[Dovecot] Dovecot dies with PAM error?

[Jason Walton]

Just setup a new server on the weekend with Ubuntu 8.10 beta, and Dovecot
1.1.4. Every now and then, the IMAP server dies, and won't let users
authenticate. It happens about once or twice a day. In /var/log/mail.log,
you can see dovecot complaining about critial errors:

Oct 21 14:46:16 tachikoma dovecot: imap-login: Login: user=<jason>,
method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, TLS
Oct 21 14:46:16 tachikoma dovecot: IMAP(jason): Disconnected: Logged out
bytes=769/9124
Oct 21 14:47:15 tachikoma dovecot: auth-worker(default):
pam(jason,127.0.0.1): pam_start() failed: Critical error - immediate abort
Oct 21 14:47:17 tachikoma dovecot: imap-login: Disconnected (auth failed, 1
attempts): user=<jason>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, TLS

If I have a look at /var/log/auth.log, I see:

Oct 21 14:47:15 tachikoma dovecot-auth: PAM _pam_init_handlers: error
reading /etc/pam.d/dovecot
Oct 21 14:47:15 tachikoma dovecot-auth: PAM _pam_init_handlers: [Critical
error - immediate abort]
Oct 21 14:47:15 tachikoma dovecot-auth: PAM error reading PAM configuration
file
Oct 21 14:47:15 tachikoma dovecot-auth: PAM pam_start: failed to initialize
handlers

This sounds ominous. If I try to cat /etc/pam.d/dovecot, though, the file
is obviously there:

jason at tachikoma:/var/log$ cat /etc/pam.d/dovecot
#%PAM-1.0
@include common-auth
@include common-account
@include common-session

And restarting dovecot seems to fix the problem. Dovecot WAS running just
fine, servicing mail all day long, and then suddenly it won't read the PAM
config file, and then it won't let anyone log in until I log in and kill
it. Any ideas?

My IMAP client is either Thunderbird or Roundcube, if that's relevant.