Linux Command Helper

Comprehensive Linux command reference with 75+ commands

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Showing 75 of 75 commands

ls

List directory contents

File Management

Syntax:

ls [options] [directory]

Common Options:

-lLong format listing
-aShow hidden files
-hHuman readable file sizes
-tSort by modification time
-RRecursive listing

Examples:

ls -la

List all files in long format

ls -lh /home

List /home directory with readable sizes

cp

Copy files and directories

File Management

Syntax:

cp [options] source destination

Common Options:

-rCopy directories recursively
-iInteractive mode (prompt before overwrite)
-vVerbose mode
-pPreserve file attributes

Examples:

cp file.txt backup.txt

Copy file to backup

cp -r folder/ backup/

Copy directory recursively

mv

Move/rename files and directories

File Management

Syntax:

mv [options] source destination

Common Options:

-iInteractive mode (prompt before overwrite)
-vVerbose mode
-nNo overwrite

Examples:

mv old.txt new.txt

Rename file

mv file.txt /home/user/

Move file to directory

rm

Remove files and directories

File Management

Syntax:

rm [options] file...

Common Options:

-rRemove directories recursively
-fForce removal without prompts
-iInteractive mode (prompt before removal)
-vVerbose mode

Examples:

rm file.txt

Remove file

rm -rf directory/

Force remove directory and contents

mkdir

Create directories

File Management

Syntax:

mkdir [options] directory...

Common Options:

-pCreate parent directories as needed
-vVerbose mode
-mSet file mode (permissions)

Examples:

mkdir newdir

Create directory

mkdir -p path/to/dir

Create nested directories

rmdir

Remove empty directories

File Management

Syntax:

rmdir [options] directory...

Common Options:

-pRemove parent directories if empty
-vVerbose mode

Examples:

rmdir emptydir

Remove empty directory

rmdir -p path/to/empty

Remove empty nested directories

touch

Create empty files or update timestamps

File Management

Syntax:

touch [options] file...

Common Options:

-aChange access time only
-mChange modification time only
-cDo not create file if it doesn't exist

Examples:

touch newfile.txt

Create empty file

touch file1 file2 file3

Create multiple files

ln

Create links between files

File Management

Syntax:

ln [options] target linkname

Common Options:

-sCreate symbolic link
-fForce creation
-vVerbose mode

Examples:

ln -s /path/to/file link

Create symbolic link

ln file hardlink

Create hard link

cd

Change directory

Navigation

Syntax:

cd [directory]

Common Options:

-Go to previous directory
~Go to home directory
..Go to parent directory

Examples:

cd /home/user

Change to specific directory

cd ..

Go to parent directory

cd -

Go to previous directory

pwd

Print working directory (current location)

Navigation

Syntax:

pwd [options]

Common Options:

-LUse PWD from environment (logical path)
-PShow actual path without symlinks (physical path)

Examples:

pwd

Show current directory path

pwd -P

Show physical path without symlinks

pushd

Push directory onto stack and change to it

Navigation

Syntax:

pushd [directory]

Common Options:

-nDon't change directory

Examples:

pushd /tmp

Push current dir to stack and go to /tmp

popd

Pop directory from stack and change to it

Navigation

Syntax:

popd [+n | -n]

Common Options:

-nDon't change directory

Examples:

popd

Return to previous directory from stack

dirs

Display directory stack

Navigation

Syntax:

dirs [options]

Common Options:

-vVerbose listing with position numbers
-cClear directory stack

Examples:

dirs

Show directory stack

dirs -v

Show numbered directory stack

cat

Display file contents

Text Processing

Syntax:

cat [options] file...

Common Options:

-nNumber all output lines
-bNumber non-empty output lines
-AShow all characters including non-printing

Examples:

cat file.txt

Display file contents

cat -n file.txt

Display with line numbers

less

View file contents page by page

Text Processing

Syntax:

less [options] file...

Common Options:

-NShow line numbers
-SDon't wrap long lines
-iCase insensitive search

Examples:

less file.txt

View file with pagination

less -N file.txt

View file with line numbers

more

View file contents page by page (basic)

Text Processing

Syntax:

more [options] file...

Common Options:

-dDisplay help at bottom
-fCount logical lines

Examples:

more file.txt

View file with basic pagination

head

Display first lines of file

Text Processing

Syntax:

head [options] file...

Common Options:

-nNumber of lines to show
-cNumber of bytes to show

Examples:

head file.txt

Show first 10 lines

head -n 20 file.txt

Show first 20 lines

tail

Display last lines of file

Text Processing

Syntax:

tail [options] file...

Common Options:

-nNumber of lines to show
-fFollow file changes (monitor)
-FFollow with retry

Examples:

tail file.txt

Show last 10 lines

tail -f /var/log/syslog

Monitor log file

grep

Search text patterns in files

Text Processing

Syntax:

grep [options] pattern [file...]

Common Options:

-iCase insensitive search
-rRecursive search
-nShow line numbers
-vInvert match
-cCount matches

Examples:

grep -i 'error' log.txt

Find 'error' (case insensitive) in log.txt

grep -rn 'TODO' .

Find 'TODO' recursively with line numbers

sed

Stream editor for filtering and transforming text

Text Processing

Syntax:

sed [options] 'command' file...

Common Options:

-iEdit files in place
-eAdd script to commands
-nSuppress automatic printing

Examples:

sed 's/old/new/g' file.txt

Replace 'old' with 'new' globally

sed -i 's/foo/bar/g' file.txt

Replace in file directly

awk

Pattern scanning and processing language

Text Processing

Syntax:

awk [options] 'program' file...

Common Options:

-FField separator
-vAssign variable

Examples:

awk '{print $1}' file.txt

Print first column

awk -F: '{print $1}' /etc/passwd

Print usernames from passwd

sort

Sort lines in text files

Text Processing

Syntax:

sort [options] file...

Common Options:

-rReverse sort order
-nNumeric sort
-uRemove duplicates
-kSort by specific field

Examples:

sort file.txt

Sort file alphabetically

sort -n numbers.txt

Sort numerically

uniq

Report or omit repeated lines

Text Processing

Syntax:

uniq [options] file...

Common Options:

-cCount occurrences
-dOnly show duplicates
-uOnly show unique lines

Examples:

uniq file.txt

Remove consecutive duplicates

sort file.txt | uniq -c

Count unique lines

wc

Word, line, character, and byte count

Text Processing

Syntax:

wc [options] file...

Common Options:

-lCount lines
-wCount words
-cCount bytes
-mCount characters

Examples:

wc file.txt

Show lines, words, and bytes

wc -l file.txt

Count lines only

cut

Extract sections from lines

Text Processing

Syntax:

cut [options] file...

Common Options:

-dField delimiter
-fSelect fields
-cSelect characters

Examples:

cut -d: -f1 /etc/passwd

Extract usernames

cut -c1-10 file.txt

Extract first 10 characters

ping

Send ICMP echo requests to network hosts

Network

Syntax:

ping [options] destination

Common Options:

-cNumber of packets to send
-iInterval between packets
-tSet TTL value
-sPacket size

Examples:

ping google.com

Ping Google continuously

ping -c 4 8.8.8.8

Send 4 ping packets

wget

Download files from web

Network

Syntax:

wget [options] URL

Common Options:

-OOutput filename
-cContinue partial download
-rRecursive download
-qQuiet mode

Examples:

wget https://example.com/file.zip

Download file

wget -O myfile.zip https://example.com/file.zip

Download with custom name

curl

Transfer data from/to servers

Network

Syntax:

curl [options] URL

Common Options:

-oOutput to file
-LFollow redirects
-HAdd header
-dSend data

Examples:

curl https://api.example.com

GET request to API

curl -o file.html https://example.com

Download to file

ssh

Secure Shell remote login

Network

Syntax:

ssh [options] user@hostname

Common Options:

-pPort number
-iIdentity file (private key)
-vVerbose mode
-XEnable X11 forwarding

Examples:

ssh user@server.com

Connect to remote server

ssh -p 2222 user@server.com

Connect using custom port

scp

Secure copy files between hosts over SSH

Network

Syntax:

scp [options] source destination

Common Options:

-rRecursively copy directories
-PSpecify SSH port number
-vVerbose mode (show progress)
-pPreserve file permissions and timestamps
-CEnable compression during transfer
-iSpecify SSH private key file

Examples:

scp file.txt user@host:/path/

Copy local file to remote server

scp user@host:/path/file.txt .

Copy remote file to current directory

scp -r folder/ user@host:/path/

Copy directory recursively to remote server

scp -P 2222 file.txt user@host:/path/

Copy file using custom SSH port

rsync

Synchronize files/directories between locations

Network

Syntax:

rsync [options] source destination

Common Options:

-aArchive mode (preserve attributes)
-vVerbose mode
-zCompress during transfer
--deleteDelete files not in source

Examples:

rsync -av source/ dest/

Sync directories with archive mode

rsync -avz user@host:/path/ local/

Sync from remote with compression

netstat

Display network connections and statistics

Network

Syntax:

netstat [options]

Common Options:

-aShow all connections
-nShow numerical addresses
-tShow TCP connections
-uShow UDP connections
-lShow listening ports

Examples:

netstat -an

Show all connections with numerical addresses

netstat -tlnp

Show listening TCP ports with process info

ps

Display running processes

System Information

Syntax:

ps [options]

Common Options:

auxShow all processes with detailed info
-efShow all processes in full format
-uShow processes for specific user

Examples:

ps aux

Show all running processes

ps -ef | grep nginx

Find nginx processes

top

Display and update sorted information about running processes

System Information

Syntax:

top [options]

Common Options:

-dDelay between updates
-nNumber of iterations
-uMonitor specific user

Examples:

top

Show real-time process information

top -u username

Show processes for specific user

htop

Interactive process viewer (enhanced top)

System Information

Syntax:

htop [options]

Common Options:

-dDelay between updates
-uShow processes for specific user

Examples:

htop

Interactive process monitor

df

Display filesystem disk space usage

System Information

Syntax:

df [options] [filesystem...]

Common Options:

-hHuman readable format
-TShow filesystem type
-iShow inode information

Examples:

df -h

Show disk usage in human readable format

df -T

Show disk usage with filesystem types

du

Display directory space usage

System Information

Syntax:

du [options] [directory...]

Common Options:

-hHuman readable format
-sSummary (total only)
-aShow all files
--max-depthLimit directory depth

Examples:

du -h

Show directory sizes in human readable format

du -sh *

Show size of each item in current directory

free

Display memory usage

System Information

Syntax:

free [options]

Common Options:

-hHuman readable format
-mShow in megabytes
-gShow in gigabytes

Examples:

free -h

Show memory usage in human readable format

uname

Display system information

System Information

Syntax:

uname [options]

Common Options:

-aShow all information
-sShow kernel name
-rShow kernel release
-mShow machine hardware name

Examples:

uname -a

Show all system information

uname -r

Show kernel version

uptime

Show system uptime and load average

System Information

Syntax:

uptime [options]

Common Options:

-pShow uptime in pretty format
-sShow system up since

Examples:

uptime

Show system uptime and load

uptime -p

Show uptime in readable format

whoami

Display current username

System Information

Syntax:

whoami

Common Options:

No common options

Examples:

whoami

Show current user

id

Display user and group IDs

System Information

Syntax:

id [options] [user]

Common Options:

-uShow user ID only
-gShow group ID only
-GShow all group IDs

Examples:

id

Show current user and group IDs

id username

Show IDs for specific user

kill

Terminate processes by PID

Process Management

Syntax:

kill [options] PID...

Common Options:

-9Force kill (SIGKILL)
-15Terminate gracefully (SIGTERM)
-lList available signals

Examples:

kill 1234

Terminate process with PID 1234

kill -9 1234

Force kill process

killall

Terminate processes by name

Process Management

Syntax:

killall [options] name...

Common Options:

-9Force kill
-iInteractive mode
-vVerbose mode

Examples:

killall firefox

Kill all Firefox processes

killall -9 chrome

Force kill all Chrome processes

jobs

Display active jobs

Process Management

Syntax:

jobs [options]

Common Options:

-lShow process IDs
-pShow process IDs only

Examples:

jobs

List active background jobs

jobs -l

List jobs with PIDs

bg

Put jobs in background

Process Management

Syntax:

bg [job_spec]

Common Options:

No common options

Examples:

bg

Put current job in background

bg %1

Put job 1 in background

fg

Bring jobs to foreground

Process Management

Syntax:

fg [job_spec]

Common Options:

No common options

Examples:

fg

Bring current job to foreground

fg %1

Bring job 1 to foreground

nohup

Run commands immune to hangups

Process Management

Syntax:

nohup command [args...]

Common Options:

No common options

Examples:

nohup ./script.sh &

Run script in background, immune to hangups

chmod

Change file permissions

Permissions

Syntax:

chmod [options] mode file...

Common Options:

-RRecursive (apply to directories and contents)
-vVerbose mode

Examples:

chmod 755 script.sh

Set rwxr-xr-x permissions

chmod +x file

Add execute permission

chmod -R 644 directory/

Set permissions recursively

chown

Change file ownership

Permissions

Syntax:

chown [options] owner[:group] file...

Common Options:

-RRecursive
-vVerbose mode

Examples:

chown user file.txt

Change owner to user

chown user:group file.txt

Change owner and group

chown -R user:group directory/

Change ownership recursively

chgrp

Change group ownership

Permissions

Syntax:

chgrp [options] group file...

Common Options:

-RRecursive
-vVerbose mode

Examples:

chgrp staff file.txt

Change group to staff

chgrp -R users directory/

Change group recursively

umask

Set default file permissions

Permissions

Syntax:

umask [mode]

Common Options:

-SShow symbolic mode

Examples:

umask

Show current umask

umask 022

Set umask to 022

tar

Archive files

Archive/Compression

Syntax:

tar [options] archive file...

Common Options:

-cCreate archive
-xExtract archive
-vVerbose mode
-fSpecify archive file
-zUse gzip compression
-jUse bzip2 compression

Examples:

tar -czf archive.tar.gz directory/

Create compressed archive

tar -xzf archive.tar.gz

Extract compressed archive

tar -tvf archive.tar

List archive contents

gzip

Compress files

Archive/Compression

Syntax:

gzip [options] file...

Common Options:

-dDecompress
-rRecursive
-vVerbose mode
-9Best compression

Examples:

gzip file.txt

Compress file

gzip -d file.txt.gz

Decompress file

gunzip

Decompress gzip files

Archive/Compression

Syntax:

gunzip [options] file...

Common Options:

-vVerbose mode
-tTest archive integrity

Examples:

gunzip file.txt.gz

Decompress gzip file

zip

Create ZIP archives

Archive/Compression

Syntax:

zip [options] archive file...

Common Options:

-rRecursive
-vVerbose mode
-9Best compression

Examples:

zip -r archive.zip directory/

Create ZIP archive

zip archive.zip file1 file2

Add files to ZIP

unzip

Extract ZIP archives

Archive/Compression

Syntax:

unzip [options] archive

Common Options:

-dExtract to directory
-lList archive contents
-vVerbose mode

Examples:

unzip archive.zip

Extract ZIP archive

unzip -d /tmp archive.zip

Extract to specific directory

find

Search for files and directories

Search

Syntax:

find [path] [expression]

Common Options:

-nameSearch by filename
-typeSearch by file type (f=file, d=directory)
-sizeSearch by file size
-mtimeSearch by modification time
-execExecute command on found files

Examples:

find . -name '*.txt'

Find all .txt files in current directory

find /home -type d -name 'Documents'

Find directories named 'Documents'

find . -size +100M

Find files larger than 100MB

locate

Find files by name (uses database)

Search

Syntax:

locate [options] pattern

Common Options:

-iCase insensitive
-cCount matches
-rUse regex

Examples:

locate filename

Find files containing 'filename'

locate -i readme

Case insensitive search for readme

which

Locate command

Search

Syntax:

which command

Common Options:

-aShow all matches

Examples:

which python

Find location of python command

which -a gcc

Find all gcc installations

whereis

Locate binary, source, and manual page files

Search

Syntax:

whereis [options] command

Common Options:

-bSearch only for binaries
-mSearch only for manuals
-sSearch only for sources

Examples:

whereis ls

Find ls binary, source, and manual

whereis -b gcc

Find only gcc binary

env

Display or set environment variables

Environment

Syntax:

env [options] [variable=value...] [command]

Common Options:

-iStart with empty environment
-uUnset variable

Examples:

env

Show all environment variables

env PATH=/usr/bin command

Run command with modified PATH

export

Set environment variables

Environment

Syntax:

export [variable[=value]...]

Common Options:

-nRemove variable from export list
-pDisplay all exported variables

Examples:

export PATH=$PATH:/new/path

Add to PATH variable

export EDITOR=vim

Set default editor

echo

Display text

Environment

Syntax:

echo [options] [string...]

Common Options:

-nDon't output trailing newline
-eEnable interpretation of backslash escapes

Examples:

echo 'Hello World'

Display text

echo $PATH

Display PATH variable

history

Display command history

Environment

Syntax:

history [options] [n]

Common Options:

-cClear history
-dDelete history entry

Examples:

history

Show command history

history 10

Show last 10 commands

alias

Create command aliases

Environment

Syntax:

alias [name[=value]...]

Common Options:

No common options

Examples:

alias ll='ls -la'

Create alias for long listing

alias

Show all aliases

unalias

Remove command aliases

Environment

Syntax:

unalias [name...]

Common Options:

-aRemove all aliases

Examples:

unalias ll

Remove ll alias

unalias -a

Remove all aliases

apt

Package manager for Debian/Ubuntu

Package Management

Syntax:

apt [options] command [package...]

Common Options:

updateUpdate package list
upgradeUpgrade packages
installInstall packages
removeRemove packages
searchSearch packages

Examples:

apt update

Update package list

apt install package-name

Install package

apt search keyword

Search for packages

yum

Package manager for Red Hat/CentOS

Package Management

Syntax:

yum [options] command [package...]

Common Options:

updateUpdate packages
installInstall packages
removeRemove packages

Examples:

yum update

Update all packages

yum install package-name

Install package

dnf

Modern package manager for Fedora/Red Hat

Package Management

Syntax:

dnf [options] command [package...]

Common Options:

updateUpdate packages
installInstall packages
removeRemove packages

Examples:

dnf update

Update all packages

dnf install package-name

Install package

systemctl

Control systemd services

System Control

Syntax:

systemctl [options] command [service...]

Common Options:

startStart service
stopStop service
restartRestart service
enableEnable service at boot
disableDisable service at boot
statusShow service status

Examples:

systemctl start nginx

Start nginx service

systemctl enable ssh

Enable SSH at boot

systemctl status apache2

Check Apache status

service

Control system services (SysV)

System Control

Syntax:

service service_name command

Common Options:

startStart service
stopStop service
restartRestart service
statusShow service status

Examples:

service nginx start

Start nginx service

service ssh restart

Restart SSH service

crontab

Schedule tasks

System Control

Syntax:

crontab [options]

Common Options:

-eEdit crontab
-lList crontab
-rRemove crontab

Examples:

crontab -e

Edit scheduled tasks

crontab -l

List scheduled tasks

mount

Mount filesystems

System Control

Syntax:

mount [options] device mountpoint

Common Options:

-tFilesystem type
-oMount options
-aMount all filesystems in fstab

Examples:

mount /dev/sdb1 /mnt

Mount device to /mnt

mount -t ext4 /dev/sdb1 /mnt

Mount with specific filesystem type

umount

Unmount filesystems

System Control

Syntax:

umount [options] mountpoint|device

Common Options:

-fForce unmount
-lLazy unmount

Examples:

umount /mnt

Unmount /mnt

umount -f /mnt

Force unmount