# chmod 666 — What It Means & When to Use It

> Everyone can read and write; nobody can execute. Symbolic: `rw-rw-rw-` · Dangerous — avoid on real systems.

666 gives every user read and write access, with no execute bit. Any account or process on the system can change or empty the file.

Linux uses it for device files that must be universally usable — `/dev/null` and `/dev/zero` are `crw-rw-rw-` — but for ordinary files it's rarely right.

## Permission by permission

| Who | Permissions |
|---|---|
| owner | read and write |
| group | read and write |
| others | read and write |

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

## Use it for

- Device files and similar special cases that genuinely must be writable by all.

## Avoid it for

- Config files, logs and data — anyone could tamper with them. Use `644`, or `664` with a shared group.
- Upload targets on web servers.

## FAQ

### Is 666 safer than 777?

Slightly — it can't be executed directly — but anyone can still change the contents. A script with 666 could be modified by any user and then run by someone who trusts it.

## Related modes

- [chmod 644](https://www.devkult.com/chmod/644.md): Owner can read and write; everyone else can read
- [chmod 664](https://www.devkult.com/chmod/664.md): Owner and group can read and write; others can read
- [chmod 777](https://www.devkult.com/chmod/777.md): Everyone can read, write and execute
- [chmod 600](https://www.devkult.com/chmod/600.md): Only the owner can read and write

Open the interactive page: https://www.devkult.com/chmod/666