getenv
getenv check user in /etc/passwd and in NSS
User from AD is not in /etc/passwd.
root@site-dev:~# getent passwd dpatokin
dpatokin:*:60204:60204:User Surname:/home/aduser:/bin/bash
root@site-dev:~# getent -s files passwd aduser
root@site-dev:~# echo $?
2