Essential Linux Commands: Quick Reference for Everyday Tasks

This guide compiles frequently used Linux commands, organized as numbered questions and answers.

File and Directory Operations

Locate user accounts: /etc/passwd Delete a non‑empty directory: rm -rf directory_name Show current working directory: pwd Create a directory: mkdir directory_name Display file contents: cat filename or more filename Show last 10 lines of a file: tail -n 10 filename Count lines in a file: wc -l filename Find files containing "bin" in their name under root: ll | grep bin Create multiple files (e.g., 1 to 100):

touch file{1..100}

User and Permission Management

Create a user: useradd zhangsan Set user password: passwd zhangsan123456 Delete a user: userdel username Switch user: su username Root home directory: /root Standard user home directory: /home/zhangsan Create a group and add user to it: groupadd super then usermod -g super zhangsan Change file ownership: chown root:root test1.txt Modify permissions (owner read/write/execute only):

chmod 700 directory

System Information and Control

Show current date/time: date Reboot system: reboot Shutdown immediately: halt -p shutdown now Check network connectivity: ping host Display IP configuration: ifconfig -a Find where a command is installed: whereis command Install or remove software (YUM): yum install package_name / yum remove package_name Download files:

wget URL

Shell Redirection and Piping

Standard output (1) and error (2) redirection: 1> file, 2> error.log Combine error with output: 2>&1 Pipe output of one command to another:

command1 | command2

Vi Editor Basics

Modes: command, insert, visual

Enter insert mode: press i Enter visual mode: press v Copy a line: press y Paste: press p Delete lines 3 to 15: :3,15d Save and quit: :wq Quit without saving:

:q!

File Permission Notation

rw‑xrwxrwx (777): all users can read, write, execute.

drwx------ (700): directory, owner has full rights, others none.

Miscellaneous

Help for commands: man command Difference between /bin and /sbin: /bin contains general system binaries usable by all users; /sbin holds binaries for system administration, typically requiring root.