Stateful start/stop

1

I notice that incus start has a flag

      --stateless             Ignore the instance state

and incus stop has a flag

      --stateful              Store the instance state

However, I can’t find any documentation for what those flags actually mean. The incus manual just duplicates the above flag definitions.

As far as I can tell from the source code, it looks like a stop --stateful will store some additional state (what kind of state? is it like CRIU?) and start will by default restore that state unless told not to:

                        if shutdownAction == "stateful-stop" {
                                // Attempt to restore state.
                                err = inst.Start(true)
                        } else {
                                // Normal startup.
                                err = inst.Start(false)
                        }

Therefore, this suggest to me that it’s like a suspend/resume operation, i.e. stop --stateful doesn’t shutdown the container but freezes its state. Is that correct?

Does it work for containers and VMs?

Thanks,

Brian.

2

That’s CRIU or QEMU runtime state, yeah.
The CRIU side of things almost never works so can be mostly ignored :slight_smile:

On the VM side of things, if your VM has migration.stateful=true set and you have a sufficiently large size.state set on the root device, you can then do incus stop --stateful foo which will not really stop the VM so much as do an on-disk hibernate of it.

Then incus start will restore it the way it was, unless you pass incus start --stateless in which case that state will be ignored and the VM will go through a normal full boot.

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