On Di, 12.05.20 14:21, Fedora Development ML (devel@xxxxxxxxxxxxxxxxxxxxxxx) wrote:
> > > By the way, what would you and (and others) recommend as a replacement for
> > > libcgroup-tools?[fn:2]
> >
> > No idea. I don't use cgroups for anything on purpose. As far as I know,
> > cgroups membership in Fedora is defined by systemd's logind. Whether it suits
> > your needs, I have no idea. I also think it's possible to manage the
> > membership manually by editing files in cgroup2 pseudo file system.
>
> Yes as I understand it you're not supposed to fiddle with cgroups
> manually, you're supposed to use systemd-run or something and let
> systemd do the necessary.
cgroupsv2 is built around a single-writer scheme. That means any
section of the tree shall only have a singler writer, i.e. one
subsystem 'owning' it. On systemd systems the root of the tree is
owned by systemd, it's the single writer of it. Other software may
read from the tree but not make changes to it.
You can ask systemd for a delegated subtree of the main cgroup tree
however. You can do this via Delegate=yes in a service file, or by
doing "systemd-run --scope -p Delegate=yes -t /bin/bash" on the
command line. If you do that you get your own subtree in which you can
do whatever you want, and systemd will not step on your toes.
Making changes to the top-level cgroup tree, i.e. stepping into
systemd's explicitly owned territory means voiding your warranty
though.
This design choice is made by the cgroupsv2 subsystem in the kernel
btw, it's not something systemd came up with.
It's documented here in all detail:
https://systemd.io/CGROUP_DELEGATION
hence, if libcgroups wants to do cgroup stuff it really needs to ask
systemd for delegation first (or be invoked inside a service where
something else asked for it). If it doesn't then it's simply broken.
In general, I am not sure why one would even want the cgroup tools on
a systemd system though. We should provide most of it natively anyway,
though possibly in a different manner.
Lennart
--
Lennart Poettering, Berlin
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