Erlang cgroups interface

An interface for cgroups manipulation that handles cgroup version details
(i.e., differences between v1 and v2) and provides safe usage of the
cgroups filesystem mount.


    rebar compile


Update or create the cgroup "group1/nested1" with the OS pid 19368,
then delete the cgroup path after moving the OS pid back to the root cgroup.

    $ erl -pz ebin
    1> application:start(cgroups).
    2> OSPid0 = 19368.
    3> CGroupPath = "group1/nested1".
    4> {ok, CGroups} = cgroups:new().
    5> MemoryLimit = case cgroups:version(CGroups) of 1 -> "memory.limit_in_bytes"; 2 -> "memory.high" end.
    6> cgroups:update_or_create(CGroupPath,
                                [{MemoryLimit, "10000000"}],
    7> cgroups:update("", [OSPid0], [], CGroups).
    8> cgroups:delete_recursive(CGroupPath, CGroups).
    9> cgroups:destroy(CGroups).


**`cgroups:update/4` and `cgroups:update_or_create/4` Errors:**
* A Linux/systemd setup may have the control group setup mode set to `hybrid`
  due to it being the [recommended default](
  for distributions.  However, that mode blocks the use of cgroup controllers
  (the file `/sys/fs/cgroup/unified/cgroup.controllers` is empty)
  because the cgroup controllers can only be [mounted in one hierarchy](
  (v1 or v2).  If cgroup v1 should be used, the Linux kernel argument
  `systemd.legacy_systemd_cgroup_controller=1` can be used.
  If cgroup v2 should be used, the Linux kernel argument
  `systemd.unified_cgroup_hierarchy=1` can be used
  (with systemd >= `v226` and kernel >= `4.2`) or
  `cgroup_no_v1=all` can be used (with kernel >= `4.6`).


Michael Truog (mjtruog at protonmail dot com)


MIT License