Control groups

vpsAdminOS supports primarily cgroups mounted in a hybrid hierarchy: cgroupv1 is used for controllers and cgroupv2 only tracks processes. cgroupv2 in a unified hierarchy is fully supported and we expect to make it the new default in 2023.

Configuring cgroup hierarchy

vpsAdminOS defaults to the hybrid hierarchy, but optionally can be booted into the unified hierarchy by setting boot.enableUnifiedCgroupHierarchy. Cgroup mode can also be changed using kernel parameter osctl.cgroupv.

Container cgroups

Available cgroups hierarchies in the containers depend on the host system. If the host uses the hybrid hierarchy, then containers must use it as well. If, on the other hand, the host uses unified hierarchy, then containers must use it, too.

Containers with systemd are handled automatically. osctld adds or removes systemd parameter systemd.unified_cgroup_hierarchy which controls its behaviour.

Containers without systemd need up-to-date init script from container images provided by vpsAdminOS in order to support the unified hierarchy.

Cgroupv2 support in distributions

The following distributions support cgroupv2:

  • Alpine Linux with up-to-date init script
  • CentOS / Alma Linux / Rocky Linux >= 8
  • Debian >= 9
  • Devuan with up-to-date init script
  • Fedora >= 31 (possibly older)
  • NixOS >= 19.03 (possibly older)
  • openSUSE Leap >= 15.1 (possibly older)
  • Ubuntu >= 18.04
  • Void Linux with up-to-date init script

Older distributions with systemd that does not support cgroupv2 will not start on vpsAdminOS using the unified hierarchy.