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Linux Cheat Sheet

August 14, 2024 · 12 min read

Trainer @ DevOps Medium

Linux is a family of open-source Unix-like operating systems based on the Linux kernel. Linux is known for its stability, security, and flexibility, making it widely used in servers, desktops, embedded systems, and other platforms. It supports a wide range of hardware and provides a robust environment for software development and deployment.

Basic Linux Commands with Examples

This Linux cheat sheet covers all the most important Linux commands from the basics.

File Management

Command	Description	Options	Examples
ls	List files and directories.	-l: Long format listing. -a: Include hidden files. -h: Human-readable file sizes.	ls -l displays files and directories with detailed information. ls -a shows all files and directories, including hidden ones. ls -lh displays file sizes in a human-readable format.
cd	Change directory.		cd /path/to/directory changes the current directory to the specified path.
pwd	Print current working directory.		pwd displays the current working directory.
mkdir	Create a new directory.	-p: Create the parent directories as needed	mkdir my_directory Creates a new directory named “my_directory”. mkdir -p /path/to/my_directory Creates a new directory named "my_directory" at specified. If the path doesn't exsist it will also be created.
rm	Remove files and directories.	-r: Remove directories recursively. -f: Force removal without confirmation.	rm file.txt deletes the file named “file.txt”. rm -r my_directory deletes the directory “my_directory” and its contents. rm -f file.txt forcefully deletes the file “file.txt” without confirmation.
cp	Copy files and directories.	-r: Copy directories recursively.	cp -r directory destination copies the directory “directory” and its contents to the specified destination. cp file.txt destination copies the file “file.txt” to the specified destination.
mv	Move/rename files and directories.		mv file.txt new_name.txt renames the file “file.txt” to “new_name.txt”. mv file.txt directory moves the file “file.txt” to the specified directory.
touch	Create an empty file or update file timestamps.		touch file.txt creates an empty file named “file.txt”.
cat	View the contents of a file.		cat file.txt displays the contents of the file “file.txt”.
head	Display the first few lines of a file.	-n: Specify the number of lines to display.	head file.txt shows the first 10 lines of the file “file.txt”. head -n 5 file.txt displays the first 5 lines of the file “file.txt”.
tail	Display the last few lines of a file.	-n: Specify the number of lines to display. -f: It makes the command keep the file open and continuously output new lines as they are added to the file.	tail file.txt shows the last 10 lines of the file “file.txt”. tail -n 5 file.txt displays the last 5 lines of the file “file.txt”. tail -f file.txt will display the last 10 lines of the "file.txt" file and then continue to display any new lines added to the file in real-time.
ln	Create links between files.	-s: Create symbolic (soft) links.	ln -s source_file link_name creates a symbolic link named “link_name” pointing to “source_file”.
find	Search for files and directories.	-name: Search by filename. -type: Search by file type.	*find /path/to/search -name “.txt”** searches for all files with the extension “.txt” in the specified directory.

File Permission Commands

Each file and directory has three types of users who can interact with it:

Owner: The user who owns the file.
Group: Users who are part of the file's group.
Others: All other users.

Permissions are represented by three bits for each user type:

r: Read permission (4)
w: Write permission (2)
x: Execute permission (1)

Permissions can be set using a three-digit octal number. Each digit corresponds to the owner, group, and others, respectively.

0: No permission
1: Execute only
2: Write only
3: Write and execute
4: Read only
5: Read and execute
6: Read and write
7: Read, write, and execute

Command	Description	Options	Examples
chmod	Change file permissions.	u: User/owner permissions. g: Group permissions. o: Other permissions. +: Add permissions. –: Remove permissions. =: Set permissions explicitly.	chmod 700 file.txt grant full permissions (rwx) to the Owner, and no permissions for the group and others. chmod -R 755 /path/to/directory sets the permissions to rwx for the owner and rw- for the group and others for all files within the directory and subdirectories. chmod u+rwx,g+rx,o+r file.txt This command grants read, write, and execute permissions to the owner, read and execute permissions to the group, and read permission to others.
chown	Change file ownership.		chown user file.txt changes the owner of “file.txt” to the specified user.
chgrp	Change group ownership.		chgrp group file.txt changes the group ownership of “file.txt” to the specified group.
umask	Set default file permissions.		umask 022 sets the default file permissions to read and write for the owner, and read-only for group and others.

File Compression and Archiving Commands

Command	Description	Options	Examples
tar	Create or extract archive files.	-c: Create a new archive. -x: Extract files from an archive. -f: Specify the archive file name. -v: Verbose mode. -z: Compress the archive with gzip. -j: Compress the archive with bzip2.	tar -czvf archive.tar.gz files/ creates a compressed tar archive named “archive.tar.gz” containing the files in the “files/” directory. tar -xzf archive.tar.gz This extracts a gzip-compressed tar archive from “archive.tar.gz”
gzip	Compress files.	-d: Decompress files.	gzip file.txt compresses the file “file.txt” and renames it as “file.txt.gz”.
zip	Create compressed zip archives.	-r: Recursively include directories.	zip archive.zip file1.txt file2.txt creates a zip archive named “archive.zip” containing “file1.txt” and “file2.txt”.
unzip	Extract files from zip archives.	-l: List the contents of the ZIP file without extracting. -d: Extract files into a specified directory. -o: Overwrite existing files without prompting. -n: Never overwrite existing files.	unzip archive.zip file1.zip extracts all the contents of archive.zip into the current directory.

Process Management Commands

Command	Description	Options	Examples
ps	Display running processes.	aux: Show all processes.	ps aux shows all running processes with detailed information.
top	Monitor system processes in real-time.		top displays a dynamic view of system processes and their resource usage.
kill	Terminate a process.	-9: Forcefully kill a process.	kill PID terminates the process with the specified process ID.
pkill	Terminate processes based on their name.		pkill process_name terminates all processes with the specified name.
pgrep	List processes based on their name.		pgrep process_name lists all processes with the specified name.
grep	Used to search for specific patterns or regular expressions in text files or streams and display matching lines.	-i: Ignore case distinctions while searching. -v: Invert the match, displaying non-matching lines. -r or -R: Recursively search directories for matching patterns. -l: Print only the names of files containing matches. -n: Display line numbers alongside matching lines. -w: Match whole words only, rather than partial matches. -c: Count the number of matching lines instead of displaying them. -e: Specify multiple patterns to search for. -A: Display lines after the matching line. -B: Display lines before the matching line. -C: Display lines both before and after the matching line.	grep -i “hello” file.txt grep -v “error” file.txt grep -l “keyword” file.txt grep -n “pattern” file.txt these examples will return our desired output from “file.txt”

System Information Commands

Command	Description	Options	Examples
uname	Print system information.	-a: All system information.	uname -a displays all system information.
whoami	View Current User		whoami
df	Show disk space usage.	-h: Human-readable sizes.	df -h displays disk space usage in a human-readable format.
du	Check User's Disk Usage		du -sh /home/john
free	Display memory usage information.	-h: Human-readable sizes.	free -h displays memory usage in a human-readable format.
uptime	Show system uptime.		uptime shows the current system uptime.
lscpu	Display CPU information.		lscpu provides detailed CPU information.
lspci	List PCI devices.		lspci list all PCI devices connected.
lsusb	List USB devices.		lsusb list all connected USB devices.

Networking Commands

Command	Description	Options	Examples
ip	Display and manage networking, routing, and tunnel configurations.	addr: Diplay IP Addresses. route: Display/Manage route table. link: Manage network interface	ip addr shows the details of all network interfaces. ip route show shows the details of Routes in Route Table. ip link set dev eth0 down brings eth0 interface down.
ifconfig	Display network interface information.	-a: Display all Interfaces	ifconfig -a shows the details of all network interfaces.
ping	Send ICMP echo requests to a host.	-4: Sends ICMP request to IPv4 address of network host. -6: Sends ICMP request to IPv6 address of network host.	ping google.com sends ECHO_REQUEST to google.com
netstat	Display network connections and statistics.	-a: Displays all connections. -n: Show numerical addresses and ports. -l: Shows listening ports. -t: Shows TCP connnections information only. -u: Shows UDP connections information only.	netstat displays network connections. netstat -nlt displays only TCP listenting connections. netstat -nlu displays only UCP listenting connections.
ssh	Securely connect to a remote server.	-p: Specify a Port for connection. -i: Path of Identity (Private Key) File. -L: Tunneling with SSH (Local port forwarding). -R: Reverse Tunneling	ssh user@remote_host stablish basic SSH connection ssh -p 25 user@remote_host stablish SSH connection on port 25 ssh -i /path/to/private_key user@remote_host connects to remote host using a specific private key ssh -L 8080:locahost:80 user@remote_host Forwards all traffic send to port '8080' on local machine to remote host port '80' ssh -R 9090:localhost:3000 user@remote_host Forwards all traffic sent to port '9090' on remote host to port '3000' of local machine
scp	Securely copy files between hosts.	-r: Copy Directory recursively	scp file.txt user@remote_host:/path/to/destination Copy local file 'file.txt' to remote host scp user@remote_host:/path/to/file.txt /local/path Copy file 'file.txt' from remote host to local machine scp -r /local/directory/ user@remote_host:/remote/directory/ Copies an entire directory and its contents to the remote host.
wget	Download files from the web.	-O: Download file with defined Output Filename -A: Download only specific file types	wget http://example.com/file.txt Downloads the file file.txt from the specified URL. wget -O myfile.txt http://example.com/file.txt Downloads the file and saves it as myfile.txt instead of the original filename. *wget -A ".jpg,.png" http://example.com* Downloads only .jpg and .png image files. wget --user=username --password=password http://example.com/secure-file.zip Downloads a file from a password-protected server.
curl	Transfer data to or from a server.	-L: Follow Redirects -O: Download a file -o: Download file with defined Output Filename -X: Change the HTTP method -d: Send data in body of HTTP request -H: Send headers with HTTP request -u: Download with Authentication -x: Download Using a Proxy -F: Upload Binary File (e.g., ZIP file) via POST -k: Ignore Invalid SSL Certificates	curl http://example.com Sends an HTTP GET request to the specified URL and displays the response. curl -L http://example.com Follows any redirects (3xx responses) automatically. curl -O http://example.com/file.txt Downloads the file from the specified URL and saves it with the original filename. curl -o myfile.txt http://example.com/file.txt Downloads the file and saves it as myfile.txt curl -X POST -d "param1=value1¶m2=value2" http://example.com Sends a POST request with the data param1=value1¶m2=value2 curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' http://example.com Sends a POST request with JSON data. curl -u username:password http://example.com/secure-file.txt Downloads a file using basic HTTP authentication. curl -x http://proxyserver:8080 http://example.com Send HTTP request via the specified proxy server. curl -X POST -F 'file=@/path/to/file.zip' http://example.com/upload Uploads a binary file (such as a ZIP file) via a POST request. curl -k https://example.com Ignores SSL certificate errors when making requests to HTTPS URLs.

IO Redirection Commands

Name	Description	Examples
Standard Output Redirection	> : Redirects output, overwriting the file if it exists. >> : Redirects output, appending to the file if it exists.	echo "Hello, World!" > file.txt Writes "Hello, World!" to file.txt, overwriting it if it exists. echo "Another Line" >> file.txt Appends "Another Line" to file.txt.
Standard Input Redirection	<: Redirects input from a file to a command.	cat < file.txt Reads content from file.txt and displays it.
Standard Error Redirection	2> : Redirects error output, overwriting the file. 2>> : Redirects error output, appending to the file.	ls /nonexistent-dir 2> error.log Sends the error message to error.log, overwriting the file. ls /another-nonexistent-dir 2>> error.log Appends the error message to error.log.
Redirect Both Output and Error	&> : Redirects both standard output and error, overwriting the file. &>> : Redirects both standard output and error, appending to the file.	command &> output.log Writes both output and error to output.log. command &>> output.log Appends both output and error to output.log.
Combine Standard Output and Error	2>&1: Redirects standard error to the same location as standard output.	ls /dir/ > output.log 2>&1 Sends both output and error to output.log.
Discard Output	/dev/null: Send unwanted output or error to the null device (acts as a "black hole").	command > /dev/null Ignores the output of the command. command 2> /dev/null Ignores the error output of the command. command &> /dev/null Ignores both the output and the error.
Here Document	<<: Used to pass a multiline string as input to a command.	cat << EOF This is a multiline string EOF Passes the multiline string as input to the cat command.
Here String	<<<: Redirects a string as input to a command.	grep "Hello" <<< "Hello, World!" Searches for "Hello" in the string "Hello, World!".
Piping	\|: Sends the output of one command as input to another command.	ls \| grep "file" Passes the output of ls to grep, searching for "file".

Environment Variable Commands

Command / Name

Description

Examples

env

Displays all environment variables.

env

printenv

Prints specific or all environment variables.

printenv PATH

Displays the value of PATH

export

Temporary Environment Variable (Only for current shell session)

MY_VAR="HelloWorld"
export MY_VAR
echo $MY_VAR

echo will return HelloWorld

Persisting Environment Variables

Add to .bashrc or .bash_profile

echo 'export VAR_NAME="value"' >> ~/.bashrc
source ~/.bashrc

Unsetting Environment Variables

Removes an environment variable.

unset MY_VAR echo $MY_VAR

echo will return emtpy output

Predefined Environment Variables

Name	Description	Examples
Home	User's home directory	/home/username
USER	Current logged-in username	username
PATH	List of directories for executable searching	/usr/local/sbin:/usr/local/bin:/usr/sbin:/bin
SHELL	Path to the current shell	/bin/bash
PWD	Current working directory	/home/username/projects
LANG	Current language setting	en_US.UTF-8
TERM	Type of terminal to emulate	xterm-256color

Special Variables in Shell Scripting

Name	Description	Examples
$0	The script's filename	script.sh
$1, $2, ...	Positional parameters (arguments passed to script)	arg1, arg2
$#	Number of arguments	2
$?	Exit status of the last command	0 (success), non-zero (failure)
$$	Process ID of the current shell	12345
$@	All positional parameters	arg1 arg2

User Management Commands

Command	Description	Options	Examples
useradd	Create a new user	-d /home/USERNAME : Specify user's home directory -m : Create the user's home directory -s /bin/bash : Specify the login shell -c "COMMENT" : Add a comment for the user	sudo useradd [OPTIONS] USERNAME sudo useradd -m -d /home/john -s /bin/bash -c "John Doe" john
passwd	Set or Update a User Password		sudo passwd USERNAME
userdel	Delete a User	-r : Remove the user's home directory and mail spool	sudo userdel [OPTIONS] USERNAME sudo userdel -r john
usermod	Modify an Existing User	-l NEW_USERNAME : Change the user's login name. -d /new/home/directory : Change the user's home directory -s /bin/sh : Change the login shell -aG GROUP : Add the user to a group (non-destructive) -g:Change User's Primary Group -L: lock a user account -L: lock a user account	sudo usermod [OPTIONS] USERNAME sudo usermod -l john_doe john Update 'john' username to 'john_doe' sudo usermod -aG sudo john_doe add john_doe to sudo group sudo usermod -g devops john change the default group of 'john' to 'devops' sudo usermod -L john Locks john account sudo usermod -U john Unlocks john account
groupadd	Create a new group		sudo groupadd GROUPNAME sudo groupadd devops
su	Switch to another user	- : Start a login shell	su [OPTIONS] USERNAME su - john
groups	List user groups		groups USERNAME groups john
lastlog	Show Last Login Information		lastlog -u john
whoami	View Current User		whoami
du	Check User's Disk Usage		du -sh /home/john

Shortcuts Commands

Bash Comman Shortcuts:

Command	Description
Ctrl + A	Move to the beginning of the line
Ctrl + E	Move to the end of the line
Ctrl + U	Cut text from cursor to start
Ctrl + K	Cut text from cursor to end
Ctrl + Y	Paste the last cut text
Ctrl + L	Clear the terminal screen
Ctrl + R	Search command history
Tab	Autocomplete file or command
!!	Repeat the last command
!n	Run command number n from history

Bash Useful Commands:

Command	Description	Examples
alias	Create an alias for a command	alias ll='ls -la'
history	Show command history	alias ll='ls -la'
export	Set environment variables	export PATH=$PATH:/opt/bin
grep	Search text using patterns	grep "pattern" file.txt
find	Search for files in a directory	find /path -name file.txt
chmod	Change file permissions	chmod 755 script.sh
chown	Change file owner and group	chown user:group file.txt
ps	Display currently running processes	ps aux
kill	Terminate a process by PID	kill -9 12345
top	Display real-time system processes	top

Nano Shortcuts Commands:

Command	Description
Ctrl + O	Write (save) the file
Ctrl + X	Exit Nano
Ctrl + G	Display Help
Ctrl + K	Cut current line
Ctrl + U	Paste the cut line
Ctrl + W	Search for a text in the file
Ctrl + C	Show cursor position (line/column)
Alt + A	Start marking text
Ctrl + \	Find and replace text
Ctrl + _	Go to a specific line

VI Shortcuts Commands:

Vi Modes

Insert Mode: Press i to insert text.
Command Mode: Press Esc to switch to command mode.
Visual Mode: Press v to start visual selection.

Command	Description
i	Enter insert mode
Esc	Exit insert mode and return to command mode
:w	Save the file
:q	Quit
:wq	Save and quit
:q!	Quit without saving
dd	Delete the current line
yy	Copy the current line
p	Paste copied content
/text	Search for 'text'
n	Repeat the last search
u	Undo last action
Ctrl + r	Redo an undone action

Vim Shortcuts Commands:

Vim is a improved version of vi

Vim Modes

Normal Mode: For navigating and executing commands.
Insert Mode: For inserting text (i to enter).
Command-Line Mode: For running commands (: to enter).
Visual Mode: For selecting text (v to enter).

Command	Description
i	Enter insert mode
Esc	Exit insert mode and return to command mode
:w	Save the file
:q	Quit
:wq	Save and quit
:q!	Quit without saving
dd	Delete the current line
yy	Copy the current line
p	Paste copied content
/text	Search for 'text'
n	Repeat the last search
u	Undo last action
Ctrl + r	Redo an undone action
gg	Go to the beginning of the file
G	Go to the end of the file
v	Enter visual mode (to select text)

Docker Cheat Sheet

July 17, 2024 · 4 min read

Nabeel Hassan

Trainer @ DevOps Medium

Docker provides the ability to package and run an application in an isolated environment called a container. The isolation and security allows you to run many containers simultaneously on a given host. Containers are lightweight and contain everything needed to run the application, so you do not need to rely on what is currently installed on the host. You can easily share containers while you work, and be sure that everyone you share with gets the same container that works in the same way.

General Commands

Start the docker daemon

docker -d

Get help with Docker. Can also use –help on all subcommands

docker --help

Display system-wide information

docker info

Images

Docker images are a lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, system libraries and settings.

Build an Image from a Dockerfile

docker build -t [image_name]

Build an Image from a Dockerfile without the cache

docker build -t [image_name] . –no-cache

List local images

docker images

Delete an Image

docker rmi [image_name]

Remove all unused images

docker image prune

Docker Hub

Docker Hub is a service provided by Docker for finding and sharing container images with your team. Learn more and find images at Docker Hub Container Image Library | App Containerization

docker login -u [username]

Publish an image to Docker Hub

docker push [username]/[image_name]

Search Hub for an image

docker search [image_name]

Pull an image from a Docker Hub

docker pull [image_name]

Show history of Docker Image

docker history [image_name]

Container

A container is a runtime instance of a docker image. A container will always run the same, regardless of the infrastructure. Containers isolate software from its environment and ensure that it works uniformly despite differences for instance between development and staging.

Create and run a container from an image, with a custom name:

docker run --name [container_name] [image_name]

Run a container with and publish a container’s port(s) to the host.

docker run -p [host_port]:[container_port] [image_name]

Run a container in the background

docker run -d [image_name]

Start or stop an existing container:

docker start|stop [container_name] (or [container-id])

Remove a stopped container: (add flag -f to remove a running container)

docker rm [container_name]

Open a shell inside a running container:

docker exec -it [container_name] sh

Fetch and follow the logs of a container:

docker logs -f [container_name]

To inspect a running container:

docker inspect [container_name] (or [container_id])

To list currently running containers:

docker ps

List all docker containers (running and stopped):

docker ps --all

View resource usage stats:

docker container stats

Check stats for all containers:

docker stats --all

View the running processes of a container:

docker top [container_name] (or [container_id])

-- Kill/Stop a running container:

docker kill [container_name] (or [container_id])

Networking

Networking in Docker refers to the ability for containers to connect to and communicate with each other, or to non-Docker workloads. Docker Networks are used to provide complete isolation for Docker containers.

List all docker networks:

docker network ls

Create a new Network:

docker network create [network_name]

Connect a container to a network:

docker network connect [network_name] [container_name_or_id]

Disconnect a container to a network:

docker network disconnect [network_name] [container_name_or_id]

Remove a network:

docker network rm [network_name]

Inspect a network:

docker network inspect [network_name]

Docker Compose

Docker Compose is a tool for defining and running multi-container applications. It is the key to unlocking a streamlined and efficient development and deployment experience.

Build images:

docker-compose build

docker-compose ps

docker-compose up

Start containers in the background:

docker-compose up -d

Stop and remove containers, networks, images, and volumes:

docker-compose down

Stop running containers:

docker-compose stop

Restart services:

docker-compose restart

View service logs:

docker-compose logs

View logs for a specific service:

docker-compose logs [service_name]

Receive real-time events from containers:

docker-compose events

List containers:

docker-compose ps

tip

By default, Docker Compose looks for a file named docker-compose.yml in the current directory. To specify a different file, use the -f flag:

docker-compose -f [custom-compose-file.yml] up

Basic Linux Commands with Examples​

File Management​

File Permission Commands​

File Compression and Archiving Commands​

Process Management Commands​

System Information Commands​

Networking Commands​

IO Redirection Commands​

Environment Variable Commands​

User Management Commands​

Shortcuts Commands​

Bash Comman Shortcuts:​

Bash Useful Commands:​

Nano Shortcuts Commands:​

VI Shortcuts Commands:​

Vim Shortcuts Commands:​

General Commands​

Images​

Docker Hub​

Container​

Networking​

Docker Compose​