'qemu-img snapshot' crashed, corrupting disk image

[Nelson Elhage]

Binary package hint: qemu-kvm

I have a 10GB qcow2 disk image that I use for testing various things on a clean Jaunty install. I created it with the qemu package from Jaunty, and it has been working fine for some time.

I recently upgraded to Karmic, and, after doing some work in the VM, attempting to snapshot the VM using 'qemu-img snapshot -c test jaunty.qcow2'. After a minute or so, qemu-img had grown to consume nearly all of my 2GB of RAM, and then, after another minute or two, terminated with a segfault. After this crash, all attempts to use the disk image, either via qemu-img or booting it in qemu or kvm have resulted in a segfault.

I can generate core files of the later crashes, but since qemu uses most of my RAM before crashing, they are quite large (1.5+GB). Please let me know if extracting backtraces or other information would be useful, or if I should post a core image somewhere anyways for a developer to attempt to download it.

ProblemType: Bug
Architecture: i386
Date: Sun Oct 4 17:22:31 2009
DistroRelease: Ubuntu 9.10
KvmCmdLine: Error: command ['ps', '-C', 'kvm', '-F'] failed with exit code 1: UID PID PPID C SZ RSS PSR STIME TTY TIME CMD
MachineType: LENOVO 2613CTO
Package: qemu-kvm 0.11.0-0ubuntu1
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcCmdLine: root=UUID=f9f53a9f-164b-4f56-aa03-d28ca7084928 ro quiet splash
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-11.38-generic
SourcePackage: qemu-kvm
Uname: Linux 2.6.31-11-generic i686
dmi.bios.date: 11/20/2006
dmi.bios.vendor: LENOVO
dmi.bios.version: 79ETC6WW (2.06 )
dmi.board.name: 2613CTO
dmi.board.vendor: LENOVO
dmi.board.version: Not Available
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvr79ETC6WW(2.06):bd11/20/2006:svnLENOVO:pn2613CTO:pvrThinkPadT60:rvnLENOVO:rn2613CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 2613CTO
dmi.product.version: ThinkPad T60
dmi.sys.vendor: LENOVO

[Nelson Elhage (nelhage)]

Actually, the core files in question compress down quite nicely, so find attached a 1.6M core.gz file from a crashed 'qemu-snapshot -l jaunty.qcow2'.

Be warned that it expands into a 1.6GB file.

[stefan.kamien (stefan-kamien)]

It seems that I also experienced this bug.

I installed qemu-kvm package on Ubuntu 9.10. I did following:

qemu-img create -f qcow2 disc 10G

qemu -hda disc -cdrom /dev/cdrom -m 512

Then i installed quest OS (Windows XP). I shut down VM and booted again, without cdrom:

qemu -hda disc -m 512

After windows booted and I logged in, I did ctrl+alt+2
and i entered following command in qemu monitor:
savevm john

Then Qemu quits automaticallly, and it says "Segmentation fault" in hosts command line. I was trying to load that snapshot by typing:
qemu -hda disc -m 512 -loadvm john

This command should start qemu and load saved vm state with all running apps right? In my case it only started qemu and booted windows.

I tried also in qemu monitor:
loadvm john
but it says "Could not find snapshot 'john' on device 'ide0-hd0'.
Typing "info snapshots" in qemu monitor doesnt show any avaible snapshot.
Sorry for poor english language.

[stefan.kamien (stefan-kamien)]

Hi again. Sorry if my previous comment is not related to your bug. I didnt read your description carefully and I'm new to launchpad. Do you think that I should report separate bug?

[Torsten Spindler (tspindler)]

The following command did not give an error for me on Lucid Alpha 3, 2010-03-01 updates installed:
$ qemu-img snapshot -c toast ./lucid.qcow2
Version: 0.12.3-0ubuntu2

Unfortunately I did not find a snapshot thereafter either.

[Dustin Kirkland  (kirkland)]

Hmm, I booted a vm, dropped to the QEMU console, and tried savevm, which appeared to result in a hung vm.

There seems to be at least something wrong with image snapshotting in Lucid. I'll confirm this for now.

[Anthony Liguori (anthony-codemonkey)]

qemu-img snapshot and savevm are different mechanisms. I'd suggest closing this bug and opening a separate one for savevm.

[Dustin Kirkland  (kirkland)]

Gotcha. My methods were flawed. Closing bug per Torsten's feedback. Please reopen if you can reproduce this on latest Lucid.

Thanks!

[Dustin Kirkland  (kirkland)]

Actually I tested savevm too, and that seems to work as well. Here's how, for completeness...

$ kvm-img create -f qcow2 foo.img 4G
Formatting 'foo.img', fmt=qcow2 size=4294967296 encryption=off cluster_size=0

$ kvm -m 512 -cdrom lucid-desktop-amd64.iso -hda foo.img

At some point here (even during boot), drop to monitor
ctrl-alt-2
savevm foo.img

You can watch the image grow as memory is written:
$ watch ls -alF foo.img

Once it's done, go back to the vga with ctrl-alt-1. Change the system somehow. Then roll back with
ctrl-alt-2
loadvm foo.img

Worked well for me.