This is a new one for me.
One of my servers was not getting a proper dhcp lease and therefore was not viewable on the network. This particular box is headless to make matters more annoying to troubleshoot. I needed to dig out a monitor and keyboard for troubleshooting purposes on the physical machine.
It turns out that dhclient was spewing forth the following errors:
/sbin/dhclient-script: 28: .: Can’t open /usr/share/sendmail/dynamic
I not sure what sendmail has to do with dhclient but ok. Turns out that portions of sendmail that were supposedly removed were actually not. The issue with this is that my router had exhausted the entire dhcp lease range and couldn’t give out any new leases. This machine couldn’t even get on the network at this point.
Using the following apt command removed the lingering sendmail.
apt-get purge sendmail sendmail-base sendmail-bin
Then you can force a renew from the dhcp server.
dhclient -r eth0