Okay, so I found solution for my problem above, but maybe someone can tell me if and how it would be possible to change runtime from runc to crun in existing cluster?

we don’t support crun

there is crun on the host (shipped together with podman) but I guess it is on wrong path then?

if you’ve done that, then setting it to be the default runtime should work… but you’ll still need to manually delete all the existing pods if you want them switched over to it.

cat /var/lib/rancher/k3s/agent/etc/containerd/config.toml | grep crun
  default_runtime_name = "crun"
[plugins.'io.containerd.cri.v1.runtime'.containerd.runtimes.'crun']
[plugins.'io.containerd.cri.v1.runtime'.containerd.runtimes.'crun'.options]
  BinaryName = "/usr/bin/crun"

Does this mean it found it?

yep

Everything works, but still under runc apparently

what are you seeing that suggests its still using runc

cat /var/lib/rancher/k3s/agent/etc/containerd/config.toml | grep runtime_type
  runtime_type = "io.containerd.runc.v2"
  runtime_type = "io.containerd.runhcs.v1"
  runtime_type = "io.containerd.runc.v2"

and I see processes ending with

containerd-shim-runc-v2

that is just the type. that does not determine what runtime binary is actually used.

okay, so maybe it actually uses crun, I kinda eexpected the

containerd-shim-runc-v2

to be gone

no that does not change

ok, so thx for help, I will try read on how that stuff works

what are you hoping to get out of using crun? it sounds like you’re not quite sure what to look for.

I was reading it is faster, more lightweight. Also I like to tinker with stuff.

note that even in the example config for crun provided by upstream, it still uses the runc.v2 runtime type. That is because crun has the same calling api as runc. https://github.com/containerd/containerd/blob/v2.1.3/docs/cri/config.md?plain=1#L97-L101