What is the 'chmod' command?

The chmod command in Linux is used to change the file permissions of a file or directory. The name stands for "change mode," and it allows users to specify who can read, write, or execute a file.

Syntax

The basic syntax of the chmod command is:

chmod [options] mode file

Modes

Permissions can be set using two notations:

1. Symbolic Notation: Uses letters to represent permissions.

   • r: Read
   • w: Write
   • x: Execute
   • u: User (owner)
   • g: Group
   • o: Others
   • a: All (user, group, and others)

   Example:

   chmod u+x file.txt  # Adds execute permission for the owner
   chmod go-w file.txt  # Removes write permission for group and others

2. Octal Notation: Uses numbers to represent permissions.

   • 4: Read
   • 2: Write
   • 1: Execute

   The permissions are combined by adding the values. For example, 7 (4+2+1) gives read, write, and execute permissions.

   Example:

   chmod 755 file.txt  # Sets read, write, execute for owner; read and execute for group and others

Usage

The chmod command is essential for managing file security and access control in a Linux environment, allowing users to specify who can perform actions on files and directories.