Essential Linux Command Cheat Sheet for System Administrators

1. Basic Commands

<code>uname -m          # Show machine architecture
uname -r          # Show kernel version
dmidecode -q      # Show hardware components
hdparm -i /dev/hda    # List disk characteristics
hdparm -tT /dev/sda   # Perform test read on disk
arch               # Show machine architecture
cat /proc/cpuinfo   # Display CPU info
cat /proc/interrupts   # Show interrupts
cat /proc/meminfo   # Check memory usage
cat /proc/swaps     # List active swap spaces
cat /proc/version   # Show kernel version
cat /proc/net/dev   # Show network adapters and statistics
cat /proc/mounts    # List mounted filesystems
lspci -tv          # List PCI devices
lsusb -tv          # Show USB devices
date               # Display system date
cal 2007          # Show calendar for 2007
date 041217002007.00   # Set date and time (MMDDhhmmYY.ss)
clock -w           # Save system time to BIOS</code>

2. Shutdown

<code>shutdown -h now          # Power off now (method 1)
init 0                  # Power off now (method 2)
telinit 0              # Power off now (method 3)
shutdown -h HH:MM       # Schedule shutdown
shutdown -c             # Cancel scheduled shutdown
shutdown -r now        # Reboot now (method 1)
reboot                  # Reboot now (method 2)
logout                  # Log out</code>

3. Files and Directories

<code>cd /home               # Change to /home directory
cd ..                  # Go up one level
cd ../..               # Go up two levels
cd ~                    # Go to personal home directory
cd ~user1              # Switch to another user's home
cd -                   # Return to previous directory
pwd                    # Show current working directory
ls                     # List files in current directory
ls -F                  # List with file type indicators
ls -l                  # Detailed list
ls -a                  # Show hidden files
ls *[0-9]*             # List files containing numbers
tree                   # Tree view of directories (method 1)
lstree                 # Tree view (method 2)
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            # Remove directory and its contents
rm -rf dir1 dir2       # Remove two directories recursively
mv dir1 new_dir        # Rename or move directory
cp file1 file2         # Copy file1 to file2
cp dir/* .             # Copy all files from dir to current directory
cp -a /tmp/dir1 .      # Archive copy of dir1 to current directory
ln -s file1 link1      # Create symbolic link
ln file1 link1         # Create hard link
touch -t 0712250000 file1   # Change timestamp (YYMMDDhhmm)
file file1             # Show MIME type of file
iconv -l               # List known encodings
iconv -f from -t to input > output   # Convert file encoding
find . -maxdepth 1 -name *.jpg -exec convert "{}" -resize 80x60 "thumbs/{}" \;   # Batch resize images</code>

4. File Search

<code>find / -name file1                 # Search from root
find / -user user1                # Search files owned by user1
find /home/user1 -name *.bin      # Search .bin files in a directory
find /usr/bin -type f -atime +100   # Files not accessed in 100 days
find /usr/bin -type f -mtime -10   # 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 devices
locate *.ps                        # Locate .ps files (requires updatedb)
whereis halt                       # Locate binary, source, man page
which halt                         # Show full path of executable</code>

5. Mount a Filesystem

<code>mount /dev/hda2 /mnt/hda2               # Mount partition hda2
umount /dev/hda2                       # Unmount partition hda2
fuser -km /mnt/hda2                    # Force unmount if busy
umount -n /mnt/hda2                    # Unmount without updating /etc/mtab
mount /dev/fd0 /mnt/floppy              # Mount floppy
mount /dev/cdrom /mnt/cdrom            # Mount CD-ROM/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
mount /dev/sda1 /mnt/usbdisk            # Mount USB flash drive
mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share   # Mount Windows share</code>

6. Disk Space

<code>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 -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 DEBs by size</code>

7. Users and Groups

<code>groupadd group_name          # Create new group
groupdel group_name          # Delete group
groupmod -n new old         # Rename group
useradd -c "Name Surname" -g admin -d /home/user1 -s /bin/bash user1   # Add user with details
useradd user1               # Simple user add
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 user1                # Change user password (root only)
chage -E 2005-12-31 user1   # Set password expiration date
pwck                         # Verify /etc/passwd format
grpck                        # Verify /etc/group format
newgrp group_name           # Switch to new primary group</code>

8. File Permissions

<code>ls -lh                     # Show permissions in long format
chmod ugo+rwx directory1   # Give read/write/execute to all
chmod go-rwx directory1    # Remove rwx from group and others
chown user1 file1           # Change file owner
chown -R user1 directory1   # Recursively change owner
chgrp group1 file1          # Change group ownership
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 o+t /home/public     # Set sticky bit
chmod +x file               # Add execute permission
chmod -x file               # Remove execute permission</code>

9. Special File Attributes

<code>chattr +a file1   # Append‑only
chattr +c file1   # Auto‑compress
chattr +d file1   # Exclude from dump
chattr +i file1   # Immutable
chattr +s file1   # Secure delete
chattr +S file1   # Synchronous updates
chattr +u file1   # Undelete support
lsattr            # List special attributes</code>

10. Packing and Compression

<code>bunzip2 file1.bz2
bzip2 file1
gunzip file1.gz
gzip file1
gzip -9 file1
rar a file1.rar test_file
rar x file1.rar
unrar x file1.rar
tar -cvf archive.tar file1
tar -tf archive.tar
tar -xvf archive.tar
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</code>

11. RPM Packages (Fedora/RedHat)

<code>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 -V package_name
rpm -Va
rpm -Vp package.rpm
rpm2cpio package.rpm | cpio --extract --make-directories *bin*</code>

12. YUM Package Manager

<code>yum install package_name
yum localinstall package.rpm
yum update package_name
yum remove package_name
yum list
yum search package_name
yum clean packages
yum clean headers
yum clean all</code>

13. DEB Packages (Debian/Ubuntu)

<code>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-get update
apt-get upgrade
apt-get remove package_name
apt-get clean
apt-cache search searched-package</code>

14. View File Content

<code>cat file1
tac file1
more file1
less file1
head -2 file1
tail -2 file1
tail -f /var/log/messages</code>

15. Text Processing

<code>cat file1 file2 | command > output.txt
grep pattern /var/log/messages
sed 's/old/new/g' file.txt
awk '{print $1}' file.txt
sort file.txt | uniq
comm -1 file1 file2
...</code>

16. Character Set Conversion

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

17. Filesystem Analysis

<code>badblocks -v /dev/hda1
fsck /dev/hda1
fsck.ext2 /dev/hda1
fsck.ext3 /dev/hda1
fsck.vfat /dev/hda1</code>

18. Initialise a Filesystem

<code>mkfs /dev/hda1
mke2fs /dev/hda1
mke2fs -j /dev/hda1
mkfs -t vfat 32 -F /dev/hda1
fdformat -n /dev/fd0
mkswap /dev/hda3</code>

19. SWAP Filesystem

<code>mkswap /dev/hda3
swapon /dev/hda3
swapon /dev/hda2 /dev/hdb3</code>

20. Backup

<code>dump -0aj -f /tmp/home0.bak /home
restore -if /tmp/home0.bak
rsync -rogpav --delete /home /tmp
rsync -az -e ssh --delete /home user@remote:/tmp
dd if=/dev/hda | gzip | ssh user@host '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@host 'cd /home/share && tar x -p'
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</code>

21. Optical Media

<code>cdrecord -v dev=/dev/cdrom cd.iso
mkisofs /dev/cdrom > cd.iso
mount -o loop cd.iso /mnt/iso
cd-paranoia -B
dd if=/dev/hdc | md5sum</code>

22. Network (Ethernet & Wi‑Fi)

<code>ifconfig eth0
ifup eth0
ifdown eth0
ifconfig eth0 192.168.1.1 netmask 255.255.255.0
ifconfig eth0 promisc
dhclient eth0
route -n
route add -net 0/0 gw IP_Gateway
netstat -tup
tcpdump tcp port 80
iwlist scan
iwconfig eth1
hostname
nslookup www.example.com
whois www.example.com</code>

23. List Directory Contents

<code>ls -a
ls -l
ls -R
ls -ld
pwd</code>

24. Determine File Type

<code>file filename</code>

25. Copy, Move, Delete Operations

<code>cp source dest
cp -r src_dir dest_dir
mv old new
rm file
rm -r dir
rmdir dir
mkdir dir
mkdir -p a/b/c
ln -s target link
ln target link</code>

26. Common System Commands

<code>date
hwclock
cal
uptime
echo "text"
cat file
more file
less file
head -n file
tail -n file
tail -f file</code>

27. VIM Editor

<code>:q          # Quit Vim
i           # Insert mode
Esc         # Return to command mode
dd          # Delete line
yy          # Yank (copy) line
p           # Paste after cursor
u           # Undo
/keyword    # Search</code>

28. RPM Package Management

<code>rpm -ivh package.rpm          # Install
rpm -e package_name           # Remove
rpm -Uvh package.rpm           # Upgrade
rpm -Fvh package.rpm           # Update
rpm -q package_name            # Query
rpm -ql package_name           # List files
rpm -qi package_name           # Info
rpm --import keyfile           # Import GPG key</code>