What is the chmod command?

The chmod command in Unix-like systems is used to change the file permissions of a file or directory. It stands for "change mode." With chmod, you can specify who can read, write, or execute a file.

Basic Syntax

chmod [options] mode file

Common Options

• + : Adds a permission
• - : Removes a permission
• = : Sets the permission and overrides existing ones

Modes

Permissions can be set using:

• Symbolic notation:
  • u : user (owner)
  • g : group
  • o : others
  • r : read
  • w : write
  • x : execute

Example:

chmod u+x file.txt  # Adds execute permission for the user

• Octal notation:
  • 4 : read
  • 2 : write
  • 1 : execute

Example:

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

Example Command

To make a script executable:

chmod +x script.sh

This command adds execute permission to the script.sh file.