Essential Linux Command Cheat Sheet for System Administration

1. Basic Commands

uname -m            # display processor architecture
uname -r            # display kernel version
dmidecode -q        # display hardware components (SMBIOS/DMI)
hdparm -i /dev/hda  # list disk architecture features
hdparm -tT /dev/sda # perform read test on disk
arch                # display processor architecture
cat /proc/cpuinfo   # show CPU info
cat /proc/interrupts# show interrupts
cat /proc/meminfo   # verify memory usage
cat /proc/swaps     # show used swap spaces
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            # save system time to BIOS

2. Shutdown

shutdown -h now          # power off immediately
init 0                  # power off (alternative)
telinit 0               # power off (alternative)
shutdown -h hh:mm       # schedule shutdown
shutdown -c              # cancel scheduled shutdown
shutdown -r now          # reboot immediately
reboot                  # reboot (alternative)
logout                  # log out

3. Files and Directories

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

4. File Search

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

5. Mount a Filesystem

mount /dev/hda2 /mnt/hda2          # mount partition (ensure mount point exists)
umount /dev/hda2                 # unmount partition
fuser -km /mnt/hda2               # force unmount when busy
umount -n /mnt/hda2                # unmount without updating /etc/mtab
mount /dev/fd0 /mnt/floppy        # mount floppy
mount /dev/cdrom /mnt/cdrom       # mount CD/DVD
mount /dev/hdc /mnt/cdrecorder    # mount CD-RW/DVD-RW
mount -o loop file.iso /mnt/cdrom  # mount ISO image
mount -t vfat /dev/hda5 /mnt/hda5 # mount Windows FAT32 filesystem
mount /dev/sda1 /mnt/usbdisk      # mount USB drive
mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share # mount Windows share

6. Disk Space

df -h                                 # show 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                   # sort files/directories by size
rpm -qa --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 new group
groupdel group_name          # delete group
groupmod -n new_name old_name# rename group
useradd -c "Name Surname" -g admin -d /home/user1 -s /bin/bash user1 # create user in admin group
useradd user1               # create new user
userdel -r user1            # delete user and home directory
usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1 # modify user attributes
passwd                      # change password
passwd user1                # change password for user1 (root only)
chage -E 2005-12-31 user1   # set password expiry date
pwck                         # verify /etc/passwd format
grpck                        # verify /etc/group format
newgrp group_name           # switch to new group

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

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

9. Special File Attributes (using "+" 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)
chattr +s file1   # secure deletion flag
chattr +S file1   # sync changes to disk immediately after write
chattr +u file1   # allow undeletion
lsattr file1       # display special attributes

10. Archiving and Compression

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

11. RPM Packages

rpm -ivh package.rpm                 # install RPM package
rpm -ivh --nodeps package.rpm       # install ignoring dependencies
rpm -U package.rpm                   # upgrade without changing config files
rpm -F package.rpm                   # reinstall already installed package
rpm -e package.rpm                   # erase package
rpm -qa                              # list all installed RPMs
rpm -qa | grep httpd                # filter installed RPMs by name
rpm -qi package_name                 # query detailed info
rpm -qg "System Environment/Daemons"# list RPMs in a group
rpm -ql package_name                  # list files provided by package
rpm -qc package_name                  # list config files of package
rpm -q --whatrequires package_name  # show packages that depend on it
rpm -q --whatprovides package_name   # show what provides the package
rpm -q --scripts package_name        # show install/remove scripts
rpm -q --changelog package_name      # 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 GPG key
rpm --checksig package.rpm            # verify package integrity
rpm -V package_name                    # verify package files
rpm -Va                              # verify all installed packages (use with care)
rpm2cpio package.rpm | cpio --extract --make-directories *bin* # run executable from RPM
rpm -ivh /usr/src/redhat/RPMS/`arch`/package.rpm # install built package from source
rpmbuild --rebuild package.src.rpm   # rebuild source RPM

12. YUM Package Manager

yum install package_name                     # download and install RPM
yum localinstall package.rpm                # install local RPM with dependency resolution
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 repository for package
yum clean packages                          # clean downloaded packages
yum clean headers                           # clean header files
yum clean all                               # clean all cached data

13. DEB Packages

dpkg -i package.deb               # install or upgrade DEB package
dpkg -r package_name             # remove DEB package
dpkg -l                         # list installed DEB packages
dpkg -l | grep httpd           # filter installed DEB packages
dpkg -s package_name            # show information about installed package
dpkg -L package_name            # list files provided by installed package
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 DEB package
apt-get update                  # update package index
apt-get upgrade                 # upgrade all installed packages
apt-get remove package_name     # remove DEB package
apt-get check                   # verify package dependencies
apt-get clean                  # clean downloaded package files
apt-cache search searched-package # search package names

14. Viewing File Contents

cat file1                     # display file from start
tac file1                     # display file in reverse order
more file1                    # paginate long file
less file1                    # paginate with forward/backward scrolling
head -2 file1                 # show first two lines
tail -2 file1                 # show last two lines
tail -f /var/log/messages    # follow file updates in real time

15. Text Processing

cat file1 file2 ... | command > file1_out.txt   # pipe output to file
cat file1 | grep pattern > result.txt           # filter with grep
grep Aug /var/log/messages                     # search for "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
sed 's/string1/string2/g' example.txt          # replace string1 with string2
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' example.txt                # print lines containing string1
sed -e 's/ *$//' example.txt                    # trim trailing spaces
sed -e 's/string1//g' example.txt              # delete string1
sed -n '1,5p;5q' example.txt                   # show lines 1‑5 then quit
sed -n '5p;5q' example.txt                     # show line 5 then quit
sed -e 's/00*/0/g' example.txt                # replace multiple zeros with single zero
cat -n file1                                    # number lines
cat example.txt | awk 'NR%2==1'               # print 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 side by side
paste -d '+' file1 file2                        # merge with '+' delimiter
sort file1 file2                                # sort combined files
sort file1 file2 | uniq                         # unique lines
sort file1 file2 | uniq -u                     # lines unique to one file
sort file1 file2 | uniq -d                     # common 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 to UNIX line endings
unix2dos fileunix.txt filedos.txt   # convert UNIX to DOS line endings
recode ..HTML < page.txt > page.html # convert text to HTML
recode -l | more                    # list supported conversions

17. Filesystem Analysis

badblocks -v /dev/hda1               # check for bad blocks
fsck /dev/hda1                        # check and repair filesystem
fsck.ext2 /dev/hda1                   # check ext2 filesystem
e2fsck /dev/hda1                      # check ext2/ext3 filesystem
e2fsck -j /dev/hda1                   # check ext3 filesystem with journal
fsck.ext3 /dev/hda1                   # check ext3 filesystem
fsck.vfat /dev/hda1                   # check FAT filesystem
fsck.msdos /dev/hda1                  # check DOS filesystem
dosfsck /dev/hda1                     # check DOS filesystem

18. Initialise a Filesystem

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

19. Swap Filesystem

mkswap /dev/hda3                      # create swap partition
swapon /dev/hda3                      # enable swap
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 interactive backup
rsync -rogpav --delete /home /tmp           # sync directories
rsync -rogpav -e ssh --delete /home user@ip:/tmp # sync over SSH
rsync -az -e ssh --delete /home user@ip:/backup # compressed sync over SSH
dd bs=1M if=/dev/hda | gzip | ssh user@ip 'dd of=hda.gz' # remote backup via SSH
dd if=/dev/sda of=/tmp/file1               # copy disk to file
tar -Puf backup.tar /home/user            # incremental backup
(cd /tmp/local && tar c .) | ssh -C user@ip 'cd /home/share && tar x -p' # copy directory over SSH
(tar c /home) | ssh -C user@ip 'cd /home/backup && tar x -p' # copy entire /home over SSH
tar cf - . | (cd /tmp/backup ; tar xf -)   # local copy preserving permissions
find /home/user1 -name '*.txt' | xargs cp -av --target-directory=/home/backup/ --parents # copy matching files preserving hierarchy
find /var/log -name '*.log' | tar cv --files-from=- | bzip2 > log.tar.bz2 # archive log files
dd if=/dev/hda of=/dev/fd0 bs=512 count=1 # copy MBR to floppy
dd if=/dev/fd0 of=/dev/hda bs=512 count=1 # restore MBR from floppy

21. Optical Discs

cdrecord -v gracetime=2 dev=/dev/cdrom -eject -blank=fast -force   # erase rewritable CD
mkisofs /dev/cdrom > cd.iso                                      # create ISO image
mkisofs /dev/cdrom | gzip > cd_iso.gz                            # create compressed ISO
mkisofs -J -allow-leading-dots -R -V "Label CD" -iso-level 4 -o ./cd.iso data_cd # create ISO with Joliet and Rock Ridge
cdrecord -v dev=/dev/cdrom cd.iso                                 # burn ISO to CD
gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom -                    # burn compressed ISO
mount -o loop cd.iso /mnt/iso                                      # mount ISO image
cd-paranoia -B > track.wav                                         # extract audio tracks to WAV
cd-paranoia -- "-3" > track.wav                                   # extract with -3 option
cdrecord --scanbus                                                # scan SCSI bus
dd if=/dev/hdc | md5sum                                            # compute MD5 of CD

22. Network (Ethernet and Wi‑Fi)

ifconfig eth0                     # show Ethernet config
ifup eth0                         # enable interface
ifdown eth0                       # disable interface
ifconfig eth0 192.168.1.1 netmask 255.255.255.0 # set static IP
ifconfig eth0 promisc            # enable promiscuous mode
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 # static route
route del 0/0 gw IP_Gateway      # delete static 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         # resolve hostname to IP
ip link show                     # list interfaces
mii-tool eth0                    # show link status
ethtool eth0                     # show interface statistics
netstat -tup                     # list active connections with PID
netstat -tupl                    # list listening services with PID
tcpdump tcp port 80              # capture HTTP traffic
iwlist scan                      # scan wireless networks
iwconfig eth1                     # show wireless interface config

23. List Directory Contents

ls -a               # show all files, including hidden
ls -l               # detailed list
ls -R               # recursive listing
ls -ld              # list directory itself
ctrl+r              # search command history
pwd                 # show current directory

24. Determine File Type

file file1          # display file type

25. Copy Files and Directories

cp source destination                     # copy file or directory
cp -r src_dir dest_dir                    # recursive copy of directory tree
cp -v src dest                            # verbose copy
cp -a src dest                            # archive copy preserving attributes

26. Common System Commands

26.1 Display Commands

date                # show current date/time
date -s "..."      # set system date/time
hwclock             # show hardware clock (requires root)
cal                 # display calendar
uptime              # show system uptime

26.2 Output and Viewing Commands

echo "text" >> file   # append text to file
cat file               # display file content
cat file | more         # paginate output
cat file >> other      # append file to another
head -n 2 file         # first two lines
tail -n 2 file         # last two lines
tail -f /var/log/...   # follow log updates
more file              # simple pager (forward only)
less file              # pager with forward/backward navigation

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

26.5 Archiving and Compression

zip file.zip file          # create zip archive
unzip file.zip             # extract zip archive
gzip file                  # compress with gzip
tar -cvf out.tar files...  # create tar archive
tar -xvf out.tar           # extract tar archive
tar -cvzf backup.tar.gz /etc # create gzip‑compressed tarball

26.6 Search

locate keyword            # fast file locate (requires updatedb)
find . -name "pattern"    # find files by name
find / -name *.conf       # find all .conf files from root
find / -perm 777          # find files with specific permissions
find / -type d            # list all directories
find . -name "a*" -exec ls -l {} \; # execute command on matches

26.7 Miscellaneous

Ctrl+C                 # terminate current command
who / w                # show logged‑in users
dmesg                  # display kernel ring buffer messages
df                     # show filesystem space usage
du                     # estimate directory space usage
free                   # display memory and swap usage

27. VIM Editor

vim file                # open file in VIM
:q                      # quit VIM
:i                      # enter insert mode
:o                      # open new line below
:dd                     # delete current line
:yy                     # yank (copy) current line
:n+yy                   # yank n lines
:p                      # paste after cursor
:u                      # undo last change
:r                      # replace character under cursor
:/pattern               # search for pattern
:! command              # execute shell command
:w                      # write (save) file
:wq or :x               # write and quit
:set number             # show line numbers
:! sh                  # drop to shell (return with Ctrl+D)

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 (does not remove modified config files)

28.3 Upgrade Packages

rpm -Uvh package.rpm   # upgrade to newer version

28.4 Update Packages

rpm -Fvh package.rpm   # update if older version is present

28.5 Query Packages

rpm -q package_name    # query installed package
rpm -ql package_name   # list files installed by package