Essential Linux Command Cheat Sheet for System Administrators

1. Basic Commands

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

2. Shutdown and Reboot

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

3. Files and Directories

cd /home                 # Change to /home</code>
<code>cd ..                    # Up one level</code>
<code>cd ../..                 # Up two levels</code>
<code>cd ~                     # Go to home directory</code>
<code>cd ~user1                # Home of user1</code>
<code>cd -                     # Return to previous directory</code>
<code>pwd                      # Print working directory</code>
<code>ls                       # List files</code>
<code>ls -F                    # List with type indicators</code>
<code>ls -l                    # Detailed list</code>
<code>ls -a                    # Show hidden files</code>
<code>ls *[0-9]*               # Show names containing digits</code>
<code>tree                     # Tree view of directories</code>
<code>mkdir dir1               # Create directory</code>
<code>mkdir dir1 dir2          # Create two directories</code>
<code>mkdir -p /tmp/dir1/dir2  # Create nested directories</code>
<code>rm -f file1              # Force delete file</code>
<code>rmdir dir1               # Remove empty directory</code>
<code>rm -rf dir1              # Remove directory and its contents</code>
<code>mv dir1 new_dir          # Rename or move directory</code>
<code>cp file1 file2           # Copy file</code>
<code>cp dir/* .               # Copy all files from dir to current</code>
<code>ln -s file1 link1        # Create symbolic link</code>
<code>ln file1 link1           # Create hard link</code>
<code>touch -t 0712250000 file1 # Set timestamp (YYMMDDhhmm)</code>
<code>file file1               # Show MIME type</code>
<code>iconv -l                # List known encodings</code>
<code>iconv -f from -t to input > output # Convert encoding</code>
<code>find . -maxdepth 1 -name *.jpg -exec convert "{}" -resize 80x60 "thumbs/{}" \; # Batch resize images

4. File Search

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

5. Mounting Filesystems

mount /dev/hda2 /mnt/hda2                # Mount partition</code>
<code>umount /dev/hda2                        # Unmount partition</code>
<code>fuser -km /mnt/hda2                    # Force unmount if busy</code>
<code>mount -o loop file.iso /mnt/cdrom       # Mount ISO image</code>
<code>mount -t vfat /dev/hda5 /mnt/hda5      # Mount FAT32</code>
<code>mount /dev/sda1 /mnt/usbdisk           # Mount USB drive</code>
<code>mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share # Mount Windows share

6. Disk Space

df -h                     # Show mounted partitions</code>
<code>du -sh dir1               # Estimate disk usage of dir1</code>
<code>rpm -qa | sort -k1,1n   # List installed RPMs by size</code>
<code>dpkg-query -W -f='${Installed-Size}\t${Package}
' | sort -k1,1n # List installed DEBs by size

7. Users and Groups

groupadd group_name       # Create group</code>
<code>useradd -c "Name" -g admin -d /home/user1 -s /bin/bash user1 # Add user to group admin</code>
<code>passwd user1            # Change password (root only)</code>
<code>chage -E 2005-12-31 user1 # Set password expiry date</code>
<code>newgrp group_name        # Switch primary group

8. File Permissions

chmod ugo+rwx file        # Grant rwx to user, group, others</code>
<code>chmod go-rwx file        # Remove rwx from group and others</code>
<code>chown user1 file         # Change owner</code>
<code>chgrp group1 file        # Change group</code>
<code>chmod u+s /bin/file1    # Set SUID bit</code>
<code>chmod g+s /home/public  # Set SGID on directory</code>
<code>chmod o+t /home/public  # Set sticky bit

9. Special File Attributes

chattr +i file1          # Make immutable</code>
<code>chattr +a file1          # Append‑only</code>
<code>lsattr                  # List attributes

10. Archiving and Compression

bzip2 file1               # Compress</code>
<code>gzip -9 file1            # Maximum compression</code>
<code>tar -cvf archive.tar file1          # Create tarball</code>
<code>tar -xvf archive.tar     # Extract tarball</code>
<code>zip file1.zip file1      # Create zip archive</code>
<code>unzip file1.zip          # Extract zip archive

11. RPM Package Management (Fedora/RedHat)

rpm -ivh package.rpm      # Install</code>
<code>rpm -U package.rpm       # Upgrade</code>
<code>rpm -e package_name      # Remove</code>
<code>rpm -qa                  # List installed RPMs</code>
<code>rpm -q package_name      # Query package

12. YUM Package Manager (Fedora/RedHat)

yum install pkg           # Install</code>
<code>yum update pkg           # Update</code>
<code>yum remove pkg           # Remove</code>
<code>yum list                # List all packages

13. DEB Package Management (Debian/Ubuntu)

dpkg -i package.deb      # Install/upgrade</code>
<code>apt-get install pkg     # Install via APT</code>
<code>apt-get update          # Refresh package lists</code>
<code>apt-get upgrade         # Upgrade all packages

14. Viewing File Contents

cat file1                # Show file</code>
<code>less file1               # Paginated view</code>
<code>head -2 file1           # First two lines</code>
<code>tail -f /var/log/messages # Follow log

15. Text Processing

grep pattern file        # Search</code>
<code>sed 's/old/new/g' file # Replace</code>
<code>awk '{print $1}' file   # Print first column</code>
<code>sort file | uniq        # Unique lines

16. Character Set Conversion

dos2unix file.txt        # Convert DOS to UNIX line endings</code>
<code>unix2dos file.txt        # Convert UNIX to DOS

17. Filesystem Checks

fsck /dev/hda1           # Check/repair filesystem</code>
<code>badblocks -v /dev/hda1  # Find bad blocks

18. Creating Filesystems

mkfs /dev/hda1           # Create generic filesystem</code>
<code>mke2fs -j /dev/hda1    # Create ext3 with journaling

19. Swap Management

mkswap /dev/hda3        # Create swap area</code>
<code>swapon /dev/hda3       # Enable swap

20. Backup and Restore

dump -0aj -f /tmp/home0.bak /home   # Full backup</code>
<code>restore -if /tmp/home0.bak          # Restore</code>
<code>rsync -avz /home /tmp               # Sync directories</code>
<code>dd if=/dev/sda of=/tmp/image.img    # Disk image copy

21. Network Commands

ifconfig eth0           # Show interface config</code>
<code>ping www.example.com    # Test connectivity</code>
<code>netstat -tup            # List active connections</code>
<code>tcpdump -i eth0 port 80 # Capture HTTP traffic

22. VIM Editor Basics

:q                      # Quit VIM</code>
<code>i                       # Insert mode</code>
<code>dd                      # Delete line</code>
<code>yy                      # Yank (copy) line</code>
<code>p                       # Paste</code>
<code>:w                      # Write (save)</code>
<code>:wq                     # Write and quit

23. Additional System Utilities

date                     # Show or set date</code>
<code>uptime                  # System uptime</code>
<code>top                     # Interactive process viewer</code>
<code>dmesg                   # Kernel ring buffer</code>
<code>free -h                 # Memory usage

This reference compiles over a hundred frequently used Linux commands, grouped by functional areas, to serve as a quick‑lookup cheat sheet for system administrators, developers, and anyone working in a Unix‑like environment.