[systemd-devel] Moving a service from one systemd slice to another..

[Lennart Poettering]

On Mo, 04.05.20 11:52, nitish nagesh (nagesh.nitish at gmail.com) wrote:

> Hello,
>
>    We have this odd want to move a daemon between different systemd slices.
> Not sure if that's even a valid thing to do, but here is the
> requirement.

The Linux kernel gets a bit confused with accounting if you migrate
running processes between cgroups. One usually shouldn't do that
except when forking off/execing new stuff.

>    The daemon while booting up belongs to a systemd slice (say X) which has
> parameters like startupCPUShares tuned to bring the system up faster.
> However for normal operations after bootup, it would be apt to make it
> belong to another slice (say Y) with different cgroup parameters
> configurations (ex: CPUShares). The set of daemons that belong to X and Y
> are totally different, except for this one daemon. Also the cgroup
> parameter that are set via slice Y are totally different than those set via
> slice X.

This is not supported. In systemd you can migrate services between
slices only by stopping them and starting them again.

>   A few basic questions:
> - Can a daemon be a part of 2 slices?

no.

> - If yes, going by the example above, if slice X loads first followed by
> slice Y, does it mean when slice X is in force this daemon will have
> startUpCPUShares set & when slice Y is loaded the CPUShares will be
> set?

I don't grok this, sorry.

>    Please suggest if there are alternate ways in systemd to handle this
> requirement.

We don't support that. Slice assignments are sticky during service
runtime.

Lennart

--
Lennart Poettering, Berlin