From: Wolfgang Bumiller Date: Mon, 28 Jun 2021 11:44:01 +0000 (+0200) Subject: pct: add short cgroup section X-Git-Url: https://git.proxmox.com/?p=pve-docs.git;a=commitdiff_plain;h=17238cd311d3d667a825d47dc6bb6369a731d20f pct: add short cgroup section Signed-off-by: Wolfgang Bumiller Reviewed-By: Stoiko Ivanov --- diff --git a/pct.adoc b/pct.adoc index 0c90106..b03b6ba 100644 --- a/pct.adoc +++ b/pct.adoc @@ -484,7 +484,54 @@ lxc.apparmor.profile = unconfined WARNING: Please note that this is not recommended for production use. -// TODO: describe cgroups + seccomp a bit more. +[[pct_cgroup]] +Control Groups ('cgroup') +~~~~~~~~~~~~~~~~~~~~~~~~~ + +'cgroup' is a kernel +mechanism used to hierarchically organize processes and distribute system +resources. + +The main resources controlled via 'cgroups' are CPU time, memory and swap +limits, and access to device nodes. 'cgroups' are also used to "freeze" a +container before taking snapshots. + +There are 2 versions of 'cgroups' currently available, +https://www.kernel.org/doc/html/v5.11/admin-guide/cgroup-v1/index.html[legacy] +and +https://www.kernel.org/doc/html/v5.11/admin-guide/cgroup-v2.html['cgroupv2']. + +Since {pve} 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 +https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html[kernel +parameter documentation] for details.) + +The main difference between pure 'cgroupv2' and the old hybrid environments +regarding {pve} is that with 'cgroupv2' memory and swap are now controlled +independently. The memory and swap settings for containers can map directly to +these values, whereas previously only the memory limit and the limit of the +*sum* of memory and swap could be limited. + +Another important difference is that the 'devices' controller is configured in a +completely different way. Because of this, file system quotas are currently not +supported in a pure 'cgroupv2' environment. + +If file system quotas are not required and the containers are new enough to +understand 'cgroupv2', it is recommended to stick to the new default. + +To switch back to the previous version the following kernel command line +parameter can be used: + +---- +systemd.unified_cgroup_hierarchy=0 +---- + +See xref:sysboot_edit_kernel_cmdline[this section] on editing the kernel boot +command line on where to add the parameter. + +// TODO: seccomp a bit more. // TODO: pve-lxc-syscalld @@ -603,6 +650,8 @@ Using Quotas Inside Containers Quotas allow to set limits inside a container for the amount of disk space that each user can use. +NOTE: This currently requires the use of legacy 'cgroups'. + NOTE: This only works on ext4 image based storage types and currently only works with privileged containers.