Comment 27 for bug 1312836

I think I found the culprit...

my /etc/network/interfaces file contains lines like:

auto em0
iface em0 inet manual

auto eth0
iface eth0 inet manual

They refer to previous names of the same interface as it went from being called "eth0" to now "em0". When attempting to start networking via systemctl start networking, it times out with:

Mar 09 11:23:26 my_hostname_here systemd[1]: Starting LSB: Raise network interfaces....
Mar 09 11:23:26 my_hostname_here networking[7235]: * Configuring network interfaces...
Mar 09 11:23:26 my_hostname_here networking[7235]: Cannot find device "eth0"
Mar 09 11:23:26 my_hostname_here networking[7235]: Failed to bring up eth0.
Mar 09 11:28:26 my_hostname_here systemd[1]: networking.service start operation timed out. Terminating.
Mar 09 11:28:26 my_hostname_here systemd[1]: Failed to start LSB: Raise network interfaces..
Mar 09 11:28:26 my_hostname_here systemd[1]: Unit networking.service entered failed state.
Mar 09 11:28:26 my_hostname_here systemd[1]: networking.service failed.
Mar 09 11:28:26 my_hostname_here networking[7235]: Cannot find device "em0"
Mar 09 11:28:26 my_hostname_here networking[7235]: Failed to bring up em0.

Commenting out said lines fixed the problem. Although I have not restarted yet to actually verify, but systemctl start networking is now happy. I'll restart and report back if this didn't fix the problem.