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In Process
David Tonhofer
Asked: 2019-10-21 04:41:16 +0800 CST

Ubuntu KVM crashed nastily and is now corrupted. Any way to salvage stuff?

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I was running Ubuntu 18.04 in a KVM VM on Fedora 30.

At some point the host machine got into trouble with Spice. The kernel of the host machine says:

Oct 20 14:16:46 host.name kernel: traps: SPICE Worker[22505] trap int3
ip:7f43f3c9e095 sp:7f43e8ffe1f0 error:0 in 
libglib-2.0.so.0.6000.7[7f43f3c63000+82000]

In the guest system log /var/log/libvirt/qemu/muh-ubuntu.log we find:

(process:22445): Spice-ERROR **: 14:16:46.760: 
red-parse-qxl.c:349:red_get_clip_rects: assertion 
`(uint64_t) num_rects * sizeof(QXLRect) == size' failed
2019-10-20 12:16:47.427+0000: shutting down, reason=crashed

The whole host GUI froze, then VM keeled over like a sick beluga.

Now the Virtual Machine image seems to have been seriously affected (surprise!). When I start it, I just get "error: attempt to read or write outside of disk `hd0'. Press any key to continue..." but keyboard input isn't even being accepted.

Is it foobared or is there some way to salvage something? (As in, access the filesystem in the VM image?)

linux

1 Answers

  1. All right, I have been able to access the image's filesystem and copy files off it using qemu-nbd. This utility comes with package qemu-img on Fedora.

    Specifically:

    modprobe nbd
qemu-nbd -c /dev/nbd0 /var/lib/libvirt/muh-ubuntu.qcow2
# The unique partition of the Ubuntu installation appears under /dev/nbd0p1
fsck /dev/nbd0p1

    No errors found? Nice.

    Then:

    mkdir ~/ubuntufs
mount /dev/nbd0p1 /root/ubuntufs/

    With some luck, the filesystem of the image can be accessed under ~/ubuntufs and one can copy files off it.

    This also allows one to check the VM's kernel log last messages:

    Oct 20 14:15:33 studio kernel: [35329.053397] f 4026531994#146742: failed to wait on release 154 after spincount 301
Oct 20 14:15:34 studio kernel: [35329.375923] f 4026531994#146742: failed to wait on release 154 after spincount 301
Oct 20 14:15:34 studio kernel: [35329.700598] f 4026531994#146742: failed to wait on release 154 after spincount 301
Oct 20 14:15:34 studio kernel: [35330.092221] f 4026531996#146744: failed to wait on release 156 after spincount 301
Oct 20 14:15:35 studio kernel: [35330.418666] f 4026531996#146744: failed to wait on release 156 after spincount 301
Oct 20 14:15:35 studio kernel: [35330.744602] f 4026531996#146744: failed to wait on release 156 after spincount 301
Oct 20 14:15:35 studio kernel: [35331.141117] f 4026531998#146746: failed to wait on release 158 after spincount 301
Oct 20 14:15:36 studio kernel: [35331.468580] f 4026531998#146746: failed to wait on release 158 after spincount 301
Oct 20 14:15:36 studio kernel: [35331.795974] f 4026531998#146746: failed to wait on release 158 after spincount 301
Oct 20 14:15:36 studio kernel: [35332.187849] f 4026532000#146748: failed to wait on release 160 after spincount 301
Oct 20 14:15:37 studio kernel: [35332.518850] f 4026532000#146748: failed to wait on release 160 after spincount 301
Oct 20 14:15:37 studio kernel: [35332.844414] f 4026532000#146748: failed to wait on release 160 after spincount 301

    Addendum

    I tried starting the VM again and it worked this time. This is really weird. Did it self-repair?

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