Project: runc (Runtime / Container Runtime)
File: systemd.md

By default, runc creates cgroups and sets cgroup limits on its own (this mode is known as fs cgroup driver). When `--systemd-cgroup` global option is given (as in e.g. `runc --systemd-cgroup run ...`), runc switches to systemd cgroup driver. This document describes its features and peculiarities. When creating a container, runc requests systemd (over dbus) to create a transient unit for the container, and place it into a specified slice. The name of the unit and the containing slice is derived from the container runtime spec in the following way: If `Linux.CgroupsPath` is set, it is expected to be in the form `[slice]:[prefix]:[name]`. Here `slice` is a systemd slice under which the container is placed. If empty, it defaults to `system.slice`, except when cgroup v2 is used and rootless container is created, in which case it defaults to `user.slice`. Note that `slice` can contain dashes to denote a sub-slice (e.g. `user-1000.slice` is a correct notation, meaning a subslice of `user.slice`), but it must not contain slashes (e.g. `user.slice/user-1000.slice` is invalid). A `slice` of `-` represents a root slice. Next, `prefix` and `name` are used to compose the unit name, which is `<prefix>-<name>.scope`, unless `name` has `.slice` suffix, in which case `prefix` is ignored and the `name` is used as is. If `Linux.CgroupsPath` is not set or empty, it works the same way as if it would be set to `:runc:<container-id>`. See the description above to see what it transforms to. As described above, a unit being created can either be a scope or a slice. For a scope, runc specifies its parent slice via a Slice= systemd property, and also sets Delegate=true. For a slice, runc specifies a weak dependency on the parent slice via a Wants= property. runc always enables accounting for all controllers, regardless of any limits being set. This means it unconditionally sets the following properties for the systemd unit being created: CPUAccounting=true IOAccounting=true (BlockIOAccounting for cgroup v1) MemoryAccounting=true TasksAccounting=true The resource limits of the systemd unit are set by runc by translating the runtime spec resources to systemd unit properties. Such translation is by no means complete, as there are some cgroup properties that can not be set via

Therefore, runc systemd cgroup driver is backed by fs driver (in other words, cgroup limits are first set via systemd unit properties, and when by writing to cgroupfs files). The set of runtime spec resources which is translated by runc to systemd unit properties depends on kernel cgroup version being used (v1 or v2), and on the systemd version being run. If an older systemd version (which does not support some resources) is used, runc do not set those resources. The following tables summarize which properties are translated. | runtime spec resource | systemd property name | min systemd version | |--|--|| | memory.limit | MemoryLimit | | | cpu.shares | CPUShares | | | blockIO.weight | BlockIOWeight | | | pids.limit | TasksMax | | | cpu.cpus | AllowedCPUs | v244 | | cpu.mems | AllowedMemoryNodes | v244 | | runtime spec resource | systemd property name | min systemd version | |-|--|| | memory.limit | MemoryMax | | | memory.reservation | MemoryLow | | | memory.swap | MemorySwapMax | | | cpu.shares | CPUWeight | | | pids.limit | TasksMax | | | cpu.cpus | AllowedCPUs | v244 | | cpu.mems | AllowedMemoryNodes | v244 | | unified.cpu.max | CPUQuota, CPUQuotaPeriodSec | v242 | | unified.cpu.weight | CPUWeight | | | unified.cpu.idle | CPUWeight | v252 | | unified.cpuset.cpus | AllowedCPUs | v244 | | unified.cpuset.mems | AllowedMemoryNodes | v244 | | unified.memory.high | MemoryHigh | | | unified.memory.low | MemoryLow | | | unified.memory.min | MemoryMin | | | unified.memory.max | MemoryMax | | | unified.memory.swap.max | MemorySwapMax | | | unified.pids.max | TasksMax | | For documentation on systemd unit resource properties, see `systemd.resource-control(5)` man page. Auxiliary properties of a systemd unit (as shown by `systemctl show <unit-name>` after the container is created) can be set (or overwritten) by adding annotations to the container runtime spec (`config.json`). For example: ```json "annotations": { "org.systemd.property.TimeoutStopUSec": "uint64 123456789", "org.systemd.property.CollectMode":"'inactive-or-failed'" }, ``` The above will set the following properties: `TimeoutStopSec` to 2 minutes and 3 seconds; `CollectMode` to "inactive-or-failed". The values must be in the gvariant text format, as described in . To find out which type systemd expects for a particular parameter, please consult systemd sources.