DevToolsmith

Chmod 660

chmod 660 sets the permissions to rw-rw----: it lets the owner and group read and write, and others nothing. Here is exactly what that allows on files and directories, when to use it, and the commands to apply it.

Runs 100% in your browser — nothing is uploaded

ClassreadwriteexecuteValue
owner6
group6
others0
Common:
$ chmod 660 file.sh
$ chmod u=rw,g=rw,o= file.sh
  • • The owner can read and write.
  • • The group can read and write.
  • • Everyone else can do nothing.

What chmod 660 means

WhoDigitLettersOn a fileOn a directory
owner 6 rw- Can read and modify Can list files (write has no effect without execute)
group 6 rw- Can read and modify Can list files (write has no effect without execute)
others 0 --- No access No access

Each digit is the sum of read (4), write (2) and execute (1). In ls -l output it looks like this: 

$ ls -l
-rw-rw----  1 alice  staff  1834 Oct 21 10:30 example.txt
  • The owner can read and write.
  • The group can read and write.
  • Everyone else can do nothing.

When to use 660

  • Sockets and logs shared with a group
  • Database files
  • Serial devices like /dev/ttyUSB0

660 is common for resources that a service and one group share, like /run/docker.sock (group docker) or serial devices (group dialout). Adding a user to that group, rather than loosening the mode, is the right way to grant access.

660 is also the default mode for new files, with umask 007.

Is chmod 660 safe?

Yes. Nobody outside the owner and group can access it at all (except root).

Commands

# One file
chmod 660 file

# Same thing in symbolic form
chmod u=rw,g=rw,o= file

# Every file under a tree (leaves directories alone)
find /path/to/dir -type f -exec chmod 660 {} +

# Check the result
stat -c '%a %A %n' file    # Linux
stat -f '%Lp %Sp %N' file  # macOS

Avoid chmod -R 660 on a whole tree: it gives files and directories the same mode. The find form above changes only files.

Compare with similar modes

ModeSymbolicDifference
666 rw-rw-rw- Lets everyone read and write, with no execute permission
664 rw-rw-r-- Lets the owner and group read and write, and others only read
640 rw-r----- Lets the owner read and write, the group read, and others nothing
600 rw------- Lets only the owner read and write

Other chmod values

777 · 775 · 770 · 755 · 751 · 750 · 744 · 711 · 700 · 666 · 664 · 644 · 640 · 600 · 555 · 500 · 444 · 400 · 000 · 1777 · 2775 · 4755

Need a different combination? Use the Chmod Calculator.

Sources

Spotted a mistake? Email hello@devtoolsmith.com and we’ll fix it.

Frequently asked questions

What does chmod 660 mean?

chmod 660 sets the permissions to rw-rw----. The owner can read and write. The group can read and write. Everyone else can do nothing.

Is chmod 660 safe?

Yes. Nobody outside the owner and group can access it at all (except root).