Linux Command Line 101 : Essential Commands for Software Engineers

Summarizing the Most Used Commands and Tools for Daily Tasks in Backend Development, DevOps, and Beyond 👨‍💻

We all know that Linux and Unix based operating systems have a wide range of commands that can be difficult to remember and fully understand. Even I often forget some commands (especially when it comes to searching for files😅). I find myself repeatedly searching the web to remember the right command. So, I decided to write this article to help anyone who, like me, struggles with remembering these commands. This article aims to provide a simple guide that you can refer to whenever you need help with these commands.

I have structured this article in a way that begins by categorizing commands based on their domains. Following this categorization, we will explore a selection of highly practical use cases for each command .At the end, I have provided some cool tricks and shortcuts that can help you work more efficiently in the CLI environment. Lets Dive In 😉!

Table Of Content:

• File and Directory Operations
• Text Processing
• System Information
• Monitoring
• Process Management
• Network Operations
• User and Group Management
• Package Management
• File Compression and Archiving
• System Administration
• File Permissions and Ownership
• Input and Output Redirection
• System Startup and Shutdown
• File and Data Transfer
• Disk and Filesystem Operations
• Shell Scripting
• System Configuration
• Text Editing and Manipulation
• File Searching and Locating
• Working with Environment Variables
• Tips & Tricks

File and Directory Operations:

Manipulate files and directories, such as listing, creating, removing, copying, and moving them.

• ls : List files and directories

Ls -lash 

• cd : Change directory.

cd [directory_name]

• mkdir : Create a new directory.

mkdir [directory_name]

//Make directory wit
mkdir -m 755 new_directory

• touch : Create an empty file.

touch [file_name]

• rm : Remove files and directories.

#Simple remove
rm [directory/file_names]

#Recursive and Forced remove
rm -rf [directory_name / path to directory]

• cp : Copy files and directories.

#Simple copy
cp source-file.txt destination-file.txt

#Recursive copy
cp -R source-directory destination-directory

• mv : Move or rename files and directories.

mv [directory/file_name] [target_path]

• stat: Display file or file system status.

stat [directory/file_name]

• pwd : Print working directory.

Text Processing:

Search, manipulate, and analyze text files using tools like concatenation, searching for patterns, and text transformations.

• cat : Display the contents of a file . suitable for short files

cat [textfile]

• Less :same as cat but suitable for large files and offers more features

less [textfile]

• grep : Search for a pattern in files.

#Searches for occurrences of the pattern in file
grep pattern [file_name]

#Recursively searche over directory
grep -r pattern [directory_name]

System Information:

Retrieve information about the system’s hardware, software.

Photo by Shaine Tsou on Unsplash

• uname : Print system information . displays all system information, including the kernel name, network node hostname, kernel release, kernel version, machine hardware name, and processor architecture.

uname -a 

• Lsblk : list information about block devices, such as hard drives and storage devices

#List only disk devices and their rotational status (SSD or not).
lsblk -d -o name,rota 

• Lspci : displays information about all PCI (Peripheral Component Interconnect) devices connected to your system, including graphics cards, network adapters, sound cards, and other devices.
• Lshw : List hardware information including , memory, storage devices, network interfaces, and more
• Lscpu : Display CPU information including the architecture, vendor, model name, CPU cores, cache sizes, and other CPU-related details

Monitoring:

monitor resource utilization

Image from Grafana labs

• top : Monitor and display real-time system resource usage.
• free : Display available and used memory.

#Available and used memory in human readable format
free -h

• df : Show disk space usage of file systems.

#Shows disk usage in human readable format
df -h

• du : Estimate file and directory space usage. This command is at its best when you need to see the size of a given directory or subdirectory

#Shows directory size in a summarized and human readble format
du -sh directory_name

Process Management:

Control and manage running processes, including listing, terminating, and monitoring them.

• ps : Display running processes.

#Detailed and comprehensive view of the processes running
ps aux

• kill : Terminate a process by its process ID (PID).

#Sending SIGKILL to process 
kill -9 [PID]

• killall : Terminate processes by their name. command is used to terminate processes by their names rather than their PIDs

#Sending SIGKILL to process
killall -KILL [process_name]

• pkill : It’s like killall but It allows you to send signals to processes based on various criteria such as process names, user ownership, process attributes, and more.

#Kill pricess bt name 
pkill [process_name]

#terminate processes matching a particular pattern using regular expressions
pkill -f "pattern"

#terminate processes owned by a specific user
pkill -u [user_name]

#terminate processes in a specific process group
pkill -g [group_ID]

• pgrep : List processes based on their name or other attributes.

#Get process IDs by name 
pgrep -a [process_name]

• nice : Set the priority of a process.

#Set value from -20(highest priority) to 19 (lowest priority)
nice -n [value] [command]

• renice : Change the priority of a running process.

#Changing process niceness
renice [value] [PID]

• jobs : lists the currently running jobs or processes in the background.
• bg : move a job or process into the background.

bg [job_id]

• fg : bring a job or process back to the foreground.

fg [job_id]

Network Operations:

Configure network interfaces, troubleshoot connectivity, and communicate with other network hosts.

Photo by Jordan Harrison on Unsplash

• ifconfig : Configure and display network interfaces.
• ip : Configure and display network interfaces (more powerful than ifconfig).

ip addr show

• ping : Send ICMP echo requests to a network host.

ping [host_name/ip]

• ufw: Firewall Manager, a user-friendly interface to manage netfilter firewall rules in Linux.

#Activate the firewall
ufw enable 

#Deactivate the firewall
ufw disable

#Allow incoming traffic on a specific port or protocol.
ufw allow [port/protocol]

#Deny incoming traffic on a specific port or protocol.
ufw deny [port/protocol]

#Show the status of the firewall, including which rules are active.
ufw status

#Reset all firewall rules to default settings.
ufw reset

• traceroute : Trace the route that packets take to reach a network host.

traceroute [host_name]

• netstat : Display network connections, routing tables, and network interface statistics.

#This command provides information about active network connections,
#listening ports, routing tables, and network interface statistics.
#It also show PID.
netstat -tunap

• nslookup : Query DNS servers to retrieve domain name or IP address information.

#Retrieve information about a domain name
nslookup[domain_name]

• SSH : Secure command execution on remote server

#Create SSH key pair ( creates 2 files :1- id_rsa (your private key) and 
# 2- id_rsa.pub (your public key))
ssh-keygen -t rsa

#See SSH-related files
ls ~/.ssh

#SSH into a remote server
ssh [user_name]@[host_name / IP]

User and Group Management:

Create, modify, and manage user accounts and groups on the system.

• id : Display user and group identity information.

#Username is optional
id [user_name]

• useradd : Creates a new user account.

useradd [user_name]

• userdel : Deletes a user account.

userdel [user_name]

• groupadd : Creates a new group.

groupadd [group_name]

• groupdel : Deletes a group.

groupdel [group_name]

• passwd : Sets or changes a user's password.

passwd [user_name]

• usermod : Modifies user account properties

#To add a user to additional groups without removing from existing groups
sudo usermod -aG [group_name] [user_name]

• groupmod : Modifies group properties.

#Add a user to a group,
sudo groupmod -A [user_name] [group_name]

#Remove user from group
sudo groupmod -R [user_name] [group_name]

Package Management:

Install, update, and remove software packages on the system.

Photo by CHUTTERSNAP on Unsplash

• apt : Package handling utility for Debian-based systems.

#Update pkg list
apt update

#Upgrade installed pkgs
apt upgrade

#Install pkg
apt install [pkg_name]

#Uninstall pkg
apt remove [pkg_name]

#List installed pkgs
apt list

#Search pkg
apt search [pkg_name]

#Show pkg detail
apt show [pkg_name] 

#Remove unused dependencies
apt autoremove

#Autoremove and upgrade together
apt full-upgrade

• yum : Package manager for RPM-based systems.

#Update pkg list
yum update

#Upgrade installed pkgs
yum upgrade

#List installed pkgs
yum list

#Search pkg
yum search [pkg_name]

#show pkg detail
yum info [pkg_name]

• snaps : Package manager with easy distribution and automatic updates.

#Install a snap
snap install [snap_name]

#Remove snap
snap remove [snap_name]

#List installed snaps
snap list

#View snap info
snap info [snap_name]

#Search for snaps
snap find [search_term]

File Compression and Archiving :

Compress and archive files and directories into a single file for storage or transmission.

• tar : Archive files into a tarball.

#Create an archive (tarball) of files or directories(not compressed)
tar -cf archive.tar [file_name1] [file_name2] directory

#Compressed archive
tar -zcf archive.tar [file_name1] [file_name2] directory

#Extract the contents of an archive
tar -xvf archive.tar

• gzip : Compress files using gzip compression.

#Maximum compression level
gzip -v9 [file_name1] [file_name2]

#Decompress 
gzip -d mydoc.txt.gz

• zip : Compress files into a zip archive

#Create zip archive
zip [archive_name.zip] [file_name1] [file_name2]

#list the contents of a zip archive
zip -sf <archive_name.zip>

#Extract the content of zip archive
unzip [archive_name.zip]

System Administration:

Perform administrative tasks such as managing users, configuring system settings, and maintaining system security.

• sudo : Execute commands with superuser privileges.

#Change to root user
sudo su

• su : Switch to a different user account.

su [user_name]

• systemctl : Control system services.

#Start service
systemctl start {service_name}

#Stop service
systemctl stop {service_name}

#Restart service
systemctl restart {service_name}

#Service status
systemctl status {service_name}

• service : Control system services (legacy). Exactly like systemctl but for older versions.
• chroot : Used to change the root directory for a specific command or process, creating a restricted environment.

sudo chroot [new_root] [command]

• visudo : Used to edit the sudoers file . The sudoers file determines which users or groups are allowed to run commands with administrative privileges using sudo.

sudo visudo

File Permissions and Ownership:

Set permissions and ownership for files and directories to control access rights.

• chmod: Change file permissions.

#Add permissions
chmod +rwx [directory/file_name]

#Remove permissions
chmod -rwx [directory/file_name]

#Read, write, and execute permissions for everyone
chmod 777 [directory_name]

• chown : Change file ownership.

chown [user_name] [file_name]

• chgrp : Change group ownership.

chgrp groupname filename

• umask : Set default file permissions. used to set the default file permissions for newly created files and directories.

#Current umask value
umask

#Set umask value
umask 022

• chown : Change file ownership with superuser privileges.

sudo chown [user_name] [file_name]

Input and Output Redirection:

Redirect input and output streams between commands and files.

• | (pipe) : Redirect output of one command as input to another command.

command1 | command2

• | | : Append output to a file.

command1 || command2

• < : Redirect input from a file.
• 2>: Redirect error output to a file.
• &: Redirect both standard output and standard error.
• tee : Read from standard input and write to both standard output and files.

System Startup and Shutdown:

Manage system startup and shutdown processes, including starting and stopping services.

• shutdown : Used to schedule system shutdowns or reboots

#Shutdown the system immediately
shutdown -h now

#Reboot the system immediately
shutdown -r now

• init : Used to change the system’s runlevel or to control the init process, which is the first process started by the Linux kernel during the boot process.

init [runlevel]

#Shutdown
init 0

#Reboot
init 6

File and Data Transfer:

Transfer files between local and remote systems securely and efficiently.

Photo by Alexander Sinn on Unsplash

• sftp : Securely transfer files over SSH.(Most used and easy to use File transfer tool)

#Connect to remote server
sftp user@host

#Commands starting with l start on local server
#Local system pwd
lpwd
#Local ls
lls

#Commands without l at the begining run on remote server
#Remote pwd
pwd
#Remote ls 
ls

#Upload file to remote server 
put localFile

#Download file from remote server
get remoteFile

• wget : Retrieve files from the web using HTTP, HTTPS, or FTP.

#download url
wget [url]

• curl : Transfer data from or to a server using various protocols.

curl [url]
-X POST|GET|DELETE or ...   ->   HTTP Verb
-H                          ->   Set Header
-b "cookie1=test"           ->   Set a Cookie
-c {"cookie jar file"}      ->   Set Cookie file
-d '{"productId": 123456, "quantity": 100}'  -> Posting body with request

• ftp : Transfer files to or from a remote server using FTP.

#Connet to FTP server
ftp  [host_name/IP]

#Download file
get [file_name]

#Upload file
put [localfile] [remotefile]

#Delete file on ftp server
delete [file_name]

#Quit and disconnect from the FTP server:
quit

Disk and Filesystem Operations:

Manage disks, partitions, and filesystems, including checking disk space usage and manipulating partitions.

Photo by Denny Müller on Unsplash

• df : Show disk space usage of file systems.

#Shows disk usage in human readable format
df -h

• du : Estimate file and directory space usage. This command is at its best when you need to see the size of a given directory or subdirectory

#Shows directory size in a summarized and human readble format
du -sh directory_name

• fsck : Check and repair a filesystem.

#Automatically repair filesystem errors (if possible)
fsck -a <device>

• mkfs : Create a new filesystem.
• mount : Mount a filesystem, making it accessible and usable within the directory tree of the Linux filesystem.

mount [device] [mount_point]

• umount : Unmount a filesystem.

umount [mount_point]

• fdisk : Manipulate disk partition table.

blkid [device]

• blkid : Display block device attributes.

blkid [device]

Shell Scripting:

Write and execute scripts to automate tasks and execute sequences of commands.

• bash : Execute a Bash script.

bash [script_name.sh]

• sh : Execute a shell script . It runs the script using the default shell interpreter defined in the system.

sh [script_name.sh]

• /etc/shells : List of available shells

cat /etc/shells

System Configuration:

Configure system settings and parameters, often related to the kernel, network, or system services.

Photo by Laura Ockel on Unsplash

• sysctl : Configure kernel parameters at runtime.

#Display all kernel variables
sysctl -a

#View the current value of a kernel parameter
sysctl [parameter_name]

#Modify a kernel parameter value
sysctl -w [parameter_name]=[new_value]

• hostnamectl : Control the system hostname.

#View the current hostname
hostnamectl

#Set a new hostname
hostnamectl set-hostname [new_hostname]

• timedatectl : Control the system time and date settings.

#Current system time
timedatectl

#Set the system time zone
sudo timedatectl set-timezone [timezone]

#Manually set the system time
sudo timedatectl set-time "<date> <time>"

Text Editing and Manipulation:

Edit and modify text files using command-line text editors.

• nano : Beginner-friendly terminal-based text editor.

nano [file_name]

• vim : Improved version of vi with additional features.

vim [file_name]

File Searching and Locating:

Search for files and directories on the system based on various criteria.

• find : Search for files and directories based on various criteria.

find [path to search] -name "file_name"

• locate : Quickly find files based on a pre-built database.

locate "filename"

• updatedb : Update the file database used by locate.
• whereis : Locate the binary, source, and manual page files for a command.

whereis [command]

• grep : Searching and filtering text patterns within files or command output.

grep [options] pattern [file...]

#Recursive search in directory
grep -r "pattern" directory/

#Search in STDOUT
cat [file_name] | grep "pattern"

Working with Environment Variables:

• env: Display or set environment variables.

#List of current env vars
env

#Set env var
env VAR1=HTF

• printenv: Display the values of environment variables.
• $VARIABLE_NAME: Access the value of an environment variable.

echo $VARIABLE_NAME

• export: Set environment variables.

export [VARIABLE_NAME]=[value]

• echo: Display the value of an environment variable.

echo $VARIABLE_NAME

• unset: Remove environment variables.

unset [VARIABLE_NAME]

• envsubst: Substitute environment variables in a file.

envsubst [inputfile-name] [outputfile_name]

Tips & Tricks:

• Ctrl+a : Cursur to the line begining
• Ctrl+e : Cursor to the line end
• Ctrl+u :Delete everything before cursor
• Ctrl+r : Reverse search command history
• Ctrl+c : Sends the SIGINT signal to the current process.
• Ctrl+z : Sends the SIGTSTP signal to the current process
• Ctrl+d : Sends the SIGOUT signal to the current process
• !!(bang bang) : Repeat last cli command

!! | grep "search term"

• #! (shebang) : Changing shell
• ~ : point to home dir

~/.bash-history

• /dev/null : special file in Linux that discards any data written to it

#Discarding output
command > /dev/null

• || : Executing the next command if the previous command fails

command1 || command2

• && : Executing the next command if the previous command succeeds

command1 && command2

• & : Running a command in the background

command &

• ; : Sequentially executing multiple commands

command1 ; command2 ; command3

Thank you 🙏 for taking the time to read blog post! Your comments 💬and claps👏would be greatly appreciated as they would motivate me to continue writing and improve.

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