su: Permission denied despite correct password

Question

In my new Gentoo installation, su doesn't work as my non-root user: After entering the correct password I get the message "su: Permission denied". What could be causing this? I have already tried reinstalling the package containng /bin/su.

EDIT: sudo works.

Answer 1

There could be many problems. Check some of these items, using the hypothetical user, erik:

1. Is erik a member of the wheel group (groups)?
2. Are you providing the root password? (And not the password for erik)
3. Does /bin/su have these privileges: rwsr-xr-x (Is it setuid root? ls -la /bin/su)
4. Can you log in as root via the console?
5. Have you looked at the logs for a clue in an error message?
6. Have you turned on grsecurity in the kernel?
7. Did it ever work? If so, when did it break?
8. What happens if erik does a sudo su -?

Answer 2

There could be many reasons. It's very likely that the reason appears in the system logs. Look in /var/log for files that got modified at the time of an su attempt (the file name depends on your syslog configuration). If you have trouble interpreting log entries, copy-paste them into your question.