[Dovecot] /etc/pam.d/dovecot missing? during high load

[Timo Sirainen]

On 4.3.2011, at 22.31, Douglas Mortensen wrote:

> This morning on our newly built server, the following was logged twice:
> auth: Error: pam(username,127.0.0.1): pam_authenticate() failed: Authentication failure (/etc/pam.d/dovecot missing?)
> 
> This also happened to be during a time of 100+ imap-login processes, where we were seeing:
> master: Warning: service(imap-login): process_limit reached, client connections are being dropped

This should be irrelevant. If this error goes away, do you still get that pam failure?

> In looking at pam documentation, it is my understanding that when a service (dovecot) does not have its own file existing under /etc/pam.d, then pam will instead use the settings from /etc/pam.d/others as defaults.

It does? I don't know. It suggests checking pam.d/dovecot file, because that has been the most common reason why it hasn't worked for some people. Maybe they didn't have the others file either.

> This seems logical to me, and would explain why things have been working fairly well with no errors regarding pam (other than the 2 logged this morning). However, what this does not explain, is why dovecot auth logged about the file missing at all.

It logged it only as a guess.

> I can only guess that it was related to logins being dropped due to high load, and was incorrectly logged??

The reason for the authentication failure could be anything. Dovecot doesn't know, because PAM doesn't tell. PAM has its own (crappy) logging, maybe it has something?

> For reference, my current /etc/pam.d/dovecot is:
> auth    required        pam_unix.so nullok
> account required        pam_unix.so

So /etc/shadow.. High load shouldn't really affect that.

In any case, PAM gave Dovecot authentication failure, and there's not much I can do to guess reasons why that happened. Either PAM logged a more specific error message, or it didn't. You could always try not using PAM at all, then you'll get Dovecot's own awesome error logging that tells exactly what goes wrong.