Just be aware that su can also be used by root to downgrade to other users on occasion.

That can also be done by sudo:

/root>sudo -u nobody whoami
nobody

/root>
[download]

Add -i to get an interactive shell, if possible. Note that the nobody account is intentionally configured to have an invalid home directory and an invalid login shell, so you won't get an interactive shell as nobody.

/root>sudo -u nobody -i
sudo: unable to change directory to /nonexistent: No such file or dire
+ctory
sudo: unable to execute /usr/sbin/nologin: No such file or directory

/root>sudo -u alex -i

/home/alex>whoami
alex

/home/alex>exit
logout

/root>
[download]

Alexander