On one of our VPS instances, I noticed some seriously erratic behavior with the DHCP client taking a long time to renew its leases when the machine was booting up, or failing to renew at all.
It took some time before I noticed this output from dhclient:
/sbin/dhclient-script: 28: .: Can't open /usr/share/sendmail/dynamic
This didn’t make any sense as we never have and never will install sendmail on any VPS. So using apt, I was able to see that one or more of the sendmail packages had “incomplete” status (displayed as ‘c’ in aptitude if you’re using that), i.e. it was not installed but some configuration files remain. After purging those packages, dhclient had no problems whatsoever in renewing the leases.
Who knew sendmail could even trash DHCP 🙂