Today I realized that `dhcpcd` has been logging several hundred thousand
of these messages every second:
libudev: received NULL device
This was causing both `dhcpcd` and `systemd-journald` to consume 100%
CPU.
I am not entirely sure what a "device management" module is in the
context of `dhcpcd`, but it does not seem to be required. Setting the
`nodev` option in `dhcpcd.conf` suppresses the messages, and seems to
have no effect on the operation of the daemon.
Dustin