Essential Linux Command Cheat Sheet: Paths, Files, Processes, and More

Question 1: How are absolute, current, parent, and home directories represented, and which command changes directories?

Absolute path: e.g., /etc/init.d Current and parent directories: ./ and ../ Home directory: ~/ Change directory command: cd Question 2: How to view current processes, exit the shell, and display the current path?

View processes: ps Exit shell: exit Show current path: pwd Question 3: How to clear the screen, terminate a command, suspend a process, view user ID, and get help for a command?

Clear screen: clear Terminate command: Ctrl+C Suspend process: Ctrl+Z (resume with fg) Show user ID: id Command help: man adduser, adduser --help, or info adduser Question 4: What does ls do and which options are common? ls lists directory contents. Common options: -a (all files), -l (long format with permissions, size, etc.)

Question 5: How to create symbolic and hard links?

Symbolic link: ln -s target source Hard link: ln target source Question 6: Commands for creating directories, files, copying files, and changing permissions?

Create directory: mkdir Create file: touch or vi Copy file: cp Change permissions: chmod (e.g., chmod u+x file, chmod 751 file)

Examples of chmod usage: chmod u+x file – add execute permission for owner chmod 751 file – set rwx for owner, r-x for group, --x for others chmod u=rwx,g=rx,o=x file chmod =r file – read for all chmod -R u+r directory – recursively add read permission for owner

Question 8: Commands to view file contents? vi filename (edit), cat filename (show all), more filename, less filename, tail filename, head filename Question 9: How to write to a file and echo a string with spaces?

Write file: vi Echo with spaces: echo hello world Question 10: Where are the terminal device and the null device located?

Terminal: /dev/tty Null device: /dev/null Question 11: Commands to move/rename files?

Move/rename: mv Question 12: Copy files and directories, with prompts?

Copy file: cp Copy recursively: cp -r (add -i for interactive prompts)

Question 13: Delete files, directories, and empty directories?

Delete file: rm Delete recursively: rm -r Remove empty directory: rmdir Question 14: Common shell wildcards and their meanings? ? – single character * – any number of characters [charset] – any single character in the set (e.g., [a-z])

Question 15: How to count lines, words, and bytes in a file?

Use wc ( -l lines, -w words, -c bytes)

Question 16: What does grep do and how to ignore case or invert match? grep searches text using patterns. Ignore case: grep -i pattern file Invert match: grep -v pattern file Question 17: Linux process states and their symbols?

Uninterruptible: D Running: R Sleeping: S Stopped/Traced: T Zombie: Z Swapped (obsolete): W Dead: X

Question 18: How to run a command in the background?

Append & to the command (e.g., mycmd &)

Question 19: Show all processes and filter by PID?

All processes: ps -ef (System V) or ps -aux (BSD) Filter by PID: ps -ef | grep pid Question 20: Command to list background jobs? jobs -l Question 21: Bring a background job to the foreground or resume a stopped job?

Foreground: fg Resume in background: bg Question 22: Terminate a process? kill with signal (e.g., kill -9 pid)

Question 23: List all supported signals? kill -l Question 24: Search for files? find [path] [conditions] [actions] Other tools: whereis, locate Question 25: Who is logged in and which terminal am I on?

Current user terminal: who am i All logged‑in users: who Question 26: Show command history? history Question 27: Disk usage and free space? df -hl Question 28: Check network connectivity? netstat Question 29: Show IP addresses and interfaces? ifconfig Question 30: View environment variables?

All: env Specific: env VAR_NAME Question 31: Customize the shell prompt?

Prompt escape sequences: \u (user), \h (host), \W (basename of cwd), \w (full cwd, ~ for home), \$ (prompt char), \# (command number), \d (date), \t (24‑h time), \T (12‑h time), \A (HH:MM), \v (bash version)

Question 32: Where does the shell look for executable files and how to modify the search path?

Use whereis with options (e.g., -b binaries, -m manuals) and which to locate commands in $PATH.

Question 33: Find the location of an executable? which command (executable only) and whereis command (binary, source, docs).

Question 34: Create an alias? alias la='ls -a' Question 35: Difference between du and df? du reports disk usage of files/directories. df reports filesystem‑level space information, including metadata.

Question 36: Brief awk overview.

Pattern‑action syntax: awk '{pattern + action}' file Example: cat /etc/passwd | awk -F ':' '{print $1"\t"$7}'

Question 37: Bind a macro or key in Bash?

Use bind (e.g., bind '"\e[24~":"date"') after obtaining the key’s escape sequence with Ctrl+V or showkey -a.

Question 38: List all available commands for a new Linux user? compgen -c Question 39: Print the current directory stack? dirs (managed with pushd / popd)

Question 40: Remove all running processes without rebooting? disown -r detaches jobs from the shell.

Question 41: Purpose of the hash builtin?

Maintains a hash table of command paths; hash displays commands and hit counts.

Question 42: Bash builtin for arithmetic? let performs integer arithmetic.

Question 43: View a large file page by page?

Pipe cat filename to more (or less).

Question 44: Which user owns the data dictionary?

It belongs to the system user SYS (and SYSEM).

Question 45: Get a brief description of an unknown command?

Use whatis command (e.g., whatis zcat).

Question 46: Check filesystem quota? repquota (requires root for other users).