[libvirt-users] What can cause "libvirtd dead but pid file exists."

Hi, # service libvirtd status libvirtd dead but pid file exists. I operated VMs(like create, edit, delte) normally for a second, but the libvirtd on host was dead. I checked the libvirtd.log but didn't find any useful information. so I want to know what can cause the problem? another question: I found the message in /var/log/message like "libvirtd: Could not find keytab file: /etc/libvirt/krb5.tab: Permission denied." what is going wrong? my libvirt version: 0.9.8. xuanmao_001