Unix Toolbox

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Revision: 11

C версии: 1.5

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.

1. SYSTEM

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

Linux

# cat /proc/cpuinfo # CPU model

# cat /proc/meminfo # Hardware memory

# grep MemTotal /proc/meminfo # Display the physical memory

# watch -n1 'cat /proc/interrupts' # Watch changeable interrupts continuously

# free -m # Used and free memory (-m for MB)

# cat /proc/devices # Configured devices

# lspci -tv # Show PCI devices

# lsusb -tv # Show USB devices

# lshal # Show a list of all devices with their properties

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

FreeBSD

# 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.

Linux

Per shell/script

The shell limits are governed by ulimit. The status is checked with ulimit -a. For example to change the open files limit from 1024 to 10240 do:

# ulimit -n 10240 # This is only valid within the shell

The ulimit command can be used in a script to change the limits for the script only.

Per user/process

Login users and applications can be configured in /etc/security/limits.conf. For example:

# cat /etc/security/limits.conf

* hard nproc 250 # Limit user processes

asterisk hard nofile 409600 # Limit application open files

System wide

Kernel limits are set with sysctl. Permanent limits are set in /etc/sysctl.conf.

# sysctl -a # View all system limits

# sysctl fs.file-max # View max open files limit

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

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

FreeBSD

Per shell/script

Use the command limits in csh or tcsh or as in Linux, use ulimit in an sh or bash shell.

Per user/process

The default limits on login are set in /etc/login.conf. An unlimited value is still limited by the

system maximal value.

System wide

Kernel limits are also set with sysctl. Permanent limits are set in /etc/sysctl.conf or /boot/

loader.conf. The syntax is the same as Linux but the keys are different.

# sysctl -a # View all system limits

# sysctl kern.maxfiles=XXXX # maximum number of file descriptors

kern.ipc.nmbclusters=32768 # Permanent entry in /etc/sysctl.conf

kern.maxfiles=65536 # Typical values for Squid

kern.maxfilesperproc=32768

kern.ipc.somaxconn=8192 # TCP queue. Better for apache/sendmail

# sysctl kern.openfiles # How many file descriptors are in use

# sysctl kern.ipc.numopensockets # How many open sockets are in use

See The FreeBSD handbook Chapter 111 for details.

Solaris

The following values in /etc/system will increase the maximum file descriptors per proc:

set rlim_fd_max = 4096 # Hard limit on file descriptors for a single proc

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

1.5 Runlevels

Linux

Once booted, the kernel starts init which then starts rc which starts all scripts belonging to a runlevel. The scripts are stored in /etc/init.d and are linked into /etc/rc.d/rcN.d with N the runlevel number.

The default runlevel is configured in /etc/inittab. It is usually 3 or 5:

# grep default: /etc/inittab

id:3:initdefault:

The actual runlevel (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

1.http://www.freebsd.org/handbook/configtuning-kernel-limits.html

# chkconfig sshd --level 35 on # Configure sshd for levels 3 and 5

# chkconfig sshd off # Disable sshd for all runlevels

Debian and Debian based distributions like Ubuntu or Knoppix use the command update-rc.d

to manage the runlevels scripts. Default is to start in 2,3,4 and 5 and shutdown in 0,1 and 6.

# update-rc.d sshd defaults # Activate sshd with the default runlevels

# update-rc.d sshd start 20 2 3 4 5 . stop 20 0 1 6 . # With explicit arguments

# update-rc.d -f sshd remove # Disable sshd for all runlevels

# shutdown -h now (or # poweroff) # Shutdown and halt the system

FreeBSD

The BSD boot approach is different from the SysV, there are no runlevels. The final boot state (single user, with or without X) is configured in /etc/ttys. All OS scripts are located in /etc/rc.d/ and in /usr/local/etc/rc.d/ for third-party applications. The activation of the service is configured in /etc/rc.conf and /etc/rc.conf.local. The default behavior is configured in /etc/defaults/rc.conf. The scripts responds at least to start|stop|status.

# /etc/rc.d/sshd status

sshd is running as pid 552.

# shutdown now # Go into single-user mode

# exit # Go back to multi-user mode

# shutdown -p now # Shutdown and halt the system

# shutdown -r now # Reboot

The process init can also be used to reach one of the following states level. For example #

init 6 for reboot.

0 Halt and turn the power off (signal USR2)

1 Go to single-user mode (signal TERM)

6 Reboot the machine (signal INT)

c Block further logins (signal TSTP)

q Rescan the ttys(5) file (signal HUP)

1.6 Reset root password

Linux method 1

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

init=/bin/sh

The kernel will mount the root partition and init will start the bourne shell instead of rc and then a runlevel. Use the command passwd at the prompt to change the password and then reboot. Forget the single user mode as you need the password for that.

If, after booting, the root partition is mounted read only, remount it rw:

# mount -o remount,rw /

# passwd # or delete the root password (/etc/shadow)

# sync; mount -o remount,ro / # sync before to remount read only

# reboot

FreeBSD 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

Linux

# lsmod # List all modules loaded in the kernel

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

FreeBSD

# kldstat # List all modules loaded in the kernel

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

1.8 Compile Kernel

Linux

# 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

FreeBSD

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/

# cp GENERIC MYKERNEL

# cd /usr/src

# make buildkernel KERNCONF=MYKERNEL

# make installkernel KERNCONF=MYKERNEL

To rebuild the full OS:

# make buildworld # Build the full OS but not the kernel

# make buildkernel # Use KERNCONF as above if appropriate

# make installkernel

# reboot

# mergemaster -p # Compares only files known to be essential

# make installworld

# mergemaster # 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. PROCESSES

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. FILE SYSTEM

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

FreeBSD

To boot an old kernel if the new kernel doesn't boot, stop the boot at during the count down.

# unload

# load kernel.old

# boot

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}'

1252

# fstat -p 1252

USER CMD PID FD MOUNT INUM MODE SZ|DV R/W

root Xorg 1252 root / 2 drwxr-xr-x 512 r

root Xorg 1252 text /usr 216016 -rws--x--x 1679848 r

root Xorg 1252 0 /var 212042 -rw-r--r-- 56987 w

The file with inum 212042 is the only file in /var:

# find -x /var -inum 212042

/var/log/Xorg.0.log

Linux

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

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

# lsof /home

COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME

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

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

About an application:

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

3324

# lsof -p 3324

COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME

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

About a single file:

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

COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME

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

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

FreeBSD

# mount -v -t cd9660 /dev/cd0c /mnt # cdrom

# mount_cd9660 /dev/wcd0c /cdrom # other method

# mount -v -t msdos /dev/fd0c /mnt # floppy

Entry in /etc/fstab:

# Device Mountpoint FStype Options Dump Pass#

/dev/acd0 /cdrom cd9660 ro,noauto 0 0

To let users do it:

# sysctl vfs.usermount=1 # Or insert the line "vfs.usermount=1" in /etc/sysctl.conf

Linux

# 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

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.

Linux

# smbclient -U user -I 192.168.16.229 -L //smbshare/ # List the shares

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

# mount -t cifs -o username=winuser,password=winpwd //192.168.16.229/myshare /mnt/share

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

example /home/user/.smb:

username=winuser

password=winpwd

And mount as follow:

# mount -t cifs -o credentials=/home/user/.smb //192.168.16.229/myshare /mnt/smbshare

FreeBSD

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

# smbutil view -I 192.168.16.229 //winuser@smbserver # List the shares

# mount_smbfs -I 192.168.16.229 //winuser@smbserver/myshare /mnt/smbshare

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

FreeBSD

With memory device (do # kldload md.ko if necessary):

# mdconfig -a -t vnode -f file.iso -u 0

# mount -t cd9660 /dev/md0 /mnt

# umount /mnt; mdconfig -d -u 0 # Cleanup the md device

Or with virtual node:

# vnconfig /dev/vn0c file.iso; mount -t cd9660 /dev/vn0c /mnt

# umount /mnt; vnconfig -u /dev/vn0c # Cleanup the vn device

Solaris and FreeBSD

with loop-back file interface or lofi:

# lofiadm -a file.iso

# mount -F hsfs -o ro /dev/lofi/1 /mnt

# umount /mnt; lofiadm -d /dev/lofi/1 # Cleanup the lofi device

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

FreeBSD does not enable DMA on ATAPI drives by default. DMA is enabled with the sysctl command and the arguments below, or with /boot/loader.conf with the following entries:

hw.ata.ata_dma="1"

hw.ata.atapi_dma="1"

Use burncd with an ATAPI device (burncd is part of the base system) and cdrecord (in sysutils/

cdrtools) with a SCSI drive.

# burncd -f /dev/acd0 data imagefile.iso fixate # For ATAPI drive

# cdrecord -scanbus # To find the burner device (like 1,0,0)

# cdrecord dev=1,0,0 imagefile.iso

Linux

Also use cdrecord with Linux as described above. Additionally it is possible to use the native ATAPI interface which is found with:

# cdrecord dev=ATAPI -scanbus

And burn the CD/DVD as above.

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.

FreeBSD

# 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

Linux

# dd if=/dev/zero of=/usr/vdisk.img bs=1024k count=1024

# mkfs.ext3 /usr/vdisk.img

2.http://freshmeat.net/projects/bchunk/

# 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:

FreeBSD

# mount_mfs -o rw -s 64M md /memdisk

# umount /memdisk; mdconfig -d -u 0 # Cleanup the md device

md /memdisk mfs rw,-s64M 0 0 # /etc/fstab entry

Linux

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

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. NETWORK

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

FreeBSD

# route add 212.117.0.0/16 192.168.1.1

# route delete 212.117.0.0/16

# route add default 192.168.1.1

Add the route permanently in /etc/rc.conf

static_routes="myroute"

route_myroute="-net 212.117.0.0/16 192.168.1.1"

Linux

# route add -net 192.168.20.0 netmask 255.255.255.0 gw 192.168.16.254

# ip route add 192.168.20.0/24 via 192.168.16.254 # same as above with ip route

# route add -net 192.168.20.0 netmask 255.255.255.0 dev eth0

# route add default gw 192.168.51.254

# ip route add default via 192.168.51.254 # same as above with ip route

# route delete -net 192.168.20.0 netmask 255.255.255.0

Windows

# Route add 192.168.50.0 mask 255.255.255.0 192.168.51.253

# Route add 0.0.0.0 mask 0.0.0.0 192.168.51.254

Use add -p to make the route persistent.

4.3 Configure additional IP addresses

Linux

# ifconfig eth0 192.168.50.254 netmask 255.255.255.0 # First IP

# ifconfig eth0:0 192.168.51.254 netmask 255.255.255.0 # Second IP

FreeBSD

# ifconfig fxp0 inet 192.168.50.254/24 # First IP

# ifconfig fxp0 alias 192.168.51.254 netmask 255.255.255.0 # Second IP

Permanent entries in /etc/rc.conf

ifconfig_fxp0="inet 192.168.50.254 netmask 255.255.255.0"

ifconfig_fxp0_alias0="192.168.51.254 netmask 255.255.255.0"

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):

Linux

# 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

FreeBSD

# 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

Linux

Check and then enable IP forward with:

# cat /proc/sys/net/ipv4/ip_forward # Check IP forward 0=off, 1=on

# echo 1 > /proc/sys/net/ipv4/ip_forward

or edit /etc/sysctl.conf with:

net.ipv4.ip_forward = 1

FreeBSD

Check and enable with:

# sysctl net.inet.ip.forwarding # Check IP forward 0=off, 1=on

# sysctl net.inet.ip.forwarding=1

# sysctl net.inet.ip.fastforwarding=1 # For dedicated router or firewall

Permanent with entry in /etc/rc.conf:

gateway_enable="YES" # Set to YES if this host will be a gateway.

4.8 NAT Network Address Translation

Linux

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

# iptables -t nat -A PREROUTING -p tcp -d 78.31.70.238 --dport 20022 -j DNAT \

--to 192.168.16.44:22 # Port forward 20022 to internal IP port ssh

# iptables -t nat -A PREROUTING -p tcp -d 78.31.70.238 --dport 993:995 -j DNAT \

--to 192.168.16.254:993:995 # Port forward of range 993-995

# ip route flush cache

# iptables -L -t nat # Check NAT status

Delete the port forward with -D instead of -A.

FreeBSD

# natd -s -m -u -dynamic -f /etc/natd.conf -n fxp0

Or edit /etc/rc.conf with:

firewall_enable="YES" # Set to YES to enable firewall functionality

firewall_type="open" # Firewall type (see /etc/rc.firewall)

natd_enable="YES" # Enable natd (if firewall_enable == YES).

natd_interface="tun0" # Public interface or IP address to use.

natd_flags="-s -m -u -dynamic -f /etc/natd.conf"

Port forward with:

# cat /etc/natd.conf

same_ports yes

use_sockets yes

unregistered_only

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

redirect_port udp 192.168.51.103:7777 7777

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:

nameserver 78.31.70.238

search sleepyowl.net intern.lab

domain sleepyowl.net

Check the system domain name with:

# hostname -d # Same as dnsdomainname

Windows

On Windows the DNS are configured per interface. To display the configured DNS and to flush the DNS cache use:

# ipconfig /? # Display help

# ipconfig /all # See all information including DNS

# ipconfig /flushdns # Flush the DNS cache

Forward queries

Dig is you friend to test the DNS settings. For example the public DNS server 213.133.105.2

ns.second-ns.de can be used for testing. See from which server the client receives the answer

(simplified answer).

# dig sleepyowl.net

sleepyowl.net. 600 IN A 78.31.70.238

;; SERVER: 192.168.51.254#53(192.168.51.254)

The router 192.168.51.254 answered and the response is the A entry. Any entry can be queried and the DNS server can be selected with @:

The program host is also powerful.

# host -t MX cb.vu # Get the mail MX entry

# host -t NS -T sun.com # Get the NS record over a TCP connection

# host -a sleepyowl.net # Get everything

Reverse queries

Find the name belonging to an IP address (in-addr.arpa.). This can be done with dig, host and

nslookup:

# dig -x 78.31.70.238

# host 78.31.70.238

# nslookup 78.31.70.238

/etc/hosts

Single hosts can be configured in the file /etc/hosts instead of running named locally to resolve the hostname queries. The format is simple, for example:

78.31.70.238 sleepyowl.net sleepyowl

The priority between hosts and a dns query, that is the name resolution order, can be

configured in /etc/nsswitch.conf AND /etc/host.conf. The file also exists on Windows, it is

usually in:

C:\WINDOWS\SYSTEM32\DRIVERS\ETC

4.10 DHCP

Linux

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:

/var/lib/dhcpcd/dhcpcd-eth0.info

FreeBSD

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

# dhclient bge0

The lease with the full information is stored in:

/var/db/dhclient.leases.bge0

Use

/etc/dhclient.conf

to prepend options or force different options:

# cat /etc/dhclient.conf

interface "rl0" {

prepend domain-name-servers 127.0.0.1;

default domain-name "sleepyowl.net";

supersede domain-name "sleepyowl.net";

}

Windows

# 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 \(192.168.16.121 or 192.168.16.54\)

# 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 192.168.16.0/24 # Find out which IP are used and by which host on 0/24

# nmap -sS -sV -O cb.vu # Do a stealth SYN scan with version and OS detection

PORT STATE SERVICE VERSION

22/tcp open ssh OpenSSH 3.8.1p1 FreeBSD-20060930 (protocol 2.0)

25/tcp open smtp Sendmail smtpd 8.13.6/8.13.6

80/tcp open http Apache httpd 2.0.59 ((FreeBSD) DAV/2 PHP/4.

[...]

Running: FreeBSD 5.X

Uptime 33.120 days (since Fri Aug 31 11:41:04 2007)

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)

speed.

3.http://people.suug.ch/~tgr/bmon/

4.http://insecure.org/nmap/

Linux

For a 512 Kbit upload modem.

# tc qdisc add dev eth0 root tbf rate 480kbit latency 50ms burst 1540

# tc -s qdisc ls dev eth0 # Status

# tc qdisc del dev eth0 root # Delete the queue

# tc qdisc change dev eth0 root tbf rate 220kbit latency 50ms burst 1540

FreeBSD

FreeBSD uses the dummynet traffic shaper which is configured with ipfw. Pipes are used to set limits the bandwidth in units of [K|M]{bit/s|Byte/s}, 0 means unlimited bandwidth. Using the same pipe number will reconfigure it. For example limit the upload bandwidth to 500 Kbit.

# kldload dummynet # load the module if necessary

# ipfw pipe 1 config bw 500Kbit/s # create a pipe with limited bandwidth

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

Quality of service

Linux

Priority queuing with tc to optimize VoIP. See the full example on voip-info.org or

www.howtoforge.com. Suppose VoIP uses udp on ports 10000:11024 and device eth0 (could also be ppp0 or so). The following commands define the QoS to three queues and force the VoIP traffic to queue 1 with QoS 0x1e (all bits set). The default traffic flows into queue 3 and QoS

Minimize-Delay flows into queue 2.

# tc qdisc add dev eth0 root handle 1: prio priomap 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 0

# tc qdisc add dev eth0 parent 1:1 handle 10: sfq

# tc qdisc add dev eth0 parent 1:2 handle 20: sfq

# tc qdisc add dev eth0 parent 1:3 handle 30: sfq

# tc filter add dev eth0 protocol ip parent 1: prio 1 u32 \

match ip dport 10000 0x3C00 flowid 1:1 # use server port range

match ip dst 123.23.0.1 flowid 1:1 # or/and use server IP

Status and remove with

# tc -s qdisc ls dev eth0 # queue status

# tc qdisc del dev eth0 root # delete all QoS

Calculate port range and mask

The tc filter defines the port range with port and mask which you have to calculate. Find the 2^N ending of the port range, deduce the range and convert to HEX. This is your mask.

Example for 10000 -> 11024, the range is 1024.

# 2^13 (8192) < 10000 < 2^14 (16384) # ending is 2^14 = 16384

# echo "obase=16;(2^14)-1024" | bc # mask is 0x3C00

FreeBSD

The max link bandwidth is 500Kbit/s and we define 3 queues with priority 100:10:1 for

VoIP:ssh:all the rest.

# ipfw pipe 1 config bw 500Kbit/s

# ipfw queue 1 config pipe 1 weight 100

# ipfw queue 2 config pipe 1 weight 10

# ipfw queue 3 config pipe 1 weight 1

# ipfw add 10 queue 1 proto udp dst-port 10000-11024

# ipfw add 11 queue 1 proto udp dst-ip 123.23.0.1 # or/and use server IP

# ipfw add 20 queue 2 dsp-port ssh

# ipfw add 30 queue 3 from me to any # all the rest

Status and remove with

# ipfw list # rules status

# ipfw pipe list # pipe status

# ipfw flush # deletes all rules but default

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.

Linux

# cat /etc/yp.conf

ypserver servername

domain domain.net broadcast

5. SSH SCP

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

New....

• I use Key type DSA; key length 2048.

• Copy the public key generated by the ssh.com client to the server into the ~/.ssh folder.

• The keys are in C:\Documents and Settings\%USERNAME%\Application

Data\SSH\UserKeys.

• Use the ssh-keygen command on the server to convert the key:

# cd ~/.ssh

# ssh-keygen -i -f keyfilename.pub >> authorized_keys2

Notice: We used a DSA key, RSA is also possible. The key is not protected by a password.

Using putty for Windows

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

Settings\%USERNAME%\.ssh).

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

# scp .ssh/puttykey.pub root@192.168.51.254:.ssh/

• Use the ssh-keygen command on the server to convert the key for OpenSSH:

# cd ~/.ssh

# ssh-keygen -i -f puttykey.pub >> authorized_keys2

• Point the private key location in the putty settings: Connection - SSH - Auth

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 (192.168.16.54)' can't be established.

DSA key fingerprint is 14:4a:aa:d9:73:25:46:6d:0a:48:35:c7:f4:16:d4:ee.

Are you sure you want to continue connecting (yes/no)? yes

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

5.http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html

6.http://fuse.sourceforge.net/sshfs.html

This will connect to gate and forward the local port to the host desthost:destport. Note desthost is the destination host as seen by the gate, so if the connection is to the gate, then desthost is localhost. More than one port forward is possible.

Direct forward on the gate

Let say we want to access the CVS (port 2401) and http (port 80) which are running on the gate. This is the simplest example, desthost is thus localhost, and we use the port 8080 locally instead of 80 so we don't need to be root. Once the ssh session is open, both services are accessible on the local ports.

# ssh -L 2401:localhost:2401 -L 8080:localhost:80 user@gate

Netbios and remote desktop forward to a second server

Let say a Windows smb server is behind the gate and is not running ssh. We need access to the smb share and also remote desktop to the server.

# ssh -L 139:smbserver:139 -L 3388:smbserver:3389 user@gate

The smb share can now be accessed with \\127.0.0.1\, but only if the local share is disabled, because the local share is listening on port 139.

It is possible to keep the local share enabled, for this we need to create a new virtual device with a new IP address for the tunnel, the smb share will be connected over this address.

Furthermore the local RDP is already listening on 3389, so we choose 3388. For this example let's use a virtual IP of 10.1.1.1.

• With putty use Source port=10.1.1.1:139. It is possible to create multiple loop devices

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

• With the ssh.com client, disable "Allow local connections only". Since ssh.com will bind

to all addresses, only a single share can be connected.

Now create the loopback interface with IP 10.1.1.1:

• # System->Control Panel->Add Hardware # Yes, Hardware is already connected # Add

a new hardware device (at bottom).

• # Install the hardware that I manually select # Network adapters # Microsoft , Microsoft

Loopback Adapter.

• Configure the IP address of the fake device to 10.1.1.1 mask 255.255.255.0, no

gateway.

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

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

Networks.

I HAD to reboot for this to work. Now connect to the smb share with \\10.1.1.1 and remote

desktop to 10.1.1.1:3388.

Debug

If it is not working:

• Are the ports forwarded: netstat -an? Look at 0.0.0.0:139 or 10.1.1.1:139

• Does telnet 10.1.1.1 139 connect?

• You need the checkbox "Local ports accept connections from other hosts".

• Is "File and Printer Sharing for Microsoft Networks" disabled on the loopback interface?

Connect two clients behind NAT

Suppose two clients are behind a NAT gateway and client cliadmin has to connect to client

cliuser (the destination), both can login to the gate with ssh and are running Linux with sshd.

You don't need root access anywhere as long as the ports on gate are above 1024. We use 2022

on gate. Also since the gate is used locally, the option GatewayPorts is not necessary.

On client cliuser (from destination to gate):

# ssh -R 2022:localhost:22 user@gate # forwards client 22 to gate:2022

On client cliadmin (from host to gate):

# ssh -L 3022:localhost:2022 admin@gate # forwards client 3022 to gate: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

6. VPN WITH SSH

As of version 4.3, OpenSSH can use the tun/tap device to encrypt a tunnel. This is very similar to other TLS based VPN solutions like OpenVPN. One advantage with SSH is that there is no need to install and configure additional software. Additionally the tunnel uses the SSH authentication like pre shared keys. The drawback is that the encapsulation is done over TCP which might result in poor performance on a slow link. Also the tunnel is relying on a single (fragile) TCP connection. This technique is very useful for a quick IP based VPN setup. There is no limitation as with the single TCP port forward, all layer 3/4 protocols like ICMP, TCP/UDP, etc. are forwarded over the VPN. In any case, the following options are needed in the sshd_conf

file:

PermitRootLogin yes

PermitTunnel yes

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 10.0.1.1 (server) and 10.0.1.2 (client) and we create a device tun5 (this could also be an other number). The procedure is very simple:

• Connect with SSH using the tunnel option -w

• Configure the IP addresses of the tunnel. Once on the server and once on the client.

Connect to the server

Connection started on the client and commands are executed on the server.

Server is on Linux

cli># ssh -w5:5 root@hserver

srv># ifconfig tun5 10.0.1.1 netmask 255.255.255.252 # Executed on the server shell

Server is on FreeBSD

cli># ssh -w5:5 root@hserver

srv># ifconfig tun5 10.0.1.1 10.0.1.2 # Executed on the server shell

Configure the client

Commands executed on the client:

cli># ifconfig tun5 10.0.1.2 netmask 255.255.255.252 # Client is on Linux

cli># ifconfig tun5 10.0.1.2 10.0.1.1 # Client is on FreeBSD

The two hosts are now connected and can transparently communicate with any layer 3/4

protocol using the tunnel IP addresses.

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 192.168.51.0/24 and netB

192.168.16.0/24. The procedure is similar as above, we only need to add the routing. NAT must

be activated on the private interface only if the gates are not the same as the default gateway

of their network.

192.168.51.0/24 (netA)|gateA <-> gateB|192.168.16.0/24 (netB)

• Connect with SSH using the tunnel option -w.

• Configure the IP addresses of the tunnel. Once on the server and once on the client.

• Add the routing for the two networks.

• If necessary, activate NAT on the private interface of the gate.

The setup is started from gateA in netA.

Connect from gateA to gateB

Connection is started from gateA and commands are executed on gateB.

gateB is on Linux

gateA># ssh -w5:5 root@gateB

gateB># ifconfig tun5 10.0.1.1 netmask 255.255.255.252 # Executed on the gateB shell

gateB># route add -net 192.168.51.0 netmask 255.255.255.0 dev tun5

gateB># echo 1 > /proc/sys/net/ipv4/ip_forward # Only needed if not 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 10.0.1.1 10.0.1.2 # Executed on the gateB shell

gateB># route add 192.168.51.0/24 10.0.1.2

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 10.0.1.2 netmask 255.255.255.252

gateA># route add -net 192.168.16.0 netmask 255.255.255.0 dev tun5

gateA># echo 1 > /proc/sys/net/ipv4/ip_forward

gateA># iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

gateA is on FreeBSD

gateA># ifconfig tun5 10.0.1.2 10.0.1.1

gateA># route add 192.168.16.0/24 10.0.1.2

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

gateA># natd -s -m -u -dynamic -n fxp0 # see NAT (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.

7. RSYNC

Rsync can almost completely replace cp and scp, furthermore interrupted transfers are

efficiently restarted. A trailing slash (and the absence thereof) has different meanings, the man page is good... Here some examples:

Copy the directories with full content:

# rsync -a /home/colin/ /backup/colin/

# 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.

@ECHO OFF

REM rsync the directory My Documents

SETLOCAL

SET CWRSYNCHOME=C:\PROGRAM FILES\CWRSYNC

SET CYGWIN=nontsec

SET CWOLDPATH=%PATH%

REM uncomment the next line when using cygwin

SET PATH=%CWRSYNCHOME%\BIN;%PATH%

echo Press Control-C to abort

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

'user@server:My\ Documents/'

pause

8. SUDO

Sudo is a standard way to give users some administrative rights without giving out the root password. Sudo is very useful in a multi user environment with a mix of server and

workstations. Simply call the command with sudo:

# sudo /etc/init.d/dhcpd restart # Run the rc script as root

# sudo -u sysadmin whoami # Run cmd as an other user

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 = 212.118.81.40/28

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 DMZ = (ALL) NOPASSWD: SYSTEM,PW,DEBUG

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

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

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

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

9. ENCRYPT FILES

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.

10. ENCRYPT PARTITIONS

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

Attach

# cryptsetup luksOpen /dev/sdc1 sdc1

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

Detach

# umount /mnt

# cryptsetup luksClose sdc1

dm-crypt without LUKS

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

8.http://www.freebsd.org/handbook/disks-encrypting.html

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

Attach

# 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

Detach

The detach procedure is done automatically on shutdown.

# umount /mnt

# geli detach /dev/ad1.eli

/etc/fstab

The encrypted partition can be configured to be mounted with /etc/fstab. The password will be

prompted when booting. The following settings are required for this example:

# grep geli /etc/rc.conf

geli_devices="ad1"

geli_ad1_flags="-k /root/ad1.key"

# grep geli /etc/fstab

/dev/ad1.eli /home/private ufs rw 0 0

Use password only

It is more convenient to encrypt a USB stick or file based image with a passphrase only and no key. In this case it is not necessary to carry the additional key file around. The procedure is very much the same as above, simply without the key file. Let's encrypt a file based image

/cryptedfile of 1 GB.

# dd if=/dev/zero of=/cryptedfile bs=1M count=1000 # 1 GB file

# mdconfig -at vnode -f /cryptedfile

# geli init /dev/md0 # encrypts with password only

# geli attach /dev/md0

# newfs -U -m 0 /dev/md0.eli

# mount /dev/md0.eli /mnt

# umount /dev/md0.eli

# geli detach md0.eli

It is now possible to mount this image on an other system with the password only.

# mdconfig -at vnode -f /cryptedfile

# geli attach /dev/md0

# mount /dev/md0.eli /mnt

— Encrypt Partitions —

29

11. SSL CERTIFICATES

So called SSL/TLS certificates are cryptographic public key certificates and are composed of a public and a private key. The certificates are used to authenticate the endpoints and encrypt the data. They are used for example on a web server (https) or mail server (imaps).

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 —

30

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:

-----BEGIN RSA PRIVATE KEY-----

MIICXQIBAAKBgQDutWy+o/XZ/[...]qK5LqQgT3c9dU6fcR+WuSs6aejdEDDqBRQ

-----END RSA PRIVATE KEY-----

-----BEGIN CERTIFICATE-----

MIIERzCCA7CgAwIBAgIBBDANB[...]iG9w0BAQQFADCBxTELMAkGA1UEBhMCREUx

-----END CERTIFICATE-----

What we have now in the directory /usr/local/certs/:

CA/private/cakey.pem (CA server private key)

CA/cacert.pem (CA server public key)

certs/servernamekey.pem (server private key)

certs/servernamecert.pem (server signed certificate)

certs/servername.pem (server certificate with private key)

Keep the private key secure!

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

root):

# mkdir -p /usr/local/cvs

# setenv CVSROOT /usr/local/cvs # Set CVSROOT to the new location (local)

# cvs init # Creates all internal CVS config files

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

# cd CVSROOT

edit config ( fine as it is)

# cvs commit config

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

colin

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

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

# cvs edit checkoutlist

# cat >> checkoutlist

writers

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

# cvs commit # Commit all the configuration changes

Add a readers file if you want to differentiate read and write permissions Note: Do not (ever) edit files directly into the main cvs, but rather checkout the file, modify it and check it in. We did this with the file writers to define the write access.

There are three popular ways to access the CVS at this point. The first two don't need any

further configuration. See the examples on CVSROOT below for how to use them:

• Direct local access to the file system. The user(s) need sufficient file permission to

access the CS directly and there is no further authentication in addition to the OS login.

However this is only useful if the repository is local.

• Remote access with ssh with the ext protocol. Any use with an ssh shell account and

read/write permissions on the CVS server can access the CVS directly with ext over ssh

without any additional tunnel. There is no server process running on the CVS for this to

work. The ssh login does the authentication.

• Remote access with pserver. 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):