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winet
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what happens to guest, when host...?

Thu Nov 24, 2011 4:38 am

i currently run some kvm guest. i wish to know how stable it is. i wonder what happens to the guest ROS when:
1. the host is rebooted. is it also doing a shut down and automatically started again when the host is ready?
2. the host is upgraded. is it also going to upgrade the guest? or do i have to upgrade them just like the host? i kind of confused a little bit about a note on the wiki which states:
Note: Leaving initrd and kernel properties empty is dangerous if Host and Guest will be running different RouterOS versions .
why is it dangerous? because of it, i don't leave their properties empty, i fill them as is on wiki.

thanks for any info :)
 
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janisk
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Re: what happens to guest, when host...?

Thu Nov 24, 2011 9:25 am

running KVM you have 2 different systems (unlike with metarouter, where guests RouterOS is booted from same files as host system, hence the space requirements are very low). So using KVM if you update host, you have to update guest separately. If those 2 fields (initrd and kernel) are left empty, then KVM might use kernel and initrd from host system, that might differ from guest, as result, when guest kernel modules are loaded signatures might not match, and drivers cannot be loaded. When doing shutdown host sends shutdown command to guest - waits for some time and then kills every single one of them (about 10 seconds is wait time)

Also, about initrd and kernel fields - if you are running same major release, it is usually fine to leave them blank. But 4.x guest on 5.x with blanks can cause problems.
 
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winet
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Re: what happens to guest, when host...?

Thu Nov 24, 2011 10:53 am

i see. thanks :) i got 2 qemu machine running now. everything running smoothly except that i am lack of one port :lol:
 
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winet
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Re: what happens to guest, when host...?

Mon Jan 09, 2012 3:40 am

after upgrading the host from v5.8 to v5.11, the guest won't run until i leave the Kernel, Kernel CmdLine, and Initrd empty.

edit: i did something stupid :-? i left those boxes empty, and boot the guest up. it is running well except that it says its version still v5.8, so i upgrade them just like i did to the host. when it reboot, the host is on kernel panic. i had to hard reset the host, to restart it. i think what it did is changing the host kernel file as well. i wonder if there's gonna be permanent damage to the host system? i did /system check-installation, the result is ok anyway.
luckily i backup the entire guest image, so i just restore it, and it is running on v5.8. i can't find a way to upgrade them to v5.11. any idea?

thank you
 
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winet
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Re: what happens to guest, when host...?

Mon Jan 09, 2012 5:12 am

kernel panic again... i decided to downgrade to v5.8 again :(
 
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janisk
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Re: what happens to guest, when host...?

Mon Jan 09, 2012 11:57 am

best course of action:

Upgrade KVM guest first (even if it does not boot after the upgrade, that is ok, you should have an export ready, if everything fails) then update the host. After host update guest should work normally.

Crash of guest might happen if services (actual software) or kernel has changed and different output from either of them is expected.

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