Basic Terminal Commands: sudo, chmod, and chown

Introduction

Managing permissions and privileges is a crucial aspect of working in a Unix-based system. Three essential commands—sudo, chmod, and chown—allow users to execute tasks with elevated privileges, modify file permissions, and change ownership. This guide introduces these commands, their options, and practical examples.

The sudo Command: Execute Commands as Superuser

The sudo command temporarily grants administrative privileges to execute commands that require elevated permissions.

Syntax

sudo [command]

Common Usage

1. Execute a Command as Superuser

   sudo apt update
   

   • Runs apt update with administrative privileges.

2. Edit a Protected File

   sudo nano /etc/hosts
   

   • Opens the hosts file for editing with elevated privileges.

3. Switch to Superuser

   sudo -i
   

   • Opens a shell session with root privileges.

Note

• You may be prompted to enter your password when using sudo.

The chmod Command: Modify File Permissions

The chmod command changes the read, write, and execute permissions of a file or directory.

Syntax

chmod [options] mode file_name

Permission Basics

• r: Read (4)
• w: Write (2)
• x: Execute (1)

Common Usage

1. Grant Execute Permission

   chmod +x script.sh
   

   • Adds execute permission to script.sh.

2. Set Specific Permissions

   chmod 644 file.txt
   

   • Sets file.txt permissions to:
     • Owner: read and write
     • Group: read-only
     • Others: read-only

3. Recursively Change Permissions

   chmod -R 755 folder/
   

   • Sets folder and its contents to:
     • Owner: read, write, and execute
     • Group: read and execute
     • Others: read and execute

The chown Command: Change File Ownership

The chown command changes the owner and group of a file or directory.

Syntax

chown [options] owner[:group] file_name

Common Usage

1. Change File Owner

   sudo chown username file.txt
   

   • Changes the owner of file.txt to username.

2. Change Owner and Group

   sudo chown username:groupname file.txt
   

   • Sets username as the owner and groupname as the group for file.txt.

3. Recursively Change Ownership

   sudo chown -R username:groupname folder/
   

   • Changes the owner and group of folder and all its contents.

Practical Example

Let’s combine these commands in a typical workflow:

1. Create a Script and Set Permissions

   echo "#!/bin/bash
   echo 'Hello, World!'" > script.sh
   chmod +x script.sh
   

2. Run the Script with Elevated Privileges

   sudo ./script.sh
   

3. Change Ownership of the Script

   sudo chown username:groupname script.sh
   

Conclusion

Understanding and using sudo, chmod, and chown commands effectively ensures secure and efficient management of files, directories, and system operations. Practice these commands to build confidence in handling permissions and privileges on Unix-based systems.