1. ls Command

Description

ls Command Function: List directory contents (displays the list of files and subdirectories in the current or specified directory)

In the terminal of Ubuntu (or other Linux distributions), the ls command is used to list files and subdirectories within a directory (folder). If no parameters are provided after the command, it displays non-hidden files and folders in the current directory by default:

ls

In Linux, hidden files (files or directories starting with .) are not displayed by default. If you need to see all files (including hidden files), add the -a parameter:

ls -a

If you need detailed information (including permissions, owner, size, modification time, etc.), add -l:

ls -l

A common combination is -a and -l (the order can vary):

ls -al
# or
ls -la

Files starting with . are hidden files. For example, .cache.

Common ls -l output explanation (columns from left to right):

File Type and Permissions	Links	Owner	Group	File Size (bytes)	Last Modified Time	File/Directory Name
drwxr-xr-x	2	root	root	4096	Dec 9 10:41	file/directory name

• First column: File type and permissions. The first character represents the type:
  • d: directory
  • -: regular file
  • l: symbolic link
  • p: named pipe
  • b: block device
  • c: character device
  • s: socket
• Next 9 characters: Permission indicators (in order: owner, group, and other users' read r/write w/execute x permissions)
• Second column: Number of hard links
  • For regular files, this is the number of hard links to the file
  • For directories, this is the number of subdirectories (including itself and parent directory)
• Third/Fourth columns: Owner, Group
• Fifth column: File size (in bytes)
• Sixth column: Last modification time
• Last column: File or directory name

. represents the current directory, .. represents the parent directory

Common parameter descriptions:

• -a Display all files, including hidden files
• -l Use long format to display detailed information
• -t Sort by modification time
• -s Display file size (in blocks)

2. cd Command

Description

cd Command Function: Change the current working directory

Usage is simple: cd <directory path>, switches the current Shell to the target directory.

• Go to the parent directory:

cd ..

• Go into the TaishanPi-3-Linux subdirectory:

cd TaishanPi-3-Linux/

Tip: After entering the first few letters of a directory name, press Tab key to auto-complete the file or directory name.

3. pwd Command

Description

pwd Command Function: Display the absolute path of the current working directory

Executing pwd displays the full path of the current directory (starting from root /).

4. mkdir Command

Description

mkdir Command Function: Create a new directory (folder)

• Single directory

mkdir test

• To create multiple levels of directories (e.g., test/test1), it is recommended to use the -p parameter, which creates both parent and child directories at once:

mkdir -p test/test1

5. rmdir Command

Description

rmdir Command Function: Remove an empty directory

rmdir can only delete empty directories. If the directory is not empty, use rm -r

In practice, rm -r is generally used to delete non-empty directories.

6. rm Command

Description

rm Command Function: Remove files or directories

• Remove a file:

rm file.txt

• To remove a directory (including contents), add -r (recursive):

rm -r testdir

• Force removal without prompt:

rm -rf testdir

• Ask for confirmation before each deletion (interactive mode):

rm -ri testdir

Once deleted, recovery is not easy. Be careful with this operation!

7. touch Command

Description

touch Command Function: Create an empty file or modify the timestamp of an existing file

• Create a new empty file:

touch filename.txt

• If the file already exists, touch will modify its modification time without changing the file content.

8. clear Command

Description

clear Command Function: Clear the terminal display content (but does not delete command history)

After executing clear, the terminal window display is cleared, but the history can still be retrieved using the up arrow.

9. reset Command

Description

reset Command Function: Reinitialize the terminal

reset reinitializes terminal settings, restoring display and input, similar to restarting the terminal. It clears the current screen display and historical content.

10. cp Command

Description

cp Command Function: Copy files or directories

• Copy a file:

cp source_file target_file

• When copying a directory, add the -r parameter:

cp -r source_dir target_dir

11. mv Command

Description

mv Command Function: Move (cut) files or directories, or rename files/directories

• Move files/directories:

mv source_file target_directory/

• Rename a file or directory:

mv old_name new_name

12. ifconfig Command

Description

ifconfig Command Function: Display and configure network interfaces (it is recommended to use ip a on newer systems)

The ifconfig utility is used to display or configure network interfaces. Most modern Linux distributions recommend using the ip command instead:

ifconfig
# or
ip a

If ifconfig is not installed, you can use sudo apt update && sudo apt install -y net-tools to install it.

13. cat Command

Description

cat Command Function: Concatenate and display file contents

Commonly used to quickly view the contents of a text file:

cat filename

For longer files, it is recommended to use less or more for paginated viewing.

14. reboot Command

Description

reboot Command Function: Restart the computer

Executing this will restart immediately. Sometimes superuser permissions are required:

sudo reboot

15. poweroff Command

Description

poweroff Command Function: Shut down the computer

Executing this will begin the shutdown process immediately. Superuser permissions are also often required:

sudo poweroff