Linux/Unix – Linux command line reference for common operations..

This is a Linux command line reference for common operations. All these commands have been tested both on Red Hat and Debian distros.




apropos whatis

Show commands pertinent to string.


man -t man | ps2pdf – > man.pdf

make a pdf of a manual page


which command

Show full path name of command


time command

See how long a command takes


time cat

Start stopwatch. Ctrl-d to stop.


nice info

Run a low priority command (The “info” reader in this case)


renice 19 -p $$

Make shell (script) low priority. Use for non interactive tasks

dir navigation


cd –

Go to previous directory



Go to $HOME directory


(cd dir && command)

Go to dir, execute command and return to current dir


pushd .

Put current dir on stack so you can popd back to it

file searching


alias l=’ls -l –color=auto’

quick dir listing


ls -lrt

List files by date.


ls /usr/bin | pr -T9 -W$COLUMNS

Print in 9 columns to width of terminal


find -name ‘*.[ch]’ | xargs grep -E ‘expr’

Search ‘expr’ in this dir and below.


find -type f -print0 | xargs -r0 grep -F ‘example’

Search all regular files for ‘example’ in this dir and below


find -maxdepth 1 -type f | xargs grep -F ‘example’

Search all regular files for ‘example’ in this dir


find -maxdepth 1 -type d | while read dir; do echo $dir; echo cmd2; done

Process each item with multiple commands (in while loop)


find -type f ! -perm -444

Find files not readable by all (useful for web site)


find -type d ! -perm -111

Find dirs not accessible by all (useful for web site)


locate -r ‘file[^/]*.txt’

Search cached index for names. This re is like glob *file*.txt


look reference

Quickly search (sorted) dictionary for prefix


grep –color reference /usr/share/dict/words

Highlight occurances of regular expression in dictionary

archives and compression


gpg -c file

Encrypt file


gpg file.gpg

Decrypt file


tar -c dir/ | bzip2 > dir.tar.bz2

Make compressed archive of dir/


bzip2 -dc dir.tar.bz2 | tar -x

Extract archive (use gzip instead of bzip2 for tar.gz files)


tar -c dir/ | gzip | gpg -c | ssh user@remote ‘dd of=dir.tar.gz.gpg’

Make encrypted archive of dir/ on remote machine


find dir/ -name ‘*.txt’ | tar -c –files-from=- | bzip2 > dir_txt.tar.bz2

Make archive of subset of dir/ and below


find dir/ -name ‘*.txt’ | xargs cp -a –target-directory=dir_txt/ –parents

Make copy of subset of dir/ and below


( tar -c /dir/to/copy ) | ( cd /where/to/ && tar -x -p )

Copy (with permissions) copy/ dir to /where/to/ dir


( cd /dir/to/copy && tar -c . ) | ( cd /where/to/ && tar -x -p )

Copy (with permissions) contents of copy/ dir to /where/to/


( tar -c /dir/to/copy ) | ssh -C user@remote ‘cd /where/to/ && tar -x -p’

Copy (with permissions) copy/ dir to remote:/where/to/ dir


dd bs=1M if=/dev/sda | gzip | ssh user@remote ‘dd of=sda.gz’

Backup harddisk to remote machine

rsync (Network efficient file copier: Use the –dry-run option for testing)


rsync -P rsync:// file

Only get diffs. Do multiple times for troublesome downloads


rsync –bwlimit=1000 fromfile tofile

Locally copy with rate limit. It’s like nice for I/O


rsync -az -e ssh –delete ~/public_html/’~/public_html’

Mirror web site (using compression and encryption)


rsync -auz -e ssh remote:/dir/ . && rsync -auz -e ssh . remote:/dir/

Synchronize current directory with remote one

ssh (Secure SHell)


ssh $USER@$HOST command

Run command on $HOST as $USER (default command=shell)


ssh -f -Y $USER@$HOSTNAME xeyes

Run GUI command on $HOSTNAME as $USER


scp -p -r $USER@$HOST: file dir/

Copy with permissions to $USER’s home directory on $HOST


ssh -g -L 8080:localhost:80 root@$HOST

Forward connections to $HOSTNAME:8080 out to $HOST:80


ssh -R 1434:imap:143 root@$HOST

Forward connections from $HOST:1434 in to imap:143

wget (multi purpose download tool)


(cd cli && wget -nd -pHEKk http://www. /cmdline.html)

Store local browsable version of a page to the current dir


wget -c

Continue downloading a partially downloaded file


wget -r -nd -np -l1 -A ‘*.jpg’

Download a set of files to the current directory


wget ftp://remote/file[1-9].iso/

FTP supports globbing directly


wget -q -O- | grep ‘a href’ | head

Process output directly


echo ‘wget url’ | at 01:00

Download url at 1AM to current dir


wget –limit-rate=20k url

Do a low priority download (limit to 20KB/s in this case)


wget -nv –spider –force-html -i bookmarks.html

Check links in a file


wget –mirror

Efficiently update a local copy of a site (handy from cron)

networking (Note ifconfig, route, mii-tool, nslookup commands are obsolete)


ethtool eth0

Show status of ethernet interface eth0


ethtool –change eth0 autoneg off speed 100 duplex full

Manually set ethernet interface speed


iwconfig eth1

Show status of wireless interface eth1


iwconfig eth1 rate 1Mb/s fixed

Manually set wireless interface speed


iwlist scan

List wireless networks in range


ip link show

List network interfaces


ip link set dev eth0 name wan

Rename interface eth0 to wan


ip link set dev eth0 up

Bring interface eth0 up (or down)


ip addr show

List addresses for interfaces


ip addr add brd + dev eth0

Add (or del) ip and mask (


ip route show

List routing table


ip route add default via

Set default gateway to


tc qdisc add dev lo root handle 1:0 netem delay 20msec

Add 20ms latency to loopback device (for testing)


tc qdisc del dev lo root

Remove latency added above



Lookup DNS ip address for name or vice versa


hostname -i

Lookup local ip address (equivalent to host `hostname`)



Lookup whois info for hostname or ip address


netstat -tupl

List internet services on a system


netstat -tup

List active connections to/from system

windows networking (Note samba is the package that provides all this windows specific networking support)


Find windows machines. See also findsmb


nmblookup -A

Find the windows (netbios) name associated with ip address


smbclient -L windows_box

List shares on windows machine or samba server


mount -t smbfs -o fmask=666,guest //windows_box/share /mnt/share

Mount a windows share


echo ‘message’ | smbclient -M windows_box

Send popup to windows machine (off by default in XP sp2)

text manipulation (Note sed uses stdin and stdout. Newer versions support inplace editing with the -i option)


sed ‘s/string1/string2/g’

Replace string1 with string2


sed ‘s/(.*)1/12/g’

Modify anystring1 to anystring2


sed ‘/ *#/d; /^ *$/d’

Remove comments and blank lines


sed ‘:a; /$/N; s/n//; ta’

Concatenate lines with trailing


sed ‘s/[ t]*$//’

Remove trailing spaces from lines


sed ‘s/([`”$\])/1/g’

Escape shell metacharacters active within double quotes


seq 10 | sed “s/^/      /; s/ *(.{7,})/1/”

Right align numbers


sed -n ‘1000p;1000q’

Print 1000th line


sed -n ‘10,20p;20q’

Print lines 10 to 20


sed -n ‘s/.*<title>(.*)</title>.*/1/ip;T;q’

Extract title from HTML web page


sed -i 42d ~/.ssh/known_hosts

Delete a particular line


sort -t. -k1,1n -k2,2n -k3,3n -k4,4n

Sort IPV4 ip addresses


echo ‘Test’ | tr ‘[:lower:]’ ‘[:upper:]’

Case conversion


tr -dc ‘[:print:]’ < /dev/urandom

Filter non printable characters


history | wc -l

Count lines

set operations (Note you can export LANG=C for speed. Also these assume no duplicate lines within a file)


sort file1 file2 | uniq

Union of unsorted files


sort file1 file2 | uniq -d

Intersection of unsorted files


sort file1 file1 file2 | uniq -u

Difference of unsorted files


sort file1 file2 | uniq -u

Symmetric Difference of unsorted files


join -a1 -a2 file1 file2

Union of sorted files


join file1 file2

Intersection of sorted files


join -v2 file1 file2

Difference of sorted files


join -v1 -v2 file1 file2

Symmetric Difference of sorted files



echo ‘(1 + sqrt(5))/2’ | bc -l

Quick math (Calculate φ).


echo ‘pad=20; min=64; (100*10^6)/((pad+min)*8)’ | bc

More complex (int) e.g. This shows max FastE packet rate


echo ‘pad=20; min=64; print (100E6)/((pad+min)*8)’ | python

Python handles scientific notation


echo ‘pad=20; plot [64:1518] (100*10**6)/((pad+x)*8)’ | gnuplot -persist

Plot FastE packet rate vs packet size


echo ‘obase=16; ibase=10; 64206’ | bc

Base conversion (decimal to hexadecimal)


echo $((0x2dec))

Base conversion (hex to dec) ((shell arithmetic expansion))


units -t ‘100m/9.69s’ ‘miles/hour’

Unit conversion (metric to imperial)


units -t ‘500GB’ ‘GiB’

Unit conversion (SI to IEC prefixes)


units -t ‘1 googol’

Definition lookup


seq 100 | (tr ‘n’ +; echo 0) | bc

Add a column of numbers.



cal -3

Display a calendar


cal 9 1752

Display a calendar for a particular month year


date -d fri

What date is it this friday.


[ $(date -d “tomorrow” +%d) = “01” ] || exit

exit a script unless it’s the last day of the month


date –date=’25 Dec’ +%A

What day does xmas fall on, this year


date –date=’@2147483647′

Convert seconds since the epoch (1970-01-01 UTC) to date


TZ=’:America/Los_Angeles’ date

What time is it on West coast of US (use tzselect to find TZ)


echo “mail -s ‘get the train’ < /dev/null” | at 17:45

Email reminder


echo “DISPLAY=$DISPLAY xmessage cooker” | at “NOW + 30 minutes”

Popup reminder



printf “%’dn” 1234

Print number with thousands grouping appropriate to locale


BLOCK_SIZE=’1 ls -l

get ls to do thousands grouping appropriate to locale


echo “I live in `locale territory`”

Extract info from locale database


LANG=en_IE.utf8 locale int_prefix

Lookup locale info for specific country. See also ccodes


locale | cut -d= -f1 | xargs locale -kc | less

List fields available in locale database

recode (Obsoletes iconv, dos2unix, unix2dos)


recode -l | less

Show available conversions (aliases on each line)


recode windows-1252.. file_to_change.txt

Windows “ansi” to local charset (auto does CRLF conversion)


recode utf-8/CRLF.. file_to_change.txt

Windows utf8 to local charset


recode iso-8859-15..utf8 file_to_change.txt

Latin9 (western europe) to utf8


recode ../b64 < file.txt > file.b64

Base64 encode


recode /qp.. < file.txt > file.qp

Quoted printable decode


recode ..HTML < file.txt > file.html

Text to HTML


recode -lf windows-1252 | grep euro

Lookup table of characters


echo -n 0x80 | recode latin-9/x1..dump

Show what a code represents in latin-9 charmap


echo -n 0x20AC | recode ucs-2/x2..latin-9/x

Show latin-9 encoding


echo -n 0x20AC | recode ucs-2/x2..utf-8/x

Show utf-8 encoding



gzip < /dev/cdrom > cdrom.iso.gz

Save copy of data cdrom


mkisofs -V LABEL -r dir | gzip > cdrom.iso.gz

Create cdrom image from contents of dir


mount -o loop cdrom.iso /mnt/dir

Mount the cdrom image at /mnt/dir (read only)


cdrecord -v dev=/dev/cdrom blank=fast

Clear a CDRW


gzip -dc cdrom.iso.gz | cdrecord -v dev=/dev/cdrom –

Burn cdrom image (use dev=ATAPI -scanbus to confirm dev)


cdparanoia -B

Rip audio tracks from CD to wav files in current dir


cdrecord -v dev=/dev/cdrom -audio *.wav

Make audio CD from all wavs in current dir (see also cdrdao)


oggenc –tracknum=’track’ track.cdda.wav -o ‘track.ogg’

Make ogg file from wav file

Disk space


ls -lSr

Show files by size, biggest last


du -s * | sort -k1,1rn | head

Show top disk users in current dir. See also dutop


df -h

Show free space on mounted filesystems


df -i

Show free inodes on mounted filesystems


fdisk -l

Show disks partitions sizes and types (run as root)


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

List all packages by installed size (Bytes) on rpm distros


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

List all packages by installed size (KBytes) on deb distros


dd bs=1 seek=2TB if=/dev/null of=ext3.test

Create a large test file (taking no space). See also truncate


> file

truncate data of file or create an empty file


tail -f /var/log/messages

Monitor messages in a log file


strace -c ls >/dev/null

Summarise/profile system calls made by command


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

List system calls made by command


ltrace -f -e getenv ls >/dev/null

List library calls made by command


lsof -p $$

List paths that process id has open


lsof ~

List processes that have specified path open


tcpdump not port 22

Show network traffic except ssh. See also tcpdump_not_me


ps -e -o pid,args –forest

List processes in a hierarchy


ps -e -o pcpu,cpu,nice,state,cputime,args –sort pcpu | sed ‘/^ 0.0 /d’

List processes by % cpu usage


ps -e -orss=,args= | sort -b -k1,1n | pr -TW$COLUMNS

List processes by mem usage.


ps -C firefox-bin -L -o pid,tid,pcpu,state

List all threads for a particular process


ps -p 1,2

List info for particular process IDs


last reboot

Show system reboot history


free -m

Show amount of (remaining) RAM (-m displays in MB)


watch -n.1 ‘cat /proc/interrupts’

Watch changeable data continuously

System information (‘#’ means root access is required)


uname -a

Show kernel version and system architecture


head -n1 /etc/issue

Show name and version of distribution


cat /proc/partitions

Show all partitions registered on the system


grep MemTotal /proc/meminfo

Show RAM total seen by the system


grep “model name” /proc/cpuinfo

Show CPU(s) info


lspci -tv

Show PCI info


lsusb -tv

Show USB info


mount | column -t

List mounted filesystems on the system (and align output)


grep -F capacity: /proc/acpi/battery/BAT0/info

Show state of cells in laptop battery


dmidecode -q | less

Display SMBIOS/DMI information


smartctl -A /dev/sda | grep Power_On_Hours

How long has this disk (system) been powered on in total


hdparm -i /dev/sda

Show info about disk sda


hdparm -tT /dev/sda

Do a read speed test on disk sda


badblocks -s /dev/sda

Test for unreadable blocks on disk sda




Line editor used by bash, python, bc, gnuplot, …



Virtual terminals with detach capability, …



Powerful file manager that can browse rpm, tar, ftp, ssh, …



Interactive/scriptable graphing



Web browser



open a file or url with the registered desktop application



alias hd=’od -Ax -tx1z -v’

Handy hexdump. (usage e.g.: • hd /proc/self/cmdline | less)


alias realpath=’readlink -f’

Canonicalize path. (usage e.g.: • realpath ~/../$USER)


set | grep $USER

Search current environment


touch -c -t 0304050607 file

Set file timestamp (YYMMDDhhmm)


python -m SimpleHTTPServer

Serve current directory tree at http://$HOSTNAME:8000/



About msotela

This blog is for anyone who wants to access the power of a Linux system as a systems administrator or user. You may be a Linux enthusiast, a Linux professional, or possibly a computer professional who is increasingly finding the Windows systems in your data center supplanted by Linux boxes.

Posted on March 15, 2009, in Unix/Linux and tagged , , . Bookmark the permalink. Leave a comment.

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