Essential Linux Command Cheat Sheet: Over 100 Commands Every Sysadmin Should Know

Today we present a very complete Linux command summary that includes the most frequently used operations in daily work.

1. Basic Commands

uname -m   # Show processor architecture
uname -r   # Show kernel version
arch       # Show processor architecture
cat /proc/cpuinfo   # Display CPU information
cat /proc/interrupts   # Show interrupts
cat /proc/meminfo   # Check memory usage
cat /proc/swaps   # Show swap usage
cat /proc/version   # Show kernel version
cat /proc/net/dev   # Show network adapters and statistics
cat /proc/mounts   # Show mounted filesystems
lspci -tv   # List PCI devices
lsusb -tv   # Show USB devices
date        # Show system date
cal 2007    # Show calendar for 2007
date 041217002007.00   # Set date and time (MMDDhhmmYY.ss)
clock -w    # Save time to BIOS

2. Shutdown

shutdown -h now          # Power off immediately (1)
init 0                  # Power off (2)
shutdown -h hours:minutes &   # Schedule shutdown
shutdown -c             # Cancel scheduled shutdown
shutdown -r now         # Reboot (1)
reboot                  # Reboot (2)
logout                  # Log out

3. Files and Directories

cd /home                # Change to /home directory
cd ..                   # Go up one level
cd ../..                # Go up two levels
cd ~user1               # Change to user1's home directory
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 (1)
lstree                  # Tree view (2)
mkdir dir1              # Create directory dir1
mkdir dir1 dir2         # Create two directories
mkdir -p /tmp/dir1/dir2 # Create directory tree
rm -f file1             # Delete file1
rmdir dir1              # Remove empty directory dir1
rm -rf dir1             # Remove directory and its contents
mv dir1 new_dir         # Rename/move directory
cp file1 file2          # Copy file
cp dir/* .              # Copy all files from dir to current directory
cp -a /tmp/dir1 .       # Copy directory preserving attributes
ln -s file1 lnk1        # Create symbolic link
ln file1 lnk1           # Create hard link
touch -t 0712250000 file1   # Set timestamp (YYMMDDhhmm)

4. File Search

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

5. Mount a Filesystem

mount /dev/hda2 /mnt/hda2                # Mount partition hda2
umount /dev/hda2                        # Unmount hda2
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/iso          # Mount ISO image
mount -t vfat /dev/hda5 /mnt/hda5       # Mount FAT32 filesystem
mount /dev/sda1 /mnt/usbdisk            # Mount USB flash drive
mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share   # Mount Windows share

6. Disk Space

df -h                     # Show mounted partitions
ls -lSr | more           # List files sorted by size
du -sh dir1              # Estimate disk usage of dir1
du -sk * | sort -rn     # Sort directories/files by size
rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n   # List installed RPMs by size
dpkg-query -W -f='${Installed-Size;10}\t${Package}n' | sort -k1,1n   # List installed DEB packages by size

7. Users and Groups

groupadd group_name
groupdel group_name
groupmod -n new_group_name old_group_name
useradd -c "Name Surname" -g admin -d /home/user1 -s /bin/bash user1
useradd user1
userdel -r user1
usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1
passwd
passwd user1
chage -E 2005-12-31 user1
pwck
grpck
newgrp group_name

8. File Permissions

chmod ugo+rwx directory1
chmod go-rwx directory1
chown user1 file1
chown -R user1 directory1
chgrp group1 file1
chown user1:group1 file1
find / -perm -u+s               # List files with SUID
chmod u+s /bin/file1            # Set SUID bit
chmod u-s /bin/file1            # Remove SUID bit
chmod g+s /home/public          # Set SGID on directory
chmod g-s /home/public          # Remove SGID
chmod o+t /home/public          # Set sticky bit
chmod o-t /home/public          # Remove sticky bit
chmod +x file_path              # Add execute permission
chmod -x file_path              # Remove execute permission
chmod u+x file_path              # Add execute for owner
chmod g+x file_path              # Add execute for group
chmod o+x file_path              # Add execute for others
chmod ug+x file_path             # Add execute for owner and group
chmod =wx file_path             # Set write and execute, remove read
chmod ug=wx file_path            # Set write and execute for owner and group

9. Special File Attributes

chattr +a file1   # Append-only
chattr +c file1   # Compress automatically
chattr +d file1   # Exclude from backups
chattr +i file1   # Immutable
chattr +s file1   # Secure deletion
chattr +S file1   # Write changes immediately to disk
chattr +u file1   # Undelete
lsattr

10. Pack and Compress Files

bunzip2 file1.bz2
bzip2 file1
gunzip file1.gz
gzip file1
gzip -9 file1
rar a file1.rar test_file
rar a file1.rar file1 file2 dir1
rar x file1.rar
unrar x file1.rar
tar -cvf archive.tar file1
tar -cvf archive.tar file1 file2 dir1
tar -tf archive.tar
tar -xvf archive.tar
tar -xvf archive.tar -C /tmp
tar -cvfj archive.tar.bz2 dir1
tar -xvfj archive.tar.bz2
tar -cvfz archive.tar.gz dir1
tar -xvfz archive.tar.gz
zip file1.zip file1
zip -r file1.zip file1 file2 dir1
unzip file1.zip

11. RPM Packages

rpm -ivh package.rpm
rpm -ivh --nodeps package.rpm
rpm -U package.rpm
rpm -F package.rpm
rpm -e package_name.rpm
rpm -qa
rpm -qa | grep httpd
rpm -qi package_name
rpm -qg "System Environment/Daemons"
rpm -ql package_name
rpm -qc package_name
rpm -q package_name --whatrequires
rpm -q package_name --whatprovides
rpm -q package_name --scripts
rpm -q package_name --changelog
rpm -qf /etc/httpd/conf/httpd.conf
rpm -qp package.rpm -l
rpm --import /media/cdrom/RPM-GPG-KEY
rpm --checksig package.rpm
rpm -qa gpg-pubkey
rpm -V package_name
rpm -Va
rpm -Vp package.rpm
rpm2cpio package.rpm | cpio --extract --make-directories *bin*
rpm -ivh /usr/src/redhat/RPMS/`arch`/package.rpm
rpmbuild --rebuild package_name.src.rpm

12. YUM Package Manager

yum install package_name
yum localinstall package_name.rpm
yum update package_name.rpm
yum update package_name
yum remove package_name
yum list
yum search package_name
yum clean packages
yum clean headers
yum clean all

13. DEB Packages

dpkg -i package.deb
dpkg -r package_name
dpkg -l
dpkg -l | grep httpd
dpkg -s package_name
dpkg -L package_name
dpkg --contents package.deb
dpkg -S /bin/ping
apt-get install package_name
apt-cdrom install package_name
apt-get update
apt-get upgrade
apt-get remove package_name
apt-get check
apt-get clean
apt-cache search searched-package

14. Character Set and File Format Conversion

dos2unix filedos.txt fileunix.txt
unix2dos fileunix.txt filedos.txt
recode ..HTML < page.txt > page.html
recode -l | more

15. File System Analysis

badblocks -v /dev/hda1
fsck /dev/hda1
fsck.ext2 /dev/hda1
e2fsck /dev/hda1
e2fsck -j /dev/hda1
fsck.ext3 /dev/hda1
fsck.vfat /dev/hda1
fsck.msdos /dev/hda1
dosfsck /dev/hda1

16. Initialize a Filesystem

mkfs /dev/hda1
mke2fs /dev/hda1
mke2fs -j /dev/hda1   # ext3
mkfs -t vfat 32 -F /dev/hda1   # FAT32
fdformat -n /dev/fd0   # Format floppy
mkswap /dev/hda3

17. SWAP Filesystem

mkswap /dev/hda3
swapon /dev/hda3
swapon /dev/hda2 /dev/hdb3

18. Backup

dump -0aj -f /tmp/home0.bak /home
dump -1aj -f /tmp/home0.bak /home
restore -if /tmp/home0.bak
rsync -rogpav --delete /home /tmp
rsync -rogpav -e ssh --delete /home ip_address:/tmp
rsync -az -e ssh --delete ip_addr:/home/public /home/local
rsync -az -e ssh --delete /home/local ip_addr:/home/public
dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr 'dd of=hda.gz'
dd if=/dev/sda of=/tmp/file1
tar -Puf backup.tar /home/user
( cd /tmp/local/ && tar c . ) | ssh -C user@ip_addr 'cd /home/share/ && tar x -p'
( tar c /home ) | ssh -C user@ip_addr 'cd /home/backup-home && tar x -p'
tar cf - . | (cd /tmp/backup ; tar xf - )
find /home/user1 -name "*.txt" | xargs cp -av --target-directory=/home/backup/ --parents
find /var/log -name "*.log" | tar cv --files-from=- | bzip2 > log.tar.bz2
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

19. CD-ROM

cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force   # Erase rewritable CD
mkisofs /dev/cdrom > cd.iso
mkisofs /dev/cdrom | gzip > cd_iso.gz
mkisofs -J -allow-leading-dots -R -V "Label CD" -iso-level 4 -o ./cd.iso data_cd
cdrecord -v dev=/dev/cdrom cd.iso
gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom -
mount -o loop cd.iso /mnt/iso
cd-paranoia -B
cd-paranoia -- "-3"
cdrecord --scanbus
dd if=/dev/hdc | md5sum

20. Network

ifconfig eth0
ifup eth0
ifdown eth0
ifconfig eth0 192.168.1.1 netmask 255.255.255.0
ifconfig eth0 promisc
dhclient eth0
route -n show
route add -net 0/0 gw IP_Gateway
route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1
route del 0/0 gw IP_gateway
echo "1" > /proc/sys/net/ipv4/ip_forward
hostname show
host www.example.com
nslookup www.example.com
ip link show
mii-tool eth0
ethtool eth0
netstat -tup
netstat -tupl
tcpdump tcp port 80
iwlist scan
iwconfig eth1
hostname
host www.example.com
nslookup www.example.com
whois www.example.com

21. List Directory Contents

ls -a   # Show all files including hidden
ls -l   # Detailed list
ls -R   # Recursive
ls -ld  # Show directory/link info
ctrl+r  # Search command history
pwd     # Show current directory

22. View File Type

file filename

23. Copy Files and Directories

cp source_file target_file
cp -r source_dir target_dir
cp -v source_file target_file

24. Modify File Timestamps

touch filename               # Create empty file or update timestamps
touch -d 20040210 filename  # Set specific date

25. Move or Rename Files

mv source target
mv a.txt b.txt   # Rename
mv file ../        # Move up one directory

26. Delete Files

rm file1
rm -i file1   # Interactive delete
rm -r dir1     # Recursive delete (files and subdirs)
rm -f *.txt   # Force delete without prompts

27. Create Directories

mkdir dir1
mkdir -p dir1/dir2   # Create nested directories

28. Remove Directories

rmdir dir1            # Remove empty directory
rm -r dir1           # Remove directory and contents
rmdir -p dir1/dir2   # Remove dir2 and parent if empty

29. Search

find / -name "*.txt"
grep "pattern" file.txt
locate keyword
which command

30. VIM

vim filename          # Open file in VIM
:q                   # Quit VIM

31. VIM Modes

# Command mode (default): i, o, dd, yy, p, u, r, /, etc.
# Insert mode: press i to insert text, Esc to return.
# Ex mode: press : to enter, then :w (save), :q (quit), :wq (save & quit), :x, :set number, :!command, :sh

32. RPM Package Management Commands

# Install
rpm -ivh package.rpm
# Delete
rpm -e package_name
# Upgrade
rpm -Uvh package.rpm
# Update
rpm -Fvh package.rpm
# Query
rpm -q package_name
rpm -ql package_name
rpm -qi package_name