DevOps Shack
LINUX CHEAT SHEET
1. Basic Commands
● pwd – Print current working directory
● ls – List files and directories
○ ls -l – Long format listing
○ ls -a – Show hidden files
○ ls -lh – Human-readable sizes
● cd <directory> – Change directory
○ cd .. – Move up one directory
○ cd - – Go to previous directory
● mkdir <dir> – Create a directory
● rmdir <dir> – Remove an empty directory
● rm -r <dir> – Remove a directory and its contents
● touch <file> – Create an empty file
● cp <source> <destination> – Copy files/directories
○ cp -r <dir1> <dir2> – Copy a directory recursively
● mv <old> <new> – Move/rename files or directories
● rm <file> – Delete a file
● cat <file> – View file contents
● less <file> – View file with navigation
● head <file> – Show the first 10 lines of a file
● tail <file> – Show the last 10 lines of a file
○ tail -f <file> – Live update file output
2. File Permissions & Ownership
● ls -l – View file permissions
● chmod 755 <file> – Change file permissions
○ chmod u+x <file> – Grant execute permission to user
○ chmod g-w <file> – Remove write permission from group
○ chmod o+r <file> – Add read permission to others
● chown <user>:<group> <file> – Change ownership
● chown -R <user>:<group> <dir> – Change ownership recursively
3. File Searching
● find <dir> -name "<pattern>" – Find files by name
● find <dir> -type d -name "<pattern>" – Find directories by name
● find <dir> -type f -size +100M – Find files larger than 100MB
● locate <file> – Find file using index
● updatedb – Update the locate database
4. File Compression & Archiving
● tar -cvf archive.tar <files> – Create a tar archive
● tar -xvf archive.tar – Extract a tar archive
● tar -czvf archive.tar.gz <files> – Create a compressed archive
● tar -xzvf archive.tar.gz – Extract a compressed archive
● zip archive.zip <files> – Create a zip archive
● unzip archive.zip – Extract a zip archive
5. Process Management
● ps aux – List running processes
● top – Show real-time system processes
● htop – Interactive process viewer (requires installation)
● kill <PID> – Terminate a process
● kill -9 <PID> – Force kill a process
● pkill <name> – Kill process by name
● nohup <command> & – Run process in background
● jobs – List background processes
● fg %1 – Bring background job to foreground
● bg %1 – Resume a background job
6. Disk Usage
● df -h – Show disk usage in human-readable format
● du -sh <dir> – Show directory size
● du -h --max-depth=1 <dir> – Show size of each subdirectory
● lsblk – Show block devices
● mount /dev/sdX /mnt – Mount a partition
● umount /dev/sdX – Unmount a partition
7. User Management
● whoami – Show current user
● who – Show logged-in users
● id – Show user ID (UID) and group ID (GID)
● adduser <username> – Add a user
● passwd <username> – Change password
● usermod -aG <group> <user> – Add user to group
● deluser <username> – Delete a user
● groups <user> – Show user groups
8. Network Commands
● ifconfig – Show network interfaces (deprecated)
● ip a – Show IP addresses
● ip r – Show routing table
● ping <host> – Check connectivity
● traceroute <host> – Trace route to a host
● netstat -tulnp – Show listening ports
● ss -tulnp – Alternative to netstat
● curl -I <url> – Fetch HTTP headers
● wget <url> – Download a file
9. Package Management
Debian/Ubuntu:
● apt update – Update package lists
● apt upgrade – Upgrade installed packages
● apt install <package> – Install a package
● apt remove <package> – Remove a package
● dpkg -i <package.deb> – Install a .deb package
●
RHEL/CentOS:
● yum update – Update packages
● yum install <package> – Install a package
● yum remove <package> – Remove a package
● rpm -i <package.rpm> – Install an .rpm package
Arch Linux:
● pacman -Syu – Update system
● pacman -S <package> – Install package
● pacman -R <package> – Remove package
10. Log Management
● cat /var/log/syslog – View system logs
● cat /var/log/auth.log – View authentication logs
● dmesg – Show boot messages
● journalctl -xe – View systemd logs
● tail -f /var/log/syslog – Monitor logs live
11. SSH & Remote Access
● ssh user@host – Connect to a remote server
● ssh -i <key> user@host – Connect using an SSH key
● scp <file> user@host:/path – Copy file to a remote server
● scp user@host:/file . – Copy file from remote server
● rsync -av <src> <dest> – Sync files locally or remotely
12. Text Processing
● grep "pattern" <file> – Search for a pattern in a file
● grep -r "pattern" <dir> – Search recursively in a directory
● awk '{print $1}' <file> – Print the first column
● sed 's/old/new/g' <file> – Replace text in a file
● sort <file> – Sort lines in a file
uniq <file> – Remove duplicate lines
● cut -d':' -f1 /etc/passwd – Extract first field from file
13. Crontab (Task Scheduling)
● crontab -e – Edit crontab
● crontab -l – List crontab jobs
● Example cron job:
○ 0 * * * * /path/to/script.sh (Runs every hour)
○ @reboot /path/to/script.sh (Runs on startup)
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14. System Monitoring
● uptime – Show system uptime
● free -h – Show memory usage
● vmstat – Show system performance
● iostat – Show CPU and disk I/O stats
● sar -u 5 10 – CPU usage every 5 sec for 10 times
15. Miscellaneous
alias ll='ls -lah' – Create a command alias
● unalias ll – Remove alias
● history – Show command history
● !! – Repeat last command
● !n – Run command from history (e.g., !100)
● echo $PATH – Show system PATH
● which <command> – Find command location
● man <command> – Show command manual
16. System Performance & Optimization
● top – Monitor system performance interactively
● htop – Advanced interactive process viewer (needs installation)
● vmstat 1 – Show system performance every second
● iostat -x 1 – Show disk I/O statistics
● sar -r 5 10 – Monitor memory usage every 5 seconds for 10 times
● free -m – Show memory usage in MB
● uptime – Show system uptime and load average
● watch -n 1 <command> – Run a command every second
17. Firewall & Security
● ufw status – Check firewall status (Ubuntu)
● ufw enable – Enable UFW firewall
● ufw allow <port> – Allow incoming traffic on a port
● ufw deny <port> – Deny traffic on a port
● iptables -L -v – List firewall rules (RHEL/CentOS)
● iptables -A INPUT -p tcp --dport 22 -j ACCEPT – Allow SSH
● iptables -A INPUT -p tcp --dport 80 -j ACCEPT – Allow HTTP
● iptables -D INPUT -p tcp --dport 80 -j ACCEPT – Remove rule
● fail2ban-client status – Check Fail2Ban status (if installed)
● passwd -l <user> – Lock a user account
● passwd -u <user> – Unlock a user account
18. Kernel & System Information
● uname -r – Show kernel version
● uname -a – Show full kernel details
● cat /etc/os-release – Show OS details
● hostnamectl – Show system hostname and details
● lsmod – List loaded kernel modules
● modinfo <module> – Show details of a kernel module
● dmesg | tail – View recent kernel messages
● sysctl -a – Show all system configurations
19. Mounting & Unmounting File Systems
● mount – Show mounted file systems
● mount /dev/sdX /mnt – Mount a device
● umount /mnt – Unmount a device
● df -h – Show available disk space
● du -sh /directory – Show directory size
● fsck /dev/sdX – Check and repair a filesystem
● mkfs.ext4 /dev/sdX – Format a partition as ext4
20. System Shutdown & Restart
● shutdown -h now – Shutdown immediately
● shutdown -h +10 – Shutdown in 10 minutes
● shutdown -r now – Restart system immediately
● reboot – Reboot the system
● poweroff – Power off the system
● halt – Halt the system
21. Disk Partitioning
● fdisk -l – List all partitions
● fdisk /dev/sdX – Manage partitions on a disk
● parted /dev/sdX – Create and resize partitions
● mkfs.ext4 /dev/sdX1 – Format partition as ext4
● mount /dev/sdX1 /mnt – Mount a partition
22. Environment Variables
● echo $PATH – Show system PATH
● export VAR=value – Set an environment variable
● printenv VAR – Show variable value
● unset VAR – Remove a variable
● env – List all environment variables
23. Disk & Storage Management
● lsblk – List storage devices
● blkid – Show UUIDs of partitions
● mount -o loop file.iso /mnt – Mount an ISO file
● lsof /path/to/file – Show processes using a file
● tune2fs -m 5 /dev/sdX1 – Set reserved space on ext4
24. Service Management (Systemd & SysVinit)
Systemd (Ubuntu, CentOS 7+, RHEL 7+)
● systemctl start <service> – Start a service
● systemctl stop <service> – Stop a service
● systemctl restart <service> – Restart a service
● systemctl status <service> – Show service status
● systemctl enable <service> – Enable service at boot
● systemctl disable <service> – Disable service at boot
SysVinit (Older Systems)
● service <service> start – Start a service
● service <service> stop – Stop a service
● chkconfig <service> on – Enable service at boot
● chkconfig <service> off – Disable service at boot
25. File & Directory Permissions (Advanced)
● chmod 777 <file> – Full permissions (rwxrwxrwx)
● chmod 644 <file> – Read/write for owner, read-only for others
● chmod 700 <dir> – Full access for owner, no access for others
● chmod +x <file> – Add execute permission
● chmod -w <file> – Remove write permission
● chown user:group <file> – Change ownership
● chown -R user:group <dir> – Change ownership recursively
26. Advanced File Operations
● ls -lt – List files by modification time
● ls -S – List files by size
● find / -type f -name "file.txt" – Search for a file
● find . -type d -empty – Find empty directories
● find . -mtime -1 – Find files modified in the last 24 hours
● ln -s /path/to/original /path/to/link – Create a symbolic link
27. Backup & Restore
● tar -cvf backup.tar /path/to/dir – Create a tar backup
● tar -xvf backup.tar – Extract a tar archive
● rsync -av /source/ /destination/ – Sync files
● dd if=/dev/sdX of=backup.img – Create a disk image
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28. Performance Tuning
● nice -n 10 <command> – Run a command with lower priority
● renice -n 10 -p <PID> – Change priority of a
running process
● ulimit -n 65535 – Increase file descriptor limit
● sysctl vm.swappiness=10 – Reduce swap usage
29. Debugging & Troubleshooting
● dmesg | tail -20 – Show recent system messages
● journalctl -xe – View recent logs
● strace -p <PID> – Trace system calls of a process
● lsof -i :80 – Show processes using port 80
● tcpdump -i eth0 – Capture network packets
30. Kernel Module Management
● lsmod – List loaded modules
● modprobe <module> – Load a module
● rmmod <module> – Remove a module
● modinfo <module> – Show module details
