This bug was fixed in the package lxc - 2.0.0~rc5-0ubuntu1
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lxc (2.0.0~rc5-0ubuntu1) xenial; urgency=medium
* New usptream release (2.0.0~rc5)
- Fix a number of cgfs issues (LP: #1549363, LP: #1543697, LP: #1552355)
- Fix attach failing to allocate a tty (LP: #1551960)
There are two problems.
First is that cgfs is not falling back to $container-1 when $container
cgroup is not available for reuse.
Second is that cgroups are not being cleaned up on container shutdown.
lxcfs will need to prune those by hand either at shutdown or startup.
Doing so at shutdown is on