# chmod 660 — What It Means & When to Use It

> Owner and group can read and write; others have no access. Symbolic: `rw-rw----` · Safe when used as intended.

660 lets the owner and the group read and write, and hides the file from everyone else. It suits files that two cooperating accounts — say, an app and its worker — both need to update, but that nobody else should see.

## Permission by permission

| Who | Permissions |
|---|---|
| owner | read and write |
| group | read and write |
| others | no permissions |

Symbolic chmod argument: `u=rw,g=rw,o=`

## Use it for

- Shared data or state files between services in one group.
- Unix sockets meant for a specific group (database and app sockets often use it).

## Avoid it for

- Files only one account uses: `600` is tighter.
- Files the group should only read: `640`.

## FAQ

### 660 vs 640?

660 lets the group write; 640 lets it only read. Grant group write only when the group really modifies the file.

## Related modes

- [chmod 640](https://www.devkult.com/chmod/640.md): Owner can read and write; group can read; others have no access
- [chmod 600](https://www.devkult.com/chmod/600.md): Only the owner can read and write
- [chmod 664](https://www.devkult.com/chmod/664.md): Owner and group can read and write; others can read
- [chmod 770](https://www.devkult.com/chmod/770.md): Owner and group can do everything; everyone else has no access

Open the interactive page: https://www.devkult.com/chmod/660