Understanding File Permissions

Every file and directory in Linux has permissions controlling who can read, write, or execute it.

Reading permissions

ls -la

-rwxr-xr-- 1 student student 1234 Jan 15 10:00 script.sh

Permission structure

 -  rwx  r-x  r--
[1] [2]  [3]  [4]

1. Type: - file, d directory, l symlink
2. Owner permissions (rwx)
3. Group permissions (r-x)
4. Others permissions (r--)

Permission characters

Numeric (octal) notation

Permissions are often written as 3 digits:

755 = rwxr-xr-x
644 = rw-r--r--
600 = rw-------
777 = rwxrwxrwx

Calculate: add the values for each permission:

• rwx = 4+2+1 = 7
• r-x = 4+0+1 = 5
• r-- = 4+0+0 = 4

Common permission sets