Linux Command Line Cheatsheet

Comprehensive Linux command line reference covering file operations, system administration, networking, text processing, process management, and shell scripting. Essential Linux commands and examples for developers and system administrators.

Linux

File System Navigation

Basic navigation commands for moving through directories

navigation

Navigation: Commands to move through the directory structure and view current location

bash

# Current directory
pwd                    # Print working directory
cd                     # Go to home directory
cd ~                   # Go to home directory
cd /                   # Go to root directory
cd ..                  # Go up one directory
cd -                   # Go to previous directory

bash

# Directory listing
ls                     # List files in current directory
ls -l                  # Long format (detailed)
ls -a                  # Show hidden files
ls -la                 # Long format with hidden files
ls -lh                 # Human-readable file sizes
ls -lt                 # Sorted by modification time
ls -R                  # Recursive listing

bash

# Directory operations
mkdir dirname          # Create directory
mkdir -p path/to/dir   # Create nested directories
rmdir dirname          # Remove empty directory
rm -rf dirname         # Remove directory and contents (careful!)

File Operations - Viewing and Reading

Commands to view and read file contents

file-operations

Viewing Files: Commands to display file contents in different ways

bash

# View entire file
cat filename           # Display entire file
cat file1 file2        # Concatenate multiple files
cat > newfile          # Create file (Ctrl+D to save)

bash

# View file page by page
less filename         # View file (scroll with arrows, q to quit)
more filename         # View file (space for next page, q to quit)
head filename         # First 10 lines
head -n 20 filename   # First 20 lines
tail filename         # Last 10 lines
tail -n 20 filename   # Last 20 lines

bash

# Real-time file monitoring
tail -f filename      # Follow file (watch updates in real-time)
tail -F filename      # Follow with retry (useful for log rotation)

File Operations - Creating and Editing

Commands to create and edit files

file-operations

Creating Files: Various methods to create new files

bash

# Create empty file
touch filename        # Create empty file or update timestamp
touch file1 file2    # Create multiple files
touch -t 202401011200 file  # Set specific timestamp

bash

# Create file with content
echo "text" > file           # Create/overwrite file
echo "text" >> file          # Append to file
cat > file                   # Type content (Ctrl+D to save)
cat >> file                  # Append content (Ctrl+D to save)
printf "text\n" > file      # Formatted output

bash

# Text editors
nano filename        # Simple editor (Ctrl+X to exit)
vim filename         # Vim editor (:wq to save and quit)
vi filename          # Vi editor (same as vim)
gedit filename       # GUI editor (if available)

File Operations - Copying and Moving

Commands to copy, move, and rename files

file-operations

Copying and Moving: Commands to duplicate and relocate files

bash

# Copy files
cp source dest           # Copy file
cp file1 file2 dir/      # Copy multiple files to directory
cp -r dir1 dir2          # Copy directory recursively
cp -p file dest           # Preserve permissions and timestamps
cp -a source dest         # Archive mode (preserve everything)

bash

# Move and rename
mv oldname newname       # Rename file
mv file dir/             # Move file to directory
mv file1 file2 dir/      # Move multiple files
mv -i file dest          # Interactive (prompt before overwrite)
mv -b file dest           # Backup existing file

File Operations - Deleting and Finding

Commands to delete files and find files

file-operations

Deleting Files: Commands to remove files and directories

bash

# Delete files
rm filename             # Delete file
rm -f filename          # Force delete (no prompt)
rm -i filename          # Interactive (prompt before delete)
rm -r dirname            # Delete directory recursively
rm -rf dirname           # Force delete directory (dangerous!)

bash

# Find files
find . -name "*.txt"              # Find files by name
find . -type f -name "*.log"      # Find files only
find . -type d -name "dir"        # Find directories only
find /home -user username         # Find files by owner
find . -size +100M                # Find files larger than 100MB
find . -mtime -7                 # Find files modified in last 7 days

bash

# Locate command (faster, uses database)
locate filename          # Find file (requires updatedb)
updatedb                 # Update locate database
locate -i "*.txt"        # Case-insensitive search

File Permissions

Understanding and modifying file permissions

permissions

Permissions: Linux uses read (r), write (w), and execute (x) permissions for owner, group, and others

bash

# View permissions
ls -l                   # Long format shows permissions
stat filename           # Detailed file information
# Permission format: -rwxrwxrwx
# First char: file type (- = file, d = directory)
# Next 3: owner permissions (rwx)
# Next 3: group permissions (rwx)
# Last 3: others permissions (rwx)

bash

# Change permissions (numeric)
chmod 755 filename      # rwxr-xr-x (owner: all, group/others: read+execute)
chmod 644 filename      # rw-r--r-- (owner: read+write, others: read)
chmod 777 filename      # rwxrwxrwx (all permissions for all)
chmod -R 755 dir/       # Recursive permission change

bash

# Change permissions (symbolic)
chmod u+x filename      # Add execute for owner
chmod g-w filename      # Remove write for group
chmod o+r filename      # Add read for others
chmod a+x filename      # Add execute for all (a = all)
chmod u=rwx,g=rx,o=r filename  # Set specific permissions

bash

# Change ownership
chown user:group file   # Change owner and group
chown user file         # Change owner only
chown -R user:group dir/ # Recursive ownership change
chgrp group file        # Change group only

Text Processing - grep and sed

Searching and manipulating text

text-processing

Text Search: grep searches for patterns in files

bash

# grep - search for patterns
grep "pattern" file           # Search for pattern in file
grep -i "pattern" file        # Case-insensitive search
grep -r "pattern" dir/         # Recursive search
grep -n "pattern" file         # Show line numbers
grep -v "pattern" file         # Invert match (show non-matching lines)
grep -E "pattern" file         # Extended regex

bash

# sed - stream editor
sed 's/old/new/g' file         # Replace all occurrences
sed 's/old/new/' file          # Replace first occurrence per line
sed -i 's/old/new/g' file      # Edit file in place
sed '2d' file                  # Delete line 2
sed '2,5d' file                # Delete lines 2-5
sed '/pattern/d' file          # Delete lines matching pattern

bash

# awk - pattern scanning and processing
awk '{print $1}' file          # Print first column
awk -F: '{print $1}' file      # Use : as field separator
awk '/pattern/ {print}' file    # Print lines matching pattern
awk '{sum+=$1} END {print sum}' file  # Sum first column

Text Processing - cut, sort, and uniq

Extracting, sorting, and filtering text

text-processing

Text Manipulation: Commands to extract, sort, and filter text data

bash

# cut - extract columns
cut -d: -f1 file        # Extract first field (colon delimiter)
cut -c1-10 file         # Extract characters 1-10
cut -f1,3 file          # Extract fields 1 and 3 (tab delimiter)

bash

# sort - sort lines
sort file               # Sort alphabetically
sort -n file           # Sort numerically
sort -r file           # Reverse sort
sort -k2 file          # Sort by second field
sort -u file           # Unique sort (remove duplicates)

bash

# uniq - remove duplicates
uniq file              # Remove consecutive duplicates
uniq -c file           # Count occurrences
uniq -d file           # Show only duplicates
uniq -u file           # Show only unique lines

bash

# wc - word count
wc file                # Lines, words, characters
wc -l file            # Line count only
wc -w file            # Word count only
wc -c file            # Character count only

Process Management - Viewing Processes

Commands to view and monitor running processes

process-management

Process Monitoring: Commands to view running processes and their status

bash

# ps - process status
ps                      # Current user's processes
ps aux                  # All processes (detailed)
ps -ef                  # All processes (full format)
ps aux | grep process   # Find specific process
ps -p PID               # Process by PID

bash

# top - real-time process monitor
top                     # Interactive process viewer
top -u username          # Processes for specific user
# Press 'q' to quit, 'k' to kill process
# Press 'M' to sort by memory, 'P' to sort by CPU

bash

# htop - enhanced top (if installed)
htop                    # Better interface than top
# F5: tree view, F6: sort, F9: kill process

# Other monitoring tools
pgrep process_name      # Find process ID by name
pidof process_name      # Find PID of process
pstree                  # Show process tree

Process Management - Controlling Processes

Commands to start, stop, and manage processes

process-management

Process Control: Commands to start, stop, and manage processes

bash

# Running processes
command &               # Run in background
nohup command &         # Run in background (survives logout)
command > output.log 2>&1 &  # Redirect output and run in background

bash

# Killing processes
kill PID                # Terminate process (SIGTERM)
kill -9 PID             # Force kill (SIGKILL)
killall process_name    # Kill all processes by name
pkill process_name      # Kill processes by name pattern
kill -HUP PID           # Reload process (SIGHUP)

bash

# Job control
jobs                    # List background jobs
fg %1                   # Bring job 1 to foreground
bg %1                   # Send job 1 to background
Ctrl+Z                  # Suspend current process
Ctrl+C                  # Terminate current process

System Information

Commands to view system information and resources

system-info

System Info: Commands to check system status and resources

bash

# System information
uname -a                # All system information
uname -r                # Kernel version
hostname                # System hostname
uptime                  # System uptime and load
whoami                  # Current username

bash

# Resource usage
free -h                 # Memory usage (human-readable)
df -h                   # Disk space (human-readable)
du -h dir/              # Directory size (human-readable)
du -sh dir/             # Total directory size
iostat                  # I/O statistics (if installed)

bash

# CPU information
lscpu                   # CPU architecture information
cat /proc/cpuinfo       # Detailed CPU info
nproc                   # Number of CPU cores
top                     # Real-time CPU usage

Networking - Basic Commands

Basic network commands for connectivity and information

networking

Network Basics: Commands to check connectivity and network configuration

bash

# Network configuration
ifconfig                # Network interfaces (deprecated, use ip)
ip addr                 # Show IP addresses
ip link                 # Show network interfaces
hostname -I             # Show IP address

bash

# Connectivity testing
ping hostname           # Test connectivity
ping -c 4 hostname      # Send 4 packets
traceroute hostname     # Trace route to host
mtr hostname            # Continuous traceroute (if installed)

bash

# Network connections
netstat -tulpn          # All listening ports
ss -tulpn               # Modern replacement for netstat
lsof -i                 # List open network connections
lsof -i :80             # Connections on port 80

Networking - Download and Transfer

Commands to download files and transfer data

networking

File Transfer: Commands to download files and transfer data over network

bash

# wget - download files
wget URL                 # Download file
wget -O filename URL      # Save with specific name
wget -c URL               # Continue interrupted download
wget -r URL               # Recursive download

bash

# curl - transfer data
curl URL                 # Download and display
curl -O URL              # Download file
curl -o filename URL      # Save with specific name
curl -L URL              # Follow redirects
curl -I URL              # Show headers only

bash

# scp - secure copy
scp file user@host:/path    # Copy to remote
scp user@host:/path file     # Copy from remote
scp -r dir user@host:/path   # Copy directory recursively

# rsync - efficient file transfer
rsync -av source dest        # Archive mode, verbose
rsync -avz source dest       # With compression
rsync -av --delete source dest  # Mirror (delete extra files)

Compression and Archiving

Commands to compress and archive files

compression

Compression: Commands to compress and decompress files

bash

# tar - archive files
tar -cf archive.tar files    # Create archive
tar -xf archive.tar          # Extract archive
tar -czf archive.tar.gz dir/ # Create gzipped archive
tar -xzf archive.tar.gz      # Extract gzipped archive
tar -tf archive.tar          # List archive contents

bash

# gzip/gunzip
gzip file                 # Compress file (creates file.gz)
gunzip file.gz            # Decompress file
gzip -d file.gz           # Decompress (alternative)
zcat file.gz              # View compressed file

bash

# zip/unzip
zip archive.zip files     # Create zip archive
unzip archive.zip         # Extract zip archive
unzip -l archive.zip      # List zip contents
zip -r archive.zip dir/   # Recursive zip

Package Management - Debian/Ubuntu

APT package manager commands

package-management

APT: Advanced Package Tool for Debian/Ubuntu systems

bash

# Update package lists
sudo apt update         # Refresh package database
sudo apt upgrade        # Upgrade all packages
sudo apt full-upgrade   # Full system upgrade

bash

# Install packages
sudo apt install package    # Install package
sudo apt install pkg1 pkg2 # Install multiple packages
sudo apt install -y package # Auto-confirm installation

bash

# Remove packages
sudo apt remove package     # Remove package
sudo apt purge package      # Remove package and config files
sudo apt autoremove         # Remove unused dependencies

bash

# Search and info
apt search keyword      # Search for packages
apt show package        # Show package information
apt list --installed    # List installed packages
apt list --upgradable   # List upgradable packages

Package Management - Red Hat/CentOS

YUM and DNF package manager commands

package-management

YUM/DNF: Package managers for Red Hat-based systems

bash

# Update packages
sudo yum update         # Update all packages (YUM)
sudo dnf update         # Update all packages (DNF)
sudo yum check-update   # Check for updates

bash

# Install packages
sudo yum install package    # Install package
sudo dnf install package    # Install package (DNF)
sudo yum install -y package # Auto-confirm

bash

# Remove packages
sudo yum remove package     # Remove package
sudo yum erase package      # Remove package (alternative)
sudo dnf remove package     # Remove package (DNF)

bash

# Search and info
yum search keyword      # Search for packages
yum info package        # Show package information
yum list installed      # List installed packages
yum list available      # List available packages

User and Group Management

Commands to manage users and groups

user-management

User Management: Commands to create, modify, and manage user accounts

bash

# User operations
sudo useradd username      # Create new user
sudo useradd -m username    # Create user with home directory
sudo userdel username      # Delete user
sudo userdel -r username    # Delete user and home directory
sudo usermod -aG group user # Add user to group

bash

# Password management
passwd                     # Change own password
sudo passwd username       # Change user's password
sudo passwd -l username    # Lock user account
sudo passwd -u username    # Unlock user account

bash

# Group operations
sudo groupadd groupname    # Create new group
sudo groupdel groupname    # Delete group
groups                     # Show current user's groups
id                         # Show user and group IDs
id username                # Show user's IDs

Shell Scripting - Basics

Basic shell scripting syntax and concepts

shell-scripting

Script Basics: Essential syntax for writing shell scripts

bash

# Shebang and variables
#!/bin/bash              # Shebang line
VAR="value"              # Variable assignment
echo $VAR                # Print variable
echo ${VAR}              # Alternative syntax
readonly VAR="value"     # Read-only variable

bash

# Special variables
$0                       # Script name
$1, $2, $3...           # Command line arguments
$#                       # Number of arguments
$@                       # All arguments
$*                       # All arguments (as single string)
$?                       # Exit status of last command
$$                       # Process ID

bash

# Conditional statements
if [ condition ]; then
    commands
fi

if [ condition ]; then
    commands
else
    commands
fi

if [ condition ]; then
    commands
elif [ condition ]; then
    commands
else
    commands
fi

Shell Scripting - Loops and Functions

Looping constructs and function definitions

shell-scripting

Loops: Iteration constructs in shell scripts

bash

# For loop
for i in 1 2 3; do
    echo $i
done

for i in {1..10}; do
    echo $i
done

for file in *.txt; do
    echo $file
done

bash

# While loop
while [ condition ]; do
    commands
done

# Until loop
until [ condition ]; do
    commands
done

bash

# Functions
function_name() {
    commands
    return value
}

# Call function
function_name

# Function with parameters
myfunc() {
    echo "First: $1"
    echo "Second: $2"
}
myfunc arg1 arg2

I/O Redirection and Pipes

Redirecting input/output and using pipes

io-redirection

Redirection: Controlling where command input and output go

bash

# Output redirection
command > file          # Overwrite file
command >> file         # Append to file
command 2> file         # Redirect stderr
command > file 2>&1     # Redirect both stdout and stderr
command &> file         # Redirect both (bash 4+)

bash

# Input redirection
command < file          # Read from file
command << EOF          # Here document
text
EOF

command <<< "text"      # Here string

bash

# Pipes
command1 | command2    # Pipe output to next command
command1 | command2 | command3  # Chain pipes
ls -l | grep ".txt"   # List files, filter .txt files
ps aux | grep process  # Find process

Environment Variables

Common environment variables and their usage

environment

Environment Variables: System and user environment variables

bash

# View variables
env                     # Show all environment variables
printenv                # Show all environment variables
echo $HOME              # Show specific variable
echo $PATH              # Show PATH variable
set                     # Show all variables (including shell)

bash

# Set variables
export VAR="value"      # Set and export variable
VAR="value"             # Set variable (current shell only)
export PATH=$PATH:/new/path  # Append to PATH

bash

# Common variables
$HOME                   # Home directory
$PATH                   # Executable search path
$USER                   # Current username
$SHELL                  # Current shell
$PWD                    # Current directory
$OLDPWD                 # Previous directory

System Services - systemd

Managing system services with systemctl

services

systemd: Modern system and service manager

bash

# Service status
systemctl status service    # Check service status
systemctl is-active service # Check if active
systemctl is-enabled service # Check if enabled

bash

# Control services
sudo systemctl start service     # Start service
sudo systemctl stop service     # Stop service
sudo systemctl restart service  # Restart service
sudo systemctl reload service   # Reload configuration

bash

# Enable/disable services
sudo systemctl enable service   # Enable on boot
sudo systemctl disable service  # Disable on boot
sudo systemctl enable --now service  # Enable and start

bash

# List services
systemctl list-units --type=service  # List all services
systemctl list-unit-files           # List all unit files
systemctl --failed                  # List failed services

Log Files and Monitoring

Viewing and monitoring system logs

logging

Log Files: System logs and how to view them

bash

# Common log locations
/var/log/syslog         # System log (Debian/Ubuntu)
/var/log/messages       # System messages (RHEL/CentOS)
/var/log/auth.log       # Authentication log
/var/log/kern.log      # Kernel log
/var/log/apache2/      # Apache logs (if installed)
/var/log/nginx/         # Nginx logs (if installed)

bash

# journalctl - systemd journal
journalctl              # View all logs
journalctl -u service   # Logs for specific service
journalctl -f            # Follow logs (like tail -f)
journalctl -n 50         # Last 50 entries
journalctl --since today # Since today
journalctl --since "1 hour ago"

bash

# View and filter logs
tail -f /var/log/syslog  # Follow system log
grep "error" /var/log/syslog  # Search for errors
less /var/log/syslog     # View log file

Back

Linux Command Line Cheatsheet

Linux

File System Navigation

Basic navigation commands for moving through directories

navigation

Navigation: Commands to move through the directory structure and view current location

bash

# Current directory
pwd                    # Print working directory
cd                     # Go to home directory
cd ~                   # Go to home directory
cd /                   # Go to root directory
cd ..                  # Go up one directory
cd -                   # Go to previous directory

bash

# Directory listing
ls                     # List files in current directory
ls -l                  # Long format (detailed)
ls -a                  # Show hidden files
ls -la                 # Long format with hidden files
ls -lh                 # Human-readable file sizes
ls -lt                 # Sorted by modification time
ls -R                  # Recursive listing

bash

# Directory operations
mkdir dirname          # Create directory
mkdir -p path/to/dir   # Create nested directories
rmdir dirname          # Remove empty directory
rm -rf dirname         # Remove directory and contents (careful!)

File Operations - Viewing and Reading

Commands to view and read file contents

file-operations

Viewing Files: Commands to display file contents in different ways

bash

# View entire file
cat filename           # Display entire file
cat file1 file2        # Concatenate multiple files
cat > newfile          # Create file (Ctrl+D to save)

bash

# View file page by page
less filename         # View file (scroll with arrows, q to quit)
more filename         # View file (space for next page, q to quit)
head filename         # First 10 lines
head -n 20 filename   # First 20 lines
tail filename         # Last 10 lines
tail -n 20 filename   # Last 20 lines

bash

# Real-time file monitoring
tail -f filename      # Follow file (watch updates in real-time)
tail -F filename      # Follow with retry (useful for log rotation)

File Operations - Creating and Editing

Commands to create and edit files

file-operations

Creating Files: Various methods to create new files

bash

# Create empty file
touch filename        # Create empty file or update timestamp
touch file1 file2    # Create multiple files
touch -t 202401011200 file  # Set specific timestamp

bash

# Create file with content
echo "text" > file           # Create/overwrite file
echo "text" >> file          # Append to file
cat > file                   # Type content (Ctrl+D to save)
cat >> file                  # Append content (Ctrl+D to save)
printf "text\n" > file      # Formatted output

bash

# Text editors
nano filename        # Simple editor (Ctrl+X to exit)
vim filename         # Vim editor (:wq to save and quit)
vi filename          # Vi editor (same as vim)
gedit filename       # GUI editor (if available)

File Operations - Copying and Moving

Commands to copy, move, and rename files

file-operations

Copying and Moving: Commands to duplicate and relocate files

bash

# Copy files
cp source dest           # Copy file
cp file1 file2 dir/      # Copy multiple files to directory
cp -r dir1 dir2          # Copy directory recursively
cp -p file dest           # Preserve permissions and timestamps
cp -a source dest         # Archive mode (preserve everything)

bash

# Move and rename
mv oldname newname       # Rename file
mv file dir/             # Move file to directory
mv file1 file2 dir/      # Move multiple files
mv -i file dest          # Interactive (prompt before overwrite)
mv -b file dest           # Backup existing file

File Operations - Deleting and Finding

Commands to delete files and find files

file-operations

Deleting Files: Commands to remove files and directories

bash

# Delete files
rm filename             # Delete file
rm -f filename          # Force delete (no prompt)
rm -i filename          # Interactive (prompt before delete)
rm -r dirname            # Delete directory recursively
rm -rf dirname           # Force delete directory (dangerous!)

bash

# Find files
find . -name "*.txt"              # Find files by name
find . -type f -name "*.log"      # Find files only
find . -type d -name "dir"        # Find directories only
find /home -user username         # Find files by owner
find . -size +100M                # Find files larger than 100MB
find . -mtime -7                 # Find files modified in last 7 days

bash

# Locate command (faster, uses database)
locate filename          # Find file (requires updatedb)
updatedb                 # Update locate database
locate -i "*.txt"        # Case-insensitive search

File Permissions

Understanding and modifying file permissions

permissions

Permissions: Linux uses read (r), write (w), and execute (x) permissions for owner, group, and others

bash

# View permissions
ls -l                   # Long format shows permissions
stat filename           # Detailed file information
# Permission format: -rwxrwxrwx
# First char: file type (- = file, d = directory)
# Next 3: owner permissions (rwx)
# Next 3: group permissions (rwx)
# Last 3: others permissions (rwx)

bash

# Change permissions (numeric)
chmod 755 filename      # rwxr-xr-x (owner: all, group/others: read+execute)
chmod 644 filename      # rw-r--r-- (owner: read+write, others: read)
chmod 777 filename      # rwxrwxrwx (all permissions for all)
chmod -R 755 dir/       # Recursive permission change

bash

# Change permissions (symbolic)
chmod u+x filename      # Add execute for owner
chmod g-w filename      # Remove write for group
chmod o+r filename      # Add read for others
chmod a+x filename      # Add execute for all (a = all)
chmod u=rwx,g=rx,o=r filename  # Set specific permissions

bash

# Change ownership
chown user:group file   # Change owner and group
chown user file         # Change owner only
chown -R user:group dir/ # Recursive ownership change
chgrp group file        # Change group only

Text Processing - grep and sed

Searching and manipulating text

text-processing

Text Search: grep searches for patterns in files

bash

# grep - search for patterns
grep "pattern" file           # Search for pattern in file
grep -i "pattern" file        # Case-insensitive search
grep -r "pattern" dir/         # Recursive search
grep -n "pattern" file         # Show line numbers
grep -v "pattern" file         # Invert match (show non-matching lines)
grep -E "pattern" file         # Extended regex

bash

# sed - stream editor
sed 's/old/new/g' file         # Replace all occurrences
sed 's/old/new/' file          # Replace first occurrence per line
sed -i 's/old/new/g' file      # Edit file in place
sed '2d' file                  # Delete line 2
sed '2,5d' file                # Delete lines 2-5
sed '/pattern/d' file          # Delete lines matching pattern

bash

# awk - pattern scanning and processing
awk '{print $1}' file          # Print first column
awk -F: '{print $1}' file      # Use : as field separator
awk '/pattern/ {print}' file    # Print lines matching pattern
awk '{sum+=$1} END {print sum}' file  # Sum first column

Text Processing - cut, sort, and uniq

Extracting, sorting, and filtering text

text-processing

Text Manipulation: Commands to extract, sort, and filter text data

bash

# cut - extract columns
cut -d: -f1 file        # Extract first field (colon delimiter)
cut -c1-10 file         # Extract characters 1-10
cut -f1,3 file          # Extract fields 1 and 3 (tab delimiter)

bash

# sort - sort lines
sort file               # Sort alphabetically
sort -n file           # Sort numerically
sort -r file           # Reverse sort
sort -k2 file          # Sort by second field
sort -u file           # Unique sort (remove duplicates)

bash

# uniq - remove duplicates
uniq file              # Remove consecutive duplicates
uniq -c file           # Count occurrences
uniq -d file           # Show only duplicates
uniq -u file           # Show only unique lines

bash

# wc - word count
wc file                # Lines, words, characters
wc -l file            # Line count only
wc -w file            # Word count only
wc -c file            # Character count only

Process Management - Viewing Processes

Commands to view and monitor running processes

process-management

Process Monitoring: Commands to view running processes and their status

bash

# ps - process status
ps                      # Current user's processes
ps aux                  # All processes (detailed)
ps -ef                  # All processes (full format)
ps aux | grep process   # Find specific process
ps -p PID               # Process by PID

bash

# top - real-time process monitor
top                     # Interactive process viewer
top -u username          # Processes for specific user
# Press 'q' to quit, 'k' to kill process
# Press 'M' to sort by memory, 'P' to sort by CPU

bash

# htop - enhanced top (if installed)
htop                    # Better interface than top
# F5: tree view, F6: sort, F9: kill process

# Other monitoring tools
pgrep process_name      # Find process ID by name
pidof process_name      # Find PID of process
pstree                  # Show process tree

Process Management - Controlling Processes

Commands to start, stop, and manage processes

process-management

Process Control: Commands to start, stop, and manage processes

bash

# Running processes
command &               # Run in background
nohup command &         # Run in background (survives logout)
command > output.log 2>&1 &  # Redirect output and run in background

bash

# Killing processes
kill PID                # Terminate process (SIGTERM)
kill -9 PID             # Force kill (SIGKILL)
killall process_name    # Kill all processes by name
pkill process_name      # Kill processes by name pattern
kill -HUP PID           # Reload process (SIGHUP)

bash

# Job control
jobs                    # List background jobs
fg %1                   # Bring job 1 to foreground
bg %1                   # Send job 1 to background
Ctrl+Z                  # Suspend current process
Ctrl+C                  # Terminate current process

System Information

Commands to view system information and resources

system-info

System Info: Commands to check system status and resources

bash

# System information
uname -a                # All system information
uname -r                # Kernel version
hostname                # System hostname
uptime                  # System uptime and load
whoami                  # Current username

bash

# Resource usage
free -h                 # Memory usage (human-readable)
df -h                   # Disk space (human-readable)
du -h dir/              # Directory size (human-readable)
du -sh dir/             # Total directory size
iostat                  # I/O statistics (if installed)

bash

# CPU information
lscpu                   # CPU architecture information
cat /proc/cpuinfo       # Detailed CPU info
nproc                   # Number of CPU cores
top                     # Real-time CPU usage

Networking - Basic Commands

Basic network commands for connectivity and information

networking

Network Basics: Commands to check connectivity and network configuration

bash

# Network configuration
ifconfig                # Network interfaces (deprecated, use ip)
ip addr                 # Show IP addresses
ip link                 # Show network interfaces
hostname -I             # Show IP address

bash

# Connectivity testing
ping hostname           # Test connectivity
ping -c 4 hostname      # Send 4 packets
traceroute hostname     # Trace route to host
mtr hostname            # Continuous traceroute (if installed)

bash

# Network connections
netstat -tulpn          # All listening ports
ss -tulpn               # Modern replacement for netstat
lsof -i                 # List open network connections
lsof -i :80             # Connections on port 80

Networking - Download and Transfer

Commands to download files and transfer data

networking

File Transfer: Commands to download files and transfer data over network

bash

# wget - download files
wget URL                 # Download file
wget -O filename URL      # Save with specific name
wget -c URL               # Continue interrupted download
wget -r URL               # Recursive download

bash

# curl - transfer data
curl URL                 # Download and display
curl -O URL              # Download file
curl -o filename URL      # Save with specific name
curl -L URL              # Follow redirects
curl -I URL              # Show headers only

bash

# scp - secure copy
scp file user@host:/path    # Copy to remote
scp user@host:/path file     # Copy from remote
scp -r dir user@host:/path   # Copy directory recursively

# rsync - efficient file transfer
rsync -av source dest        # Archive mode, verbose
rsync -avz source dest       # With compression
rsync -av --delete source dest  # Mirror (delete extra files)

Compression and Archiving

Commands to compress and archive files

compression

Compression: Commands to compress and decompress files

bash

# tar - archive files
tar -cf archive.tar files    # Create archive
tar -xf archive.tar          # Extract archive
tar -czf archive.tar.gz dir/ # Create gzipped archive
tar -xzf archive.tar.gz      # Extract gzipped archive
tar -tf archive.tar          # List archive contents

bash

# gzip/gunzip
gzip file                 # Compress file (creates file.gz)
gunzip file.gz            # Decompress file
gzip -d file.gz           # Decompress (alternative)
zcat file.gz              # View compressed file

bash

# zip/unzip
zip archive.zip files     # Create zip archive
unzip archive.zip         # Extract zip archive
unzip -l archive.zip      # List zip contents
zip -r archive.zip dir/   # Recursive zip

Package Management - Debian/Ubuntu

APT package manager commands

package-management

APT: Advanced Package Tool for Debian/Ubuntu systems

bash

# Update package lists
sudo apt update         # Refresh package database
sudo apt upgrade        # Upgrade all packages
sudo apt full-upgrade   # Full system upgrade

bash

# Install packages
sudo apt install package    # Install package
sudo apt install pkg1 pkg2 # Install multiple packages
sudo apt install -y package # Auto-confirm installation

bash

# Remove packages
sudo apt remove package     # Remove package
sudo apt purge package      # Remove package and config files
sudo apt autoremove         # Remove unused dependencies

bash

# Search and info
apt search keyword      # Search for packages
apt show package        # Show package information
apt list --installed    # List installed packages
apt list --upgradable   # List upgradable packages

Package Management - Red Hat/CentOS

YUM and DNF package manager commands

package-management

YUM/DNF: Package managers for Red Hat-based systems

bash

# Update packages
sudo yum update         # Update all packages (YUM)
sudo dnf update         # Update all packages (DNF)
sudo yum check-update   # Check for updates

bash

# Install packages
sudo yum install package    # Install package
sudo dnf install package    # Install package (DNF)
sudo yum install -y package # Auto-confirm

bash

# Remove packages
sudo yum remove package     # Remove package
sudo yum erase package      # Remove package (alternative)
sudo dnf remove package     # Remove package (DNF)

bash

# Search and info
yum search keyword      # Search for packages
yum info package        # Show package information
yum list installed      # List installed packages
yum list available      # List available packages

User and Group Management

Commands to manage users and groups

user-management

User Management: Commands to create, modify, and manage user accounts

bash

# User operations
sudo useradd username      # Create new user
sudo useradd -m username    # Create user with home directory
sudo userdel username      # Delete user
sudo userdel -r username    # Delete user and home directory
sudo usermod -aG group user # Add user to group

bash

# Password management
passwd                     # Change own password
sudo passwd username       # Change user's password
sudo passwd -l username    # Lock user account
sudo passwd -u username    # Unlock user account

bash

# Group operations
sudo groupadd groupname    # Create new group
sudo groupdel groupname    # Delete group
groups                     # Show current user's groups
id                         # Show user and group IDs
id username                # Show user's IDs

Shell Scripting - Basics

Basic shell scripting syntax and concepts

shell-scripting

Script Basics: Essential syntax for writing shell scripts

bash

# Shebang and variables
#!/bin/bash              # Shebang line
VAR="value"              # Variable assignment
echo $VAR                # Print variable
echo ${VAR}              # Alternative syntax
readonly VAR="value"     # Read-only variable

bash

# Special variables
$0                       # Script name
$1, $2, $3...           # Command line arguments
$#                       # Number of arguments
$@                       # All arguments
$*                       # All arguments (as single string)
$?                       # Exit status of last command
$$                       # Process ID

bash

# Conditional statements
if [ condition ]; then
    commands
fi

if [ condition ]; then
    commands
else
    commands
fi

if [ condition ]; then
    commands
elif [ condition ]; then
    commands
else
    commands
fi

Shell Scripting - Loops and Functions

Looping constructs and function definitions

shell-scripting

Loops: Iteration constructs in shell scripts

bash

# For loop
for i in 1 2 3; do
    echo $i
done

for i in {1..10}; do
    echo $i
done

for file in *.txt; do
    echo $file
done

bash

# While loop
while [ condition ]; do
    commands
done

# Until loop
until [ condition ]; do
    commands
done

bash

# Functions
function_name() {
    commands
    return value
}

# Call function
function_name

# Function with parameters
myfunc() {
    echo "First: $1"
    echo "Second: $2"
}
myfunc arg1 arg2

I/O Redirection and Pipes

Redirecting input/output and using pipes

io-redirection

Redirection: Controlling where command input and output go

bash

# Output redirection
command > file          # Overwrite file
command >> file         # Append to file
command 2> file         # Redirect stderr
command > file 2>&1     # Redirect both stdout and stderr
command &> file         # Redirect both (bash 4+)

bash

# Input redirection
command < file          # Read from file
command << EOF          # Here document
text
EOF

command <<< "text"      # Here string

bash

# Pipes
command1 | command2    # Pipe output to next command
command1 | command2 | command3  # Chain pipes
ls -l | grep ".txt"   # List files, filter .txt files
ps aux | grep process  # Find process

Environment Variables

Common environment variables and their usage

environment

Environment Variables: System and user environment variables

bash

# View variables
env                     # Show all environment variables
printenv                # Show all environment variables
echo $HOME              # Show specific variable
echo $PATH              # Show PATH variable
set                     # Show all variables (including shell)

bash

# Set variables
export VAR="value"      # Set and export variable
VAR="value"             # Set variable (current shell only)
export PATH=$PATH:/new/path  # Append to PATH

bash

# Common variables
$HOME                   # Home directory
$PATH                   # Executable search path
$USER                   # Current username
$SHELL                  # Current shell
$PWD                    # Current directory
$OLDPWD                 # Previous directory

System Services - systemd

Managing system services with systemctl

services

systemd: Modern system and service manager

bash

# Service status
systemctl status service    # Check service status
systemctl is-active service # Check if active
systemctl is-enabled service # Check if enabled

bash

# Control services
sudo systemctl start service     # Start service
sudo systemctl stop service     # Stop service
sudo systemctl restart service  # Restart service
sudo systemctl reload service   # Reload configuration

bash

# Enable/disable services
sudo systemctl enable service   # Enable on boot
sudo systemctl disable service  # Disable on boot
sudo systemctl enable --now service  # Enable and start

bash

# List services
systemctl list-units --type=service  # List all services
systemctl list-unit-files           # List all unit files
systemctl --failed                  # List failed services

Log Files and Monitoring

Viewing and monitoring system logs

logging

Log Files: System logs and how to view them

bash

# Common log locations
/var/log/syslog         # System log (Debian/Ubuntu)
/var/log/messages       # System messages (RHEL/CentOS)
/var/log/auth.log       # Authentication log
/var/log/kern.log      # Kernel log
/var/log/apache2/      # Apache logs (if installed)
/var/log/nginx/         # Nginx logs (if installed)

bash

# journalctl - systemd journal
journalctl              # View all logs
journalctl -u service   # Logs for specific service
journalctl -f            # Follow logs (like tail -f)
journalctl -n 50         # Last 50 entries
journalctl --since today # Since today
journalctl --since "1 hour ago"

bash

# View and filter logs
tail -f /var/log/syslog  # Follow system log
grep "error" /var/log/syslog  # Search for errors
less /var/log/syslog     # View log file

Linux Command Line Cheatsheet

Contents

File System Navigation

File Operations - Viewing and Reading

File Operations - Creating and Editing

File Operations - Copying and Moving

File Operations - Deleting and Finding

File Permissions

Text Processing - grep and sed

Text Processing - cut, sort, and uniq

Process Management - Viewing Processes

Process Management - Controlling Processes

System Information

Networking - Basic Commands

Networking - Download and Transfer

Compression and Archiving

Package Management - Debian/Ubuntu

Package Management - Red Hat/CentOS

User and Group Management

Shell Scripting - Basics

Shell Scripting - Loops and Functions

I/O Redirection and Pipes

Environment Variables

System Services - systemd

Log Files and Monitoring

Linux Command Line Cheatsheet

Contents

File System Navigation

File Operations - Viewing and Reading

File Operations - Creating and Editing

File Operations - Copying and Moving

File Operations - Deleting and Finding

File Permissions

Text Processing - grep and sed

Text Processing - cut, sort, and uniq

Process Management - Viewing Processes

Process Management - Controlling Processes

System Information

Networking - Basic Commands

Networking - Download and Transfer

Compression and Archiving

Package Management - Debian/Ubuntu

Package Management - Red Hat/CentOS

User and Group Management

Shell Scripting - Basics

Shell Scripting - Loops and Functions

I/O Redirection and Pipes

Environment Variables

System Services - systemd

Log Files and Monitoring