userns container fails to start, how to track down the reason?

When creating a userns (unprivileged) LXC container on Ubuntu 14.04 with the following command line: lxc-create -n test1 -t download -- -d $(lsb_release -si|tr 'A-Z' 'a-z') -r $(lsb_release -sc) -a $(dpkg --print-architecture) and (without touching the created configuration file) then attempting to start it with: lxc-start -n test1 -l DEBUG it fails. The log file shows me: lxc-start 1420149317.700 INFO lxc_start_ui - using rcfile /home/user/.local/share/lxc/test1/config lxc-start 1420149317.700 INFO lxc_utils - XDG_RUNTIME_DIR isn't set in the environment. lxc-start 1420149317.701 INFO lxc_confile - read uid map: type u nsid 0 hostid 100000 range 65536 lxc-start 1420149317.701 INFO lxc_confile - read uid map: type g nsid 0 hostid 100000 range 65536 lxc-start 1420149317.701 WARN lxc_log - lxc_log_init called with log already initialized lxc-start 1420149317.701 INFO lxc_lsm - LSM security driver AppArmor lxc-start 1420149317.701 INFO lxc_utils - XDG_RUNTIME_DIR isn't set in the environment. lxc-start 1420149317.702 DEBUG lxc_conf - allocated pty '/dev/pts/2' (5/6) lxc-start 1420149317.702 DEBUG lxc_conf - allocated pty '/dev/pts/7' (7/8) lxc-start 1420149317.702 DEBUG lxc_conf - allocated pty '/dev/pts/8' (9/10) lxc-start 1420149317.702 DEBUG lxc_conf - allocated pty '/dev/pts/10' (11/12) lxc-start 1420149317.702 INFO lxc_conf - tty's configured lxc-start 1420149317.702 DEBUG lxc_start - sigchild handler set lxc-start 1420149317.702 DEBUG lxc_console - opening /dev/tty for console peer lxc-start 1420149317.702 DEBUG lxc_console - using '/dev/tty' as console lxc-start 1420149317.702 DEBUG lxc_console - 14946 got SIGWINCH fd 17 lxc-start 1420149317.702 DEBUG lxc_console - set winsz dstfd:14 cols:118 rows:61 lxc-start 1420149317.905 INFO lxc_start - 'test1' is initialized lxc-start 1420149317.906 DEBUG lxc_start - Not dropping cap_sys_boot or watching utmp lxc-start 1420149317.906 INFO lxc_start - Cloning a new user namespace lxc-start 1420149317.906 INFO lxc_cgroup - cgroup driver cgmanager initing for test1 lxc-start 1420149317.907 ERROR lxc_cgmanager - call to cgmanager_create_sync failed: invalid request lxc-start 1420149317.907 ERROR lxc_cgmanager - Failed to create hugetlb:test1 lxc-start 1420149317.907 ERROR lxc_cgmanager - Error creating cgroup hugetlb:test1 lxc-start 1420149317.907 INFO lxc_cgmanager - cgroup removal attempt: hugetlb:test1 did not exist lxc-start 1420149317.908 INFO lxc_cgmanager - cgroup removal attempt: perf_event:test1 did not exist lxc-start 1420149317.908 INFO lxc_cgmanager - cgroup removal attempt: blkio:test1 did not exist lxc-start 1420149317.908 INFO lxc_cgmanager - cgroup removal attempt: freezer:test1 did not exist lxc-start 1420149317.909 INFO lxc_cgmanager - cgroup removal attempt: devices:test1 did not exist lxc-start 1420149317.909 INFO lxc_cgmanager - cgroup removal attempt: memory:test1 did not exist lxc-start 1420149317.909 INFO lxc_cgmanager - cgroup removal attempt: cpuacct:test1 did not exist lxc-start 1420149317.909 INFO lxc_cgmanager - cgroup removal attempt: cpu:test1 did not exist lxc-start 1420149317.910 INFO lxc_cgmanager - cgroup removal attempt: cpuset:test1 did not exist lxc-start 1420149317.910 INFO lxc_cgmanager - cgroup removal attempt: name=systemd:test1 did not exist lxc-start 1420149317.910 ERROR lxc_start - failed creating cgroups lxc-start 1420149317.910 INFO lxc_utils - XDG_RUNTIME_DIR isn't set in the environment. lxc-start 1420149317.910 ERROR lxc_start - failed to spawn 'test1' lxc-start 1420149317.910 INFO lxc_utils - XDG_RUNTIME_DIR isn't set in the environment. lxc-start 1420149317.910 INFO lxc_utils - XDG_RUNTIME_DIR isn't set in the environment. lxc-start 1420149317.910 ERROR lxc_start_ui - The container failed to start. lxc-start 1420149317.910 ERROR lxc_start_ui - Additional information can be obtained by setting the --logfile and --logpriority options. Now I see two errors here, the latter probably being a result of the former, which is: > lxc_start - failed creating cgroups However, I see /sys/fs/cgroup mounted: $ mount|grep cgr none on /sys/fs/cgroup type tmpfs (rw) and cgmanager is installed: $ dpkg -l|awk '$1 ~ /^ii$/ && /cgmanager/ {print $2 " " $3 " " $4}' cgmanager 0.24-0ubuntu7 amd64 libcgmanager0:amd64 0.24-0ubuntu7 amd64 Note: My host defaults still to upstart. In case there's any doubt, the kernel support cgroups: $ grep CGROUP /boot/config-$(uname -r) CONFIG_CGROUPS=y # CONFIG_CGROUP_DEBUG is not set CONFIG_CGROUP_FREEZER=y CONFIG_CGROUP_DEVICE=y CONFIG_CGROUP_CPUACCT=y CONFIG_CGROUP_HUGETLB=y CONFIG_CGROUP_PERF=y CONFIG_CGROUP_SCHED=y CONFIG_BLK_CGROUP=y # CONFIG_DEBUG_BLK_CGROUP is not set CONFIG_NET_CLS_CGROUP=m CONFIG_NETPRIO_CGROUP=m Note: My host defaults still to upstart.