Linux

How Unix Permissions Work

Each file/directory has 3 sets of permissions:

• Owner (the user who owns it)
• Group (other users in the same group)
• Others (everyone else)

Each permission is represented as a number:

• 4 = read (r)
• 2 = write (w)
• 1 = execute (x)
• 0 = no permission

You add them up:

• 7 = read + write + execute (rwx)
• 6 = read + write (rw-)
• 5 = read + execute (r-x)
• 0 = no permissions (---)

Meaning of 775

• Owner: 7 → rwx
• Group: 7 → rwx
• Others: 5 → r-x

So:

• Owner: full control
• Group: full control
• Others: can read and enter directory, but not write

Rule of Thumb:

• Directories → 775 (rwxrwxr-x)
• Socket files → 660 (rw-rw----)