1. Pacakage Manager

A package manager is a tool that allows users to install, remove, upgrade, configure and manage software packages on an operating system. The package manager can be a graphical application like a software center or a command lines tool like apt-get or Pacman.

What is a Package?

A package is usually referred to an application but it could be a GUI application, command line tool or a software library (required by other software programs). A package is essentially an archive file containing the binary executable, configuration file and sometimes information about the dependencies.

How does the package manager work?

The package manager is a generic concept and it’s not exclusive to Linux. You’ll often find package managers for different software or programming languages. There is a PIP package manager just for Python packages.

Almost all Linux distributions have software repositories which is a collections of software packages. Yes, there could be more than one repository. The repositories contain software packages of a different kinds.

Repositories also have metadata files that contain information about the packages such as the name of the package, version number, description of the package and the repository name etc. This is what you see if you use the apt show command in Ubuntu/Debian.

Your system’s package manager first interacts with the metadata. The package manager creates a local cache of metadata on your system. When you run the update option of the package manager (for example apt update), it updates this local cache of metadata by referring to metadata from the repository.

When you run the installation command of your package manager (for example apt install package_name), the package manager refers to this cache. If it finds the package information in the cache, it uses the internet connection to connect to the appropriate repository and downloads the package first before installing on your system.

A package may have dependencies. Meaning that it may require other packages to be installed. The package manager often takes care of the dependencies and installs it automatically along with the package you are installing.

Types of Package Managers:

• 1. DPKG – Debian Package Management System
• APT (Advanced Packaging Tool) :It is a very popular, free, powerful, and more so, useful command line package management system that is a front end for the dpkg package management system.Users of Debian or its derivatives such as Ubuntu and Linux Mint should be familiar with this package management tool.
• Aptitude Package ManagerThis is also a popular command line front-end package management tool for the Debian Linux family, it works similarly to APT . It was initially built for Debian and its derivatives but now its functionality stretches to the RHEL family.
• 2. RPM (Red Hat Package Manager)
• YUM (Yellowdog Updater, Modified)It is an open-source and popular command line package manager that works as an interface for users to RPM. You can compare it to APT under Debian Linux systems, it incorporates the common functionalities that APT has.
• 3. Pacman Package Manager – Arch Linux
• 4. Zypper Package Manager – openSUSE
• 5. Portage Package Manager – Gentoo

2. You have to install docker and Jenkins in your system from your terminal using package managers

Jenkins:

To install Jenkins you first have to install java. So this is some steps to install java:

Initially update all packages used in the below command. NOTE: I’m showing here for Ubuntu operating system.

sudo apt update

sudo apt update

Depending on which Java version you want to install, Java 8 or 11, run one of the following commands:

To install OpenJDK 8, run:

sudo apt install openjdk-8-jdk -y

sudo apt install openjdk-8-jdk -y

To install OpenJDK 11, run:

sudo apt install openjdk-11-jdk -y

sudo apt install openjdk-11-jdk -y

Add Jenkins Repository

The version of Jenkins included with the default Ubuntu packages is often behind the latest available version from the project itself. To ensure you have the latest fixes and features, use the project-maintained packages to install Jenkins.

First, add the repository key to your system:

wget -q -O - https://pkg.jenkins.io/debian-stable/jenkins.io.key |sudo gpg --dearmor -o /usr/share/keyrings/jenkins.gpg

wget -q -O - https://pkg.jenkins.io/debian-stable/jenkins.io.key |sudo gpg --dearmor -o /usr/share/keyrings/jenkins.gpg

The gpg --dearmor command is used to convert the key into a format that apt recognizes.

Next, let’s append the Debian package repository address to the server’s sources.list:

sudo sh -c 'echo deb [signed-by=/usr/share/keyrings/jenkins.gpg] http://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list'

sudo sh -c 'echo deb [signed-by=/usr/share/keyrings/jenkins.gpg] http://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list'

The [signed-by=/usr/share/keyrings/jenkins.gpg] portion of the line ensures that apt will verify files in the repository using the GPG key that you just downloaded.

After both commands have been entered, run apt update so that apt will use the new repository.

sudo apt update

sudo apt update

Finally, install Jenkins and its dependencies:

sudo apt install jenkins

sudo apt install jenkins

Now that Jenkins and its dependencies are in place, we’ll start the Jenkins server.

Starting Jenkins

now that Jenkins is installed, start it by using systemctl:

sudo systemctl start jenkins.service

sudo systemctl start jenkins.service

Since systemctl doesn’t display status output, we’ll use the status command to verify that Jenkins started successfully:

sudo systemctl status jenkins

sudo systemctl status jenkins

If everything went well, the beginning of the status output shows that the service is active and configured to start at boot:

you have completed the installation stage and can continue with configuring Jenkins.

Docker installation:

step 1: sudo apt update -y

step 2: sudo apt install docker.io -y

step 3: docker –version

step 4: systemctl status docker [ to check if docker is in the active state]

systemctl and systemd

systemctl is used to examine and control the state of the “systemd” system and service manager.

systemd is a system and service manager for Unix-like operating systems(most of the distributions, not all).

4. stop the service Jenkins and post before and after screenshots

Jenkins active status Screenshot:

Jenkins stop Screenshot :

Read about the commands systemctl vs service

The Service command looks up the script to run at the path /etc/init.d/SCRIPT. It then runs the script, passing the COMMAND unchanged as the arguments. The service command guarantees a predictable running environment by removing most of the variables and setting the root path as the current working directory.

eg: sudo service jenkins start

The systemctl command interacts with the SystemD service manager to manage the services. Contrary to the service command, it manages the services by interacting with the SystemD process instead of running the init script.

To start, stop, and restart a process, we can run the commands with systemctl .

eg: sudo systemctl start docker

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Introduction

As a DevOps engineer, mastering Linux is non-negotiable. Whether you’re deploying microservices, debugging performance issues, managing cloud infrastructure, or building CI/CD pipelines, Linux commands are at the core of your workflow. This guide walks you through 35 essential Linux commands, each with real-world use cases tailored for DevOps.

File & Directory Operations

1. ls – List files and directories.
   • ls -lah shows file sizes and permissions.
2. cd – Change directories.
   • Navigate efficiently in scripts: cd /var/www/html.
3. pwd – Print working directory.
   • Useful for debugging scripts.
4. mkdir – Create directories.
   • Example: mkdir -p /opt/myapp/logs creates nested folders.
5. touch – Create empty files.
   • Used to create .env or placeholder files in pipelines.
6. rm – Remove files and directories.
   • Caution: rm -rf /some/path can be destructive. Automate cleanup jobs.
7. cp – Copy files and directories.
   • Example: cp config.yaml config.yaml.bak before updates.
8. mv – Move or rename files.
   • Use in deployment steps: mv new.html index.html
9. find – Search for files.
   • find /var/log -name "*.log" to identify large log files.
10. du – Estimate file space usage.
    • du -sh * shows space used by directories.

File Viewing & Manipulation

11. cat – View file contents.
    • Combine with grep for quick searches.
12. less / more – Page through text.
    • less /var/log/syslog to view logs comfortably.
13. head / tail – View the start or end of files.
    • tail -f /var/log/nginx/access.log for live logs.
14. grep – Search text with patterns.
    • Example: grep "ERROR" /var/log/app.log
15. awk – Pattern scanning and data extraction.
    • Real use: awk -F":" '{ print $1 }' /etc/passwd to list usernames.
16. sed – Stream editor for modifying files.
    • Replace text in files: sed -i 's/foo/bar/g' config.txt
17. cut – Extract fields from text.
    • cut -d':' -f1 /etc/passwd
18. sort – Sort lines in text files.
    • Useful in processing pipeline logs or output.
19. uniq – Filter out repeated lines.
    • sort data.txt | uniq -c shows duplicates.

Permissions & Ownership

20. chmod – Change file permissions.
    • chmod 755 script.sh makes it executable.
21. chown – Change file owner and group.
    • chown www-data:www-data /var/www/html -R
22. umask – Set default permissions.
    • Often set in init scripts.
23. stat – Display detailed file info.
    • Helps in debugging file access issues.

Process & Resource Management

24. ps – Display current processes.
    • ps aux | grep nginx to locate specific services.
25. top / htop – Monitor system resource usage.
    • htop is interactive and user-friendly.
26. kill / killall – Terminate processes.
    • kill -9 <PID> to forcefully stop rogue processes.
27. nice / renice – Set process priority.
    • Adjust priority for resource-hungry tasks.
28. lsof – List open files.
    • Debug file locks: lsof | grep deleted
29. strace – Trace system calls.
    • Debug startup issues: strace ./myapp

Networking & Troubleshooting

30. curl – Transfer data to/from a server.
    • Test APIs: curl -X POST -d '{}' https://api.example.com
31. wget – Non-interactive file download.
    • wget https://downloads.example.com/tool.sh
32. netstat / ss – Network statistics.
    • ss -tulnp shows listening ports.
33. tcpdump – Capture network traffic.
    • Debug latency: tcpdump -i eth0 port 80
34. ping / traceroute – Network connectivity.
    • Identify broken routes or DNS issues.

Automation & Scripting

35. xargs – Build and execute commands from input.
    • Bulk operations: cat urls.txt | xargs wget

Real DevOps Use Case Highlights:

• Using awk in CI/CD: Extract version info from files and pass it to Docker.
• lsof to troubleshoot: Find services holding deleted files and causing disk bloat.
• sed in automation: Replace environment variables during deployment.
• tail -f in monitoring: View live logs in Kubernetes pods.
• xargs for batch tasks: Automate bulk log rotation or file downloads.

Conclusion

Mastering these 35 Linux commands will not only boost your productivity but also help you troubleshoot and automate your infrastructure with confidence. Bookmark this list and start integrating these commands into your daily workflow. Want more DevOps content? Follow me on LinkedIn and stay tuned for upcoming posts on Ansible, Docker, Kubernetes, and Terraform!

The post 35 Must-Know Linux Commands Every DevOps Engineer Should Master (with Real DevOps Use Cases) appeared first on abdulrahmanuk.com.

1. ls – The most frequently used command in Linux to list directories
2. pwd – Print working directory command in Linux
3. cd – Linux command to navigate through directories
4. mkdir – Command used to create directories in Linux
5. mv – Move or rename files in Linux
6. cp – Similar usage as mv but for copying files in Linux
7. rm – Delete files or directories
8. touch – Create blank/empty files
9. ln – Create symbolic links (shortcuts) to other files
10. cat – Display file contents on the terminal
11. clear – Clear the terminal display
12. echo – Print any text that follows the command
13. less – Linux command to display paged outputs in the terminal
14. man – Access manual pages for all Linux commands
15. uname – Linux command to get basic information about the OS
16. whoami – Get the active username
17. tar – Command to extract and compress files in Linux
18. grep – Search for a string within an output
19. head – Return the specified number of lines from the top
20. tail – Return the specified number of lines from the bottom
21. diff – Find the difference between two files
22. cmp – Allows you to check if two files are identical
23. comm – Combines the functionality of diff and cmp
24. sort – Linux command to sort the content of a file while outputting
25. export – Export environment variables in Linux
26. zip – Zip files in Linux
27. unzip – Unzip files in Linux
28. ssh – Secure Shell command in Linux
29. service – Linux command to start and stop services
30. ps – Display active processes
31. kill and killall – Kill active processes by process ID or name
32. df – Display disk filesystem information
33. mount – Mount file systems in Linux
34. chmod – Command to change file permissions
35. chown – Command for granting ownership of files or folders
36. ifconfig – Display network interfaces and IP addresses
37. traceroute – Trace all the network hops to reach the destination
38. wget – Direct download files from the internet
39. ufw – Firewall command
40. iptables – Base firewall for all other firewall utilities to interface with
41. apt, pacman, yum, rpm – Package managers depending on the distro
42. sudo – Command to escalate privileges in Linux
43. cal – View a command-line calendar
44. alias – Create custom shortcuts for your regularly used commands
45. dd – Majorly used for creating bootable USB sticks
46. whereis – Locate the binary, source, and manual pages for a command
47. whatis – Find what a command is used for
48. top – View active processes live with their system usage
49. useradd and usermod – Add new user or change existing users data
50. passwd – Create or update passwords for existing users

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Install VIM on Ubuntu Linux
sudo apt install vim

Verify installation
vim – -version

Edit file with VIM
vim filename

Switch to insert mode
press i

Switch back to command mode
press esc

Save and exist from the file
:wq!

Exit without saving(force exit)
:q!

Undo changes
press u

Redo changes
ctrl+r

Move cursor at first line of the file
gg

Move cursor at last line of the file
G

Copy line
yy

Copy n lines
n yy

Paste
p

Delete line
dd

Delete n lines
n dd

Set line numbers in the file
:se nu

To replace all the matching word in the file
:s/searchword/replaceword/g

To search word in the file
:/searchword

#aws #linux #devops #cloud #learner

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