Hello since I changed my hypervisor from centos 6.3 to Fedora-23 I had many problems with differents VMs. Very often once by day ( I have about 150 VM ), some VMs crash or  freeze indifferently and I got messages like this on console.    [<fffffffff8000a08bd>] wake_bit_funtion +0w0/0x23.....    [<fffffffff8800a0ead>] :jbd:journal_get_write_access+0x22/0x33 ;;;;    [<fffffffff800013ccd>] :ext3:ext3_dirty_inode+0x63/0x7b And so the VM is crashed and can't be accessed but often the ping command can respond Before my migration I never meet these problems, It 's strictly the same VMs between the  6.3 and fedora23 release. I just changed the parameter :   <type arch='x86_64' machine='rhel-6.0.0'>hvm</type> to   <type arch='x86_64' machine='pc-i440fx-2.4'>hvm</type> and do a virsh define I tried some other version of the parameters without success. and I also added a lockd manager in fedora23. Before and I used libvirt.0.9.5 or 1.0.2 on centos 6.03 without lockd A major problem with these crashs is that  the VMs couldn't be destroyed by the virsh command, the qemu process is notified as defunct by the ps command If I try a virsh destroy I get in log file 2016-04-20 20:32:47.318+0000: 5541: info : virEventPollRunOnce:641 : EVENT_POLL_RUN: nhandles=11 timeout=-1 2016-04-20 20:32:55.028+0000: 5567: debug : virProcessKillPainfully:368 : Timed out waiting after SIGTERM to process 8720, sending SIGKILL 2016-04-20 20:33:00.032+0000: 5567: error : virProcessKillPainfully:398 : Failed to terminate process 8720 with SIGKILL: Périphérique ou ressource occupé or on console Failed to terminate process xxx with SIGTERM: Device or resource busy and the VM is still in the list in a "Stopping" state Result of ps ps on the the qemu process attached to the VM qemu      8720     1  0 avril20 ?      00:07:16 [qemu-system-x86] <defunct> root      8733     2  0 avril20 ?      00:00:01 [vhost-8720] root      8735     2  0 avril20 ?      00:00:00 [kvm-pit/8720] libvirtd seems to be in an anormal state. If I restart the libvirtd the virsh command just hang and never remove the VM from the list. The only seems to reboot the hypervisor but all the VMs in production too. Is there a way to remove the process qemu in defunct state without reboot the hypervisor. Perhaps the probleme come from the VM parameters which have been created on 6.3 Centos and libvirt <1.0 version. Do I need to convert some other parameters ? I 'am trying to put a new hypervisor in aFailed to terminate process X with SIGKILL: Device or resource busy version level less than fedora23 perhaps a Centos 7.2 to see what 's happen and if there is a problem like mine. Thanks PS: I put the log_level to 1 ----------------------information in logfile [root@kvmserver6 ~]# ls -al /var/lib/libvirt/qemu/domain-1-TEST-VM-A total 8 drwxr-x---   2 qemu qemu 4096 20 avril 22:01 . drwxr-x--x. 18 qemu qemu 4096 20 avril 22:01 .. srwxrwxr-x   1 qemu qemu    0 20 avril 22:01 monitor.sock /var/lib/libvirt/qemu/channel/target/domain-1-TEST-VM-A/ [root@kvmserver6 ~]# cat /var/log/libvirt/qemu/TEST-VM-A.log 2016-04-20 20:01:36.714+0000: starting up libvirt version: 1.3.3, package: 1.fc23 (Unknown, 2016-04-06-15:17:39, thinkpad2), qemu version: 2.4.1 (qemu-2.4.1-8.fc23), hostname: kvmserver6.univ-brest.fr LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin QEMU_AUDIO_DRV=none /usr/bin/qemu-kvm -name TEST-VM-A,debug-threads=on -S -machine pc-i440fx-2.4,accel=kvm,usb=off -m 1024 -realtime mlock=off -smp 1,sockets=1,cores=1,threads=1 -uuid 1e4c27e4-123e-719a-9fdf-f783d34cbb40 -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-1-TEST-VM-A/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=/var/lib/libvirt/images/POOL_PROD4/TEST-VM-A.img,format=raw,if=none,id=drive-virtio-disk0 -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -drive if=none,id=drive-ide0-1-0,readonly=on -device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -netdev tap,fd=26,id=hostnet0,vhost=on,vhostfd=28 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:77:11:11,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -vnc 0.0.0.0:0,password -k fr -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device ES1370,id=sound0,bus=pci.0,addr=0x4 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -msg timestamp=on char device redirected to /dev/pts/1 (label charserial0) qemu: terminating on signal 15 from pid 5541 -- Michel Villeneuve Tel 02 98 01 71 61