unpriveleged containers no longer could start due to start.c: lxc_spawn: 1555 Failed initializing cgroup support

[George Shuklin]

After upgrade from xenial to bionic (beta) I no longer could start unpriveleged containers, they failed with following message:

lxc-start: test: start.c: lxc_spawn: 1555 Failed initializing cgroup support
                                                                                                       lxc-start: test: start.c: __lxc_start: 1868 Failed to spawn container "test"
                                                                                             The container failed to start.
Additional information can be obtained by setting the --logfile and --logpriority options.

Moreover, I could see this in auth log:

Mar 23 18:21:46 host sudo: PAM unable to dlopen(pam_cgfs.so): /lib/security/pam_cgfs.so: cannot open shared object file: No such file or directory
Mar 23 18:21:46 host sudo: PAM adding faulty module: pam_cgfs.so

I have installed libpam-cgfs, but it provides only /lib/x86_64-linux-gnu/security/pam_cgfs.so

Moreover, if I create a symlink from /lib/security/pam_cgfs.so to /lib/x86_64-linux-gnu/security/pam_cgfs.so it fails with follwing message:

PAM unable to dlopen(pam_cgfs.so): /lib/security/pam_cgfs.so: undefined symbol: file_exists

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: lxc 3.0.0~beta2-0ubuntu2
ProcVersionSignature: Ubuntu 4.15.0-12.13-generic 4.15.7
Uname: Linux 4.15.0-12-generic x86_64
ApportVersion: 2.20.8-0ubuntu10
Architecture: amd64
CurrentDesktop: X-Cinnamon
Date: Fri Mar 23 18:20:38 2018
DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-xenial-amd64-20160624-2
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-06-22 (274 days ago)
InstallationMedia: Ubuntu 16.04 "Xenial" - Build amd64 LIVE Binary 20160624-10:47
PackageArchitecture: all
SourcePackage: lxc
UpgradeStatus: No upgrade log present (probably fresh install)
defaults.conf:
 lxc.net.0.type = veth
 lxc.net.0.link = lxcbr0
 lxc.net.0.flags = up
 lxc.net.0.hwaddr = 00:16:3e:xx:xx:xx