[systemd-devel] enabling cgroups v2

[Neal Gompa]

On Fri, Sep 8, 2023 at 4:30 AM jai <jaimin at webuzo.com> wrote:
>
> ISSUE 1:
> In ubuntu20, centos8 and almalinux8:
> root at host:~# grep cgroup /proc/filesystems
> nodev   cgroup
> nodev   cgroup2
>
> In centos7:
> root at centos:~# grep cgroup /proc/filesystems
> nodev   cgroup
>
> In my centos 7, command 'grep cgroup /proc/filesystems' does not output "nodev cgroup2". Does this mean cgroups v2 is not supported in it and cannot be enabled in it?
>

Yes. RHEL 7 is too old. It was introduced as a tech preview in RHEL 8,
and made default in RHEL 9.

> ISSUE 2:
> In my ubuntu20, centos8 and alma8 server, I enable cgroups v2 by:
> 1. adding "systemd.unified_cgroup_hierarchy=1" to GRUB_CMDLINE_LINUX in /etc/default/grub,
> 2. executing the command "grub2-mkconfig" or "update-grub" as root and then
> 3. reboot the server.
>
> Without reboot, cgroups v2 does not come into effect when i check using the below command:
> root at host:~# stat -fc %T /sys/fs/cgroup/
> tmpfs
>
> Is there a way this can be done without a reboot? I am looking for a way to enable cgroups v2 which should n't need a reboot.

Not without completely breaking everything. Since systemd is the
service manager and the cgroups manager, it needs to be initialized
with the correct mode.


-- 
真実はいつも一つ！/ Always, there's only one truth!