cgroup v1 maintenance mode

content/en/docs/tasks/administer-cluster/cgroupv1-maintenance-mode.md

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+--- title: Moving cgroup v1 support into maintenance mode
+min-kubernetes-server-version: 1.31 content_type: task weight: 90 ---
+
+<!-- overview -->
+
+The Linux kernel community has made cgroup v2 the focus for new features,
+offering better functionality, a more consistent interface, and improved
+scalability. As a result, major Linux distributions and projects like systemd
+are phasing out support for cgroup v1. This trend creates an imperative for
+Kubernetes to align with these changes.
+
+
+<!-- steps -->
+
+
+## Why switch to cgroup v2?
+
+Switching to cgroup v2 offers enhanced functionality, a more consistent
+interface, and improved scalability, making it a superior choice for resource
+management in Kubernetes. The Linux kernel community and major projects like
+systemd are phasing out cgroup v1 in favor of cgroup v2, which is becoming
+the industry standard. By aligning with this trend, Kubernetes ensures
+better compatibility with the broader ecosystem, benefits from increased
+security and efficiency, and stays current with the latest advancements in
+Linux kernel resource management.
+
+
+## What Does Maintenance Mode Mean?
+
+Maintenance mode for cgroup v1 support in Kubernetes implies several key
+changes and priorities. Firstly, no new features will be introduced to
+the cgroup v1 support code; its existing functionality will be considered
+complete and stable. To ensure ongoing validation, a set of end-to-end (e2e)
+tests will be maintained for the currently supported features of cgroup
+v1. In terms of security, the Kubernetes community may provide fixes for
+Critical and Important CVEs related to cgroup v1, as long as the release
+is not end-of-life. Best-effort bug fixes will address critical security
+vulnerabilities on a priority basis, and major bugs will be evaluated for
+potential fixes if feasible solutions exist. However, some bugs in cgroup
+v1 support may remain unresolved, particularly those requiring substantial
+changes or fixes in the kernel or other dependencies.
+
+Importantly, removing cgroup v1 support is not a goal of this phase;
+deprecation and removal, if required, will be addressed in a future Kubernetes
+releases.
+
+## How to Determine the cgroup Version Used by Your Nodes
+
+To find out which version of cgroup your cluster nodes are using, refer to
+the `kubelet_cgroup_version` metric. For nodes running Linux, this metric
+will return either `1` for cgroup v1 or `2` for cgroup v2. For non-Linux
+operating systems, it will return `0`.
+
+Additionally, kubelet logs and events will display following warning message
+on cgroup v1 hosts: "Cgroup v1 support is in maintenance mode, please migrate
+to Cgroup v2."
+
+## Failing on cgroup v1 Nodes
+
+If you want to ensure that your cluster does not use nodes with cgroup v1,
+you can use the kubelet flag `--fail-cgroup-v1`. This flag will cause the
+kubelet to exit if it detects that the host is using cgroup v1. Note that
+this flag is disabled by default. Alternatively, you can set this option in
+the kubelet configuration by setting `FailCgroupV1` to `true`.
+
+
+
+