Linux Commands for Beginners

ls - Lists all files and directories in the present working directory

Variations:

• ls -R - Lists files in sub-directories as well (recursive)
• ls -a - Shows hidden files (files starting with .)
• ls -al - Lists files with detailed information like permissions, size, owner, etc.

Example: ls -al

cd directoryname - Changes the directory (navigate to a folder)

• cd .. - Moves one level up (go to parent directory)
• cd ~ - Goes to home directory
• cd / - Goes to root directory
• cd - - Goes back to previous directory

Examples:

cd Documents      # Go to Documents folder
cd ..            # Go to parent folder
cd ~             # Go to home folder

pwd - Displays the present working directory (shows your current location)

Example output: /home/username/Documents

cat > filename - Creates a new file (type content, then Ctrl+D to save)

cat filename - Displays the file content

touch filename - Creates or modifies a file (updates timestamp)

View file options:

• less filename - Views file page by page (scroll with arrow keys)
• head filename - Views first 10 lines of file
• tail filename - Views last 10 lines of file

Copy: cp source destination - Copies files from source to destination

Move: mv source destination - Moves/renames files

Delete: rm filename - Deletes a file (⚠️ permanent!)

Find: find / -name filename - Finds a file starting from root directory

file filename - Determines the file type

lsof - Shows which files are opened by which process

Examples:

cp file1.txt file2.txt       # Copy file
mv file1.txt Documents/      # Move to folder
rm oldfile.txt              # Delete file
find / -name "*.pdf"        # Find all PDF files

du -h --max-depth=1 - Shows size of each directory in human-readable format

df - Shows disk usage of all mounted filesystems

df -h - Disk usage in human-readable format (MB, GB)

fdisk - Disk partition manipulation command

mkdir directoryname - Creates a new directory (folder)

rmdir directoryname - Deletes an empty directory

rm -r directoryname - Removes directory and all contents (recursive, careful!)

cp -r source destination - Copies directories recursively (with all contents)

mv oldname newname - Renames or moves directories

Examples:

mkdir myproject          # Create folder
rmdir empty_folder       # Delete empty folder
cp -r folder1 folder2    # Copy entire folder
mv oldname newname       # Rename folder

ps - Displays currently active processes for the user

top - Displays all running processes in real-time (like Task Manager)

kill pid - Kills a process with given process ID

pkill name - Kills a process by name

bg - Resumes suspended jobs in background

fg - Brings the most recent job to foreground

fg n - Brings job number n to foreground

Examples:

ps aux              # List all processes
top                # View processes live
kill 1234          # Kill process with ID 1234
pkill firefox      # Kill Firefox browser
command &          # Run command in background

chmod octal filename - Changes file permissions (0-7 for each user type)

chown ownername filename - Changes file owner

chgrp groupname filename - Changes group owner

Permission Numbers:

• 4 = Read (r)
• 2 = Write (w)
• 1 = Execute (x)
• 0 = No permission

Example: chmod 755 script.sh

7 = 4+2+1 (owner: read, write, execute)
5 = 4+1   (group: read, execute)
5 = 4+1   (others: read, execute)

ping host - Ping a host and check if it's reachable

ifconfig - Displays IP addresses of all network interfaces

ip address - Modern way to display IP addresses (newer systems)

ssh user@host - Remote login into a host as a user

scp file user@host - Transfers files between hosts over SSH

wget url - Downloads files from the web

curl url - Sends a request to URL and returns response

netstat -pnltu - Displays network connections and statistics

traceroute domain - Shows the route packets take to reach domain

whois domain - Get WHOIS information for domain

dig domain - Get DNS information for domain

Examples:

ping google.com                # Check connectivity
ifconfig                      # Show IP addresses
ssh [email protected]        # Remote login
wget https://example.com/file # Download file

tar cf file.tar files - Create a tar archive named file.tar

tar xf file.tar - Extract files from file.tar

tar -cvf archive.tar dirname/ - Create tar archive verbosely

tar -xvf archive.tar - Extract tar archive verbosely

gzip file - Compresses file and renames to file.gz

gzip -d file.gz - Decompresses file.gz back to original

zip -r file.zip files - Create a ZIP archive

unzip file.zip - Extract ZIP archive contents

tar -jcvf archive.tar.bz2 dirname/ - Create compressed bz2 archive

tar -jxvf archive.tar.bz2 - Extract bz2 archive

Examples:

tar cf backup.tar folder/          # Create tar
tar xf backup.tar                  # Extract tar
gzip largefile.txt                 # Compress
zip -r project.zip src/            # Create ZIP

grep pattern files - Search for pattern in files

grep -r pattern dir - Search recursively for pattern in directory

command | grep pattern - Pipe output to grep for searching

echo 'text' - Prints text to terminal

sed 's/string1/string2/g' file - Replaces string1 with string2

sed -i 's/string1/string2/g' file - Replace in-place (modifies file)

diff file1 file2 - Compares two files and shows differences

wc filename - Count lines, words, characters in file

cut -d':' -f1 /etc/passwd - Cut specific field from file

awk - Versatile programming language for working on files

Examples:

grep "error" logfile.txt           # Find errors
grep -r "TODO" src/                # Find in directory
sed 's/old/new/g' file.txt         # Replace text
wc -l script.sh                    # Count lines
ps aux | grep firefox              # Find firefox process

date - Shows current date and time

cal - Shows calendar for current month

uptime - Shows how long system has been running

uname -a - Shows kernel information and system details

whoami - Shows current logged-in username

w - Displays who is currently online

free - Shows memory usage

free -m - Shows memory in MB format

df - Shows disk usage for mounted filesystems

du -sh - Shows disk usage of current directory

Examples:

date                    # Current date/time
uname -a               # System info
uptime                 # Running time
free -m                # Memory usage
whoami                 # Current user

Apt (Ubuntu/Debian):

• sudo apt-get update - Updates package lists
• sudo apt-get upgrade - Upgrades all packages
• sudo apt-get install pkgname - Installs a package
• sudo apt-get remove pkgname - Removes a package

Python Pip:

• pip install packagename - Installs Python package
• pip uninstall packagename - Uninstalls Python package
• pip freeze > requirements.txt - Saves installed packages to file
• pip install -r requirements.txt - Installs from requirements file

Examples:

sudo apt-get install python3       # Install Python
pip install numpy                  # Install Python library
sudo apt-get update                # Update package lists

#!/bin/bash - Shebang line specifying script interpreter

$0, $1, ..., $9 - Script arguments (command-line parameters)

Conditional: if [condition]; then ... fi

Loop: for i in {1..10}; do ... done

While Loop: while [condition]; do ... done

Function: function name() {...}

Operators:

• command1 ; command2 - Run command1 then command2
• command1 && command2 - Run command2 if command1 succeeds
• command1 || command2 - Run command2 if command1 fails
• command & - Run command in background

Simple script example:

#!/bin/bash
echo "Hello, $1"
for i in {1..5}; do
    echo "Number: $i"
done

git init - Initialize a local git repository

git clone url - Clone a remote repository

git add filename - Stage file for commit

git commit -m "message" - Commit changes with message

git status - Check status of working directory

git push - Push changes to remote repository

git pull - Pull latest changes from remote

git branch - List all branches

git branch branchname - Create new branch

git checkout branchname - Switch to a branch

git merge branchname - Merge branch into current branch

git log - View commit history

git stash - Stash changes temporarily

Basic workflow:

git init                          # Create repo
git add file.txt                 # Stage file
git commit -m "Initial commit"   # Commit
git push origin main             # Push to remote

top - Interactive real-time process viewer (like Task Manager)

htop - More user-friendly alternative to top

iostat - Reports CPU and I/O statistics

vmstat - Reports memory, paging, and CPU statistics

ps aux - List all running processes with details

free -h - Show available memory in human-readable format

df -h - Show disk usage in human-readable format

Examples:

top                  # Real-time process monitoring
htop                 # Better visual process monitor
free -h              # Memory status
df -h                # Disk space status

env - Display all environment variables

echo $VARIABLE - Display value of a specific variable

export VARIABLE=value - Set environment variable

echo $PATH - Shows directories where executables are searched

export PATH=$PATH:/new/path - Add directory to PATH

alias new_command='old_command options' - Create command alias

Examples:

echo $HOME              # Show home directory
export MYVAR=hello     # Set variable
echo $MYVAR            # Use variable
alias ll='ls -al'      # Create shortcut

crontab -l - List all your cron jobs

crontab -e - Edit your cron jobs

crontab -r - Remove all your cron jobs

crontab -v - Display last time you edited cron jobs

crontab file - Install cron job from file

@reboot command - Schedule job to run at startup

Cron time format:

* * * * * command
| | | | |
| | | | └─ Day of week (0-6)
| | | └─── Month (1-12)
| | └───── Day (1-31)
| └─────── Hour (0-23)
└───────── Minute (0-59)

Example: 0 2 * * * backup.sh
This runs backup.sh every day at 2:00 AM

find / -name filename - Find file/directory starting from root

find /path -type f -name "*.txt" - Find all text files in path

locate filename - Quick file search (uses database)

whereis programname - Locate binary, source, and manual for command

which commandname - Shows full path of (shell) command

Examples:

find / -name "*.log"           # Find all log files
locate apache2             # Quick search for apache2
which python3              # Full path to python3
whereis gcc                # Locate gcc binary and docs

iostat - CPU and I/O statistics

vmstat - Virtual memory statistics

htop - Interactive process viewer

dmesg - Boot and system messages

journalctl - Query system logs

strace <command> - Trace system calls

lsof <file> - Show processes using file

watch -n 1 free - Watch memory usage every second

netstat -pnltu - Show network connections

ss - Socket statistics (modern alternative)

Examples:

top                    # Interactive system monitor
htop -p 1234          # Monitor specific process
pidstat               # Show per-process statistics
mpstat -P ALL 1       # CPU usage per core
free -h               # Memory usage in human format