How to check which Linux distribution I'm using?

Run `cat /etc/os-release` or `hostnamectl` to see distribution name and version.

What's the difference between apt and yum?

apt is used by Debian/Ubuntu, yum/dnf by RHEL/CentOS/Fedora. The commands differ but the concepts (install/remove/update/search) are the same.

How to recover a deleted file?

There's no built-in undelete in Linux. Always backup important data. For accidental text file deletions, some editors keep swap files (.filename.swp).

How to check what's using all my memory?

Run `free -h` for memory overview, `top` or `htop` for process-level usage, and `ps aux --sort=-%mem | head -10` for top memory consumers.

Linux Command Cheatsheet

Linux is the foundation of server development and operations. This cheatsheet organizes essential Linux commands by scenario — from file operations to system administration, each with practical examples. Whether you're new to Linux or need a quick reference, this guide has you covered.

Updated: 2026-07-16·47 commands

Quick Reference

Task

Command

Print working directory	`pwd`
List files	`ls -la`
Change directory	`cd /path`
View processes	`ps aux` / `top`
Search files	`find / -name "file"`
Search content	`grep "text" file`
Change permissions	`chmod 755 file`
Check disk usage	`df -h` / `du -sh`
Install software	`apt install pkg`
Check service status	`systemctl status`

File Operations

### File & Directory Management

``bash # Current path pwd

# List directory contents ls -la # Detailed (with hidden files) ls -lh # Human-readable sizes ls -ltr # Sort by time, newest last

# Change directory cd /tmp # Go to absolute path cd ~ # Go home cd - # Go to previous directory

# Create & delete mkdir -p a/b/c # Recursively create directories touch file.txt # Create empty file rm -rf dir/ # Recursively force delete (⚠️ dangerous) cp -r src dst # Recursively copy mv src dst # Move or rename`

### View File Content

`bash cat file.txt # Display all less file.txt # Paginated view (Space=next, q=quit) head -n 20 file # First 20 lines tail -f log.log # Follow log in real-time wc -l file # Count lines`

> Tip: rm -rf / will destroy your entire system. Always double-check paths with rm.

`Process Management`

`bash # View processes ps aux # All processes ps aux | grep nginx # Filter top # Real-time monitor (q to quit, 1 for CPU cores)

# Manage processes kill PID # Terminate by PID kill -9 PID # Force kill (SIGKILL) pkill -f "name" # Terminate by process name nohup command & # Run in background, survive terminal close jobs # List background jobs fg %1 # Bring job to foreground`

`Networking`

`bash # Diagnostics ping -c 4 8.8.8.8 # Connectivity test curl -I https://example.com # HTTP headers wget -O output.zip https://... # Download file traceroute host # Route tracing

# Ports & connections ss -tulpn # Listening ports (replaces netstat) ss -tulpn | grep :80 # Check port 80

# Remote access ssh user@host -p 22 # SSH login scp file user@host:/path/ # File transfer rsync -av src/ dst/ # Incremental sync`

`Search & Find`

`bash # Search files find /home -name "*.log" # By filename find /home -type f -size +10M # By type and size

# Search content grep "error" logfile # Basic search grep -r "TODO" src/ # Recursive directory search grep -i "warning" log # Case-insensitive grep -C 3 "error" log # Show 3 lines context

# Locate commands which nginx # Command path whereis nginx # Binary + source + man path`

`Permissions`

`bash # Change permissions chmod 755 script.sh # rwx r-x r-x chmod +x script.sh # Add executable chmod -R 644 dir/ # Recursive file permissions

# Change owner chown user:group file chown -R user:group dir/

# View permissions ls -la # First column: -rwxr-xr-x`

> Permission bits: r=4, w=2, x=1 → rwx=7, r-x=5, r--=4, ---=0

`Disk Management`

`bash # Check disk df -h # Disk space (human-readable) du -sh * # Directory sizes in current dir du -sh /var/log/ # Specific directory total

# Mount management mount # View mounts mount /dev/sdb1 /mnt # Mount device umount /mnt # Unmount`

`Package Management`

`bash # Debian/Ubuntu (apt) apt update # Update package index apt install nginx # Install package apt remove nginx # Remove package apt search "keyword" # Search packages

# RHEL/CentOS (yum/dnf) yum install nginx # Install dnf install nginx # Fedora (newer)`

> Tip: apt and yum have different commands but similar concepts. Not sure your distro? Run cat /etc/os-release.

`System Administration`

`bash # System info uname -a # Kernel version hostnamectl # Hostname + OS info uptime # Uptime + load average whoami # Current user

# Service management (systemd) systemctl status nginx # Check service status systemctl start nginx # Start service systemctl stop nginx # Stop service systemctl restart nginx # Restart service systemctl enable nginx # Enable on boot

# Logs journalctl -u nginx # View service logs journalctl -u nginx -n 50 # Last 50 lines journalctl -u nginx -f # Follow in real-time

# System load free -h # Memory usage uptime # Load averages (1m/5m/15m) htop # Interactive monitor (if installed)`

`Pro Tips`

`bash # Pipe & redirection command | grep "xxx" # Pipe to filter command > file.log # Redirect output (overwrite) command >> file.log # Redirect output (append) command 2>&1 # Redirect stderr too

# Command history history # View history !! # Repeat last command !$ # Last argument of last command ctrl+r # Search history (press repeatedly to cycle)

# Shortcuts ctrl+c # Force quit ctrl+d # Exit shell or EOF ctrl+z # Suspend current task`

`Troubleshooting`

Symptom

Cause

Fix


command not found Not installed or not in PATH which command to check, use full path /usr/bin/command
Permission denied No execute permission chmod +x file or prefix with sudo
Disk full / partition at 100% df -h to locate, du -sh /* to find big dirs
Port in use Another process is listening ss -tulpn \ grep :port to find PID, kill PID
Process won't die Zombie process Try kill, then kill -9`, then reboot if needed

`File(13)`

Command	Level	Example
`pwd` Print working directory	Basic	`pwd`
`ls` List directory contents	Basic	`ls -la`
`cd` Change working directory	Basic	`cd /home/user/project`
`mkdir` Create directories	Basic	`mkdir -p a/b/c`
`touch` Create empty file or update file timestamps	Basic	`touch file.txt`
`cp` Copy files or directories	Basic	`cp -r src/ dst/`
`mv` Move or rename files	Basic	`mv old.txt new.txt`
`rm` Remove files or directories rm -rf / will delete your entire system! Always double-check paths	Basic	`rm -rf dir/`
`cat` Display file contents	Basic	`cat file.txt`
`less` View file contents page by page	Basic	`less file.txt`
`head` Display first lines of a file	Basic	`head -n 20 file.txt`
`tail` Display last lines of a file	Basic	`tail -f log.log`
`wc` Count lines, words, and bytes in a file	Basic	`wc -l file.txt`

`Process(6)`

Command	Level	Example
`ps` Display running processes	Basic	`ps aux`
`top` Real-time view of system processes and resource usage	Intermediate	`top`
`kill` Terminate a process by PID Use kill -9 (SIGKILL) as a last resort, prefer kill (SIGTERM) first	Intermediate	`kill -9 1234`
`nohup` Run command immune to hangups (survives terminal close)	Intermediate	`nohup long-running-script.sh &`
`pkill` Kill processes by name	Intermediate	`pkill -f "node server"`
`htop` Interactive process viewer (enhanced top)	Intermediate	`htop`

`Network(8)`

Command	Level	Example
`ping` Test network connectivity	Basic	`ping -c 4 8.8.8.8`
`curl` Send HTTP requests or download files	Intermediate	`curl -I https://example.com`
`wget` Download files from the web	Basic	`wget -O output.zip https://example.com/file.zip`
`ss` Socket statistics (modern netstat replacement)	Intermediate	`ss -tulpn`
`ssh` Remote login to SSH server	Intermediate	`ssh user@hostname -p 22`
`scp` Securely copy files over SSH	Intermediate	`scp file.txt user@host:/tmp/`
`rsync` Fast incremental file transfer tool	Intermediate	`rsync -av src/ user@host:/dst/`
`traceroute` Trace the route packets take to a host	Intermediate	`traceroute example.com`

`Search(4)`

Command	Level	Example
`find` Search for files by criteria Can be slow on large scopes, use -maxdepth to limit depth	Intermediate	`find /home -name "*.log"`
`grep` Search for text patterns in files	Intermediate	`grep -r "TODO" src/`
`which` Show the full path of a command	Basic	`which nginx`
`whereis` Locate binary, source, and man page for a command	Basic	`whereis nginx`

`Permission(2)`

Command	Level	Example
`chmod` Change file or directory permissions	Intermediate	`chmod 755 script.sh`
`chown` Change file or directory owner	Intermediate	`chown user:group file.txt`

`Disk(4)`

Command	Level	Example
`df` Report file system disk space usage	Basic	`df -h`
`du` Estimate file/directory disk usage	Basic	`du -sh /var/log/`
`mount` Mount a filesystem or device	Intermediate	`mount /dev/sdb1 /mnt`
`umount` Unmount a mounted filesystem	Intermediate	`umount /mnt`

`Package(3)`

Command	Level	Example
`apt` Debian/Ubuntu package manager	Intermediate	`apt install nginx`
`yum` RHEL/CentOS package manager	Intermediate	`yum install nginx`
`dnf` Fedora/RHEL next-gen package manager	Intermediate	`dnf install nginx`

`System(6)`

Command	Level	Example
`uname` Display system kernel information	Basic	`uname -a`
`uptime` Show system uptime and load averages	Basic	`uptime`
`systemctl` systemd service manager	Intermediate	`systemctl status nginx`
`journalctl` View systemd logs	Intermediate	`journalctl -u nginx -n 50 -f`
`free` Display system memory usage	Basic	`free -h`
`hostnamectl` View or set hostname and system info	Basic	`hostnamectl`

`Shell(1)`

Command	Level	Example
`history` View command history	Basic	`history \| grep "git"`

`FAQ`

This cheatsheet is compiled from official tool documentation. Last updated: 2026-07-16.

command not found	Not installed or not in PATH	which command `to check, use full path` /usr/bin/command
Permission denied	No execute permission	chmod +x file `or prefix with` sudo
Disk full	/ `partition at 100%`	df -h `to locate,` du -sh /* `to find big dirs`
Port in use	Another process is listening	ss -tulpn \	grep :port `to find PID,` kill PID
Process won't die	Zombie process	Try kill`, then` kill -9`, then reboot if needed