What are octal permissions?

Octal permissions are a way to represent file permissions in Linux using a three-digit octal (base-8) number. Each digit corresponds to a different set of permissions for the owner, group, and others. Here's how it works:

1. Octal Representation:

   • Each permission type is represented by a number:
     • Read (r) = 4
     • Write (w) = 2
     • Execute (x) = 1
   • The permissions for each category (owner, group, others) are summed to form a single digit.

2. Permission Groups:

   • The first digit represents the owner's permissions.
   • The second digit represents the group's permissions.
   • The third digit represents the permissions for others.

3. Examples:

   • For example, if a file has the permissions rwxr-xr--:
     • Owner: rwx = 4 + 2 + 1 = 7
     • Group: r-x = 4 + 0 + 1 = 5
     • Others: r-- = 4 + 0 + 0 = 4
     • Therefore, the octal representation is 754.

4. Common Octal Permissions:

   • 777: Read, write, and execute for everyone.
   • 755: Read, write, and execute for the owner; read and execute for group and others.
   • 644: Read and write for the owner; read for group and others.
   • 600: Read and write for the owner only.

5. Using chmod:

   • You can set permissions using the octal representation with the chmod command. For example:

     chmod 755 filename

Understanding octal permissions allows for efficient management of file access in a Linux environment.