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

[Serge Hallyn]

Quoting Dwight Engen (dwight.engen at oracle.com):
> 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

Just to be sure - is there any downside to doing this, other than the
inconvenience of having to do it?