Chmod 620 Explained
Chmod 620: owner can read and write, group can only write, others have no access. Used for log files and TTY devices.
Permission
620
rw--w----
chmod 620 filename
Permission Breakdown
| Role | Read (4) | Write (2) | Execute (1) | Octal | Meaning |
|---|---|---|---|---|---|
| Owner | r | w | - | 6 | read, write |
| Group | - | w | - | 2 | write |
| Others | - | - | - | 0 | no permissions |
Visual Permission Grid
Detailed Explanation
The permission 620 gives the owner read-write access, the group write-only access, and blocks others entirely.
Octal breakdown:
- 6 (Owner): read (4) + write (2) = read and write
- 2 (Group): write (2) only
- 0 (Others): no access
In symbolic notation this is rw--w----. The owner can read and write the file. Group members can only write to it (they cannot read its contents). Others have no access.
This is actually the standard permission for terminal devices (TTY) on many Unix systems. The terminal is owned by the logged-in user (who can read input and write output), while the tty group has write access (allowing programs like write and wall to send messages to the terminal). This permission is also useful for log files where a group of processes needs to write log entries but should not read logs written by other processes.
Use Case
The standard permission for TTY devices on Unix systems. Also used for log files where the writing group should not be able to read entries from other writers.