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

Question 1: Path symbols and directory navigation

Absolute path: e.g., /etc/init.d. Current directory: ./. Parent directory: ../. Home directory: ~/. Change directory command: cd.

Question 2: Viewing processes, exiting, and current path

View current processes: ps. Exit the shell: exit. Show current working directory: pwd.

Question 3: Clearing screen, exiting commands, sleeping, user ID, and help

Clear screen: clear. Abort current command: Ctrl+C. Suspend a job (sleep): Ctrl+Z then resume with fg. Show current user ID: id. View command help: man <command> or <command> --help or info <command>.

Question 4: ls functionality and options

ls

lists directories and files. Common options: -a (show all files, including hidden) and -l (long format with permissions, size, etc.).

Question 5: Creating symbolic and hard links

Symbolic link: ln -s <source> <link>. Hard link: ln <source> <link>.

Question 6: Creating directories, files, and copying files

Create directory: mkdir <dir>. Create file: touch <file> or use editors like vi. Copy file: cp <source> <dest>. Change file permissions: chmod with symbolic (e.g., chmod u+x file) or numeric modes (e.g., chmod 751 file).

Source: https://www.cnblogs.com/hystj/p/8552757.html

Question 8: Viewing file contents

vi <file>

– edit and view cat <file> – display entire file more <file> – paginate forward less <file> – paginate forward and backward tail <file> – show last lines (optional -n) head <file> – show first lines

Question 9: Writing files and echoing strings with spaces

Write file: use vi or redirect output. Echo a string with spaces: echo hello world.

Question 10: Terminal device and null device

Terminal device file: /dev/tty. Null (black hole) device: /dev/null.

Question 11: Moving and renaming files

Move or rename: mv <source> <dest>.

Question 12: Copying directories and prompting

Copy directories recursively: cp -r <src_dir> <dest_dir>. Add prompt with -i option (e.g., cp -ri).

Question 13: Deleting files and directories

Delete file: rm <file>. Delete directory and its contents: rm -r <dir>. Remove empty directory: rmdir <dir>.

Question 14: Shell wildcard characters

?

matches a single character. * matches zero or more characters. [charset] matches any single character in the set, e.g., [a-z] or [abABC].

Question 15: Counting lines, words, and bytes

Use wc: -l lines, -w words, -c bytes.

Question 16: grep usage

Search text with regular expressions. Ignore case with -i. Show lines not matching with -v. Example: grep pattern filename or grep -v pattern filename.

Question 17: Process states in Linux

Common states: Uninterruptible (D), Running (R), Sleeping (S), Stopped/Traced (T), Zombie (Z), etc. Symbols shown by ps correspond to these states.

Question 18: Running a command in the background

Append & to the command, e.g., command &.

Question 19: Listing all processes with ps

System‑V style: ps -ef. BSD style: ps -aux. Filter by PID: ps -ef | grep <pid>.

Question 20: Viewing background jobs

List jobs: jobs -l.

Question 21: Bringing jobs to foreground/background

Foreground: fg %<job>. Resume stopped job in background: bg %<job>.

Question 22: Terminating processes

Terminate: kill [-s SIGNAL] <pid> or kill -9 <pid> for forceful kill.

Question 23: Listing all supported signals

Show signals: kill -l.

Question 24: Searching for files

General search: find <path> -name <pattern>. Locate binary: whereis <name>. Quick name search: locate <name>.

Question 25: Wildcard characters (repeated)

Same as Question 14.

Question 26: Viewing command history

Show history: history.

Question 27: Checking disk usage

Show filesystem usage: df -hl.

Question 28: Checking network connectivity

Use netstat (or ss on newer systems).

Question 29: Displaying IP addresses and interfaces

Use ifconfig (or ip addr on newer systems).

Question 30: Viewing environment variables

List all: env. Show specific: echo $HOME or env | grep VAR.

Question 31: Customizing the shell prompt

Set PS1 with escape sequences: \u (user), \h (host), \W (basename of cwd), \w (full cwd, ~ for home), \$ (prompt symbol), \d (date), \t (24‑hour time), \T (12‑hour time), etc.

Question 32: Finding executable files

Search with whereis (binary, source, manual) or which (first executable in $PATH).

Question 33: Creating command aliases

Define alias: alias la='ls -a'.

Question 34: Difference between du and df

du

reports disk usage of files/directories (user‑level). df reports filesystem‑level space allocation, including metadata.

Question 35: awk basics

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

Question 36: Binding macros or keys in Bash

Use bind to assign a key sequence to a command, e.g., bind '"\e[24~":"date"'. Obtain key sequences with Ctrl+V or showkey -a.

Question 37: Listing the directory stack

Show stack: dirs. Manipulate with pushd and popd.

Question 38: Removing all running processes without reboot

Detach all jobs: disown -r.

Question 39: Bash hash command

Displays the internal hash table of command paths and usage counts.

Question 40: Bash arithmetic

Use built‑in let for integer arithmetic, e.g., let c=a+b.

Question 41: Paging through large files

Pipe to more or less: cat file | more or cat file | less.

Question 42: Data dictionary ownership (Oracle context)

Owned by the SYS user (system‑created).

Question 43: Getting a command’s summary

Use whatis <command> to display a brief description.