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Thread: downgrading qemu on Ubuntu 18.04

  1. #11
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    Re: downgrading qemu on Ubuntu 18.04

    There is no downgrading. AFAIK the only Linux distros that let you downgrade are Arch and its derivatives (there is actually a utility called downgrade from the AUR)

    Maybe upgrading your qemu-kvm and libvirt packages will solve your problem. Upgrading the host to 20.04 because of this seems to be massive overkill. I would try this ppa first instead.

  2. #12
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    Re: downgrading qemu on Ubuntu 18.04

    I'm on
    Code:
    $ dpkg -l *kvm* |egrep '^ii'
    ii  qemu-kvm       1:2.11+dfsg-1ubuntu7.37 amd64        QEMU Full virtualization on x86 hardware
    Haven't had any issues on either Intel or Ryzen CPUs with any VMs.

    The KVM host kernels on 3 systems are:
    Code:
    $ uname -r
    5.4.0-80-generic
    that's the HWE kernel.

    The guest VMs are almost every supported Ubuntu version and a few EoL Windows systems.

    What do the log files show related to warnings and errors on the VM host? Always check the logs.

    Update:
    I run apt-cacher-ng, but the APT cache doesn't keep packages forever. They automatically expire. Only have
    Code:
    -rw-r--r-- 1 apt-cacher-ng apt-cacher-ng 13176 Jul 17 09:44 /var/cache/apt-cacher-ng/uburep/pool/main/q/qemu/qemu-kvm_2.11+dfsg-1ubuntu7.37_amd64.deb
    Let me check my system backups for that machine. I don't usually backup /var/ stuff. Nope. Nothing from /var/ in the backups. Sorry.
    Last edited by TheFu; August 1st, 2021 at 03:53 AM.

  3. #13
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    Re: downgrading qemu on Ubuntu 18.04

    As an example, the KVM version of KVM in 18.04 is 2.11. This is what TheFu is currently on. He knows KVM inside and out.

    In 20.04.2, KVM is version 4.2.1. 21.10 Dev, KVM is version 6.0. These are what I am currently on and testing.

    KVM upstream now in dev is version 6.1-beta, which monkeybrains compiled and is testing... KVM releases 6.1 at the end of August. I see that as the version for 22.04.

    You now have 3 people here to help you... If you can explain what is going on.

    Concurrent coexistance of Windows, Linux and UNIX...
    Ubuntu user # 33563, Linux user # 533637
    Sticky: [all variants] Graphics Resolution- Upgrade /Blank Screen after reboot
    UbuntuForums system-info Script

  4. #14
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    Re: downgrading qemu on Ubuntu 18.04

    Interesting, I may try the HWE kernel, though my system is a Dell XPS from around 2017. The problem Iis that the VM's hang and ultimately the whole system hangs, if not during operation of the VM, during system shutdown. I will gather more info the next time it occurs.

  5. #15
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    Re: downgrading qemu on Ubuntu 18.04

    Quote Originally Posted by nataraj88 View Post
    Interesting, I may try the HWE kernel, though my system is a Dell XPS from around 2017. The problem Iis that the VM's hang and ultimately the whole system hangs, if not during operation of the VM, during system shutdown. I will gather more info the next time it occurs.
    Did you check the logs for issues? There should be something in the logs which will provide a hint. I was able to track down a RAM issue by reviewing the logs last week and about a month before that.

  6. #16
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    Re: downgrading qemu on Ubuntu 18.04

    The logs he is referring to are located at /var/log/libvirt/qemu/<domain_name.>.log ... There should be one log file for each VM Guest you have...

    So a soft lockup? Interesting read on this qemu-kvm bug report at launchpad, between response #3 and #15...

    LaunchPad > Bug # 1730717 > Some VMs fail to reboot with "watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [systemd:1]"
    = https://bugs.launchpad.net/ubuntu/+s.../+bug/1730717\

    At first you are going to see the title and ask me what that has to do with you... Well, it's tied and intertwined with another Bug Report

    LaunchPad > Bug # 1713751 > soft lockup / stall on CPU when shutting down with hwe 4.10 kernel
    = https://bugs.launchpad.net/ubuntu/+s...x/+bug/1713751

    Is not just that kernel, but a range of Kernels... Not saying that is anything like you... but something you said reminded me of these interrelated bugs. And you are on 18.04 ,and I was thinking maybe something setup a perfect storm(?) or not.. Just me always thinking.

    You haven't even looked at "your logs" yet... But if you do see messages in those logs saying "soft lockup - CPU#0 stuck for 22s!"... Well...
    Last edited by MAFoElffen; August 2nd, 2021 at 03:18 AM.

    Concurrent coexistance of Windows, Linux and UNIX...
    Ubuntu user # 33563, Linux user # 533637
    Sticky: [all variants] Graphics Resolution- Upgrade /Blank Screen after reboot
    UbuntuForums system-info Script

  7. #17
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    Re: downgrading qemu on Ubuntu 18.04

    The Errors that I'm finding so far in my logs are these (Note this is just a few of each error, edited down )

    Code:
    Leaked cluster 253193 refcount=3 reference=2
    Leaked cluster 262568 refcount=5 reference=4
    
    ERROR cluster 267915 refcount=0 reference=1
    ERROR cluster 267916 refcount=0 reference=1
    
    Leaked cluster 275793 refcount=5 reference=4
    Leaked cluster 412410 refcount=5 reference=4
    
    Rebuilding refcount structure
    Repairing cluster 250896 refcount=1 reference=0
    Repairing cluster 250897 refcount=1 reference=0

    I took the VM down and ran this:

    Code:
    # qemu-img info ubuntu18.04.qemu
    image: ubuntu18.04.qemu
    file format: qcow2
    virtual size: 15G (16106127360 bytes)
    disk size: 33G
    cluster_size: 65536
    Snapshot list:
    ID        TAG                 VM SIZE                DATE       VM CLOCK
    1         Ubuntu 18.04 initial install      0 2018-04-24 01:16:36   00:00:00.00\
    0
    153       21-01-22-01               0 2021-01-22 08:21:28   00:00:00.000
    156       21-03-22-01               0 2021-03-22 14:11:23   00:00:00.000
    159       21-06-04-02               0 2021-06-04 01:52:25   00:00:00.000
    160       21-07-16-01               0 2021-07-16 20:11:04   00:00:00.000
    Format specific information:
        compat: 1.1
        lazy refcounts: true
        refcount bits: 16
        corrupt: false
    # qemu-img check ubuntu18.04.qemu
    No errors were found on the image.
    245760/245760 = 100.00% allocated, 15.12% fragmented, 0.00% compressed clusters
    Image end offset: 60129673216
    So if the image was corrupt it has been repaired now.

  8. #18
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    Re: downgrading qemu on Ubuntu 18.04

    So at this point, I will see if the problem recurs and try to track down more information. I will also run memtest on my system later tonight.

  9. #19
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    Re: downgrading qemu on Ubuntu 18.04

    Quote Originally Posted by nataraj88 View Post
    So at this point, I will see if the problem recurs and try to track down more information. I will also run memtest on my system later tonight.
    I use LVM LVs for my VM storage. The LV is passed as a block device into the VM. libvirt understands how to use an LVM storage pool. Creating a 50G VM storage area is nearly instant - another reason to use LVM for storage. Being able to resize the storage while the VM keeps running in 5 seconds is handy too. Too hard to get a perfectly clean backup from a running VM without using LVM snapshots.

    File-based VM storage is so ... so ... 2010. Though I do admit to using it for a few needs, but nothing used in production.

  10. #20
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    Re: downgrading qemu on Ubuntu 18.04

    Thank you. That is a good point. I do have LVM storage on a few of my VM's that do heavier IO.

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