Linux Administration Cookbook

Other execute characters

Instead of the humble x in the execute column, it's possible to also see other characters, the most common of which are s and t.

Take a look at these permissions for the wall program:

$ ls -l /usr/bin/wall-r-xr-sr-x. 1 root tty 15344 Jun 9 2014 /usr/bin/wall

Note how the group has s set in place of an x.

This is known as the setuid and setgid bit, depending on if it's in the user or group triad, and effectively it changes the executing user's permissions to those of the owner or group, again depending on the triad. In this case, those users executing the wall command get the permissions of the tty group (allowing wall to output to all ttys).

Here, I'm using wall as the vagrant user:

$ wall There is no Hitchhikers ...