Linux Kernel Version Requirements

Many features rely on specific kernel functionalities and have minimum kernel version requirements. However, relying solely on kernel version numbers may not be sufficient for certain operating system distributions, as maintainers for distributions such as RHEL, Ubuntu and SUSE often backport selected features to older kernel releases (retaining the older kernel version).

Pod sysctls

On Linux, the sysctl() system call configures kernel parameters at run time. There is a command line tool named sysctl that you can use to configure these parameters, and many are exposed via the proc filesystem.

Some sysctls are only available if you have a modern enough kernel.

The following sysctls have a minimal kernel version requirement, and are supported in the safe set:

• net.ipv4.ip_local_reserved_ports (since Kubernetes 1.27, needs kernel 3.16+);
• net.ipv4.tcp_keepalive_time (since Kubernetes 1.29, needs kernel 4.5+);
• net.ipv4.tcp_fin_timeout (since Kubernetes 1.29, needs kernel 4.6+);
• net.ipv4.tcp_keepalive_intvl (since Kubernetes 1.29, needs kernel 4.5+);
• net.ipv4.tcp_keepalive_probes (since Kubernetes 1.29, needs kernel 4.5+);
• net.ipv4.tcp_syncookies (namespaced since kernel 4.6+).
• net.ipv4.vs.conn_reuse_mode (used in ipvs proxy mode, needs kernel 4.1+);

kube proxy nftables proxy mode

For Kubernetes 1.31, the nftables mode of kube-proxy requires version 1.0.1 or later of the nft command-line tool, as well as kernel 5.13 or later.

For testing/development purposes, you can use older kernels, as far back as 5.4 if you set the nftables.skipKernelVersionCheck option in the kube-proxy config. But this is not recommended in production since it may cause problems with other nftables users on the system.

Version 2 control groups

Kubernetes cgroup v1 support is in maintained mode starting from Kubernetes v1.31; using cgroup v2 is recommended. In Linux 5.8, the system-level cpu.stat file was added to the root cgroup for convenience.

In runc document, Kernel older than 5.2 is not recommended due to lack of freezer.

Other kernel requirements

Some features may depend on new kernel functionalities and have specific kernel requirements:

1. Recursive read only mount: This is implemented by applying the MOUNT_ATTR_RDONLY attribute with the AT_RECURSIVE flag using mount_setattr(2) added in Linux kernel v5.12.
2. Pod user namespace support requires minimal kernel version 6.5+, according to KEP-127.
3. For node system swap, tmpfs set to noswap is not supported until kernel 6.3.

Linux kernel long term maintenance

Active kernel releases can be found in kernel.org.

There are usually several long term maintenance kernel releases provided for the purposes of backporting bug fixes for older kernel trees. Only important bug fixes are applied to such kernels and they don't usually see very frequent releases, especially for older trees. See the Linux kernel website for the list of releases in the Longterm category.

What's next

• See sysctls for more details.
• Allow running kube-proxy with in nftables mode.
• Read more information in cgroups v2.