[Dovecot] OT: NIS Authentication

Jeff Graves jeff at image-src.com
Fri Aug 11 22:28:00 EEST 2006

Ran into a major issue with my setup overnight:

We have a Win2K AD domain running SFU with a master and 1 slave NIS
server. Our mail server is a FC1 box that runs dovecot and a
MailScanner/sendmail config. The mail server is configured as a NIS
client. The problem is that we lost power overnight and all of the
boxes shutdown after the UPS's ran out of battery. After the power
came back on, all of the boxes automatically rebooted. The problem
is that our mail server is somewhat faster than the rest of the
servers. It booted up before the master or slave NIS servers were up
and running. Since the mail server uses a PAM NIS authentication
scheme, it knows nothing about our users unless it connects to a NIS
server. So, this morning users were getting "unknown username" type
errors with outlook. Furthermore, the mail logs show that sendmail
was rejecting mail with "unknown user" errors. It wasn't until we
rebooted the mail server and it was able to reconnect to the NIS
servers that mail resumed being received and users could access it.
It seems like a fundamental problem with our setup. Since I'll
eventually be updating the box to a newer OS and configuration, I
need to plug this hole somehow without changing the authentication
scheme. Furthermore, I'm concerned that if the master or slave went
down while the mail server was still up, we'd see similar results.
I'm thinking of one of two options to fix this but wanted to run it
by everyone to see if there was a better way:

1) Configure the boot loader to wait 5 minutes before loading the OS
(it uses GRUB so I'll set it display the OS menu screen for 5
minutes and then boot). Then if I'm doing maintenance to the box I
can just hit enter to boot immediately and hopefully the 5 minute
delay will allow the other boxes to boot after a power outage. This
won't cover me if it's not a power outage (Eg. The master or slave

2) Configure the mail server as an NIS slave. I'm thinking that this
will basically "copy" the user info (username, password, homedir,
etc.) on a schedule and store it locally on the mail server (is this
how it works?). This covers both issues - power outage and a server
dying. But I've read about problems getting password sync to happen
quickly. I'd ideally like it to happen immediately (without any
manual intervention) but I don't think this is possible.


Jeff Graves, MCSA
Customer Support Engineer
Image Source, Inc.
10 Mill Street
Bellingham, MA 02019

508.966.5200 - Phone
508.966.5170 - Fax
jeff at image-src.com - Email

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