Command

Description

# init 0

shutdown system(2)

# logout

leaving session

# reboot

reboot(2)

# shutdown -h now

shutdown system(1)

# shutdown -h 16:30 &

planned shutdown of the system at 16:30

# shutdown -c

cancel a planned shutdown of the system

# shutdown -r now

reboot(1)

# telinit 0

shutdown system(3)

Command

Description

# find /var/log -name ‘*.log’ | tar cv –files-from=- | bzip2 > log.tar.bz2

find all files with ‘.log’ extention and make an bzip archive

# find /home/user1 -name ‘*.txt’ | xargs cp -av –target-directory=/home/backup/ –parents

find and copy all files with ‘.txt’ extention from a directory to another

# dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr ‘dd of=hda.gz’

make a backup of a local hard disk on remote host via ssh

# dd if=/dev/sda of=/tmp/file1

backup content of the harddrive to a file

# dd if=/dev/hda of=/dev/fd0 bs=512 count=1

make a copy of MBR (Master Boot Record) to floppy

# dd if=/dev/fd0 of=/dev/hda bs=512 count=1

restore MBR from backup copy saved to floppy

# dump -0aj -f /tmp/home0.bak /home

make a full backup of directory ‘/home’

# dump -1aj -f /tmp/home0.bak /home

make a incremental backup of directory ‘/home’

# restore -if /tmp/home0.bak

restoring a backup interactively

# rsync -rogpav –delete /home /tmp

synchronization between directories

# rsync -rogpav -e ssh –delete /home ip_address:/tmp

rsync via SSH tunnel

# rsync -az -e ssh –delete ip_addr:/home/public /home/local

synchronize a local directory with a remote directory via ssh and compression

# rsync -az -e ssh –delete /home/local ip_addr:/home/public

synchronize a remote directory with a local directory via ssh and compression

# tar -Puf backup.tar /home/user

make a incremental backup of directory ‘/home/user’

# ( cd /tmp/local/ && tar c . ) | ssh -C user@ip_addr ‘cd /home/share/ && tar x -p’

copy content of a directory on remote directory via ssh

# ( tar c /home ) | ssh -C user@ip_addr ‘cd /home/backup-home && tar x -p’

copy a local directory on remote directory via ssh

# tar cf – . | (cd /tmp/backup ; tar xf – )

local copy preserving permits and links from a directory to another

Command

Description

# cd-paranoia -B

rip audio tracks from a CD to wav files

# cd-paranoia —

rip first three audio tracks from a CD to wav files

# cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force

clean a rewritable cdrom

# cdrecord -v dev=/dev/cdrom cd.iso

burn an ISO image

# gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom –

burn a compressed ISO image

# cdrecord –scanbus

scan bus to identify the channel scsi

# dd if=/dev/hdc | md5sum

perform an md5sum on a device, like a CD

# mkisofs /dev/cdrom > cd.iso

create an iso image of cdrom on disk

# mkisofs /dev/cdrom | gzip > cd_iso.gz

create a compressed iso image of cdrom on disk

# mkisofs -J -allow-leading-dots -R -V

create an iso image of a directory

# mount -o loop cd.iso /mnt/iso

mount an ISO image

Command

Description

# dos2unix filedos.txt fileunix.txt

convert a text file format from MSDOS to UNIX

# recode ..HTML page.html

convert a text file to html

# recode -l | more

show all available formats conversion

# unix2dos fileunix.txt filedos.txt

convert a text file format from UNIX to MSDOS

Command

Description

# dpkg -i [package.deb]

install / upgrade a deb package

# dpkg -r [package]

remove a deb package from the system

# dpkg -l

show all deb packages installed on the system

# dpkg -l | grep httpd

show all deb packages with the name «httpd»

# dpkg -s [package]

obtain information on a specific package installed on system

# dpkg -L [package]

show list of files provided by a package installed on system

# dpkg –contents [package.deb]

show list of files provided by a package not yet installed

# dpkg -S /bin/ping

verify which package belongs to a given file

Command

Description

# df -h

show list of partitions mounted

# dpkg-query -W -f=’${Installed-Size;10}t${Package}n’ | sort -k1,1n

show the used space by installed deb packages, sorting by size (debian, ubuntu and alike)

# du -sh dir1

estimate space used by directory ‘dir1’

# du -sk * | sort -rn

show size of the files and directories sorted by size

# ls -lSr |more

show size of the files and directories ordered by size

# rpm -q -a –qf ‘%10{SIZE}t%{NAME}n’ | sort -k1,1n

show the used space by rpm packages installed sorted by size (fedora, redhat and alike)

Command

Description

# find / -name file1

search file and directory into root filesystem from ‘/’

# find / -user user1

search files and directories belonging to ‘user1’

# find /home/user1 -name \*.bin

search files with ‘. bin’ extension within directory ‘/ home/user1’

# find /usr/bin -type f -atime +100

search binary files are not used in the last 100 days

# find /usr/bin -type f -mtime -10

search files created or changed within 10 days

# find / -name *.rpm -exec chmod 755 ‘{}’ \;

search files with ‘.rpm’ extension and modify permits

# find / -xdev -name \*.rpm

search files with ‘.rpm’ extension ignoring removable partitions as cdrom, pen-drive, etc.…

# locate \*.ps

find files with the ‘.ps’ extension – first run ‘updatedb’ command

# whereis halt

show location of a binary file, source or man

# which halt

show full path to a binary / executable

Command

Description

# cd /home

enter to directory ‘/ home’

# cd ..

go back one level

# cd ../..

go back two levels

# cd

go to home directory

# cd ~user1

go to home directory

# cd –

go to previous directory

# cp file1 file2

copying a file

# cp dir/* .

copy all files of a directory within the current work directory

# cp -a /tmp/dir1 .

copy a directory within the current work directory

# cp -a dir1 dir2

copy a directory

# cp file file1

outputs the mime type of the file as text

# iconv -l

lists known encodings

# iconv -f fromEncoding -t toEncoding inputFile > outputFile

converting the coding of characters from one format to another

# find . -maxdepth 1 -name *.jpg -print -exec convert

batch resize files in the current directory and send them to a thumbnails directory (requires convert from Imagemagick)

# ln -s file1 lnk1

create a symbolic link to file or directory

# ln file1 lnk1

create a physical link to file or directory

# ls

view files of directory

# ls -F

view files of directory

# ls -l

show details of files and directory

# ls -a

show hidden files

# ls *[0-9]*

show files and directory containing numbers

# lstree

show files and directories in a tree starting from root(2)

# mkdir dir1

create a directory called ‘dir1’

# mkdir dir1 dir2

create two directories simultaneously

# mkdir -p /tmp/dir1/dir2

create a directory tree

# mv dir1 new_dir

rename / move a file or directory

# pwd

show the path of work directory

# rm -f file1

delete file called ‘file1’

# rm -rf dir1

remove a directory called ‘dir1’ and contents recursively

# rm -rf dir1 dir2

remove two directories and their contents recursively

# rmdir dir1

delete directory called ‘dir1’

# touch -t 0712250000 file1

modify timestamp of a file or directory – (YYMMDDhhmm)

# tree

show files and directories in a tree starting from root(1)

Command

Description

# badblocks -v /dev/hda1

check bad blocks on disk hda1

# dosfsck /dev/hda1

repair / check integrity of dos filesystems on disk hda1

# e2fsck /dev/hda1

repair / check integrity of ext2 filesystem on disk hda1

# e2fsck -j /dev/hda1

repair / check integrity of ext3 filesystem on disk hda1

# fsck /dev/hda1

repair / check integrity of linux filesystem on disk hda1

# fsck.ext2 /dev/hda1

repair / check integrity of ext2 filesystem on disk hda1

# fsck.ext3 /dev/hda1

repair / check integrity of ext3 filesystem on disk hda1

# fsck.vfat /dev/hda1

repair / check integrity of fat filesystem on disk hda1

# fsck.msdos /dev/hda1

repair / check integrity of dos filesystem on disk hda1

Command

Description

# mkswap /dev/hda3

create a swap filesystem

# swapon /dev/hda3

activating a new swap partition

# swapon /dev/hda2 /dev/hdb3

activate two swap partitions

Command

Description

# fdformat -n /dev/fd0

format a floppy disk

# mke2fs /dev/hda1

create a filesystem type linux ext2 on hda1 partition

# mke2fs -j /dev/hda1

create a filesystem type linux ext3 (journal) on hda1 partition

# mkfs /dev/hda1

create a filesystem type linux on hda1 partition

# mkfs -t vfat 32 -F /dev/hda1

create a FAT32 filesystem

# mkswap /dev/hda3

create a swap filesystem

Command

Description

# iptables -t filter -L

show all chains of filtering table

# iptables -t nat -L

show all chains of nat table

# iptables -t filter -F

clear all rules from filtering table

# iptables -t nat -F

clear all rules from table nat

# iptables -t filter -X

delete any chains created by user

# iptables -t filter -A INPUT -p tcp –dport telnet -j ACCEPT

allow telnet connections to input

# iptables -t filter -A OUTPUT -p tcp –dport http -j DROP

block HTTP connections to output

# iptables -t filter -A FORWARD -p tcp –dport pop3 -j ACCEPT

allow POP3 connections to forward chain

# iptables -t filter -A INPUT -j LOG –log-prefix

Logging on input chain

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

configure a PAT (Port Address Traslation) on eth0 masking outbound packets

# iptables -t nat -A PREROUTING -d 192.168.0.1 -p tcp -m tcp –dport 22 -j DNAT –to-destination 10.0.0.2:22

redirect packets addressed to a host to another host

Command

Description

# mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share

mount a windows network share

# nbtscan ip_addr

netbios name resolution

# nmblookup -A ip_addr

netbios name resolution

# smbclient -L ip_addr/hostname

show remote shares of a windows host

# smbget -Rr smb://ip_addr/share

like wget can download files from a host windows via smb

Command

Description

# fuser -km /mnt/hda2

force umount when the device is busy

# mount /dev/hda2 /mnt/hda2

mount disk called hda2 – verify existence of the directory ‘/ mnt/hda2’

# mount /dev/fd0 /mnt/floppy

mount a floppy disk

# mount /dev/cdrom /mnt/cdrom

mount a cdrom / dvdrom

# mount /dev/hdc /mnt/cdrecorder

mount a cdrw / dvdrom

# mount /dev/hdb /mnt/cdrecorder

mount a cdrw / dvdrom

# mount -o loop file.iso /mnt/cdrom

mount a file or iso image

# mount -t vfat /dev/hda5 /mnt/hda5

mount a Windows FAT32 file system

# mount /dev/sda1 /mnt/usbdisk

mount a usb pen-drive or flash-drive

# mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share

mount a windows network share

# umount /dev/hda2

unmount disk called hda2 – exit from mount point ‘/ mnt/hda2’ first

# umount -n /mnt/hda2

run umount without writing the file /etc/mtab – useful when the file is read-only or the hard disk is full

Command

Description

# free -m

displays status of RAM in megabytes

# kill -9 process_id

force closure of the process and finish it

# kill -1 process_id

force a process to reload configuration

# last reboot

show history reboot

# lsmod

display kernel loaded

# lsof -p process_id

display a list of files opened by processes

# lsof /home/user1

displays a list of open files in a given path system

# ps -eafw

displays linux tasks

# ps -e -o pid,args –forest

displays linux tasks in a hierarchical mode

# pstree

mostra un albero dei processi sistema Shows a tree system processes

# smartctl -A /dev/hda

monitoring reliability of a hard-disk through SMART

# smartctl -i /dev/hda

check if SMART is active on a hard-disk

# strace -c ls >/dev/null

display system calls made and received by a process

# strace -f -e open ls >/dev/null

display library calls

# tail /var/log/dmesg

show events inherent to the process of booting kernel

# tail /var/log/messages

show system events

# top

display linux tasks using most cpu

# watch -n1 ‘cat /proc/interrupts’

display interrupts in real-time

Command

Description

# dhclient eth0

active interface ‘eth0’ in dhcp mode

# ethtool eth0

show network statistics of eth0

# host www.example.com

lookup hostname to resolve name to ip address and viceversa

# hostname

show hostname of system

# ifconfig eth0

show configuration of an ethernet network card

# ifconfig eth0 192.168.1.1 netmask 255.255.255.0

configure IP Address

# ifconfig eth0 promisc

configure ‘eth0’ in promiscuous mode to gather packets (sniffing)

# ifdown eth0

disable an interface ‘eth0’

# ifup eth0

activate an interface ‘eth0’

# ip link show

show link status of all network interfaces

# iwconfig eth1

show wireless networks

# iwlist scan

wifi scanning to display the wireless connections available

# mii-tool eth0

show link status of ‘eth0’

# netstat -tup

show all active network connections and their PID

# netstat -tupl

show all network services listening on the system and their PID

# netstat -rn

show routing table alike «route -n»

# nslookup www.example.com

lookup hostname to resolve name to ip address and viceversa

# route -n

show routing table

# route add -net 0/0 gw IP_Gateway

configure default gateway

# route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1

configure static route to reach network ‘192.168.0.0/16’

# route del 0/0 gw IP_gateway

remove static route

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

activate ip routing temporarily

# tcpdump tcp port 80

show all HTTP traffic

# whois www.example.com

lookup on Whois database

Command

Description

# alias hh=’history’

set an alias for a command – hh = history

# apropos …keyword

display a list of commands that pertain to keywords of a program , useful when you know what your program does, but you don’t know the name of the command

# chsh

change shell command

# chsh –list-shells

nice command to know if you have to remote into another box

# gpg -c file1

encrypt a file with GNU Privacy Guard

# gpg file1.gpg

decrypt a file with GNU Privacy Guard

# ldd /usr/bin/ssh

show shared libraries required by ssh program

# man ping

display the on-line manual pages for example on ping command – use ‘-k’ option to find any related commands

# mkbootdisk –device /dev/fd0 `uname -r`

create a boot floppy

# wget -r www.example.com

download an entire web site

# wget -c www.example.com/file.iso

download a file with the ability to stop the download and resume later

# echo ‘wget -c www.example.com/files.iso’ | at 09:00

start a download at any given time

# whatis …keyword

displays description of what a program does

# who -a

show who is logged on, and print: time of last system boot, dead processes, system login processes, active processes spawned by init, current runlevel, last system clock change

Pacman packages tool (Arch, Frugalware and alike)

Command

Description

# pacman -S name

Install package ‘name’ with dependencies

# pacman -R name

Delete package ‘name’ and all files of it