pam_motd stalls logins

[Kees Cook]

Since pam_motd runs everything in /etc/update-motd.d, it is trivial to stall user logins. Currently the default ubuntu instance will check for package updates (which can be extremely IO intensive) or will go out to the network to check for devel releases (which can stall when lacking a network, etc). This blocks ssh and login logins until the processes finish.

This should be removed and put back to an asynchronous system. A single daily cron job would be sufficient, or pam_motd should fork the motd-update instead of being blocked by it. Stalling for 30 seconds on DNS failure is not acceptable just to have precisely accurate motd contents.

ProblemType: Bug
Architecture: amd64
Date: Wed Mar 3 14:45:16 2010
DistroRelease: Ubuntu 10.04
Package: libpam-modules 1.1.1-2ubuntu1
ProcEnviron:
 LANGUAGE=en_US.UTF-8
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.32-14.20-generic
SourcePackage: pam
Uname: Linux 2.6.32-14-generic x86_64

[Bryce Harrington (bryce)]

I ran into this too with ubuntu checking for distro updates on each ssh login (requiring network activity). Disabling that made sshing go quick again. A general purpose solution to this in pam would help prevent future regressions.

[Kees Cook (kees)]

This is arguably an update-notifier bug instead of a pam bug (i.e. update-notifier should not put anything in update-motd that takes long to run).