Comment 20 for bug 624043

This may or may not relate to this bug, and may or may not be the workaround, but recently [and only recently] became a recurring issue after accepting some updates on 9.10 machines.

Musing on the source for that mysterious SIGTERM revealed duplicate up/down scripts for dhclient:

in /etc/dhcp3/dhclient-enter-hooks.d/:
-rwxr-xr-x 1 root root 1037 2008-07-27 14:35 avahi-autoipd
-rwxr-xr-x 1 root root 1037 2011-03-04 15:51 avahi-autoipd.dpkg-new

in /etc/dhcp3/dhclient-exit-hooks.d/:
-rwxr-xr-x 1 root root 1039 2008-07-27 14:35 zzz_avahi-autoipd
-rwxr-xr-x 1 root root 1039 2011-03-04 15:51 zzz_avahi-autoipd.dpkg-new

and equivalent mess in /etc/network/if-up.d/ and if-down.d/.

All files diffed identically, so assuming dpkg is at risk to keep making a mess, I removed the earlier copies and kept *.dpkg-new. Things now appear to be working and surviving a "networking restart" and various rude pokings of the dhclient.

Hope this helps someone!