Re: [systemd-devel] Purpose of init.scope

Demi Marie Obenour <[email protected]> Tue, 18 Aug 2026 14:02:06 -0400

Newsgroups	org.kernel.vger.cgroups
Message-ID	<[email protected]>

On 8/17/26 07:32, SCOTT FIELDS wrote:
> For anyone interested:
> 
> https://github.com/systemd/systemd/pull/1116
> 
> "This moves PID 1 into a new "init.scope" implicit scope unit in the root
> slice. This is necessary since on the unified hierarchy cgroups may
> either contain subgroups or processes but not both. PID 1 hence has to
> move out of the root cgroup (strictly speaking the root cgroup is the
> only one where processes and subgroups are still allowed, but in order
> to support containers nicey, we move PID 1 into the new scope in all
> cases.) This new unit is also used on legacy hierarchy setups. It's
> actually pretty useful on all systems, as it can then be used to filter
> journal messages coming from PID 1, and so on."

Oh, that explains why PID 1 is not just left in the root cgroup.  I missed
the container use-case.

The project I am working on will never run in a container so that is not
a concern.

> On Mi, 29.07.26 16:13, Demi Marie Obenour ([email protected]) wrote:
> 
>> What is the purpose of having PID 1 in init.scope?  Is it functionally
>> necessary, or is it solely for consistency with when systemd is
>> running in a container or as a user service manager?
> 
> PID 1 needs to live somehwere, so that's where we put it. Where else
> would you put it?
> 
> Lennart
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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