changing number of CPUs for an instance

[VasiliyS]

Is it possible to change number of CPUs available to an existing instance? What about memory?

[Saviq]

Hi @VasiliyS, I'm afraid it's not, not easily at the moment. #756 designs the experience, but it's not yet implemented.

Depending on platform, you could just edit the VM in the hypervisor (Hyper-V, VirtualBox), or stop Multipass and edit its instance database.

Let us know what your environment is and we can guide you there :)

[VasiliyS]

@Saviq - Thank you. I'm on a Mac. Where can I find the instance database?

[Saviq]

@VasiliyS here are the steps:

# stop multipassd
sudo launchctl unload /Library/LaunchDaemons/com.canonical.multipassd.plist

# edit /var/root/Library/Application Support/multipassd/multipassd-vm-instances.json
# you'll need sudo for that

# start multipassd again
sudo launchctl load /Library/LaunchDaemons/com.canonical.multipassd.plist

The format should be quite easy to grok:

{
    "primary": {
        "deleted": false,
        "disk_space": "5368709120",
        "mac_addr": "52:54:00:5c:f4:14",
        "mem_size": "1073741824",
        "metadata": {
        },
        "mounts": [
        ],
        "num_cores": 1,
        "ssh_username": "ubuntu",
        "state": 0
    }
}

You want to edit num_cores for CPU and mem_size for memory :)

[VasiliyS]

@Saviq - Just tried it. The instance doesn't start - the cli times out ("timed out waiting for response"). multipass info tells me that the state is unknown and the json file has state set to 8. multipass stop ends with "process error occurred Crashed". The state key in the json file is now 0.


After stopping the multipassd, editing the num_cores key value back to 1 and re-starting the daemon, the instance starts fine.

[Saviq]

@VasiliyS hmm can you look in /Library/Logs/Multipass/multipassd.log for any errors? Does a new instance with 2 CPUs (multipass launch --cpus 2) work fine?

[VasiliyS]

@Saviq - I was able to create a new instance with 2 cpus, worked fine.

I'm attaching 2 files with excerpts from the log. One where I've edited the cpu key to 2 and the instance doesn't start.
2_cpus_doesnt_start.log

The second one where I've changed the setting back to 1 cpu and it works.
1_cpu_starts.log

[VasiliyS]

@Saviq - Update!
I've just tried something. The instance actually starts fine, it's the cli that timeouts.
multipass start exits with a timeout message, but I'm still able to ssh into the instance, etc.


The weird thing is , now even the instance that I've launch'd with --cpus 2 option from scratch doesn't start normally (i.e. multipass start timeouts), but the instance actually works fine. That gave me an idea to try again with editing the num_cores key and ignore the timeout message. Now that I know where the id_rsa is, I can login directly even when multipass shell/info/etc don't work normally. Oh well...

[townsend2010]

Hi @VasiliyS,

It looks like you are hitting #1122 when it's using 2 cpu's. The next version of Multipass has a fix for that. We have a release candidate for 0.9 up and can be found at https://github.com/CanonicalLtd/multipass/releases/download/v0.9.0-rc/multipass-0.9.0-rc.425+g37fa4305.mac-Darwin.pkg if you are interested.

[VasiliyS]

Hi @townsend2010 - thanks! The RC works just fine.
I guess now my original request has been met. I'm now able to change the number of CPUs for an existing instance.

Would be great to add a command to update the instance configuration via the cli, though. It's probably a common need, especially if one uses multipass to create a K8S machine and then discovers that the original resources are not sufficient.

[Saviq]

@VasiliyS glad you got it going. Yes, we'll allow changing the number of CPUs in due course :)

[sourcedelica]

And memory please.

[kramik1]

Just to save some people some time, the below is for Ubuntu 19.10.

sudo systemctl stop snap.multipass.multipassd.service
sudo vi /var/snap/multipass/common/data/multipassd/multipassd-vm-instances.json
sudo systemctl start snap.multipass.multipassd.service