Essential Linux Command Cheat Sheet for System Administrators

Basic Commands

uname -m            # Show processor architecture
uname -r            # Show kernel version
uname -a            # Show all system information
arch                # Show processor architecture
cat /proc/cpuinfo   # Display CPU details
cat /proc/interrupts
cat /proc/meminfo   # Show memory usage
cat /proc/swaps     # List active swap spaces
cat /proc/version   # Show kernel version
cat /proc/net/dev   # Show network interfaces
cat /proc/mounts    # List mounted filesystems
lspci -tv           # List PCI devices
lsusb -tv           # List USB devices
date                # Show system date and time
cal 2007            # Show calendar for year 2007
clock -w            # Save hardware clock

Shutdown and Reboot

shutdown -h now          # Immediate shutdown
init 0                   # Shutdown (alternative)
 telinit 0               # Shutdown (alternative)
shutdown -h hh:mm        # Schedule shutdown
shutdown -c              # Cancel scheduled shutdown
shutdown -r now          # Reboot now
reboot                   # Reboot
logout                   # Log out of session

File and Directory Operations

cd /home                 # Change to /home directory
cd ..                    # Go up one level
cd ../..                 # Go up two levels
cd ~user1                # Change to user1's home
cd -                     # Return to previous directory
pwd                      # Show current working directory
ls                       # List files
ls -F                    # List files with type indicators
ls -l                   # Detailed list
ls -a                    # Show hidden files
ls *[0-9]*               # List files containing numbers
tree                     # Tree view of directories
mkdir dir1               # Create directory dir1
mkdir dir1 dir2          # Create multiple directories
mkdir -p /tmp/dir1/dir2  # Create nested directories
rm -f file1              # Force delete file1
rmdir dir1               # Remove empty directory
rm -rf dir1              # Remove directory and contents recursively
mv dir1 new_dir          # Rename or move directory
cp file1 file2           # Copy file1 to file2
cp -a /tmp/dir1 .        # Copy directory preserving attributes
ln -s file1 link1        # Create symbolic link
ln file1 link1           # Create hard link
touch -t 0712250000 file1 # Set file timestamp (YYMMDDhhmm)
file file1               # Show MIME type of file
iconv -l                # List known encodings
iconv -f from -t to inputFile > outputFile # Convert file encoding
find . -maxdepth 1 -name *.jpg -print -exec convert "{}" -resize 80x60 "thumbs/{}" \; # Batch resize images

File Search

find / -name file1                     # Search from root for file1
find / -user user1                     # Find files owned by user1
find /home/user1 -name \*.bin          # Find .bin files in specific directory
find /usr/bin -type f -atime +100     # Find executable 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
locate \*.ps                           # Find .ps files (run updatedb first)
whereis halt                           # Locate binary, source, and man page
which halt                              # Show full path of executable

Mounting Filesystems

mount /dev/hda2 /mnt/hda2               # Mount partition hda2
umount /dev/hda2                       # Unmount partition
fuser -km /mnt/hda2                    # Force unmount if busy
umount -n /mnt/hda2                    # Unmount without writing /etc/mtab
mount /dev/fd0 /mnt/floppy              # Mount floppy
mount /dev/cdrom /mnt/cdrom            # Mount CD/DVD
mount -o loop file.iso /mnt/cdrom      # Mount ISO image
mount -t vfat /dev/hda5 /mnt/hda5      # Mount 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

Disk Space

df -h                                 # Show mounted partitions with human‑readable sizes
ls -lSr | more                        # List files sorted by size
du -sh dir1                           # Summarize disk usage of dir1
du -sk * | sort -rn                   # Sort directories/files by size
rpm -qa | grep httpd                  # List installed RPM packages containing "httpd"
dpkg-query -W -f='${Installed-Size}\t${Package}
' | sort -k1,1n # List installed DEB packages by size

User and Group Management

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 # Add user with details
useradd user1                         # Simple user creation
userdel -r user1                       # Delete user and home directory
usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1 # Modify user
passwd                                 # Change own password
passwd user1                           # Change password for user1 (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 primary group

File Permissions

ls -lh                                 # Show permissions in long format
chmod ugo+rwx directory1                # Grant rwx 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
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 o+t /home/public                 # Set sticky bit on directory
chmod +x /path/to/file                  # Add execute permission
chmod -x /path/to/file                  # Remove execute permission
chmod ug+wx file                        # Grant write and execute to user and group
chmod =wx file                         # Set only write and execute, remove read

Special File Attributes

chattr +a file1   # Append‑only attribute
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
chattr +S file1   # Sync changes immediately after write
chattr +u file1   # Allow undeletion
lsattr            # List special attributes

Archiving and Compression

bunzip2 file1.bz2                     # Decompress bzip2 file
bzip2 file1                           # Compress with bzip2
gunzip file1.gz                       # Decompress gzip file
gzip file1                             # Compress 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 -tf 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      # Recursively zip multiple items
unzip file1.zip                        # Extract zip archive

RPM Package Management (Fedora/RedHat)

rpm -ivh package.rpm                 # Install package
rpm -U package.rpm                    # Upgrade package without changing config
rpm -F package.rpm                    # Update already installed package
rpm -e package_name                   # Remove package
rpm -qa                               # List all installed RPMs
rpm -qi package_name                  # Show detailed info of a package
rpm -ql package_name                  # List files provided by package
rpm -qf /etc/httpd/conf/httpd.conf    # Find which package owns a file
rpm --import /media/cdrom/RPM-GPG-KEY # Import GPG key
rpm --checksig package.rpm             # Verify package signature
rpm -V package_name                   # Verify package files
rpm -Vp package.rpm                   # Verify an uninstalled package
rpm2cpio package.rpm | cpio --extract --make-directories *bin* # Extract executable from RPM
rpmbuild --rebuild package.src.rpm   # Rebuild package from source

YUM Package Manager (Fedora/RedHat)

yum install package_name               # Install package
yum localinstall package.rpm           # Install local RPM with dependency resolution
yum update package_name                # Update specific package
yum remove package_name                # Remove package
yum list                               # List all installed packages
yum search keyword                     # Search repository for package
yum clean packages                     # Remove downloaded packages
yum clean all                          # Clean all cached data

DEB Package Management (Debian/Ubuntu)

dpkg -i package.deb                    # Install/upgrade DEB package
dpkg -r package_name                  # Remove DEB package
dpkg -l                               # List installed DEB packages
dpkg -s package_name                  # Show status of a package
dpkg -L package_name                  # List files installed by package
dpkg -S /bin/ping                     # Find which package provides a file
apt-get install package_name           # Install package via APT
apt-get update                         # Refresh package lists
apt-get upgrade                         # Upgrade all installed packages
apt-get remove package_name            # Remove package
apt-cache search keyword               # Search package cache

Viewing File Contents

cat file1                              # Show file from start
tac file1                              # Show file in reverse order
more file1                            # Page through long file
less file1                             # Page with forward/backward navigation
head -2 file1                          # Show first two lines
tail -2 file1                          # Show last two lines
tail -f /var/log/messages              # Follow file growth in real time

Text Processing

cat file1 file2 | command > output.txt          # Pipe files into command
grep pattern file                         # Search for pattern
sed 's/old/new/g' file                    # Replace text globally
awk '{print $1}' file                     # Print first column
sort file | uniq -c                       # Count unique lines
comm -1 file1 file2                      # Show lines unique to file1
paste file1 file2                         # Merge files column‑wise

Character Set Conversion

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

Filesystem Checks and Creation

badblocks -v /dev/hda1                     # Scan for bad blocks
fsck /dev/hda1                             # Check and repair filesystem
mkfs /dev/hda1                             # Create filesystem on partition
mke2fs /dev/hda1                           # Create ext2 filesystem
mke2fs -j /dev/hda1                        # Create ext3 filesystem with journaling
mkfs -t vfat -F 32 /dev/hda1               # Create FAT32 filesystem
fdformat -n /dev/fd0                        # Format floppy
mkswap /dev/hda3                           # Create swap partition

Backup and Restore

dump -0aj -f /tmp/home0.bak /home          # Full backup of /home
dump -1aj -f /tmp/home0.bak /home          # Interactive backup
restore -if /tmp/home0.bak                  # Restore interactive backup
rsync -rogpav --delete /home /tmp            # Sync directories
rsync -az -e ssh user@host:/dev/hda | gzip > hda.gz # Remote backup via SSH
dd if=/dev/sda of=/tmp/file1                 # Disk image copy
tar -Puf backup.tar /home/user              # Incremental tar backup

Optical Media

cdrecord -v dev=/dev/cdrom -eject blank=fast   # Erase rewritable CD
mkisofs /dev/cdrom > cd.iso                     # Create ISO image
mount -o loop cd.iso /mnt/iso                   # Mount ISO image
cd-paranoia -B                                   # Extract audio tracks to WAV
dd if=/dev/hdc | md5sum                         # Verify CD image checksum

Networking

ifconfig eth0                                 # Show Ethernet config
ifup eth0                                      # Bring interface up
ifdown eth0                                    # Bring interface down
ifconfig eth0 192.168.1.1 netmask 255.255.255.0 # Set static IP
dhclient eth0                                 # Obtain IP via DHCP
route -n show                                 # Show routing table
route add -net 0.0.0.0 gw 192.168.1.1        # Set default gateway
netstat -tup                                 # List active connections with PIDs
tcpdump tcp port 80                           # Capture HTTP traffic
iwlist scan                                   # Scan wireless networks
hostname                                      # Show system hostname
host www.example.com                          # DNS lookup
nslookup www.example.com                      # DNS lookup
whois www.example.com                         # Query WHOIS database

Directory Listing

ls -a                                         # List all files, including hidden
ls -l                                         # Detailed list
ls -R                                         # Recursive listing
ls -ld                                        # List directory info
pwd                                           # Show current directory

File Type Identification

file filename                                 # Display file type

Copying Files and Directories

cp source dest                                 # Copy file
cp -r src_dir dest_dir                         # Recursive copy of directory
mv old_name new_name                           # Rename or move file/directory
rm file1                                      # Delete file
rm -r dir1                                    # Delete directory recursively
rmdir dir1                                    # Remove empty directory

System Commands Overview

date                                          # Show or set system date/time
cal                                           # Show calendar
uptime                                        # Show system uptime
echo "text" >> file                          # Append text to file
cat file                                      # Display file content
head -n 10 file                               # Show first 10 lines
tail -n 10 file                               # Show last 10 lines
more file                                     # Page forward
less file                                     # Page forward/backward
ls -al | less                                 # Long list with paging
lspci -v                                      # Show PCI devices verbosely
lsusb -v                                      # Show USB devices verbosely
lsmod                                         # List loaded kernel modules
shutdown -h now                               # Immediate shutdown
reboot                                        # Immediate reboot

VIM Editor Basics

vim file               # Open file in VIM
:i                     # Enter insert mode
:Esc                   # Return to command mode
dd                     # Delete current line
yy                     # Yank (copy) current line
p                      # Paste after cursor
u                      # Undo last change
/keyword               # Search for keyword
:w                     # Write (save) file
:q                     # Quit VIM
:wq or :x              # Save and quit
:set number            # Show line numbers
:! command            # Execute shell command from VIM

RPM Package Management Commands

rpm -ivh package.rpm                         # Install package
rpm -e package                               # Remove package
rpm -Uvh package.rpm                         # Upgrade package
rpm -Fvh package.rpm                         # Update package
rpm -qa | grep httpd                        # List installed packages matching httpd
rpm -qi package                              # Query detailed info
rpm -ql package                              # List files in package
rpm -qf /etc/httpd/conf/httpd.conf          # Find owning package of a file

Feel free to bookmark this cheat sheet for quick reference during daily Linux system administration tasks.