Linux commands, Bash scripts, and the notes I come back to.

This is the Linux and Bash side of my Java/Spring Boot backend work: working with files, running an application, reading its logs, and automating repeated tasks. I started it during my Operating Systems lab at UBIT, University of Karachi, and keep the useful notes and scripts here for revision.

Recorded work: 8 Linux chapters · 4 Bash chapters · 12 Bash practice scripts

Learning map  ·  Practical work  ·  Use the lab  ·  Connected labs

Learning map

The Linux and Bash topics I want for backend development. Linked topics open recorded notes, exercises, or project code. Plain text is coverage still to add.

01 · Files, paths, and permissions

• Navigation and paths — pwd, ls, cd, absolute and relative paths.
• Files and directories — mkdir, touch, file, stat, tree.
• Copying, moving, and deleting — source and destination paths, overwrites, and practice copies.
• Permissions and ownership — rwx, chmod, chown, chgrp, id, umask.
• Users, groups, service accounts, and when sudo is needed.
• Symbolic links and resolved paths — ln -s and readlink in the release-switching code.
• Archives and disk space — tar, zip, unzip, df, du.

02 · Logs and text processing

• Reading files and following logs — cat, less, head, tail.
• Searching text and finding files — grep, find, literal text, and patterns.
• Text processing — wc, cut, sort, uniq, tr, basic sed and awk.
• Pipes and redirection — stdin, stdout, stderr, |, >, >>, 2>, tee.
• Service logs and journal filters — journalctl.

03 · Processes and the Java runtime

• Process inspection — ps, pgrep, top, process IDs, and resource use.
• Foreground and background jobs — jobs, fg, bg, &.
• Signals and graceful termination — kill, SIGTERM, and SIGKILL.
• Environment variables — export, printenv, PATH, JAVA_HOME, and inheritance.
• Packages and JDK selection — apt, command -v, java -version, javac -version.
• Running an executable JAR — java -jar, arguments, and process exit status.

04 · Networking and remote access

• HTTP requests — curl, headers, response bodies, status codes, timeouts, and failed requests.
• Listening ports and binding addresses — ss, localhost, and port conflicts.
• Basic connectivity and name resolution — ping, hostname, DNS, and hostnames.
• SSH access — keys, host verification, and ~/.ssh/config.
• File transfer — scp and basic rsync.

05 · Bash fundamentals

• Shell and script basics — shebangs, execution order, working directories, and executable permissions.
• Variables and expansion — quoting, ${name}, $(command), arithmetic, splitting, and globbing.
• Input and output — IFS= read -r, printf, fixed formats, and failed reads.
• Operators and exit statuses — numeric and string tests, $?, &&, ||.
• Conditions and menus — if, else, case.
• Loops — for, while, break, continue.
• Arrays — indexed and associative arrays, iteration, lookup, and "${items[@]}".
• Arguments and defaults — $1, $#, "$@", shift, ${name:-default}, and usage messages.
• Functions and scope — parameters, local, return statuses, and reusable operations.

06 · Bash reliability and debugging

• Input validation — numeric formats, decimal conversion, ranges, and retry loops.
• Syntax checks and tracing — bash -n and bash -x.
• Static analysis and edge cases — ShellCheck, invalid input, EOF, whitespace, and duplicates.
• Failure handling — explicit status checks, exit, stderr, set -e, set -u, pipefail, and their limits.
• Cleanup — trap, temporary files, and mktemp.
• Repeatable runs — checking dependencies, guarding file changes, and handling existing output.

07 · Practical backend workflows

• Build and test a Java project with its Maven Wrapper.
• Run a Spring Boot JAR outside the IDE with the intended profile and environment.
• Test an API and write a health check with a clear HTTP success condition.
• Diagnose startup failures, occupied ports, and database connection errors.
• Deploy and recover a Java service — versioned releases, health and version checks, and rollback.
• Run Java under systemd — service configuration and restart behaviour.
• Write a build/test/run helper and reuse its build and test steps in CI.
• Archive sample configuration and logs, restore them elsewhere, and verify the contents.

Docker and Compose come with a later application exercise. Deep administration, advanced networking, Kubernetes, Terraform, and Ansible sit outside this lab's current scope.

Practical work

Applied · DeployLatch

For my OS project, I built a Bash tool that deploys a Java service on Ubuntu and verifies its health and version. I tested a working update and recovery from a failed one. It made one distinction clear: a running process can still be unhealthy or running the wrong release.

Deployment script · Update and rollback demo

Browse the practice scripts and their expected behaviour →

Using the lab

Ubuntu · Bash · Git · VS Code

Learn a topic, try it, change the input, check the result, and commit the useful part. Short notes and corrections stay with the code so I can return to them later.

Setup and first run

Use a Linux terminal with Bash and Git installed. Ubuntu in WSL or a VM works for the exercises.

git clone https://github.com/codewithmahad/LINUX_LAB.git
cd LINUX_LAB
bash learning/bash-scripting/01-shell-and-script-basics/hello.sh

The greeting is Hello From Bash. Use bash -n path/to/script.sh to check a script's syntax without running it.

Notes and chapter examples live in learning/; standalone exercises in practice/; illustrations and their credits in assets/.

References

• Bash and command options: GNU Bash manual, local man pages, command --help, and Bash's help builtin.
• Spring Boot: Running an application · External configuration.
• Application command reference: Build, run, and inspect a separate Spring Boot project.
• Builds and HTTP: Maven Wrapper · curl manual.
• Services and logs: systemctl · journalctl.

Found a mistake? Open an issue with the file, command, and result.

How the labs fit together

This lab keeps my Linux and Bash coursework: files, processes, logs, and scripts. My main programming practice is in the other three labs: Java for the language, DSA for problem solving, and SQL for queries and relational design.

Outside this coursework, I keep my coding practice here.

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