Add mention of mounting cgroupfs properly to PACKAGERS.md

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

docs/sources/installation/binaries.rst

@@ -29,6 +29,12 @@ To run properly, docker needs the following software to be installed at runtime:
 - iptables version 1.4 or later
 - Git version 1.7 or later
 - XZ Utils 4.9 or later
+- a `properly mounted
+  <https://github.com/tianon/cgroupfs-mount/blob/master/cgroupfs-mount>`_
+  cgroupfs hierarchy (having a single, all-encompassing "cgroup" mount point `is
+  <https://github.com/dotcloud/docker/issues/2683>`_ `not
+  <https://github.com/dotcloud/docker/issues/3485>`_ `sufficient
+  <https://github.com/dotcloud/docker/issues/4568>`_)
 
 
 Check kernel dependencies

hack/PACKAGERS.md

@@ -239,6 +239,12 @@ installed and available at runtime:
 
 * iptables version 1.4 or later
 * XZ Utils version 4.9 or later
+* a [properly
+  mounted](https://github.com/tianon/cgroupfs-mount/blob/master/cgroupfs-mount)
+  cgroupfs hierarchy (having a single, all-encompassing "cgroup" mount point
+  [is](https://github.com/dotcloud/docker/issues/2683)
+  [not](https://github.com/dotcloud/docker/issues/3485)
+  [sufficient](https://github.com/dotcloud/docker/issues/4568))
 
 Additionally, the Docker client needs the following software to be installed and
 available at runtime: