dhcpd dies for unprivileged users

[Lauri Tirkkonen]

dhcpd fails to run as an unprivileged user; this is particularly an issue when wanting to syntax-check the config file.

Reproducing:

$ dhcpd -t -cf /dev/null

Expected results: dhcpd checks configuration file (/dev/null used here) and reports errors encountered.

Actual results: dhcpd outputs:
    drop_privileges: could not set group id: Operation not permitted
and exits with status 255.

Ubuntu 12.04.4

isc-dhcp-server:
  Installed: 4.1.ESV-R4-0ubuntu5.9