U user -I -L //smbshare/ # List the shares

# mount -t smbfs -o username=winuser //smbserver/myshare /mnt/smbshare

# mount -t cifs -o username=winuser,password=winpwd // /mnt/share

Additionally with the package mount.cifs it is possible to store the credentials in a file, for

example /home/user/.smb:



And mount as follow:

# mount -t cifs -o credentials=/home/user/.smb // /mnt/smbshare


Use -I to give the IP (or DNS name); smbserver is the Windows name.

# smbutil view -I //winuser@smbserver # List the shares

# mount_smbfs -I //winuser@smbserver/myshare /mnt/smbshare

3.8 Mount an image

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 ext3 fs


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

3.9 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 (page 38).

# 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

On FreeBSD, mkisofs is found in the ports in sysutils/cdrtools.

Burn a CD/DVD ISO image


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:



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


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.

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 program2 can do this. It is in the FreeBSD ports in sysutils/bchunk.

# bchunk imagefile.bin imagefile.cue imagefile.iso

3.10 Create a file based image

For example a partition of 1GB using the file /usr/vdisk.img.


# dd if=/dev/random of=/usr/vdisk.img bs=1K count=1M

# mdconfig -a -t vnode -f /usr/vdisk.img -u 1 # Creates device /dev/md1

# bsdlabel -w /dev/md1

# newfs /dev/md1c

# mount /dev/md1c /mnt

# umount /mnt; mdconfig -d -u 1; rm /usr/vdisk.img # Cleanup the md device


# 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 /dev/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

3.11 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:


# 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


# mount -t tmpfs -osize=64m tmpfs /memdisk

3.12 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


4.1 Debugging (See also Traffic analysis) (page 18)

# mii-diag eth0 # Show the link status (Linux)

# 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

# mii-diag -F 100baseTx-FD eth0 # Force 100Mbit Full duplex (Linux)

# ifconfig fxp0 media 100baseTX mediaopt full-duplex # Same for FreeBSD

# netstat -s # System-wide statistics for each network protocol

4.2 Routing

Print routing table

# route -n # Linux

# netstat -rn # Linux, BSD and UNIX

# route print # Windows

Add and delete a route


# route add

# route delete

# route add default

Add the route permanently in /etc/rc.conf




# route add -net netmask gw

# ip route add via # same as above with ip route

# route add -net netmask dev eth0

# route add default gw

# ip route add default via # same as above with ip route

# route delete -net netmask


# Route add mask

# Route add mask

Use add -p to make the route persistent.

4.3 Configure additional IP addresses


# ifconfig eth0 netmask # First IP

# ifconfig eth0:0 netmask # Second IP


# ifconfig fxp0 inet # First IP

# ifconfig fxp0 alias netmask # Second IP

Permanent entries in /etc/rc.conf

ifconfig_fxp0="inet netmask"

ifconfig_fxp0_alias0=" netmask"

4.4 Change MAC address

# ifconfig eth0 hw ether 00:01:02:03:04:05 # Linux

# ifconfig fxp0 link 00:01:02:03:04:05 # FreeBSD

4.5 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

4.6 Firewall

Check if a firewall is running (typical configuration only):


# iptables -L -n -v # For status

Open the iptables firewall

# iptables -Z # Zero the packet and byte counters in all chains

# iptables -F # Flush all chains

# iptables -X # Delete all chains

# iptables -P INPUT ACCEPT # Open everything

# iptables -P FORWARD ACCEPT

# iptables -P OUTPUT ACCEPT


# ipfw show # For status

# ipfw list 65535 # if answer is "65535 deny ip from any to any" the fw is disabled

# sysctl net.inet.ip.fw.enable=0 # Disable

# sysctl net.inet.ip.fw.enable=1 # Enable

4.7 IP Forward for routing


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


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.

4.8 NAT Network Address Translation


# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE # to activate NAT

# iptables -t nat -A PREROUTING -p tcp -d --dport 20022 -j DNAT \

--to # Port forward 20022 to internal IP port ssh

# iptables -t nat -A PREROUTING -p tcp -d --dport 993:995 -j DNAT \

--to # 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.


# 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


# redirect_port tcp insideIP:2300-2399 3300-3399 # port range

redirect_port udp 7777

4.9 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:


search sleepyowl.net intern.lab

domain sleepyowl.net

Check the system domain name with:

# hostname -d # Same as dnsdomainname


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

# ipconfig /flushdns # Flush the DNS cache

Forward queries

Dig is you friend to test the DNS settings. For example the public DNS server

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


The router answered and the response is the A entry. Any entry can be queried and the DNS server can be selected with @:

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


# dig -x

# host

# nslookup


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: 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:


4.10 DHCP


Some distributions (SuSE) use dhcpcd as client. The default interface is eth0.

# dhcpcd -n eth0 # Trigger a renew

# dhcpcd -k eth0 # release and shutdown

The lease with the full information is stored in:



FreeBSD (and Debian) uses dhclient. To configure an interface (for example bge0) run:

# dhclient bge0

The lease with the full information is stored in:




to prepend options or force different options:

# cat /etc/dhclient.conf

interface "rl0" {

prepend domain-name-servers;

default domain-name "sleepyowl.net";

supersede domain-name "sleepyowl.net";



# 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!

4.11 Traffic analysis

Bmon3 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 \( or\)

# tcpdump -l > dump && tail -f dump # Buffered output

# tcpdump -i rl0 -w traffic.rl0 # Write traffic in binary file

# tcpdump -r traffic.rl0 # Read from file (also for ethereal

# 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 secure

# 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 ASCII

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

Nmap4 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 # 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


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)

4.12 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)





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 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 bandwidth

# ipfw add pipe 1 ip from me to any # divert the full upload into the pipe

Quality of service


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 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


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 # 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

4.13 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

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.


# cat /etc/yp.conf

ypserver servername

domain domain.net broadcast


5.1 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.

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


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


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

Putty5 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


Copy the public key to the server into the ~/.ssh folder:

# scp .ssh/puttykey.pub root@

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

5.2 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.pub

# 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.pub

Now the client connecting to this server can verify that he is connecting to the right server:

# ssh linda

The authenticity of host 'linda (' 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

5.3 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

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 sshfs6.

5.4 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 destination

# 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 \\\, 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

With putty use Source port= It is possible to create multiple loop devices

and tunnel. On Windows 2000, only putty worked for me.

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

# 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 mask, no


advanced->WINS, Enable LMHosts Lookup; Disable NetBIOS over TCP/IP.

# Enable Client for Microsoft Networks. # Disable File and Printer Sharing for Microsoft


I HAD to reboot for this to work. Now connect to the smb share with \\ and remote

desktop to


If it is not working:

Are the ports forwarded: netstat -an? Look at or

Does telnet 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:2022

Now the admin can connect directly to the client cliuser with:

# ssh -p 3022 admin@localhost # local:3022 -> gate:2022 -> client: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


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


PermitRootLogin yes

PermitTunnel yes

6.1 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 (server) and (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 netmask # Executed on the server shell

Server is on FreeBSD

cli># ssh -w5:5 root@hserver

srv># ifconfig tun5 # Executed on the server shell

Configure the client

Commands executed on the client:

cli># ifconfig tun5 netmask # Client is on Linux

cli># ifconfig tun5 # 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.

6.2 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 and netB 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. (netA)|gateA <-> gateB| (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 netmask # Executed on the gateB shell

gateB># route add -net netmask dev tun5

gateB># echo 1 > /proc/sys/net/ipv4/ip_forward # Only needed if not default 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 # Executed on the gateB shell

gateB># route add

gateB># sysctl net.inet.ip.forwarding=1 # Only needed if not default gw

gateB># natd -s -m -u -dynamic -n fxp0 # see NAT (page 15)

gateA># sysctl net.inet.ip.fw.enable=1

Configure gateA

Commands executed on gateA:

gateA is on Linux

gateA># ifconfig tun5 netmask

gateA># route add -net netmask 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

gateA># route add

gateA># sysctl net.inet.ip.forwarding=1

gateA># natd -s -m -u -dynamic -n fxp0 # see NAT (page 15)

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 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/

# rsync -a /var/ /var_bak/

# rsync -aR --delete-during /home/user/ /backup/ # use relative (see below)

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/

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

7.1 Rsync on Windows

Rsync is available for Windows through cygwin or as stand-alone packaged in cwrsync7. 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 server

# 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.


REM rsync the directory My Documents



SET CYGWIN=nontsec


REM uncomment the next line when using cygwin


echo Press Control-C to abort

rsync -av "/cygdrive/c/Documents and Settings/%USERNAME%/My Documents/" \

'user@server:My\ Documents/'



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

8.1 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 =

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 pwd!

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 password.

DEVEL DESKTOP = (ALL) NOPASSWD: ALL # Developers have full right on desktops

DEVEL DMZ = (ALL) NOPASSWD: DEBUG # Developers can debug the DMZ servers.

# User sysadmin can mess around in the DMZ servers with some commands.


sysadmin ALL,!DMZ = (ALL) NOPASSWD: ALL # Can do anything outside the DMZ.

%dba ALL = (DBA) ALL # Group dba can run as database user.

# anyone can mount/unmount a cd-rom on the desktop machines

ALL DESKTOP = NOPASSWD: /sbin/mount /cdrom,/sbin/umount /cdrom


9.1 A single file

Encrypt and decrypt:

# openssl des -salt -in file -out file.des

# openssl des -d -salt -in file.des -out file

Note that the file can of course be a tar archive.

9.2 tar and encrypt a whole directory

# tar -cf - directory | openssl des -salt -out directory.tar.des # Encrypt

# openssl des -d -salt -in directory.tar.des | tar -x # Decrypt

9.3 tar zip and encrypt a whole directory

# tar -zcf - directory | openssl des -salt -out directory.tar.gz.des # Encrypt

# openssl des -d -salt -in directory.tar.gz.des | tar -xz # Decrypt

Use -k mysecretpassword after des to avoid the interactive password request. However note that this is highly insecure.

Use des3 instead of des to get even stronger encryption (Triple-DES Cipher). This uses also more CPU.


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.

10.1 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


# cryptsetup luksOpen /dev/sdc1 sdc1

# mount -t ext3 /dev/mapper/sdc1 /mnt


# umount /mnt

# cryptsetup luksClose sdc1

dm-crypt without LUKS

# cryptsetup -y create sdc1 /dev/sdc1 # or any other partition like /dev/loop0

# 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.

10.2 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 18.68 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 disks

# geli attach -k /root/ad1.key /dev/ad1 # DO make a backup of /root/ad1.key

# dd if=/dev/random of=/dev/ad1.eli bs=1m # Optional and takes a long time

# newfs /dev/ad1.eli # Create file system

# mount /dev/ad1.eli /mnt


# geli attach -k /root/ad1.key /dev/ad1

# fsck -ny -t ffs /dev/ad1.eli # In doubt check the file system

# mount /dev/ad1.eli /mnt


The detach procedure is done automatically on shutdown.

# umount /mnt

# geli detach /dev/ad1.eli


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_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

— Encrypt Partitions —



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).

11.1 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.).

11.2 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

11.3 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

11.4 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

— SSL Certificates —


11.5 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.

11.6 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:







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!

11.7 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

12. CVS

12.1 Server setup

Initiate the CVS

Decide where the main repository will rest and create a root cvs. For example /usr/local/cvs (as


# 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

# cvs checkout CVSROOT # Checkout the config files to modify them


edit config ( fine as it is)

# cvs commit config

cat >> writers # Create a writers file (optionally also readers)


^D # Use [Control][D] to quit the edit

# cvs add writers # Add the file writers into the repository

# cvs edit checkoutlist

# cat >> checkoutlist


^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. 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


12.2 Test it

Test the login as normal user (for example here me)

# cvs -d :pserver:colin@ login

Logging in to :pserver:colin@

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 with SSH

# setenv CVS_RSH ssh # for the ext access

# setenv CVSROOT :pserver:user@cvsserver.254:/usr/local/cvs # network with pserver

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@ import MyProject MyCompany START

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@ checkout MyProject


# setenv CVSROOT :pserver:colin@

# cvs checkout MyProject

12.3 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 server. 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

12.4 CVS commands and usage


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 file

# 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

13. SVN

Subversion (SVN)9 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 book10.

13.1 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.

http:// Remote access with webdav using apache. No local users are necessary for this


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


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 control

<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


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

project1-developers = joe, jack, jane

# Give write access to the developers


@project1-developers = rw

13.2 SVN commands and usage

See also the Subversion Quick Reference Card11. Tortoise SVN12 is a nice Windows interface.


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 newdir'

Typical SVN commands

# svn co http://host.url/svn/project1/trunk # Checkout the most recent version

# 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 \


# svn status [--verbose] # Check files status into working dir

# svn add src/file.h src/file.cpp # Add two files

# svn commit -m 'Added new class file' # Commit the changes with a message

# 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


14.1 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



14.2 vi

Vi is present on ANY Linux/Unix installation 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.


: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 text

dd delete current line

D Delete to the end of the line

dw Delete word

x Delete character

u Undo last

U Undo all changes to current line

14.3 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."




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.

14.4 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


# 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


# tar -tzf home.tgz # look inside the archive without extracting (list)

# tar -xf home.tar # extract the archive here (x for extract)

# tar -xzf home.tgz # same with zip compression

# tar -xjf home.tgz # same with bzip2 compression

# tar -xjf home.tgz home/colin/file.txt # Restore a single file

More advanced

# tar c dir/ | gzip | ssh user@remote 'dd of=dir.tgz' # arch dir/ and store remotely.

# tar cvf - `find . -print` > backup.tar # arch the current directory.

# tar -cf - -C /etc . | tar xpf - -C /backup/etc # Copy directories

# tar -cf - -C /etc . | ssh user@remote tar xpf - -C /backup/etc # Remote copy.

# tar -czf home.tgz --exclude '*.o' --exclude 'tmp/' home/

14.5 dd

The program dd (disk dump) is used to copy partitions and disks and for other copy tricks.

Typical usage:

# dd if=<source> of=<target> bs=<byte size> conv=<conversion>

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 partiton 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 size)

# 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 zip

# dd bs=1M if=/dev/ad4s3e | gzip | ssh eedcoba@fry 'dd of=ad4s3e.gz' # also remote

# 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.


The command dd will read every single block of the partiton, even the blocks. 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 partiton, 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 (page 12)

# rsync -ax /mnt/ /newdisk/ # Copy on a new disk

# dd if=/dev/hda of=/dev/hda # Refresh the magnetic state

# The above is useful to refresh a disk. It is perfectly safe, but must be unmounted.


# dd if=/dev/zero of=/dev/hdc count=1 # Delete MBR and partiton table

# 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 only!)

14.6 screen

Screen 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). Detach the terminal

and reattach the same terminal from an other machine (over ssh for example).

# top

Now detach with Ctrl-a Ctrl-d. Reattach the terminal with

# screen -r

or better:

# screen -R -D

Attach here and now. 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.

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


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

— Useful Commands —


The screen session is terminated when the program within the running terminal is closed and you logout from the terminal.

14.7 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 min.

# find . -name '*.[ch]' | xargs grep -E 'expr' # Search 'expr' in this dir and below.

# find / -name "*.core" | xargs rm # Find core dumps and delete them

# find / -name "*.core" -print -exec rm {} \; # Other syntax

# find . \( -name "*.png" -o -name "*.jpg" \) -print

# iname is not case sensitive

# find . \( -iname "*.png" -o -iname "*.jpg" \) -print -exec tar -rf images.tar {} \;

# find . -type f -name "*.txt" ! -name README.txt -print # Exclude README.txt files

# find /var/ -size +1M -exec ls -lh {} \;

# find /var/ -size +1M -ls # This is simpler

# find . -size +10M -size -50M -print

# find /usr/ports/ -name work -type d -print -exec rm -rf {} \; # Clean the ports

Find files with SUID; those file have to be kept secure

# find / -type f -user root -perm -4000 -exec ls -l {} \;

14.8 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 word

# whereis java # Search path and standard directories for word

# setenv varname value # Set env. variable varname to value (csh/tcsh)

# 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

# rmdir /path/to/dir # Remove directory

# rm -rf /path/to/dir # Remove directory and its content (force)

# cp -la /dir1 /dir2 # Archive and hard link files instead of copy

# cp -lpR /dir1 /dir2 # Same for FreeBSD

# mv /dir1 /dir2 # Rename a directory


15.1 List installed packages

# rpm -qa # List installed packages (RH, SuSE, RPM based)

# dpkg -l # Debian, Ubuntu

# pkg_info -W smbd # FreeBSD show which package smbd belongs to

# pkginfo # Solaris

15.2 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


# apt-get update # First update the package lists

# apt-get install emacs # Install the package emacs

# dpkg --remove emacs # Remove the package emacs


# 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 ports. The port tree /usr/ports/ is a collection of software ready to compile and install. The ports are updated with the program portsnap.

# portsnap fetch extract # Create the tree when running the first time

# 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 for the port

15.3 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

# ldconfig -n /path/to/libs/ # Add a path to the shared libraries directories

# ldconfig -m /path/to/libs/ # FreeBSD

# LD_LIBRARY_PATH # The variable set the link library path


Sometimes one simply need to convert a video, audio file or document to another format.

16.1 Text encoding

Text encoding can get totally wrong, specially when the language requires special characters like адз. 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.

16.2 Unix - DOS newlines

Convert DOS (CR/LF) to Unix (LF) newlines within a Unix shell. See also dos2unix and unix2dos

if you have them.

# sed 's/.$//' dosfile.txt > unixfile.txt

Convert Unix to DOS newlines within a Windows environment. Use sed from mingw or cygwin.

# sed -n p unixfile.txt > dosfile.txt

16.3 PDF to Jpeg and concatenate PDF files

Convert a PDF document with gs (GhostScript) to jpeg (or png) images for each page. Also

much shorter with convert (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

Ghostscript can also concatenate multiple pdf files into a single one.

# gs -q -sPAPERSIZE=a4 -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=all.pdf \

file1.pdf file2.pdf ... # On Windows use '#' instead of '='

16.4 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

16.5 Copy an audio cd

The program cdparanoia13 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 dir

# 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



17.1 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 length


18.1 PostgreSQL

Change root or a username password

# psql -d template1 -U pgsql

> alter user pgsql with password 'pgsql_password'; # Use username instead of "pgsql"

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:


host bobdb bob password

host all all password

Backup and restore

The backups and restore are done with the user pgsql or postgres. Backup and restore a single


# 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.

18.2 MySQL

Change mysql root or username password

Method 1

# /etc/init.d/mysql stop


# 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 "root"

mysql> quit

Create user and database

# mysql -u root mysql

mysql> CREATE DATABASE bobdb;

mysql> GRANT ALL ON *.* TO 'bob'@'%' IDENTIFIED BY 'pwd'; # Use localhost instead of %

# to restrict the network access

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


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. 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 access

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.

18.1 SQLite

SQLite14 is a small powerfull self-contined, serverless, zero-configuration SQL database.


— Databases —


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


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.

19.1 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 reboot

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 -vu /home

Check that the quota is active with:

quota -v

19.2 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

19.3 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


Disk quotas for user colin (uid 1007):

Filesystem blocks soft hard inodes soft hard

/dev/sda8 108 1000 2000 1 0 0


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


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 users


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 -k4,4n

The first character in the sed pattern is a tab. To write a tab on the console, use ctrl-v ctrl-tab.

20.1 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 file.

# 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".

# 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>




# 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

20.2 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

— Shells —


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).


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.

21.1 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


TWON=`expr $N * 2` # Arithmetic expression (only integers)

TWON=$(($N * 2)) # Other syntax

TWOPI=`echo "$PI * 2" | bc -l` # Use bc for floating point operations

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


if [ $? != 0 ]; then

echo "command failed"




echo ${mypath##*/} # Display the filename only

echo ${mypath%%.*} # Full path without extention

var2=${var:=string} # Use var if set, otherwise use string

# assign string to var and then to var2.


for file in `ls`


echo $file



while [ $count -lt 5 ]; do

echo $count

sleep 1

count=$(($count + 1))


myfunction() {

find . -type f -name "*.$1" -print # $1 is first argument of the function


myfunction "txt"

Generate a file


cat > testhome.sh << _EOF

# All of this goes into the file testhome.sh

if [ -d "$MYHOME" ] ; then

echo $MYHOME exists


echo $MYHOME does not exist



sh testhome.sh

21.2 Bourne script example

As a small example, the script used to create a PDF booklet from this xhtml document:


# 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


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.book.ps

ps2pdf13 -sPAPERSIZE=a4 -sAutoRotatePages=None $fname.book.ps $fname.book.pdf

# use #a4 and #None on Windows!

exit 0 # exit 0 means successful

21.3 Some sed commands

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

21.4 Some useful commands

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 script

PID=$(ps axww | grep [p]ing | awk '{print $1}') # PID of ping (w/o grep 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 passwd

'{ printf("%s:%s\n", $1, $2) }' > /usr/local/etc/apache2/passwd

testuser=$(cat /usr/local/etc/apache2/passwd | grep -v \ # Check user in passwd

root | grep -v \*: | awk -F":" '{ printf("%s\n", $1) }' | grep ^user$)


22.1 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);

22.2 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

22.3 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

22.4 C++ example

As a slightly more realistic program in C++, let's create a class in its own header (IPv4.h) and

implementation (IPv4.cpp) and create a program which uses the class functionality. The class has a member to convert an IP address in integer format to the known quad format. This is a minimal c++ program with a class and multi-source compile.

IPv4 class


#ifndef IPV4_H

#define IPV4_H

#include <string>

namespace GenericUtils { // create a namespace

class IPv4 { // class definition




std::string IPint_to_IPquad(unsigned long ip);// member interface


} //namespace GenericUtils

#endif // IPV4_H


#include "IPv4.h"

#include <string>

#include <sstream>

using namespace std; // use the namespaces

using namespace GenericUtils;

IPv4::IPv4() {} // default constructor/destructor

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 class

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 executable

# ./simplecpp.exe

1347861486 =

Use ldd to check which libraries are used by the executable and where they are located. This command is also used to check if a shared library is missing or if the executable is static.

# ldd /sbin/ifconfig

22.5 Simple Makefile

The corresponding 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++


OBJS = IPv4.o simplecpp.o

simplecpp: ${OBJS}

${CC} -o simplecpp ${CFLAGS} ${OBJS}


rm -f ${TARGET} ${OBJS}


23.1 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

23.2 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.linuxguide.it/commands_list.php

Short Linux reference www.pixelbeat.org/cmdline.html

That's all folks!

This document: "Unix Toolbox revision 11" is licensed under a Creative Commons Licence