Legacy Linux Command Quick-Reference Index

Legacy quick-reference index

This page retains the original course order to make historical material easy to find, but it is no longer a complete learning route. Beginners should start at the unified Linux Commands entry point, which adds Shell foundations, services and logs, networking, package safety, and the integrated project.

These notes are for quickly looking up common Linux commands. They focus on completing daily file operations, viewing logs, searching text, managing processes, and using tmux in a terminal. Each category documents command purpose, meaning, basic usage, and examples.

Recommended order

1. Linux environment and Shell basics
2. Help and basics
3. Directories and paths
4. File and directory operations
5. Viewing file content
6. Searching and finding
7. Pipelines, redirection, and command composition
8. Text processing
9. Permissions and users
10. Process management
11. System information
12. Services and logs
13. Networking and ports
14. Archiving and extraction
15. Package management and safe downloads
16. Shell environment and variables
17. tmux terminal multiplexing
18. Agent service troubleshooting practice and self-check

Quick entry points

Category	Best for
Shell basics	Distinguish terminal, Shell, and Linux; understand command structure and exit status.
Help and basics	Find help, clear the screen, inspect history, and print text.
Directories and paths	Know where you are, change directory, and inspect directory structure.
File and directory operations	Create, copy, move, rename, and remove files.
Viewing file content	View text, page through it, and inspect beginnings and endings.
Searching and finding	Find files, text, and command locations.
Text processing	Sort, deduplicate, process fields, and replace text.
Pipelines and redirection	Compose commands, save output, and distinguish standard output from error output.
Permissions and users	Inspect identity, understand permissions, and apply least privilege.
Process management	Inspect, start, and stop processes in a controlled way.
System information	Inspect system, memory, disk, CPU, and load.
Services and logs	Inspect systemd services and journal data read-only.
Networking and ports	Locate issues across addresses, listening ports, DNS, TLS, and HTTP.
Archiving and extraction	Package, compress, and safely inspect archives.
Package management	Identify a package manager, verify downloads, and avoid high-risk installation pipelines.
Shell environment and variables	Manage variables, child-process environments, aliases, and Shell configuration.
tmux terminal multiplexing	Restore sessions after disconnects, split panes, and preserve an interactive terminal.
Integrated project	Complete log, resource, port, and process troubleshooting in a controlled temporary directory.

Minimal must-know commands

The following is a list of command names, not a directly pasteable script. For deletion, elevation, or process termination, return to the relevant lesson to verify target, permissions, and exit status.

pwd
ls -lah
cd
mkdir
touch
cp
mv
rm -- file_name
cat
less
tail -f
grep
find
chmod
ps
kill -TERM controlled_process_PID
df -h
tar
tmux