[SOLVED] Some LXC CT not starting after 7.0 update


Active Member
Dec 5, 2017
We updated 2 of our hypervisor from 6.4 to 7.0. Some containers started fine while other refused to start even after a backup/restore.

Here's the error I'm getting
lxc-start -n 133 -F -l DEBUG -o /tmp/lxc-133.log
Failed to mount cgroup at /sys/fs/cgroup/systemd: Operation not permitted
[!!!!!!] Failed to mount API filesystems, freezing.
Freezing execution.

I've attached the lxc-133.log file to this post

pct config 133
arch: amd64
cpulimit: 2
hostname: dev-webdav-1n1
memory: 1024
net0: bridge=vmbr0,hwaddr=EA:AD:7D:75:F3:D1,name=eth0,ip=,gw=
onboot: 1
ostype: ubuntu
rootfs: local-zfs:subvol-133-disk-1,size=350G
swap: 0

pve-manager: 7.0-10 (running version: 7.0-10/d2f465d3)
pve-kernel-5.11: 7.0-5
pve-kernel-helper: 7.0-5
pve-kernel-5.4: 6.4-4
pve-kernel-5.11.22-2-pve: 5.11.22-4
pve-kernel-5.4.124-1-pve: 5.4.124-2
pve-kernel-5.4.114-1-pve: 5.4.114-1
pve-kernel-5.4.106-1-pve: 5.4.106-1
ceph-fuse: 14.2.21-1
corosync: 3.1.2-pve2
criu: 3.15-1+pve-1
glusterfs-client: 9.2-1
ifupdown: residual config
ifupdown2: 3.1.0-1+pmx2
ksm-control-daemon: 1.4-1
libjs-extjs: 7.0.0-1
libknet1: 1.21-pve1
libproxmox-acme-perl: 1.2.0
libproxmox-backup-qemu0: 1.2.0-1
libpve-access-control: 7.0-4
libpve-apiclient-perl: 3.2-1
libpve-common-perl: 7.0-5
libpve-guest-common-perl: 4.0-2
libpve-http-server-perl: 4.0-2
libpve-storage-perl: 7.0-9
libqb0: 1.0.5-1
libspice-server1: 0.14.3-2.1
lvm2: 2.03.11-2.1
lxc-pve: 4.0.9-4
lxcfs: 4.0.8-pve2
novnc-pve: 1.2.0-3
proxmox-backup-client: 2.0.4-1
proxmox-backup-file-restore: 2.0.4-1
proxmox-mini-journalreader: 1.2-1
proxmox-widget-toolkit: 3.3-5
pve-cluster: 7.0-3
pve-container: 4.0-8
pve-docs: 7.0-5
pve-edk2-firmware: 3.20200531-1
pve-firewall: 4.2-2
pve-firmware: 3.2-4
pve-ha-manager: 3.3-1
pve-i18n: 2.4-1
pve-qemu-kvm: 6.0.0-2
pve-xtermjs: 4.12.0-1
qemu-server: 7.0-10
smartmontools: 7.2-pve2
spiceterm: 3.2-2
vncterm: 1.7-1
zfsutils-linux: 2.0.5-pve1

Any idea what might cause this ?


  • lxc-133.log
    15.9 KB · Views: 3
Last edited:


Well-Known Member
Oct 28, 2014
Did you read the upgrade page?

Old Container and CGroupv2​

Since Proxmox VE 7.0, the default is a pure cgroupv2 environment. Previously a "hybrid" setup was used, where resource control was mainly done in cgroupv1 with an additional cgroupv2 controller which could take over some subsystems via the cgroup_no_v1 kernel command line parameter. (See the kernel parameter documentation for details.)

cgroupv2 support by the container’s OS is needed to run in a pure cgroupv2 environment. Containers running systemd version 231 (released in 2016) or newer support cgroupv2, as do containers that do not use systemd as init system in the first place (e.g., Alpine Linux or Devuan).

CentOS 7 and Ubuntu 16.10 are two prominent Linux distributions releases, which have a systemd version that is too old to run in a cgroupv2 environment, for details and possible fixes see: https://pve.proxmox.com/pve-docs/chapter-pct.html#pct_cgroup_compat


Active Member
Dec 5, 2017
I did read the upgrade note. I was under the impression that the CT was a 18.04 (as all our other CT) but turned out I forgot to upgrade it and it was still stuck at 16.04. I will redeploy it as a VM instead.

Thanks for the help


Active Member
Mar 23, 2011
Ran into this exact issue this week, upgrading some older ubuntu-14-LTS containers, didn't realize rolling to 16 would kill them :(

What I did to fix it:

lxc mount $CTID

chroot /var/lib/lxc/$CTID/rootfs

apt update

apt dist-upgrade

do-release-upgrade ((( none found - had to do it by hand ))

sudo sed -i 's/xenial/bionic/g' /etc/apt/sources.list

apt update

apt dist-upgrade

(towards the end, it complained about rsyslog - so I just apt removed rsyslog and ran apt dist-update again)

exit (from chroot)
unmount /var/lib/lxc/$CTID/rootfs

start Container as normal - viola!

It did complain:
WARN: old systemd (< v232) detected, container won't run in a pure cgroupv2 environment! Please see documentation -> container -> cgroup version.
Task finished with 1 warning(s)!

But it started. I could then console in, and do-release-upgrade to get it 20 LTS, but at least it would start!!
Last edited:
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Active Member
Dec 29, 2016
I'll add a few nuances to my configuration from what @dlasher posted:
  • lxc mount $CTID did not work for me, I had to use pct mount $CTID and pct enter $CTID.
  • Proxmox must think the container is running already for pct enter to work, unfortunately. I didn't have good luck with chroot when the container was offline. This may not work for some people as Proxmox may completely block < CGroupv2 containers from starting.
  • When I was able to chroot into the container using pct enter, the network interface wasn't online. So I had to bring it online with ifup $INTERFACE (in my case it was just ifup eth0).
  • After the above steps, I was finally able to do a dist-upgrade with do-release-upgrade.
Here are the basic commands I used, in order:
pct mount $CTID

pct start $CTID

pct enter $CTID

ifup eth0



pct stop $CTID

pct unmount $CTID
Last edited:
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