[cgmanager-devel] cgmanager fails to start on Fedora (or cgmanager cannot start on distros which run systemd)

[Dwight Engen]

On Mon, 24 Mar 2014 15:28:30 +0200
David Shwatrz <dshwatrz at gmail.com> wrote:

> Hello, cgmanager-devel,
> 
> When I start cgmanager (built latest from git) on Fedora I get the
> following error:
> cgmanager: Failed mounting cpuset: Device or resource busy
> cgmanager: Error mounting subsystem cpuset
> cgmanager: Failed to set up cgroup mounts
> 
> There is no such problem (or any other problem in fact) to run
> cgmanager (which is again built latest from git) on Ubuntu.
> 
> I traced down the error to the do_mount_subsys() method in fs.c (of
> cgmanager tree), which tries to mount the cpu
> cgroup controller.
> 
> The problem is, AFAIK, that cgmanger tries to mount the cpu
> controller, which is mounted in the following way
>  by systemd (as cat /proc/mounts show):
> ...
> cgroup /sys/fs/cgroup/cpu,cpuacct cgroup
> rw,nosuid,nodev,noexec,relatime,cpuacct,cpu 0 0
> ...
> Now, since the cpu is part of a mask of cgroup
> controllers(cpu,cpuacct), as can be seen above, mounting fails, AFAIK.
> The
> cgroup subsystem does not let mount a controller which is mounted as
> part of a mask of controllers on a different path.
> 
> What I mean is that if you look at any other controller which is
> mounted as a single controller (not
> part of a mask), and try to mount on another path, it will work; for
> example, the memory controller
> is mounted thus by systemd:
> cgroup on /sys/fs/cgroup/memory type cgroup
> (rw,nosuid,nodev,noexec,relatime,memory)
> 
> And trying to mount the memory controller under a different path works
> successfully:
> mount -t cgroup -o memory test /cgroup/memtest/
> 
> From what I understand in the following article,
> http://lwn.net/Articles/575672/ ("Another daemon for managing control
> groups"),
> it seems that systemd does not intend to use cgmanager.
> 
> So the question is (assuming I was correct in what described here
> earlier): how can cgmanger run on Fedora and other distros which run
> Systemd (in the future, Debian and Ubuntu are also going to use
> Systemd).

You can tell systemd not to co-mount those controllers by
editing /etc/systemd/system.conf and putting JoinControllers= in it. It
defaults to co-mounting cpu,cpuacct and net_cls,net_prio

> Regards.
> DavidS
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