XEN user domain freezes

The problem

When working with XEN 2.0.5c (e.g. under SUSE LINUX 9.3) a guest system (a user domain) freezes. Sometimes it is possible to delete the domain (e.g., with the name testdom) with

root@linux# xm destroy testdom

and then restart. Sometimes, however, the entire host system must be rebooted.

The cause

Although the XEN version of SUSE LINUX 9.3 runs very stably, there is an error in the handling of coredumps in the user domains. If a normal user program – it does not even have to run as root – creates a core dump (e.g. by a segmentation fault), the above phenomenon may occur. The problem is not the program crash, but the creation of the core dump itself.

The solution

Unfortunately, currently we do not know of any causal solution to the problem. However, the problem no longer occurs if the generation of coredumps is prevented. This can be done by setting the maximum coredump size to 0 with ulimit. This is a setting within the shell, and it will be inherited by subprocesses. Check the setting as follows:

user@linux> ulimit -c
unlimited

In this example coredumps are activated. You deactivate them with:

user@linux> ulimit -c 0

However, this setting only applies to the current shell and processes started from there. If you want it to apply system-wide, you can add the command to /etc/profile, for example, or change an existing command there.

Note: In SUSE LINUX coredumps are deactivated by default, but can be individually reactivated by a user.