Hello,

We run a bunch of Linux machines as workstations, with ssh configured to forward X11 connnections. So each time someone uses ssh to connect to a remote machine, xauth is called to add a new entry to the user's .Xauthority file.

This works fine, until the user runs out of disk space. The best failure mode would be to have xauth refuse to add the entry and return an error to ssh, which could they say something like "not forwarding X11 connection: xauth call failed (out of disk space). The current failures modes of "xauth add" are rather less optimal...

One failure mode I've just seen is that the .Xauthority file gets truncated to 0 bytes. Then any attempt to start programs on their local desktop fails, and the user comes to see me (the sysadmin).

From memory, I think the other failure modes I've seen were: .Xauthority partially written (but without the :0.0 entry, so same problem), or xauth leaving its lock files around (so other invocations of xauth fail).

It'd be really appreciated if the updates to the .Xauthority files could be done in a safer way, and (for Linux on the desktop deployments) if special care could be taken not to lose the local Xauth cookies (especially the cookie for :0.0).

Thanks for listening.