title: docker startup failure due to cgroups misconfiguration
body: <p>I am trying to start docker on a Centos-6-<em>ish</em> OS. It is failing  for <code>cgroups</code> reasons. I believe the mount is correctly structured (docker recommends <a href="https://github.com/tianon/cgroupfs-mount/blob/master/cgroupfs-mount" rel="nofollow noreferrer">https://github.com/tianon/cgroupfs-mount/blob/master/cgroupfs-mount</a>) so the final error message is unclear to me.</p>
  
  <pre><code>thrashin(bash):/base/data/tmp# ./cgroups-mount
  
  thrashin(bash):/base/data/tmp# grep cgroup /proc/mounts
  cgroup /sys/fs/cgroup tmpfs rw,relatime,mode=755 0 0
  cgroup /sys/fs/cgroup/cpuset cgroup rw,relatime,cpuset 0 0
  cgroup /sys/fs/cgroup/blkio cgroup rw,relatime,blkio 0 0
  
  thrashin(bash):/base/data/tmp# cat /proc/cgroups
  #subsys_name    hierarchy       num_cgroups     enabled
  cpuset  4       1       1
  blkio   5       1       1
  
  thrashin(bash):/base/data/tmp# dockerd &amp;
  [1] 7201
  thrashin(bash):/base/data/tmp# WARN[0000] could not change group /var/run/docker.sock to docker: group docker not found
  INFO[0000] libcontainerd: new containerd process, pid: 7214
  WARN[0000] containerd: low RLIMIT_NOFILE changing to max  current=1024 max=4096
  WARN[0001] unable to modify root key limit, number of containers could be limited by this quota: open /proc/sys/kernel/keys/root_maxkeys: no such file or directory
  INFO[0001] [graphdriver] using prior storage driver: overlay2
  INFO[0001] Graph migration to content-addressability took 0.00 seconds
  WARN[0001] Your kernel does not support cgroup memory limit
  WARN[0001] Unable to find cpu cgroup in mounts
  WARN[0001] Your kernel does not support cgroup blkio throttle.read_bps_device
  WARN[0001] Your kernel does not support cgroup blkio throttle.write_bps_device
  WARN[0001] Your kernel does not support cgroup blkio throttle.read_iops_device
  WARN[0001] Your kernel does not support cgroup blkio throttle.write_iops_device
  WARN[0001] mountpoint for pids not found
  Error starting daemon: Devices cgroup isn't mounted
  ^C
  [1]+  Exit 1                  dockerd
  </code></pre>
  
  <p><code>cgroup</code> device <em>is</em> mounted.
  Is the failure due to the warning that the <code>cpu</code> subsystem is not provided? If so, how do I provide this? Is this a kernel build option?</p>