# External runtime dependencies k0s is packaged as a single binary, which includes all the needed components. All the binaries are statically linked which means that in typical use cases there's an absolute minimum of external runtime dependencies. However, depending on the node role and cluster configuration, some of the underlying components _may_ have specific dependencies, like OS level tools, packages and libraries. This page aims to provide a comprehensive overview. The following command checks for known requirements on a host (currently only available on Linux): ```shell k0s sysinfo ``` ## Linux specific ### Linux kernel configuration Needless to say, as k0s operates Kubernetes worker nodes, a certain number of Linux kernel modules and configurations are required on the host. This essentially stems from the requirement to run containers and set up networking for them. The needed kernel configuration items are listed below. All of them are available in Kernel versions 4.3 and above. If running on older kernels, check if the distro in use has backported some features; nevertheless, it might meet the requirements. k0s will check the Linux kernel release as part of its pre-flight checks and issue a warning if it's below 3.10. The list covers ONLY the k0s/Kubernetes components' needs on worker nodes. Your own workloads may require more. - [`CONFIG_CGROUPS`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L927): Control Group support - [`CONFIG_CGROUP_SCHED`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1081): Group CPU scheduler - [`CONFIG_FAIR_GROUP_SCHED`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1090): Group scheduling for SCHED_OTHER
[kubernetes/kubeadm#2335 (comment)](https://github.com/kubernetes/kubeadm/issues/2335#issuecomment-717996215) - _(optional)_ [`CONFIG_CFS_BANDWIDTH`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1095): CPU bandwidth provisioning for FAIR_GROUP_SCHED
Required if CPU CFS quota enforcement is enabled for containers that specify CPU limits (`--cpu-cfs-quota`). - _(optional)_ [`CONFIG_BLK_CGROUP`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1119): Block IO controller
[kubernetes/kubernetes#92287 (comment)](https://github.com/kubernetes/kubernetes/issues/92287#issuecomment-1010723587) - [`CONFIG_NAMESPACES`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1168): Namespaces support - [`CONFIG_UTS_NS`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1180): UTS namespace - [`CONFIG_IPC_NS`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1187): IPC namespace - [`CONFIG_PID_NS`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1210): PID namespace - [`CONFIG_NET_NS`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L1218): Network namespace - [`CONFIG_NET`](https://github.com/torvalds/linux/blob/v4.3/net/Kconfig#L5): Networking support - [`CONFIG_INET`](https://github.com/torvalds/linux/blob/v4.3/net/Kconfig#L58): TCP/IP networking - [`CONFIG_NETFILTER`](https://github.com/torvalds/linux/blob/v4.3/net/Kconfig#L109): Network packet filtering framework (Netfilter) - _(optional)_ [`CONFIG_NETFILTER_ADVANCED`](https://github.com/torvalds/linux/blob/v4.3/net/Kconfig#L171): Advanced netfilter configuration - [`CONFIG_NETFILTER_XTABLES`](https://github.com/torvalds/linux/blob/v4.3/net/netfilter/Kconfig#L567): Netfilter Xtables support - [`CONFIG_NETFILTER_XT_TARGET_REDIRECT`](https://github.com/torvalds/linux/blob/v4.3/net/netfilter/Kconfig#L853): REDIRECT target support - [`CONFIG_NETFILTER_XT_MATCH_COMMENT`](https://github.com/torvalds/linux/blob/v4.3/net/netfilter/Kconfig#L1002): "comment" match support - [`CONFIG_EXT4_FS`](https://github.com/torvalds/linux/blob/v4.3/fs/ext4/Kconfig#L33): The Extended 4 (ext4) filesystem - [`CONFIG_PROC_FS`](https://github.com/torvalds/linux/blob/v4.3/fs/proc/Kconfig#L1): /proc file system support **Note:** As part of its pre-flight checks, k0s will try to inspect and validate the kernel configuration. In order for that to succeed, the configuration needs to be accessible at runtime. There are some typical places that k0s will check. A bullet-proof way to ensure the accessibility is to enable [`CONFIG_IKCONFIG_PROC`](https://github.com/torvalds/linux/blob/v4.3/init/Kconfig#L807), and, if enabled as a module, to load the `configs` module: `modprobe configs`. ### Control Groups (cgroups) Both [cgroup v1] and [cgroup v2] are supported. Required [cgroup] controllers: - `cpu` - `cpuacct` - `cpuset` - `memory` - `devices` - `freezer` - `pids` Optional cgroup controllers: - `hugetlb` ([kubernetes/kubeadm#2335 (comment)]) - `blkio` ([kubernetes/kubernetes#92287 (comment)])
containerd and cri-o will use blkio to track disk I/O and throttling in both cgroup v1 and v2. [cgroup]: https://man7.org/linux/man-pages/man7/cgroups.7.html [cgroup v1]: https://www.kernel.org/doc/html/v5.16/admin-guide/cgroup-v1/ [cgroup v2]: https://www.kernel.org/doc/html/v5.16/admin-guide/cgroup-v2.html [kubernetes/kubeadm#2335 (comment)]: https://github.com/kubernetes/kubeadm/issues/2335#issuecomment-722405527 [kubernetes/kubernetes#92287 (comment)]: https://github.com/kubernetes/kubernetes/issues/92287#issuecomment-1010723587 ### No integration with Name Service Switch (NSS) APIs The k0s Linux binaries are by default statically linked against [musl libc]. This includes the binaries distributed on the GitHub releases pages. Static linking ensures that k0s can run seamlessly across a wide range of Linux environments by not requiring a specific standard C library to be installed on the host system. However, this design choice means that k0s cannot use [glibc's NSS APIs], which require dynamic linking. This limitation is particularly relevant when a system uses NSS plugins, such as [nss-myhostname], for resolving network names like `localhost`. Systems lacking a dedicated stub resolver capable of handling `localhost` DNS queries specifically will encounter issues running k0s. To mitigate this, users are advised to either activate a stub DNS resolver, such as `systemd-resolved`, or to manually add `localhost` entries to the `/etc/hosts` file as shown below: ```text 127.0.0.1 localhost ::1 localhost ``` [musl libc]: https://musl.libc.org/ [glibc's NSS APIs]: https://www.gnu.org/software/libc/manual/html_node/Name-Service-Switch.html [nss-myhostname]: https://www.freedesktop.org/software/systemd/man/latest/nss-myhostname.html ### External hard dependencies There are very few external tools that are needed or used. #### mount/umount When setting up pods, kubelet will call `mount` binary on the host. Similarly when destroying pods it will call `umount`. `mount` and `umount` are only needed on worker nodes where kubelet runs. ### External soft dependencies There are a few external tools that may be needed or used under specific circumstances: #### containerd and AppArmor In order to use containerd in conjunction with [AppArmor], it must be enabled in the kernel and the `/sbin/apparmor_parser` executable must be installed on the host, otherwise containerd will [disable][cd-aa] AppArmor support. [cd-aa]: https://github.com/containerd/containerd/blob/v1.7.30/pkg/apparmor/apparmor_linux.go#L34-L45 [AppArmor]: https://wiki.ubuntu.com/AppArmor #### iptables iptables may be executed to detect if there are any existing iptables rules and if those are in legacy or nft mode. If iptables is not found, k0s will assume that there are no pre-existing iptables rules. #### useradd / adduser During `k0s install` the external tool `useradd` will be used on the controllers to create system user accounts for k0s. If this doesn't exist it will fall-back to busybox's `adduser`. #### userdel / deluser `k0s reset` will execute either `userdel` or `deluser` to clean up system user accounts. #### modprobe On k0s worker `modprobe` will be executed to load missing kernel modules if they are not detected. #### id External `id` will be executed as a fallback if local user lookup fails, in case NSS is used. ## Windows specific TBD.