`krunkit` should create unix domain socket files

[unsuman]

Hello! I’m trying to add krunkit as a new backend driver to Lima, see: lima-vm/lima#4137. However, when attempting to add a virtio-vsock device for guest/host agent communication, krunkit fails to create the UNIX domain socket file. Is this a bug, or is it intended, and are we responsible for creating and handling the UDS file?

Krunkit Args

krunkit --memory 2048 --cpus 4 --device virtio-serial,logFilePath=/Users/ansumansahoo/.lima/krunkit/serial.log --krun-log-level 3 --restful-uri none:// --device virtio-blk,path=/Users/ansumansahoo/.lima/krunkit/diffdisk,format=raw --device virtio-blk,path=/Users/ansumansahoo/.lima/krunkit/cidata.iso --device virtio-vsock,port=2222,socketURL=/Users/ansumansahoo/.lima/krunkit/ga.sock --device virtio-net,type=unixstream,path=/Users/ansumansahoo/.lima/_networks/user-v2/user-v2_qemu.sock,mac=52:55:55:4a:a4:95 --device virtio-net,type=unixstream,path=/private/var/run/lima/socket_vmnet.shared,mac=52:55:55:0b:a2:3c

krunkit.log

[2025-10-17T08:19:24Z ERROR devices::virtio::console::device] Couldn't get terminal dimensions: ENODEV: No such device
[2025-10-17T08:19:24Z ERROR devices::virtio::console::device] Couldn't get terminal dimensions: ENODEV: No such device
[2025-10-17T08:19:25Z ERROR devices::virtio::console::device] Couldn't get terminal dimensions: ENODEV: No such device
[2025-10-17T08:20:27Z ERROR devices::virtio::vsock::muxer] unexpected dgram pkt: 3
[2025-10-17T08:21:27Z ERROR devices::virtio::vsock::muxer] unexpected dgram pkt: 3
[2025-10-17T08:22:27Z ERROR devices::virtio::vsock::muxer] unexpected dgram pkt: 3

Lima logs

time="2025-10-17T13:49:47+05:30" level=error msg="Failed to get guest agent connection: rpc error: code = Unknown desc = dial unix /Users/ansumansahoo/.lima/krunkit/ga.sock: connect: no such file or directory"

➜  krunkit pwd
/Users/ansumansahoo/.lima/krunkit
➜  krunkit ls -a | grep .sock
ha.sock
ssh.sock

In Lima, we dial to this UDS file to establish a connection. This connection is then used as the gRPC GuestAgent Client.

[jakecorrenti]

Hi @unsuman, sorry for the delay! At the moment krunkit depends on the socket path pointing to a pre-existing socket.

I would consider this intended, but if vfkit (who we're trying to keep parity with due to Podman) is creating the socket for the user, then that would make this a bug.

Thanks for your efforts on adding support to Lima!

[nirs]

@unsuman krunkit docs are missing details. Since it should be compatible with vfkit you can use vfkit docs:
https://github.com/crc-org/vfkit/blob/main/doc/usage.md#virtio-vsock-communication

@jakecorrenti we need to update krunkit docs so we don't need to tell user to go to vfkit docs. We can use this issue for this.

[unsuman]

Thanks

[unsuman]

I don't know Rust but I think krunkit is missing a connect vsockAction(available on vfkit, context: https://github.com/crc-org/vfkit/blob/main/doc/usage.md#arguments-10) which the vm creates the socket file on the host and listens on it for the host apps to connect to:

krunkit/src/virtio.rs

Lines 324 to 327 in 76fc38b

	pub enum VsockAction {
	#[default]
	Listen,
	}

And thanks to your design decision of krunkit with some tweaks to my existing krunkit branch I am able to run a vfkit instance using Lima and can confirm that vfkit handles the creation of the socket by itself and Lima successfully connects to the GuestAgent using this:

➜  krunkit pwd
/Users/ansumansahoo/.lima/krunkit
➜  krunkit ls -l
total 8036232
-rw-r--r--@ 1 ansumansahoo  staff     703007744 Oct 22 01:28 basedisk
-rw-r--r--@ 1 ansumansahoo  staff     307298304 Oct 25 20:19 cidata.iso
-r--r--r--@ 1 ansumansahoo  staff           408 Oct 25 20:19 cloud-config.yaml
srwxr-xr-x@ 1 ansumansahoo  staff             0 Oct 25 20:19 default_ep.sock
srwxr-xr-x@ 1 ansumansahoo  staff             0 Oct 25 20:19 default_fd.sock
-rw-r--r--@ 1 ansumansahoo  staff  107374182400 Oct 25 20:33 diffdisk
-rw-r--r--@ 1 ansumansahoo  staff          3154 Oct 25 20:19 driver.stderr.log
srwxr-xr-x@ 1 ansumansahoo  staff             0 Oct 25 20:19 ga.sock
-rw-r--r--@ 1 ansumansahoo  staff             6 Oct 25 20:19 ha.pid
srwxr-xr-x@ 1 ansumansahoo  staff             0 Oct 25 20:19 ha.sock
-rw-r--r--@ 1 ansumansahoo  staff         23216 Oct 25 20:32 ha.stderr.log
-rw-r--r--@ 1 ansumansahoo  staff           167 Oct 25 20:20 ha.stdout.log
-rw-r--r--@ 1 ansumansahoo  staff          2018 Oct 25 20:19 krunkit.log
-rw-r--r--@ 1 ansumansahoo  staff             6 Oct 25 20:19 krunkit.pid
-r--r--r--@ 1 ansumansahoo  staff            30 Oct 25 20:19 lima-version
-rw-r--r--@ 1 ansumansahoo  staff           474 Oct 25 20:19 lima.yaml
-rw-------@ 1 ansumansahoo  staff           131 Oct 25 20:19 serial.log
-rw-------@ 1 ansumansahoo  staff           698 Oct 25 20:19 ssh.config
srw-------@ 1 ansumansahoo  staff             0 Oct 25 20:19 ssh.sock
srwxr-xr-x@ 1 ansumansahoo  staff             0 Oct 25 20:19 vfkit-2222.sock # socket created by vfkit
-rw-------@ 1 ansumansahoo  staff        131072 Oct 25 20:19 vfkit-efi

[jakecorrenti]

Thanks @unsuman for doing the digging around to figure that out, I'll look into adding the missing vsock options this week :)