Setgid

Similar to the set user ID permission bit, there is a set group ID (SGID) permission bit. This bit allows a program to run as if it was a member of that group.

Let's look at one example:

$ ls -l /usr/bin/wall
-rwxr-sr-x 1 root tty 19024 Dec 14 11:45 /usr/bin/wall

We can see now that the permission bit is in the group permission set.

Modifying SGID

$ sudo chmod g+s myfile
$ sudo chmod 2555 myfile

The numerical representation for SGID is 2.