[Zope] Zope process dies without notice

Hi, Sometimes, the Zope server dies (Zope 2.3.3 / Debian 2.2) . I don't know why and Z2.log does not say anything (just shows the last published object) I can't see any trace of that in the usual system log files. When restarting Zope, there is no special message (no damage to data.fs) Any clue to help me to know the reason of this, where can I search for useful information ? TIA --Gilles