Special modes: Part 1

- [Instructor] Let's take a couple of minutes…to talk about the special modes of setuid, setgid,…and the sticky bit.…When you start a process,…it starts running with your user and group permissions.…We've talked about ways to run programs as others…including using the sudo command and the su command.…However, there is a special permission…you can use called setuid.…It stands for Set User ID…and it forces a process to start as the owner of the file…regardless of who executes that file.…

To tell if a file has the setuid bit set,…you can look at its ls output.…You will see an s in the execute field…of the owner section of the permissions.…The password program is one such file…that has the setuid permission.…Since the owner of the file is root,…when this program gets executed,…it runs as the root user.…The reason the password command uses setuid root…is because it needs root privileges…to modify the etc password and/or the etc shadow files…when a user changes their password.…

The ping command is another example…of setuid root permissions.…