xauth: timeout in locking authority file

Posting this error and the cause in case this is useful to someone...:

I suddenly got this error when trying to start X:
xauth: timeout in locking authority file /home/min/.serverauth.2291
(min being my userid), and after a while:
xauth: timeout in locking authority file /home/min/.Xauthority

Examining the log file /var/log/Xorg.0.log, some candidate causes:
(WW) intel: No matching Device section for instance (BusID PCI:0:2:1) found
...
(EE) intel(0): I830 Vblank Pipe Setup Failed 0

It turned out these messages are irrelevant (in fact they also show up when X has run successfully), the real cause was me having changed the HOME environment variable to a directory different from my home directory (some source package that I wanted to compile required this), and xauth uses the HOME variable to locate the .serverauth file... :-(

Update: I've also seen this error when the home directory was not writable by the user (so say your username is min, then /home/min was not writable by min).