When using a laptop, it is frequent that you have to switch from one network interface to another. As you do so on FreeBSD, you may find that your X server retreats itself into total mutism, refusing any command (xhost, xrandr…) or any new window. The only message it tells you, if by chance you still had a terminal open, is “No protocol specified”.

The reason behind this? When you switched from one interface to another, dhclient did not send your hostname to the DHCP server. Your ISP provided box-modem-router (connected directly because the gateway is down) wants to play the Good Samaritan and offers you a brand new hostname, say “new-host-7”. The DHCP client dutifully updates your hostname and as a result drives the X server completely nuts.

We can fix this in two ways. By default, the FreeBSD dhclient configuration (/etc/dhclient.conf) is empty. This means that dhclient does not send your hostname and that it requests an hostname from the DHCP server. What we want here is that the DHCP server knows about our hostname and that even if it supplies an hostname value, we supersedes this option with our real hostname. To achieve this, add two lines in /etc/dhclient.conf:

send host-name      "monty-bsd-laptop";
supersede host-name "monty-bsd-laptop";

These two lines are pretty self explanatory. It seems that FreeBSD does not expect you to aggressively switch between multiple interfaces, although it can. An example among others that FreeBSD is not originally intended for laptop usage.