Linux Commands Cheat Sheet from cmdref.net

System Commands

System Commands

Command	Description	Example
shutdown	bring the system down	shutdown -h now <- -h = Halt or poweroff after shutdown shutdown -r now <- -r : Reboot after shutdown shutdown -r -F now <- -F : Force fsck after reboot.
halt	stop the system.	halt
reboot	reboot the system.	reboot
init		init 1 #change to single usermode
uptime	Tell how long the system has been running.	uptime
runlevel	find the previous and current system runlevel.	runlevel
printenv	print all or part of environment	printenv
env	run a program in a modified environment	env
hostname	show or set the system's host name	hostname <- show the system's host name hostname NEWHOSTNASME <- set the system's host name
uname	print system information	uname -a <- print all information
locale	Get locale-specific information.	locale locale -a |grep -i ja <- -a : --all-locales

Process Management

Command	Description	Example
ps	report a snapshot of the current processes.	ps aux |grep httpd <- Check httpd rocess ps aux | grep XXX | awk '{print $2}' | xargs kill -9 ps auxwf |grep XXX
pgrep	look up processes based on name and other attributes	pgrep -f 'bash' pgrep -lf 'bash' <- output with process name pgrep -f 'bash' | xargs kill
pstree	display a tree of processes	pstree -a
pidof	find the process ID of a running program	pidof httpd /bin/kill $(/sbin/pidof qmail-popup)
kill	send a signal to a process	kill -9 PID <- (-9 or -KILL = force-quit)
pkill	signal processes based on name and other attributes	pkill -f 'bash' pkill -u user1 pkill java pkill -f jar
killall	kill processes by name	killall vi killall -i vi <- -i = Interactively killall -HUP kterm
killproc
lsof	list open files	lsof -i :80,443 <- Which process is using Port 80,443
Ctrl + C	Stop running process
Ctrl + Z	Suspend running process	Move Running Process to Background 1. ctrl + z 2. jobs 3. bg 4. disown %JOBID
jobs	The first form lists the active jobs.	jobs -l <- List job
fg	Resume jobspec in the foreground
bg	Resume each suspended job jobspec in the background
nohup	run a command immune to hangups, with output to a non-tty	nohup command.sh &
disown		disown %jobid
nice	run a program with modified scheduling priority	nice -n 19 test.sh nice -n 19 ionice -c 3 CMD nice -n 19 ionice -c 2 -n 7 COMMAND
renice	alter priority of running processes	renice 19 -p PID you can check the nice whith "top" or "ps alx".
ionice	sets or gets process io scheduling class and priority	ionice -p PID <- check ionice -c 3 -p PID nice -n 19 ionice -c 2 -n 7 COMMAND

Schedule

Command	Description	Example
crontab	maintain crontab files	crontab -l <- -l = list user's crontab crontab -u USER -l crontab -e <- -e = edit user's crontab crontab -u USER -e
at	queue jobs for later execution	echo "/sbin/shutdown -h now" |at 21:00 02/30/2009 at -t 200902302100
atq	lists the user's pending jobs	atq
atrm	delete jobs for later execution	atrm JOBID
watch	execute a program periodically, showing output fullscreen	watch ntpq -p <- By default, the program is run every 2 seconds watch -n 5 ntpq -p <- 5 seconds interval -d : highlight the differences between successive updates

etc

Command	Description	Example
alias	Alias with no arguments or with the -p option prints the list of aliases When arguments are supplied, an alias is defined for each name whose value is given.	alias <- check all alias alias ls='ls -la --color=auto' alias grep='grep --color'
unalias	Remove each name from the list of defined aliases. If -a is supplied, all alias definitions are removed.	unalias COMMAND
ntpdate	set the date and time via NTP	ntpdate -b -u IP -b : Force the time (step mode) -u : If you are running ntpd, "-u" must be added.
ntpq	standard NTP query program	ntpq -p -p : Print a list of the peers known to the server watch -n 1 ntpq -p
hwclock	query and set the hardware clock (RTC)	hwclock (-r) <- Read the Hardware Clock and print the time on standard output. hwclock -w <- Set the Hardware Clock to the current System Time. hwclock -s <- Set the System Time from the Hardware Clock.
man	an interface to the on-line reference manuals	man COMMAND
whatis	display manual page descriptions	whatis KEYWORD whatis cat whatis vi
history	GNU History Library	history 5 <- lists only the last 5 lines. HISTSIZE=1000 HISTTIMEFORMAT="%Y/%m/%d %H:%M:%S "
which	locate a command	which ls
time	time a simple command or give resource usage	time sleep 5
strace	trace system calls and signals	strace -t -o test.txt php test.php <- (-t : each line of the trace with the time of day.)
ltrace	A library call tracer	lltrace -o test.txt wget http://example.com/ ltrace -p PID ltrace -p 3365
script	make typescript of terminal session	script -afq $LOG

Files and Directories Commands

File Commands

Command	Description	Example
ls	list directory contents	ls -ltrh <- (-r : reverse order while sorting) -h : with -l, print sizes in human readable format
cp	copy files and directories	cp -p SRC DES cp -pr SRC/ DES/ <- (-r,-R : copy directories recursively) cp -p SRC DES <- (-f, --force)
mv	move (rename) files	mv file1 file2 mv dir1 dir2 mv file1 file2 file3 DIR
rename	renames multiple files	rename .htm .html *.htm <- frm .htm to .html rename "" test *.txt <- add test rename test "" *.txt <- delete test
rm	remove files or directories	rm -rf TARGET <- (-r,-R : remove directories)
touch	change file timestamps	touch file1 touch -d "2017/10/20 13:00:00" file1
ln	make links between files	ln -s SRC DES
unlink		unlink DES
wc	print newline, word, and byte counts for each file	wc -l <- (-l, --lines = print the line counts)
tree	list contents of directories in a tree-like format	tree -Dpuga /etc
col	filter reverse line feeds from input	man ifconfig

Directory Commands

Command	Description	Example
pwd	print name of current/working directory	pwd
cd	Change the current directory	cd <- go to home directory cd ~/ <- go to home directory cd .. <- go to parent directory
pushd	Adds a directory to the top of the directory stack	pushd /var/log pushd pwd pushd +2 <- check pushd directory with ''dirs -v'' and go to No.2 pushd +3 <- check pushd directory with ''dirs -v'' and go to No.3
popd	Removes entries from the directory stack.	popd
dirs	displays the list of currently remembered directories.	dirs -v
mkdir	make directories	mkdir -p /tmp/test1/test2/ <- make parent directories as needed mkdir -m 700 /home/user01/.ssh
rmdir	remove empty directories If you want to delete directory, you must use "rm -r DIR".	rmdir DIR

Commands to Access File Contents

Command	Description	Example
more	file perusal filter for crt viewing
less	opposite of more	crontab -l
view	Start in read-only mode.
cat	concatenate files and print on the standard output	cat /dev/null > access.log
tail	output the last part of files	tail -n 50 aaa.txt <- output the last N lines
head	output the first part of files	head -n 100 aaa.txt # -n , --lines) head *
diff	compare files line by line	diff --suppress-common-lines --side-by-side File1 File2 diff -r dir1 dir2 <- When comparing directories, recursively compare
sdiff	side-by-side merge of file differences	sdiff -s File1 File2 <- (-s : Do not print common lines.)
colordiff
vimdiff		vimdiff file1 file2 vim -d file1 file2

Searching

Command	Description	Example
grep	print lines matching a pattern	grep -Ev "^#|^\$" xxx.txt grep -Ev "^$|^#|^\s*#" file.txt grep "" ifcfg-eth* <- check filename and contents grep -r PATTERN --include="*.txt" DIRECTORY <- -r : recursive
egrep	egrep is the same as grep -E	egrep "aaa|bbb" file
find , xargs	search for files in a directory hierarchy	find . -name "txt" find /dir -type f -name ".log" -mtime +7 -exec rm -rf {} \; <- "-mtime +7" is 7 days ago

File Compression

Command	Description	Example
tar	The GNU version of the tar archiving utility tar warn the order of target and destination.	tar -zcvf test.tar.gz Dir <- Create, Verbose, File tar -ztvf test.tar.gz <- Test, Verbose, File tar -zxvf test.tar.gz <- eXtract, Verbose, File tar -jcvf test.tar.bz2 DIR <- Create, Verbose, File tar -jxvf test.tar.bz2
gzip, gunzip	compress or expand files	gzip file1 gunzip file1.gz gzip access_log.2011-[0][5-8]*.txt <-wild card
compress, uncompress	package and compress (archive) files	compress file1 uncompress file1.Z
bzip2 bunzip2 bz2cat	a block-sorting file compressor	bzip2 file1 bunzip2 file1.gz2 bz2cat file1.gz2
zip/unzip	package and compress (archive) files	zip file.zip file1 file2 zip -l file.zip <- -l = list for check unzip file.zip unzip -t file.zip <- -t = test
lha		lha a file.lzh file1 file2 lha t file.lzh lha x file.lzh
gzcat		gzcat file.gz gzcat file.Z
zcat		zcat file.Z
zless	file perusal filter for crt viewing of compressed text	zless file.gz
zgrep	search possibly compressed files for a regular expression	zgrep PATTERN file.gz
zegrep	search possibly compressed files for a regular expression	zegrep "new" test.txt.gz
zdiff	compare compressed files	zdiff file1.gz file2.gz

Character

Command	Description	Example
lv	a Powerful Multilingual File Viewer / Grep
qkc
nkf	Network Kanji Filter
iconv	Convert encoding of given files from one encoding to another

User Administration

User

Command	Description	Example
useradd	create a new user or update default new user information	useradd -u UID -g GROUP -G GROUP1,GROUP2 -s /bin/bash -d HOME_DIR LOGIN
whoami	print effective userid	whoami
w	Show who is logged on and what they are doing.	w
who	show who is logged on	who who --all
userdel	delete a user account and related files	userdel -r USER <- (-r, --remove : Files in the user's home directory will be removed)
vipw	edit the password, group, shadow-password or shadow-group file	vipw <- edit /etc/passwd vipw -s <- edit /etc/shadow
passwd	change user password	echo "password01" | passwd --stdin user01 passwd -S user1 <- check about the status of the password passwd -l user01 <- Lock the user passwd -u user01 <- Unlock
chpasswd	update passwords in batch mode	echo user01:password | chpasswd echo 'USER:PASS' > tmp.txt ; chpasswd < tmp.txt ; rm -f tmp.txt
mkpasswd
chage	change user password expiry information	chage -l USER <- check chage -M 90 USER <- the password expires day set 90days
usermod	modify a user account	usermod -g GROUP USER usermod -G SUBGROUP USER usermod -G SUBGROUP1,SUBGROUP2 USER usermod -G "" USER
chsh	change login shell	chsh -l <- = cat /etc/shells chsh -s /bin/bash <- changing shell chsh -s /bin/bash user01
getent	get entries from Name Service Switch libraries	getent passwd <- you can check LDAP Users getent group getent shadow
pam_tally2	The login counter (tallying) module	pam_tally2 -u USER <- check pam_tally2 -u USER --reset <- reset

Group

Command	Description	Example
groups	print the groups a user is in	groups groups USERNAME
groupadd	create a new group	groupadd -g GID GROUP groupadd -g 1100 dev
groupdel	delete a group
vigr	edit the password, group, shadow-password or shadow-group file

File Permissions

Command	Description	Example
chmod	change file mode bits	chmod 777 TARGET chmod u+s PROGRAM ← add SSUID（Set User ID）
chown	change file owner and group	chown -R TARGET <- -R : operate on files and directories recursively

Etc

Command	Description	Example
finger	user information lookup program
su	change user ID or become superuser	su - <- change root user sudo su - USER -s /bin/bash su - user1 -c "ssh [e-mail] ls -lh /tmp" >> aaa.txt
sudo	execute a command as another user	sudo -u USER COMMAND sudo sh -c 'echo "test" >> /tmp/test.txt'
id	print real and effective user and group IDs	id USERNAME
last	show listing of last logged in users	last last -5 <- last 5 logged in users
lastlog	reports the most recent login of all users or of a given user	lastlog
umask	set file mode creation mask

http://cmdref.net/os/linux/command/index.html#Network

Network

Network

Command	Description	Example
ip	show / manipulate routing, devices, policy routing and tunnels	ip a <- print ip address ip addr <- print ip address ip r <- Show IP Routing ip route <- Show IP Routing
ss	another utility to investigate sockets	ss -lt <- TCP Listening Port ss -ltp <- Process Name with Listening TCP ss -anu
ifconfig	configure a network interface	ifconfig <- check ip ifconfig -a <- -a : display all interfaces ifconfig eth0 up ifconfig eth0 down
ifdown	take a network interface down	ifdown eth0 ifdown eth0 && ifup eth0
ifup	bring a network interface up	ifup eth0 ifdown eth0 && ifup eth0
route	show / manipulate the IP routing table	route <- show the IP routing table route add -net 192.168.10.0 netmask 255.255.255.0 gw 10.50.0.1 route add -host 192.168.0.100 gw 192.168.1.100
traceroute	print the route packets trace to network host
tracepath	traces path to a network host discovering MTU along this path
ethtool	Display or change ethernet card settings	ethtool eth0
mii-tool	view, manipulate media-independent interface status	mii-tool eth0 mii-tool -vv eth0
arp	manipulate the system ARP cache	arp -a <- (-a : Shows the entries of the specified hosts.) arp -d 192.168.xx.xx <- delete arp
nmcli	line tool for controlling NetworkManager

DNS

Command	Description	Example
dig	DNS lookup utility	dig @8.8.8.8 google.com any dig @8.8.8.8 -x 74.125.235.101 dig google.com mx dig +trace google.com dig +trace -x 173.252.120.6
nslookup	query Internet name servers interactively	nslookup -type=any google.com 8.8.8.8
host	DNS lookup utility	host -t any google.com 8.8.8.8
whois	client for the whois service	whois google.com
nscd	name service cache daemon	nscd -i hosts <- chache clear

Connection

Command	Description	Example
telnet	user interface to the TELNET protocol	telnet IP PORT
ssh	OpenSSH SSH client (remote login program)	ssh USER@IP ssh xx.xx.xx.xx "hostname; netstat -rn |grep 10.110.0" ssh xx.xx.xx.xx sudo /sbin/reboot
scp	secure copy (remote file copy program) scp is changed the file's time stamp and the link file copyed as the real file.	scp -r /home/user1 user1@192.168.0.10:/home
rsync	a fast, versatile, remote (and local) file-copying tool rcync remain file's time stamp and the link file copyed as the link file. rsync -avz --delete /home/user1*/* /tmp/user1.bk/ <- rsync "/" is very important. rsync -e ssh -avz --delete /home/user1/ user2@192.168.0.2:/home/backup/server1/home/user1/ rsync -e ssh -avz –-bwlimit=1250 FILE user@192.168.0.2:/DIR/ # 1Mbps = 125KBps
ssh-keygen	authentication key generation, management and conversion	ssh-keygen -t rsa <- generate rsa key pair ssh-keygen -R HOST <- Removes all keys belonging to hostname from a known_hosts file.

Check

Command	Description	Example
ping	send ICMP ECHO_REQUEST to network hosts	ping -c 5 -s 1500 192.168.0.1 ? ping -i 0.1 192.168.0.1 # -i : interval
nmap	Network exploration tool and security / port scanner	nmap -p 443 www.google.com
nping		nping --tcp -p PORT HOST
httping	measure the latency and throughput of a webserver
http_ping
hping , hping3
fping		fping -g 192.168.0.0/24
netcat		nc -v -z 192.168.0.10 80 <- portscan nc -v -z 192.168.0.10 1-1023 <- portscan

HTTP

Command	Description	Example
curl	transfer a URL	curl -O http://example.com/images/test.jpg curl -I http://www.example.com/ <- Only Header curl -i http://www.example.com/ <- Header and Body curl --proxy http://proxy.example.com:8080 http://example.com/
wget	The non-interactive network downloader.	wget http://google.com/ wget -e http_proxy=xx.xx.xx.xx:8080 http://example.com/ wget -e https_proxy=xx.xx.xx.xx:8080 https://example.com/ wget -S --spider http://example.com/ <- Only Header

FTP

Command	Description	Example
ftp	ARPANET file transfer program
lftp	Sophisticated file transfer program

SNMP

Command	Description	Example
snmpwalk	retrieve a subtree of management values using SNMP GETNEXT requests	snmpwalk -v 2c -c public localhost sysname snmpwalk -v 2c -c public localhost .1.3.6.1.2.1
snmpget	communicates with a network entity using SNMP GET requests	snmpget -v 2c 192.168.0.10 -c public .1.3.6.1.4.1.2021.11.50.0
snmptranslate	translate MIB OID names between numeric and textual forms	snmptranslate -Tp
snmpnetstat	display networking status and configuration information from a network entity via SNMP	snmpnetstat -v 2c -c public -Can localhost snmpnetstat -v 2c -c public -Ci localhost snmpnetstat -v 2c -c public -Cs localhost

Shell Script

Shell

Command	Description	Example
date	print or set the system date and time	date --date '10day ago' +"%d%m%Y" -> 30102006 date +"%d%m%Y" -> 30102006 date +"%H:%M" -> 12:47 cp -p FILE FILE.date +%Y%m%d cp -p FILE FILE.date -d '1day ago' +%Y%m%d
tr	translate or delete characters
cut	remove sections from each line of files	echo 12345 |cut -c3-
sort	sort lines of text files	sort -t: +1 -n sample.txt
uniq	report or omit repeated lines	cat access_log.1
logger	a shell command interface to the syslog(3) system log module	logger "test test"
basename	strip directory and suffix from filenames
dirname	strip last component from file name	DIR=dirname ${0}
paste	merge lines of files	paste -d, test1.txt test2.txt
awk		echo "1 2 3 4 5"
sed		sed -e 's/xxx/XXX/g' input.txt > output.txt
mail mailx	send and receive Internet mail echo test | mail -s "test" -S "smtp=smtp://xx.xx.xx.xx:25" [e-mail]
while		while : ; do uptime ; sleep 1 ; done while : ; do uptime >> /tmp/tmp.txt ; sleep 1 ; done while : ; do ps aux
for		for i in 127.0.0.1 192.168.10.1; do ping -c 2 $i; done

Hardware

Haredware

Command	Description	Example
dmesg	print or control the kernel ring buffer	dmesg
lspci	list all PCI devices	lspci

Module

Command	Description	Example
lsmod	show the status of modules in the Linux Kernel	lsmod
modinfo	show information about a Linux Kernel module	modinfo MODULENAME modinfo bnx2
insmod	insert a module into the Linux Kernel
rmmod	remove a module from the Linux Kernel
modprobe	add and remove modules from the Linux Kernel

Disk Utilities

HDD

Command	Description	Example
du	estimate file space usage	du -sh * du -h --max-depth=1
fuser	identify processes using files or sockets	fuser -mv /mnt/test <- check fuser -mvk /mnt/test <-(-k : Kill processes)
chroot	run command or interactive shell with special root directory
hdparm	get/set hard disk parameters
dumpe2fs	dump ext2/ext3/ext4 filesystem information
badblocks	search a device for bad blocks

Partition

Command	Description	Example
df	report file system disk space usage	df -h <- (-h : print sizes in human readable format) df -BG <- Bigabyte Unite df -BM <- Megabyte Unite
sfdisk	partition table manipulator for Linux	sfdisk -l <-(-l : List the partitions of a device.)
fdisk	manipulate disk partition table	fdisk -l <- ( -l : List the partition tables) fdisk -l /dev/sdb fdisk -l -o +UUID
gdisk	Interactive GUID partition table (GPT) manipulator
parted	a partition manipulation program	parted /dev/mapper/mpath0
lsblk	list block devices	lsblk
e2label	Change the label on an ext2/ext3/ext4 filesystem

Swap

Command	Description	Example
mkswap	set up a Linux swap area
swapon	enable devices and files for paging and swapping	swapon -s <- Check swapon -a swapon /dev/xvda3
swapoff	disable devices and files for paging and swapping	swapoff -a

File Systems

Command	Description	Example
mkfs	build a Linux filesystem #you must umount the device before mkfs.	mkfs -t xfs /dev/sdb1 mkfs -t ext3 /dev/sdb1 mkfs -t ext4 /dev/sdb1
mkfs.xfs mkfs.ext4 mkfs.ext3	#you must umount the device before mkfs.	mkfs.ext4 /dev/sdb1 mkfs.ext3 /dev/sdb1
mkfs2fs	create an ext2/ext3/ext4 filesyste #you must umount the device before mkfs.	mke2fs /dev/sdb1 <- ext2 mke2fs -j /dev/sdb1 <- ext3
xfs_info		xfs_info /dev/sda1
tune2fs	adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems	tune2fs -l /dev/mapper/mpath0 <- (-l : List the contents of the filesystem superblock. tune2fs -l /dev/mapper/mpath0
fsck	check and repair a Linux filesystem you must umount the device before fsck. for example single usermode and umount. 'shutdown -r -F now' is force fsck after reboot.	fsck -p /dev/sda1 (-p : Automatically repair ("preen") the file system.)
fsck.ext4	check and repair a Linux filesystem
e2fsck	check a Linux ext2/ext3/ext4 file system
resize2fs	ext2/ext3/ext4 file system resizer	resize2fs /dev/testvg/lvol0

Data

Command	Description	Example
dd	convert and copy a file	dd if=/dev/zero of=test_100M bs=1M count=100
sync	flush file system buffers
shred	overwrite a file to hide its contents, and optionally delete it

mount

Command	Description	Example
mount	mount a filesystem	mount /mnt/test /dev/sda1 mount -o remount /dev/sda1
umount	unmount file systems	umount /mnt/test umount -f /mnt/test (-f : Force unmount(in case of an unreachable NFS system)) umount -l /mnt/test (-l : Lazy unmount.Detach the filesystem from the filesystem hierarchy now )

LVM

LVM

Command	Description	Example
lvm	LVM2 tools

PV (Physical Volume)

Command	Description	Example
pvs	report information about physical volumes
pvdisplay	display attributes of a physical volume	pvdisplay pvdisplay -C
pvcreate	initialize a disk or partition for use by LVM	pvcreate /dev/mapper/mpath0p1 pvcreate /dev/mapper/mpath0p1 /dev/mapper/mpath1p1
pvremove	remove a physical volume	pvremove /dev/mapper/mpath0p1
pvscan	scan all disks for physical volumes

VG (Volume Group)

Command	Description	Example
vgs	report information about volume groups	vgs -o +vg_tags <- check tag
vgdisplay	display attributes of volume groups	vgdisplay vgdisplay -C
vgcreate	create a volume group	vgcreate vgdata1 /dev/hdb1 /dev/hdc1
vgremove	remove a volume group	vgremove vg01
vgscan	scan all disks for volume groups and rebuild caches
vgchange	change attributes of a volume group	vgchange -a y <- activate vgchange -a n <- deactivate vgchange -a y vg01 vgchange -a n vg01 Check : lvdisplay VGDATA
vgextend	add physical volumes to a volume group	vgextend vg01 /dev/hdd1
vgrename	rename a volume group	vgrename oldvg newvg

LV (Logical Volume)

Command	Description	Example
lvs	report information about logical volumes
lvdisplay	display attributes of a logical volume	lvdisplay lvdisplay -C lvdisplay /dev/mapper/VGDATA-lv00
lvcreate	create a logical volume in an existing volume group	lvcreate -l PENUMBER vgdata lvcreate -L 150G vgdata
lvremove	remove a logical volume	lvremove /dev/testvg/lvol0
lvscan	scan (all disks) for logical volumes
lvresize	resize a logical volume	lvresize -L +5G /dev/vg0/home
lvextend	extend the size of a logical volume	lvextend -L +5G /dev/vg0/home lvextend -l +100%FREE /dev/mapper/Array00-lv00
lvreduce	reduce the size of a logical volume
lvrename	rename a logical volume	lvrename /dev/vgdata/lvol0 /dev/vgdata/lvol1

Performance

Performance

Command	Description	Example
top	display Linux processes	top -b -n 4 -d 15 <- interval 15sec , 4 times
sar	Collect, report, or save system activity information.	sar -f /var/log/sa/sa16 sar (cpu,io) sar -r (memory) sar -q (Loadaverage)
vmstat	Report virtual memory statistics	vmstat 1 <- interval 1sec (cpu, io, memory, swap) vmstat 1 5 <- interval 1sec, 5 times (cpu, io, memory, swap)
iostat	Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.	iostat -xtk 1 (cpu, io) <- interval 1sec
mpstat	Report processors related statistics.	mpstat -P ALL
uptime	Tell how long the system has been running.	while : ; do uptime ; sleep 1 ; done while : ; do uptime >> /tmp/tmp.txt ; sleep 1 ; done
w	Show who is logged on and what they are doing.
free	Display amount of free and used memory in the system	free -m <- show output in MB
tcpdump	dump traffic on a network	tcpdump host 192.168.0.10 -n -w /tmp/20110615.pcap tcpdump -r /tmp/20110615.pcap <- -r : Read packets from file
netstat	Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships	netstat -an (-a : Show both listening and non-listening sockets.) netstat -rn (-r : Display the kernel routing tables.)

Load Test

Command	Description	Example
fio

Software

Software

Command	Description	Example
make	GNU make utility to maintain groups of programs
patch	apply a diff file to an original	patch -p1 -N < ../xxx.patch
ldd	print shared library dependencies	ldd BINARY
yum	an interactive, rpm based, package manager	yum repolist <- check enabled repository yum search STRINGS yum info PACKAGE yum install PACKAGE yum --disablerepo=* --enablerepo=test-repo repolist
rpm	RPM Package Manager	rpm -ivh PACKAGE.rpm <- install rpm -e PACAGE.rpm <- uninstall
apt
dpkg
alien		alien -d package-x.x.x.rpm alien -r package-x.x.x.deb
update-alternatives		update-alternatives --config mta
rhn_register		rhn_register --nox --proxy=http://192.168.0.10:9999

etc

X Window System

Command	Description	Example
startx	initialize an X session	startx
xhost	server access control program for X	xhost + <- Access is granted to everyone
xauth	X authority file utility

TUI

Command	Description	Example
ntsysv	simple interface for configuring runlevels
authconfig-tui	an interface for configuring system authentication resources
system-config-securitylevel
system-config-network-tui

etc

Command	Description	Example
md5sum	compute and check MD5 message digest	find . -type f -exec md5sum {} \; > /tmp/md5.out <- check all files
gpg	OpenPGP encryption and signing tool
screen
kermit

http://cmdref.net/os/linux/command/