Linux Commands Cheat Sheet with Examples

COMMAND	DESCRIPTION	More details	Similar request (optional)
System information
arch	show architecture of the machine	Example
uname -m	show architecture of the machine	Example
uname -r	show kernel version used	Example
dmidecode -q	show hardware system components - (SMBIOS / DMI)	Example
hdparm -i /dev/hda	displays the characteristics of a hard-disk	Example
hdparm -tT /dev/sda	perform t est reading on a hard-disk	Example
cat /proc/cpuinfo	shows information CPU info	Example
cat /proc/interrupts	show interrupts	Example
cat /proc/meminfo	verify memory use	Example
cat /proc/swaps	show file(s) swap	Example
cat /proc/version	show version of the kernel	Example
cat /proc/net/dev	show network adpters and statistics	Example
cat /proc/mounts	show mounted file system(s)	Example
lspci -tv	display PCI devices	Example
lsusb -tv	show USB devices	Example
date	show system date	Example
cal 2007	show the timetable of 2007	Example
date 041217002007.00	set date and time - MonthDayhoursMinutesYear.Seconds	Example
clock -w	save changes of date on BIOS	Example
Shutdown, Restart of a system and Logout
shutdown -h now	shutdown system	Example
init 0	shutdown system	Example
shutdown -r hours:minutes &	planned shutdown ofthe system	Example
shutdown -c	cancel a planned shutdown of the system	Example
shutdown -r now	reboot	Example
reboot	reboot	Example
logout	leaving session	Example
Files and Directory
cd /home	enter to directory '/ home'	Example
cd ..	go back one level	Example
cd ../..	go back two levels	Example
cd	go to home directory	Example
cd ~utente	go to home directory	Example
cd -	go to previous directory	Example
pwd	show the path of work directory	Example
ls	view files of directory	Example
ls -F	view files of directory	Example
ls -l	show details of files and directory	Example
ls -a	show hidden files	Example
ls *[0-9]*	show files and directory containing numbers	Example
tree	show files and directories in a tree starting from root	Example
lstree	show files and directories in a tree starting from root	Example
mkdir dir1	create a directory called 'dir1'	Example
mkdir dir1 dir2	create two directories simultaneously	Example
mkdir -p /tmp/dir1/dir2	create a directory tree	Example
rm -f file1	delete file called 'file1'	Example
rmdir dir1	delete directory called 'dir1'	Example
rm -rf dir1	remove a directory called 'dir1' and contents recursively	Example
rm -rf dir1 dir2	remove two directories and their contents recursively	Example
mv dir1 new_dir	rename / move a file or directory	Example
cp file1 file2	copying a file	Example
cp dir/* .	copy all files of a directory within the current work directory	Example
cp -a /tmp/dir1 .	copy a directory within the current work directory	Example
cp -a dir1 dir2	copy a directory	Example
ln -s file1 lnk1	create a symbolic link to file or directory	Example
ln file1 lnk1	create a physical link to file or directory	Example
touch -t 0712250000 fileditest	modify timestamp of a fileor directory - (YYMMDDhhmm)	Example
File search
find / -name file1	search file and directory into root filesystem from '/'	Example
find / -user user1	search files and directories belonging to 'user1'	Example
find /home/user1 -name *.bin	search files with '. bin' extension within directory '/ home/user1'	Example
find /usr/bin -type f ­atime +100	search bynary files are not used in the last 100 days	Example
find /usr/bin -type f ­mtime ­10	search files created or changed within 10 days	Example
find / -name *.rpm ­exec chmod 755 {} ;	search files with '.rpm' extension and modify permits	Example
find / -xdev ­name *.rpm	search files with '.rpm'extension ignoring removable partitions as cdrom, pen-drive, etc.…	Example
locate *.ps	find files with the '.ps' extension - first run 'updatedb' command	Example
whereis halt	show location of a binary file, source or man	Example
which halt	show full path to a binary / executable	Example
Mounting a Filesystem
mount /dev/hda2 /mnt/hda2	mount disk called hda2 - verify existence of the directory '/ mnt/hda2'	Example
umount /dev/hda2	unmount disk called hda2 - exit from mount point '/ mnt/hda2' first	Example
fuser -km /mnt/hda2	force umount when the device is busy	Example
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	Example
mount /dev/fd0 /mnt/floppy	mount a floppy disk	Example
mount /dev/cdrom /mnt/cdrom	mount a cdrom / dvdrom	Example
mount /dev/hdc /mnt/cdrecorder	mount a cdrw / dvdrom	Example
mount /dev/hdb /mnt/cdrecorder	mount a cdrw / dvdrom	Example
mount -o loop file.iso /mnt/cdrom	mount a file or iso image	Example
mount -t vfat /dev/hda5 /mnt/hda5	mount a Windows FAT32 file system	Example
mount /dev/sda1 /mnt/usbdisk	mount a usb pen-drive or flash­drive	Example
mount -t smbfs ­o username=user,password=pass //winclient/share /mnt/share	mount a windows network share	Example
Disk Space
df -h	show list of partitions mounted	Example
ls -lSr |more	show size of the files and directories ordered by size	Example
du -sh dir1	estimate space used by directory 'dir1'	Example
du -sk * | sort ­rn	show size of the files and directories sorted by size	Example
rpm -q ­a ­­qf '%10{SIZE}t%{NAME}n' | sort ­k1,1n	show space used by rpm packages installed sorted by size (fedora, redhat and like)	Example
dpkg-query ­W ­f='${Installed­Size;10}t${Package}n' | sort -k1,1n	show space used by deb packages installed sorted by size (ubuntu, debian and like)	Example
Users and Groups
groupadd group_name	create a new group	Example
groupdel group_name	delete a group	Example
groupmod -n new_group_name old_group_name	rename a group	Example
useradd -c Nome Cognome" ­g admin ­d /home/user1 ­s /bin/bash user1"	create a new user belongs admin" group"	Example
useradd user1	create a new user	Example
userdel -r user1	delete a user ( '-r' eliminates home directory)	Example
usermod -c User FTP" ­g system ­d /ftp/user1 ­s /bin/nologin user1"	change user attributes	Example
passwd	change password	Example
passwd user1	change a user password (only by root)	Example
chage -E 2005­12­31 user1	set deadline for user password	Example
pwck	check correct syntax and file format of '/etc/pasws d' and users existence	Example
grpck	check correct syntax and file format of '/etc/group' and groups existence	Example
newgrp group_name	log in to a new group to change default group of newly created files	Example
Permits on File - use +" to set permissions and "-" to remove"
ls -lh	show permits	Example
ls /tmp | pr -T5 ­W$COLUMNS	divide terminal into 5 columns	Example
chmod ugo+rwx directory1	set permissions reading (r), write (w) and (x)access to users owner (u) group (g) and others (o)	Example
chmod go-rwx directory1	remove permits reading (r), write (w) and (x) access to users group (g) and others (or	Example
chown user1 file1	change owner of a file	Example
chown user1 -R directory1	change user owner of a directory and allthe files and directories contained inside	Example
chgrp gruppo1 file1	change group of files	Example
chown user1:gruppo1 file1	change user and group ownership of a file	Example
find / -perm ­u+s	view all files on the system with SUID configured	Example
chmod u+s /bin/file_eseguibile	set SUID bit on a binary file - the user that running that file gets same privileges as owner	Example
chmod u-s /bin/file_binario	disable SUID bit on a binary file	Example
chmod g+s /home/public	set SGID bit on a directory - similar to SUID but for directory	Example
chmod g-s /home/public	disable SGID bit on a directory	Example
chmod o+t /home/comune	set STIKY bit on a directory - allows files deletion only to legitimate owners	Example
chmod o-t /home/comune	disable STIKY bit on a directory	Example
Special Attributes on file - use +" to set permissions and "-" to remove"
chattr +a file1	allows write opening of a file only append mode	Example
chattr +c file1	allows that a file is compressed / decompressed automatically by the kernel	Example
chattr +d file1	makes sure that the program ignores Dump the files during backup	Example
chattr +i file1	makes it an immutable file, which cannot be removed, altered, renamed or linked	Example
chattr +s file1	allows a file to be deleted safely	Example
chattr +S file1	makes sure that if a file is modified changes are written in synchronous mode as with sync	Example
chattr +u file1	allows you to recover the contents of a file even if it is canceled	Example
lsattr	show specials attributes	Example
Archives and compressed files
bunzip2 file1.bz2	decompress a file called 'file1.bz2'	Example
bzip2 file1	compress a file called 'file1'	Example
gunzip file1.gz	decompress a file called 'file1.gz'	Example
gzip file1	compress a file called 'file1'	Example
gzip -9 file1	compress with maximum compression	Example
rar a file1.rar test_file	create an archive rar called'file1.rar'	Example
rar a file1.rar file1 file2 dir1	compress 'file1', 'file2' and 'dir1' simultaneously	Example
rar x file1.rar	decompress rar archive	Example
unrar x file1.rar	decompress rar archive	Example
tar -cvf archive.tar file1	create a uncompressed tarball	Example
tar -cvf archive.tar file1 file2 dir1	create an archive containing 'file1', 'file2' and 'dir1'	Example
tar -tf archive.tar	show contents of an archive	Example
tar -xvf archive.tar	extract a tarball	Example
tar -xvf archive.tar ­C /tmp	extract a tarball into / tmp	Example
tar -cvfj archive.tar.bz2 dir1	create a tarball compressed into bzip2	Example
tar -xvfj archive.tar.bz2	decompress a compressed tar archive in bzip2	Example
tar -cvfz archive.tar.gz dir1	create a tarball compressed into gzip	Example
tar -xvfz archive.tar.gz	decompress a compressed tar archive in gzip	Example
zip file1.zip file1	create an archive compressed in zip	Example
zip -r file1.zip file1 file2 dir1	compress in zip several files and directories simultaneously	Example
unzip file1.zip	decompress a zip archive	Example
RPM Packages - Fedora, Red Hat and like
rpm -ivh package.rpm	install a rpm package	Example
rpm -ivh ­­nodeeps package.rpm	install a rpm package ignoring dependencies requests	Example
rpm -U package.rpm	upgrade a rpm package without changing configuration files	Example
rpm -F package.rpm	upgrade a rpm package only if it is already installed	Example
rpm -e package_name.rpm	remove a rpm package	Example
rpm -qa	show all rpm packagesinstalled on the system	Example
rpm -qa | grep httpd	show all rpm packageswith the name httpd""	Example
rpm -qi package_name	obtain information on a specific package installed	Example
rpm -qg System Environment/Daemons""	show rpm packages of a groupsoftware	Example
rpm -ql package_name	show list of files provided by a rpm package installed	Example
rpm -qc package_name	show list of configuration files provided by a rpm package installed	Example
rpm -q package_name ­­whatrequires	show list of dependencies required fora rpm packet	Example
rpm -q package_name ­­whatprovides	show capability provided by a rpm package	Example
rpm -q package_name ­­scripts	show scripts started during installation / removal	Example
rpm -q package_name ­­changelog	show history of revisions of a rpm package	Example
rpm -qf /etc/httpd/conf/httpd.conf	verify which rpm package belongs to a given fiel	Example
rpm -qp package.rpm -l	show list of files provided by a rpm package not yet installed	Example
rpm -­import /media/cdrom/RPM­GPG­KEY	import public-key digital signature	Example
rpm -­checksig package.rpm	verify the integrityof a rpm package	Example
rpm -qa gpg­pubkey	verify integrity of all rpm packages installed	Example
rpm -V package_name	check file size, permissions, type, owner, group, MD5 checksum and last modification	Example
rpm -Va	check all rpm packages installed on the system - use with caution	Example
rpm -Vp package.rpm	verify a rpm package not yet installed	Example
rpm2cpio package.rpm | cpio -­extract -­make-directories *bin*	extract executable file from a rpm package	Example
rpm -ivh /usr/src/redhat/RPMS/`arch`/package.rpm	install a package built from a rpm source	Example
rpmbuild -­rebuild package_name.src.rpm	build a rpm package from a rpm source	Example
YUM packages updater - Fedora, RedHat and like
yum install package_name	download and install a rpm package	Example
yum update	update all rpm packages installed on the system	Example
yum update package_name	upgrade a rpm package	Example
yum remove package_name	remove a rpm package	Example
yum list	list all packages installed on the system	Example
yum search package_name	find a package on rpm repository	Example
yum clean packages	clean up rpm cache erasing downloaded packages	Example
yum clean headers	remove all files headers that the system uses to resolve dependency	Example
yum clean all	remove from the cache packages and headers files	Example
DEB packages - Debian, Ubuntu and like
dpkg -i package.deb	install / upgrade a deb package	Example
dpkg -r package_name	remove a deb package from the system	Example
dpkg -l	show all deb packages installed on the system	Example
dpkg -l | grep httpd	show all rpm packageswith the name httpd""	Example
dpkg -s package_name	obtain information on a specific package installed on system	Example
dpkg -L package_name	show list of files provided by a package installed on system	Example
dpkg -­contents package.deb	show list of files provided by a package not yet installed	Example
dpkg -S /bin/ping	verify which package belongs to a given file	Example
APT packages updater - Debian, Ubuntu e like
apt-get install package_name	install / upgrade a deb package	Example
apt-cdrom install package_name	install / upgrade a deb package from cdrom	Example
apt-get update	update all deb packages installed on system	Example
apt-get remove package_name	remove a deb package from system	Example
apt-get check	verify correct resolution of dependencies	Example
apt-get clean	clean up cache from packages downloaded	Example
View file content
cat file1	view the contents of a file starting from the first row	Example
tac file1	view the contents of a file starting from the last line	Example
more file1	view content of a file along	Example
less file1	similar to 'more' command but which allows backward movement in the file as well as forwardmovement	Example
head -2 file1	view first two lines of a file	Example
tail -2 file1	view last two lines of a file	Example
tail -f /var/log/messages	view in real time what is added to a file	Example
Text Manipulation
cat file_test | [operation: sed, grep, awk, grep, etc] > result.txt	syntax to elaborate the text of a file, and write result to a new file	Example
cat file_originale | [operazione: sed, grep, awk, grep, etc] >> result.txt	syntax to elaborate the text of a file and append result onto existing file	Example
grep Aug /var/log/messages	look up words Aug" in the file onto 'messages'"	Example
grep ^Aug /var/log/messages	look up words that begin with Aug" onto file 'messages'"	Example
grep [0-9] /var/log/messages	select from file 'messages' all lines that contain numbers	Example
grep Aug -R /var/log/*	search string Aug" at directory '/var/log' and below"	Example
sed 's/stringa1/stringa2/g' example.txt	replace string1" with "string2" onto example.txt"	Example
sed '/^$/d' example.txt	remove all blank lines from example.txt	Example
sed '/ *#/d; /^$/d' example.txt	remove comments andblank lines from example.txt	Example
echo 'esempio' | tr '[:lower:]' '[:upper:]'	convert from lower case in upper case	Example
sed -e '1d' result.txt	eliminates the first line from file example.txt	Example
sed -n '/stringa1/p'	view only lines that contain the word string1""	Example
sed -e 's/ *$//' example.txt	remove empty characters at the end of each row	Example
sed -e 's/stringa1//g' example.txt	remove only the word string1" from text and leave intact all"	Example
sed -n '1,5p;5q' example.txt	view from 1th to 5th row	Example
sed -n '5p;5q' example.txt	view row number 5	Example
sed -e 's/00*/0/g' example.txt	replace more zeros with a single zero	Example
cat -n file1	number row of a file	Example
cat example.txt | awk 'NR%2==1'	remove all lines even from examplet.xt	Example
echo a b c | awk '{print $1}'	view the first column of line	Example
echo a b c | awk '{print $1,$3}'	view the first and third column of line	Example
paste file1 file2	merging contents of two files for columns	Example
paste -d '+' file1 file2	merging contents of two files for columns with '+' delimiter on the center	Example
sort file1 file2	sort contents of two files	Example
sort file1 file2 | uniq	sort contents of two files omitting lines repeated	Example
sort file1 file2 | uniq -u	sort contents of two files by viewing only unique line	Example
sort file1 file2 | uniq -d	sort contents of two files by viewing only duplicate line	Example
comm -1 file1 file2	compare contents of two files by deleting only unique lines from 'file1'	Example
comm -2 file1 file2	compare contents of two files by deleting only unique lines from 'file2'	Example
comm -3 file1 file2	compare contents of two files by deleting only the lines that appear on both files	Example
Character set and Format file conversion
dos2unix filedos.txt fileunix.txt	convert a text file format from MSDOS to UNIX	Example
unix2dos fileunix.txt filedos.txt	convert a text file format from UNIX to MSDOS	Example
recode ..HTML < page.txt > page.html	convert a text file to html	Example
recode -l | more	show all available formats conversion	Example
Filesystem Analysis
badblocks -v /dev/hda1	check bad blocks onto disk hda1	Example
fsck /dev/hda1	repair / check integrity of linux filesystem on disk hda1	Example
fsck.ext2 /dev/hda1	repair / check integrity of ext2 filesystem on disk hda1	Example
e2fsck /dev/hda1	repair / check integrity of ext2 filesystem on disk hda1	Example
e2fsck -j /dev/hda1	repair / check integrity of ext3 filesystem on disk hda1	Example
fsck.ext3 /dev/hda1	repair / check integrity of ext3 filesystem on disk hda1	Example
fsck.vfat /dev/hda1	repair / check integrity of fat filesystem on disk hda1	Example
fsck.msdos /dev/hda1	repair / check integrity of dos filesystem on disk hda1	Example
dosfsck /dev/hda1	repair / check integrity of dos filesystems on disk hda1	Example
Format a Filesystem
mkfs /dev/hda1	create a filesystem type linux on hda1 partition	Example
mke2fs /dev/hda1	create a filesystem type linux ext2 on hda1 partition	Example
mke2fs -j /dev/hda1	create a filesystem type linux ext3 (journal) on hda1 partition	Example
mkfs -t vfat 32 ­F /dev/hda1	create a FAT32 filesystem	Example
fdformat -n /dev/fd0	format a floppy disk	Example
mkswap /dev/hda3	create a swap filesystem	Example
SWAP filesystem
mkswap /dev/hda3	create a swap filesystem	Example
swapon /dev/hda3	activating a new swap partition	Example
swapon /dev/hda2 /dev/hdb3	activate two swap partitions	Example
Backup
dump -0aj ­f /tmp/home0.bak /home	make a full backup of directory '/home'	Example
dump -1aj ­f /tmp/home0.bak /home	make a incremental backup of directory '/home'	Example
restore -if /tmp/home0.bak	restoring a backup interactively	Example
rsync -rogpav ­­delete /home /tmp	synchronization between directories	Example
rsync -rogpav ­e ssh ­­delete /home ip_address:/tmp	rsync via SSH tunnel	Example
rsync -az ­e ssh ­­delete ip_addr:/home/public /home/local	synchronize a local directory with a remote directory via ssh and compression	Example
rsync -az -e ssh -­delete /home/local ip_addr:/home/public	synchronize a remote directory with a local directory via ssh and compression	Example
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 sh	Example
tar -Puf backup.tar /home/user	make a incremental backup of directory '/home/user'	Example
( 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	Example
( tar c /home ) | ssh -C user@ip_addr 'cd /home/backup-home && tar x ­p'	copy a local directory on remote directory via ssh	Example
tar cf - . | (cd /tmp/backup ; tar xf ­ )	local copy preserving permits and links from a directoryto another	Example
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	Example
find /var/log -name '*.log' | tar cv -­files­from=­ | bzip2 > log.tar.bz2	find all files with '.log' extention and make an bzip archive	Example
dd if=/dev/hda of=/dev/fd0 bs=512 count=1	make a copy of MBR (Master Boot Record) to floppy	Example
dd if=/dev/fd0 of=/dev/hda bs=512 count=1	restore MBR from backup copy saved to floppy	Example
CDROM
cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force	clean a rewritable cdrom	Example
mkisofs /dev/cdrom > cd.iso	create an iso image of cdrom on disk	Example
mkisofs /dev/cdrom | gzip > cd_iso.gz	create a compressed iso image of cdrom on disk	Example
mkisofs -J -allow­leading­dots -R -V Label CD" -iso-level 4 -o ./cd.iso data_cd"	create an iso image of a directory	Example
cdrecord -v dev=/dev/cdrom cd.iso	burn an ISO image	Example
gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom ­	burn a compressed ISO image	Example
mount -o loop cd.iso /mnt/iso	mount an ISO image	Example
cd-paranoia ­B	rip audio tracks from a CD to wav files	Example
cd-paranoia ­­ ­3""	rip first three audio tracks froma CD to wav files	Example
cdrecord -­scanbus	scan bus to identify the channel scsi	Example
Networking - LAN and WiFi
ifconfig eth0	show configuration ofan ethernet network card	Example
ifup eth0	activate an interface 'eth0'	Example
ifdown eth0	disable an interface 'eth0'	Example
ifconfig eth0 192.168.1.1 netmask 255.255.255.0	configure IP Address	Example
ifconfig eth0 promisc	configure 'eth0' inpromiscuous mode to gather packets (sniffing)	Example
dhclient eth0	active interface 'eth0' in dhcp mode	Example
route -n	show routing table	Example
route add -net 0/0 gw IP_Gateway	configura default gateway	Example
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'	Example
route del 0/0 gw IP_gateway	remove static route	Example
echo 1" > /proc/sys/net/ipv4/ip_forward"	activate ip routing	Example
hostname	show hostname	Example
host linuxtutorials.net	lookup hostname to resolve name to ip addressand viceversa	Example
ip link show	show link status of all interfaces	Example
mii-tool eth0	show link status of 'eth0'	Example
ethtool eth0	show statistics of network card 'eth0'	Example
netstat -tup	show all active network connections and their PID	Example
netstat -tupl	show all network services listening on the system and their PID	Example
tcpdump tcp port 80	show all HTTP traffic	Example
iwlist scan	show wireless networks	Example
iwconfig eth1	show configuration of a wireless network card	Example
Microsoft Windows networks - SAMBA
nbtscan ip_addr	netbios name resolution	Example
nmblookup -A ip_addr	netbios name resolution	Example
smbclient -L ip_addr/hostname	show remote shares of a windows host	Example
smbget -Rr smb://ip_addr/share	like wget can download files from a host windows via smb	Example
mount -t smbfs ­o username=user,password=pass //winclient/share /mnt/share	mount a windows network share	Example
IPTABLES - firewall
iptables -t filter ­L	show all chains of filtering table	Example
iptables -t nat ­L	show all chains of nat table	Example
iptables -t filter ­F	clear all rules from filtering table	Example
iptables -t nat ­F	clear all rules from table nat	Example
iptables -t filter ­X	delete any chains created by user	Example
iptables -t filter -A INPUT -p tcp -­dport telnet -j ACCEPT	allow telnet connections to input	Example
iptables -t filter -A OUTPUT -p tcp -­dport http -j DROP	block HTTP connections to output	Example
iptables -t filter -A FORWARD -p tcp -­dport pop3 -j ACCEPT	allow POP3 connections to forward chain	Example
iptables -t filter -A INPUT -j LOG -­log­prefix DROP INPUT""	logging sulla chain di input Logging on chain input	Example
iptables -t nat ­A POSTROUTING ­o eth0 ­j MASQUERADE	configure a PAT (Port Address Traslation) on eth0 masking outbound packets	Example
iptables -t nat ­A PREROUTING ­d 192.168.0.1 ­p tcp -m tcp -­dport 22 -j DNAT -­to­destination 10.0.0.2:22	redirect packets addressed to a host to another host	Example
Monitoring and debugging
top	display linux tasks using most cpu	Example
ps -eafw	displays linux tasks	Example
ps -e ­o pid,args ­­forest	displays linux tasks in a hierarchical mode	Example
pstree	mostra un albero dei processi sistema Shows a tree system processes	Example
kill -9 ID_Processo	force closure of the process and finish it	Example
kill -1 ID_Processo	force a process to reload configuration	Example
lsof -p $$	display a list of files opened by processes	Example
lsof /home/user1	displays a list of open files in a given path system	Example
strace -c ls >/dev/null	display system calls made and received by a process	Example
strace -f ­e open ls >/dev/null	display library calls	Example
watch -n1 'cat /proc/interrupts'	display interrupts in real-time	Example
last reboot	show history reboot	Example
lsmod	display kernel loaded	Example
free -m	displays status of RAM in megabytes	Example
smartctl -A /dev/hda	monitoring reliability of a hard-disk through SMART	Example
smartctl -i /dev/hda	check if SMART is active on a hard-disk	Example
tail /var/log/dmesg	show events inherent to the process of booting kernel	Example
tail /var/log/messages	show system events	Example
Other useful commands
apropos …keyword	display a list of commands that pertainto keywords of a program , useful when youknow what your program does, but you don't know the name of the command	Example
man ping	display the on-line manual pages for example on ping command	Example
whatis …keyword	displays description of what a program does	Example
mkbootdisk -­device /dev/fd0 `uname ­r`	create a boot floppy	Example
gpg -c file1	encrypt a file with GNU Privacy Guard	Example
gpg file1.gpg	decrypt a file with GNU Privacy Guard	Example
wget -r www.example.com	download an entire web site	Example
wget -c www.example.com/file.iso	download a file with the ability to stop the download and resume later	Example
echo 'wget -c www.example.com/files.iso' | at 09:00	start a download at any given time	Example
ldd ssh	show shared libraries required by ssh program	Example
alias hh='history'	set an alias for a command - hh = history	Example
$ ip a	Show current IP address		Check the Current IP Address