So the bug from the article Get Centos 7 DomU guests booting on Xen 4.1 hit us again, after a while as we wanted to reboot a few guests.

Everything still seemed to be fine within the guest, nevertheless pygrub on host wasn’t able to find a kernel to boot.

Revisiting one of the old xen bus that we already searched on our previous experience, showed us that we also need to patch pygrub on the host:

> -            title_match = re.match('^menuentry ["\'](.*)["\'] (.*){', l)
> +            title_match = re.match('^menuentry ["\'](.*?)["\'] (.*){', l)

in /usr/lib/xen-4.1/bin/pygrub and your guests boot again.