600 Essential Linux Commands You Must Know

1. Basic Commands

uname -m               # display processor architecture
uname -r               # display kernel version
dmidecode -q           # display hardware components
hdparm -i /dev/hda     # list disk architecture features
hdparm -tT /dev/sda    # perform a test read on the disk
arch                   # display processor architecture
cat /proc/cpuinfo       # show CPU information
cat /proc/interrupts   # show interrupts
cat /proc/meminfo       # check memory usage
cat /proc/swaps         # show active swap devices
cat /proc/version       # display kernel version
cat /proc/net/dev       # show network adapters and statistics
cat /proc/mounts        # list mounted filesystems
lspci -tv              # list PCI devices
lsusb -tv              # list USB devices
date                    # show system date
cal 2007               # display calendar for 2007
date 041217002007.00   # set date and time (MMDDhhmmYYYY.ss)
clock -w               # write system time to BIOS

2. Shutdown and Reboot

shutdown -h now        # power off immediately (method 1)
init 0                # power off (method 2)
telinit 0             # power off (method 3)
shutdown -h HH:MM     # schedule shutdown at a specific time
shutdown -c           # cancel a scheduled shutdown
shutdown -r now      # reboot immediately (method 1)
reboot                # reboot (method 2)
logout                # log out of the session

3. Files and Directories

cd /home               # change to /home directory
cd ..                  # go up one level
cd ../..               # go up two levels
cd                     # go to the home directory
cd ~user1              # go to user1's home directory
cd -                   # return to the previous directory
pwd                    # print working directory
ls                     # list files in the current directory
ls -F                  # list files with type indicators
ls -l                  # detailed list of files and directories
ls -a                  # show hidden files
ls *[0-9]*             # show files/directories containing numbers
tree                   # display directory tree from root (method 1)
lstree                 # display directory tree from root (method 2)
mkdir dir1             # create a directory named dir1
mkdir dir1 dir2        # create two directories at once
mkdir -p /tmp/dir1/dir2 # create a directory tree
rm -f file1            # force delete file1
rmdir dir1             # remove empty directory dir1
rm -rf dir1            # recursively delete dir1 and its contents
rm -rf dir1 dir2       # delete two directories and their contents
mv dir1 new_dir        # rename or move a directory
cp file1 file2         # copy a file
cp dir/* .             # copy all files from a directory to the current directory
cp -a /tmp/dir1 .      # copy a directory preserving attributes
cp -a dir1 dir2        # copy a directory
ln -s file1 lnk1       # create a symbolic link
ln file1 lnk1          # create a hard link
touch -t 0712250000 file1 # modify timestamp (YYMMDDhhmm)
file file1             # output the MIME type of file1
iconv -l               # list known encodings
iconv -f fromEncoding -t toEncoding inputFile > outputFile # convert file encoding
find . -maxdepth 1 -name *.jpg -print -exec convert "{}" -resize 80x60 "thumbs/{}" \; # batch resize images

4. File Search

find / -name file1                     # search from root for file1
find / -user user1                    # search files owned by user1
find /home/user1 -name *.bin          # search for .bin files in /home/user1
find /usr/bin -type f -atime +100    # find executable files not accessed in the last 100 days
find /usr/bin -type f -mtime -10      # find files created/modified in the last 10 days
find / -name *.rpm -exec chmod 755 '{}' \; # find .rpm files and set permissions
find / -xdev -name *.rpm              # find .rpm files ignoring removable devices
locate *.ps                           # locate .ps files (run updatedb first)
whereis halt                          # show binary, source, and man page locations for halt
which halt                             # show full path of the executable

5. Mounting a Filesystem

mount /dev/hda2 /mnt/hda2               # mount partition hda2 (ensure /mnt/hda2 exists)
umount /dev/fd0 /mnt/floppy            # mount a floppy disk
mount /dev/cdrom /mnt/cdrom            # mount a CD-ROM or DVD-ROM
mount /dev/hdc /mnt/cdrecorder        # mount a CD-RW or DVD-RW
mount -o loop file.iso /mnt/cdrom       # mount an ISO image file
mount -t vfat /dev/hda5 /mnt/hda5       # mount a Windows FAT32 filesystem
mount /dev/sda1 /mnt/usbdisk            # mount a USB flash drive
mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share # mount a Windows network share

6. Disk Space

df -h                                 # display mounted partitions with human‑readable sizes
ls -lSr | more                        # list files sorted by size
du -sh dir1                           # estimate disk usage of dir1
du -sk * | sort -rn                  # list files/directories sorted by size
rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n # list installed RPM packages by size (Fedora/RedHat)
dpkg-query -W -f='${Installed-Size;10}t${Package}n' | sort -k1,1n # list installed DEB packages by size (Ubuntu/Debian)

7. Users and Groups

groupadd group_name                 # create a new group
groupdel group_name                 # delete a group
groupmod -n new_group_name old_group_name # rename a group
useradd -c "Name Surname" -g admin -d /home/user1 -s /bin/bash user1 # create user1 in group admin
useradd user1                       # create a new user
userdel -r user1                    # delete a user and its home directory
usermod -c "User FTP" -g system -d /ftp/user1 -s /nologin user1 # modify user attributes
passwd user1                        # change password for user1 (root only)
chage -E 2005-12-31 user1           # set password expiration date
pwck                                 # verify /etc/passwd syntax
grpck                                # verify /etc/group syntax
newgrp group_name                    # switch to a new group for file creation

8. File Permissions (use "+" to add, "-" to remove)

ls -lh                               # show permissions in long format with human‑readable sizes
chmod ugo+rwx directory1             # give read, write, execute to user, group, others
chmod go-rwx directory1              # remove read, write, execute from group and others
chown user1 file1                     # change file owner
chown -R user1 directory1            # recursively change owner of a directory tree
chgrp group1 file1                    # change group ownership
chown user1:group1 file1              # change both owner and group
chmod u+s /bin/file1                  # set SUID bit on a binary
chmod u-s /bin/file1                  # remove SUID bit
chmod g+s /home/public                # set SGID bit on a directory
chmod g-s /home/public                # remove SGID bit
chmod o+t /home/public                # set sticky bit on a directory
chmod o-t /home/public                # remove sticky bit
chmod +x file                         # add execute permission for all
chmod -x file                         # remove execute permission for all
chmod u+x file                        # add execute permission for owner
chmod g+x file                        # add execute permission for group
chmod o+x file                        # add execute permission for others
chmod ug+x file                       # add execute permission for owner and group
chmod =wx file                        # set write and execute for all, remove read
chmod ug=wx file                       # set write and execute for owner and group, remove read

9. Special File Attributes (use "+" to set, "-" to clear)

chattr +a file1   # allow only append writes
chattr +c file1   # enable automatic compression
chattr +d file1   # exclude from dump backups
chattr +i file1   # make immutable (cannot delete, modify, rename, or link)
chattr +s file1   # secure deletion
chattr +S file1   # sync changes to disk immediately after write
chattr +u file1   # allow undeletion of a deleted file
lsattr            # list special attributes

10. Archiving and Compression

bunzip2 file1.bz2                     # decompress a .bz2 file
bzip2 file1                           # compress a file with bzip2
gunzip file1.gz                       # decompress a .gz file
gzip file1                             # compress a file with gzip
gzip -9 file1                          # maximum compression
rar a file1.rar test_file              # create a .rar archive
rar a file1.rar file1 file2 dir1       # add multiple files/directories to a .rar archive
rar x file1.rar                       # extract a .rar archive
unrar x file1.rar                     # extract a .rar archive
tar -cvf archive.tar file1             # create an uncompressed tarball
tar -cvf archive.tar file1 file2 dir1 # create a tarball with multiple items
tar -tf archive.tar                    # list contents of a tarball
tar -xvf archive.tar                   # extract a tarball
tar -xvf archive.tar -C /tmp            # extract to /tmp
tar -cvfj archive.tar.bz2 dir1        # create a bzip2‑compressed tarball
tar -xvfj archive.tar.bz2              # extract a bzip2‑compressed tarball
tar -cvfz archive.tar.gz dir1          # create a gzip‑compressed tarball
tar -xvfz archive.tar.gz               # extract a gzip‑compressed tarball
zip file1.zip file1                    # create a zip archive
zip -r file1.zip file1 file2 dir1       # recursively zip multiple items
unzip file1.zip                         # extract a zip archive

11. RPM Packages

rpm -ivh package.rpm                     # install an RPM package
rpm -ivh --nodeps package.rpm            # install ignoring dependency warnings
rpm -U package.rpm                        # upgrade without changing config files
rpm -F package.rpm                        # upgrade an already‑installed package
rpm -e package_name.rpm                  # erase a package
rpm -qa                                 # list all installed RPMs
rpm -qa | grep httpd                    # filter installed RPMs containing "httpd"
rpm -qi package_name                    # query detailed info about a package
rpm -qg "System Environment/Daemons"    # list RPMs belonging to a group
rpm -ql package_name                    # list files provided by an installed package
rpm -qc package_name                    # list configuration files of a package
rpm -q package_name --whatrequires      # show packages that depend on this one
rpm -q package_name --whatprovides      # show what provides this package
rpm -q package_name --scripts           # show install/remove scripts
rpm -q package_name --changelog         # show changelog
rpm -qf /etc/httpd/conf/httpd.conf      # find which RPM provides a file
rpm -qp package.rpm -l                   # list files in an uninstalled RPM
rpm --import /media/cdrom/RPM-GPG-KEY  # import a GPG key
rpm --checksig package.rpm               # verify package signature
rpm -V package_name                      # verify file size, permissions, MD5, etc.
rpm -Va                                 # verify all installed RPMs (use with care)
rpm -Vp package.rpm                     # verify an uninstalled RPM
rpm2cpio package.rpm | cpio --extract --make-directories *bin* # extract executable from RPM
rpm -ivh /usr/src/redhat/RPMS/`arch`/package.rpm # install a built RPM from source
rpmbuild --rebuild package_name.src.rpm  # rebuild an RPM from source

12. YUM Package Manager

yum install package_name                 # download and install an RPM package
yum localinstall package_name.rpm       # install an RPM using local repository for dependencies
yum update package_name.rpm              # update all installed RPMs
yum update package_name                  # update a specific package
yum remove package_name                 # erase a package
yum list                                 # list all installed packages
yum search package_name                  # search for a package in repositories
yum clean packages                       # clean downloaded package files
yum clean headers                        # clean header files
yum clean all                            # clean all caches

13. DEB Packages

dpkg -i package.deb                     # install or upgrade a DEB package
dpkg -r package_name                    # remove a DEB package
dpkg -l                                 # list all installed DEB packages
dpkg -l | grep httpd                    # filter installed DEBs containing "httpd"
dpkg -s package_name                    # show status information for a package
dpkg -L package_name                    # list files provided by an installed DEB
dpkg --contents package.deb              # list files in an uninstalled DEB
dpkg -S /bin/ping                       # find which DEB provides a file
apt-get install package_name             # install or upgrade a DEB package
apt-cdrom install package_name          # install from a CD-ROM
apt-get update                          # refresh package lists
apt-get upgrade                         # upgrade all installed packages
apt-get remove package_name             # remove a DEB package
apt-get check                           # verify package dependencies
apt-get clean                           # clean downloaded package cache
apt-cache search searched-package       # search package names containing a string

14. Viewing File Contents

cat file1                               # display file from beginning
tac file1                               # display file in reverse order
more file1                              # paginate long file output
less file1                              # paginate with forward and backward navigation
head -2 file1                           # show first two lines
tail -2 file1                           # show last two lines
tail -f /var/log/messages               # follow a file as it grows (real‑time log view)

15. Text Processing

cat file1 file2 ... | command > file1_in.txt_or_file1_out.txt   # pipe data through commands
cat file1 | sed 's/string1/string2/g' > result.txt          # replace text using sed
cat file1 | grep pattern > result.txt                     # filter lines containing pattern
grep Aug /var/log/messages                                 # find lines containing "Aug"
grep ^Aug /var/log/messages                               # lines starting with "Aug"
grep [0-9] /var/log/messages                             # lines containing digits
grep Aug -R /var/log/*                                    # recursive search for "Aug"
sed 's/string1/string2/g' example.txt                     # replace all occurrences
sed '/^$/d' example.txt                                    # delete empty lines
sed '/ *#/d; /^$/d' example.txt                            # delete comments and empty lines
echo 'example' | tr '[:lower:]' '[:upper:]'                # convert to uppercase
sed -e '1d' result.txt                                     # delete first line
sed -n '/string1/p' result.txt                            # print lines containing "string1"
sed -e 's/ *$//' example.txt                              # trim trailing spaces
sed -e 's/string1//g' example.txt                           # delete all occurrences of "string1"
sed -n '1,5p;5q' example.txt                              # print lines 1‑5 then quit
sed -n '5p;5q' example.txt                                 # print line 5 then quit
sed -e 's/00*/0/g' example.txt                            # replace multiple zeros with a single zero
cat -n file1                                               # number lines
cat example.txt | awk 'NR%2==1'                            # keep odd‑numbered lines
echo a b c | awk '{print $1}'                             # print first column
echo a b c | awk '{print $1,$3}'                          # print first and third columns
paste file1 file2                                          # merge files column‑wise
paste -d '+' file1 file2                                  # merge with '+' as delimiter
sort file1 file2                                           # sort combined files
sort file1 file2 | uniq                                    # unique lines (remove duplicates)
sort file1 file2 | uniq -u                               # show lines that appear only once
sort file1 file2 | uniq -d                               # show duplicate lines
comm -1 file1 file2                                       # show lines only in file2
comm -2 file1 file2                                       # show lines only in file1
comm -3 file1 file2                                       # show common lines

16. Character Set Conversion and File Format

dos2unix filedos.txt fileunix.txt   # convert DOS line endings to UNIX
unix2dos fileunix.txt filedos.txt   # convert UNIX line endings to DOS
recode ..HTML < page.txt > page.html # convert text file to HTML
recode -l | more                    # list all supported conversion formats

17. Filesystem Analysis

badblocks -v /dev/hda1               # check for bad blocks on a disk
fsck /dev/hda1                        # check/repair filesystem integrity
fsck.ext2 /dev/hda1                   # check/repair ext2 filesystem
e2fsck /dev/hda1                     # check/repair ext2 filesystem
e2fsck -j /dev/hda1                  # check/repair ext3 filesystem (with journal)
fsck.ext3 /dev/hda1                  # check/repair ext3 filesystem
fsck.vfat /dev/hda1                  # check/repair FAT filesystem
fsck.msdos /dev/hda1                 # check/repair DOS filesystem
dosfsck /dev/hda1                    # check/repair DOS filesystem

18. Initialise a Filesystem

mkfs /dev/hda1                       # create a generic filesystem
mke2fs /dev/hda1                     # create an ext2 filesystem
mke2fs -j /dev/hda1                  # create an ext3 (journaled) filesystem
mkfs -t vfat -F 32 /dev/hda1         # create a FAT32 filesystem
fdformat -n /dev/fd0                 # format a floppy disk
mkswap /dev/hda3                     # create a swap partition

19. SWAP Filesystem

mkswap /dev/hda3                     # create a swap area
swapon /dev/hda3                     # enable the swap area
swapon /dev/hda2 /dev/hdb3           # enable two swap partitions

20. Backup

dump -0aj -f /tmp/home0.bak /home                # full backup of /home
dump -1aj -f /tmp/home0.bak /home                # interactive backup of /home
restore -if /tmp/home0.bak                       # restore an interactive backup
rsync -rogpav --delete /home /tmp                # sync two directories
rsync -rogpav -e ssh --delete /home ip_address:/tmp # sync over SSH
rsync -az -e ssh --delete ip_addr:/home/public /home/local # remote to local sync with compression
rsync -az -e ssh --delete /home/local ip_addr:/home/public # local to remote sync with compression
dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr 'dd of=hda.gz' # backup a disk over SSH
dd if=/dev/sda of=/tmp/file1                     # copy raw disk to a file
tar -Puf backup.tar /home/user                  # incremental backup of a directory
( cd /tmp/local/ && tar c . ) | ssh -C user@ip_addr 'cd /home/share/ && tar x -p' # copy a directory over SSH
( tar c /home ) | ssh -C user@ip_addr 'cd /home/backup-home && tar x -p' # copy a local directory over SSH
tar cf - . | (cd /tmp/backup ; tar xf - )        # local copy preserving permissions and links
find /home/user1 -name '*.txt' | xargs cp -av --target-directory=/home/backup/ --parents # copy all .txt files preserving directory structure
find /var/log -name '*.log' | tar cv --files-from=- | bzip2 > log.tar.bz2 # archive log files and compress
dd if=/dev/hda of=/dev/fd0 bs=512 count=1      # copy MBR to a floppy
dd if=/dev/fd0 of=/dev/hda bs=512 count=1      # restore MBR from a floppy

21. Optical Discs

cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force # erase a rewritable CD
mkisofs /dev/cdrom > cd.iso                     # create an ISO image from a disc
mkisofs /dev/cdrom | gzip > cd_iso.gz          # create a compressed ISO image
mkisofs -J -allow-leading-dots -R -V "Label CD" -iso-level 4 -o ./cd.iso data_cd # create ISO from a directory
cdrecord -v dev=/dev/cdrom cd.iso               # burn an ISO image to CD
gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom - # burn a compressed ISO image
mount -o loop cd.iso /mnt/iso                    # mount an ISO image
cd-paranoia -B                                   # extract audio tracks from a CD to WAV files
cd-paranoia -- "-3"                             # extract with parameter -3
cdrecord --scanbus                               # scan SCSI bus for devices
dd if=/dev/hdc | md5sum                         # compute MD5 checksum of a CD

22. Network (Ethernet and Wi‑Fi)

ifconfig eth0                                 # show Ethernet configuration
ifup eth0                                     # bring up eth0
ifdown eth0                                   # bring down eth0
ifconfig eth0 192.168.1.1 netmask 255.255.255.0 # set static IP address
ifconfig eth0 promisc                         # enable promiscuous mode for sniffing
dhclient eth0                                 # obtain IP via DHCP
route -n                                      # display routing table
route add -net 0/0 gw IP_Gateway             # set default gateway
route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1 # add static route
route del 0/0 gw IP_gateway                  # delete default route
echo "1" > /proc/sys/net/ipv4/ip_forward    # enable IP forwarding
hostname                                      # show system hostname
host www.example.com                         # resolve hostname to IP
nslookup www.example.com                     # DNS lookup
ip link show                                 # list all network interfaces
mii-tool eth0                                 # show link status of eth0
ethtool eth0                                 # show detailed statistics of eth0
netstat -tup                                 # list active connections with PID
netstat -tupl                                # list listening services with PID
tcpdump tcp port 80                          # capture HTTP traffic
iwlist scan                                   # scan for wireless networks
iwconfig eth1                                 # show wireless interface configuration
whois www.example.com                       # query WHOIS database

23. List Directory Contents

ls -a                                         # show all files, including hidden
ls -l                                         # long format with details
ls -R                                         # recursive listing
ls -ld                                        # show directory and link info
pwd                                           # print working directory

24. Determine File Type

file file1                                   # display file type

25. Copy Files and Directories

cp file1 file2                               # copy a file
cp -r source_dir target_dir                 # recursively copy a directory tree
cp -a /tmp/dir1 .                           # copy preserving attributes
cp -a dir1 dir2                             # copy a directory
cp -r source_folder target_folder            # copy folder recursively

26. Common System Commands

26.1 Display Commands

date                                         # show current date and time
date -s "YYYY-MM-DD HH:MM:SS"               # set system date and time
hwclock                                      # show hardware clock (requires root)
cal                                          # display calendar
cal 2004                                      # show calendar for 2004
cal -y 2003                                  # show calendar for 2003
uptime                                       # show system uptime

26.2 Output and Viewing Commands

echo "text"                                 # display text or append to a file
cat file1                                    # display file contents
cat file1 file2 > combined.txt                # concatenate files
cat file1 | more                             # paginate output
cat file1 | less                             # paginate with backward navigation
head -n 2 file1                              # first two lines
tail -n 2 file1                              # last two lines
tail -f /var/log/messages                    # follow file growth

26.3 Hardware Information

lspci -v                                    # list PCI devices with details
lsusb -v                                    # list USB devices with details
lsmod                                        # list loaded kernel modules

26.4 Shutdown and Reboot

shutdown -h now                             # immediate shutdown
shutdown -h +10                             # shutdown after 10 minutes
shutdown -h 23:30                           # shutdown at 23:30
shutdown -r now                             # immediate reboot
poweroff                                     # power off immediately
reboot                                       # reboot immediately

26.5 Archiving and Compression

zip file.zip file1                           # create zip archive
unzip file.zip                               # extract zip archive
gzip file1                                   # compress with gzip
gunzip file1.gz                              # decompress gzip file
tar -cvf archive.tar file1                   # create tar archive
tar -xvf archive.tar                         # extract tar archive
tar -cvzf archive.tar.gz dir1                # create gzip‑compressed tarball
tar -xvzf archive.tar.gz                     # extract gzip‑compressed tarball

26.6 Search

locate pattern                               # fast file name search (requires updatedb)
find . -name "*.txt"                       # find files by name
find / -perm 777                            # find files with permission 777
find / -type d                              # list all directories
find . -name "a*" -exec ls -l {} \;        # find and list matching files

26.7 Ctrl+C

Ctrl+C                                      # terminate the current command

26.8 Who / w

who                                          # list logged‑in users
w                                            # detailed list of logged‑in users

26.9 dmesg

dmesg                                        # display kernel ring buffer (diagnostic info)

26.10 df

df -h                                        # show filesystem usage

26.11 du

du -sh dir                                   # summarize disk usage of a directory

26.12 free

free -h                                      # display memory and swap usage

27. VIM Editor

vim file               # open file in VIM (creates if not existent)
:q                     # quit VIM
:q!                    # force quit without saving
:w                     # write (save) changes
:wq or :x              # write and quit
:set number            # show line numbers

VIM has three modes: command mode (default), insert mode (press i to enter), and ex mode (press : to enter). Common commands include dd (delete line), yy (yank line), p (paste), u (undo), /pattern (search), and many others for navigation and editing.

28. RPM Package Management Commands

28.1 Install Packages

rpm -ivh package.rpm                         # install package with progress bar

28.2 Remove Packages

rpm -e package_name                         # erase package (configuration files may remain)

28.3 Upgrade Packages

rpm -Uvh package.rpm                         # upgrade to newer version

28.4 Update Packages

rpm -Fvh package.rpm                         # update if newer, otherwise do nothing

28.5 Query Packages

rpm -q package_name                         # query installed package
rpm -ql package_name                        # list files provided by package
rpm -qi package_name                        # detailed info about package

End of the comprehensive Linux command reference.