How is the 'chmod' command used to change file permissions?

The chmod command is used to change the file permissions in Unix-like operating systems. It allows you to specify who can read, write, or execute a file. Permissions can be set using either symbolic notation or octal notation.

1. Symbolic Notation:

In symbolic notation, you specify the user category and the permissions you want to add or remove.

• User Categories:

  • u: User (owner)
  • g: Group
  • o: Others
  • a: All (user, group, and others)

• Permissions:

  • r: Read
  • w: Write
  • x: Execute

Example:

To add execute permission for the user (owner) on a file named script.sh:

chmod u+x script.sh

To remove write permission for others:

chmod o-w script.sh

2. Octal Notation:

In octal notation, you represent permissions with numbers:

• 4: Read
• 2: Write
• 1: Execute
• 0: No permission

You sum the values for each user category.

Example:

To set read and write permissions for the user, and read permission for the group and others on a file named file.txt:

chmod 644 file.txt

This means:

• User: 6 (4 + 2 = read + write)
• Group: 4 (read)
• Others: 4 (read)

Summary:

You can use chmod with either symbolic or octal notation to modify file permissions based on your needs. Always ensure you understand the permissions you are setting to maintain proper security.