Error "Volume path already exists" when creating multiple VMs in parallel

Hello everyone,

I’m using LXD to create multiple virtual machines in parallel or very close time range. To do this, I launch them with lxc launch, stop them with lxc stop -f, and then delete them with lxc delete -f. I repeat this process to create new VMs.

This works most of the time, but occasionally I get an error message that says:

Error: Failed creating instance from image: Volume path "/var/snap/lxd/common/lxd/storage-pools/default/virtual-machines/vm-x" already exists

This error occurs even though I have successfully stopped and deleted the VM.

What should I do to resolve this error? I appreciate any help or suggestions you can provide.

Thank you!

What lxd version?

LXD version: 5.0.2
System: Ubuntu 22.04.2 LTS

I think install via snap stable channel:

sudo snap install lxd --channel=5.0/stable

I think the issue is from parallel creation, since if I create them one by one, it does not matter how many VMs I create I’m never getting this error

On a separate machine so you get aim issue with lxd 5.11 (if you upgrade your 5.0.2 install to 5.11 you won’t be able to downgrade again)?

It’s a testing machine anyway, I will try same with the latest version and will come back to you

sudo snap install lxd
lxd init --auto

lxd version: 5.11

Now getting different error randomly during lxc launch ... (3 out of 20 machines)

Stderr: Error: Failed creating instance from image: Failed reading image info 
Failed to run: prlimit --cpu=2 --as=1000000000 qemu-img info -f qcow2 --output=json /var/snap/lxd/common/lxd/images/102c0fdafc87c8be84a604f1cf4fdc2414f90bb31b9301fae1bba4d8201095a8.rootfs:
Process exited with non-zero value 1 (aa-exec: ERROR: profile 'lxd_qemu-img-var-snap-lxd-common-lxd-images-102c0fdafc87c8be84a604f1cf4fdc2414f90bb31b9301fae1bba4d8201095a8.rootfs' does not exist)


Error: Failed to begin transaction: context deadline exceeded

I think all these errors are due to fact that I’m launching them potentially in parallel (20 of them?), otherwise they seem to work

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Thanks, I’ll see if I can recreate the issue.

Do you have a simple script that causes it on your system?

Also, please can you show lxc storage show <pool> for the storage pool you’re using with the instances?

  source: /var/snap/lxd/common/lxd/storage-pools/default
description: ""
name: default
driver: dir
- /1.0/instances/worker-init
- /1.0/instances/worker-init/snapshots/snap
- /1.0/profiles/default
status: Created
- none

Unfortunately, it’s part of a big project.
We simultaneously creating/stopping/deleting VMs

Someone on Github had same or similar issue and they provided simple bash script to run vms in parallel, I think same can be used here as well

This error seems like maybe LXD is refreshing the base image do a different hash ID at the same time that the image is being used to create an image from it. There should be a lock that prevents this, but perhaps there’s an edge case here. I’ve assigned this to myself so will try and take a look ad reproducing it.

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Problem seems to be have more VM than my CPU can handle

I used to run 20 VMs with 4vcpu when I have total 24 cores, and that VMs each run full CPU capacity.
with more realistic load like 6 VMs, everything seems to work