Ubuntu 20.04.2 LTS installer crash when letting the system determine size of additional LV

[Conny Molin]

Tested on VMware ESXi 6.5/6.7

Trying to install a VM using the graphical installer and using i.e. a 60GB disk, letting the system autoprovision the required partitions naturally creates a VG on the entire disk, and an LV of roughly 50% of the VG size. If you then create a secondary LV on the same VG and do not fill in the size of the LV, the system should claim all remaining space. However, this causes the installer to crash, not instantly, but a few seconds after having confirmed the partition layout (when you are on the user creation part of the install).

Lowering the size of the additional LV by as little as ~500MB solves the issue and the installer runs just fine through everything.

[Michael Hudson-Doyle (mwhudson)]

Are you enabling encryption in the guided screen? This sort of bug means we are mis-estimating how large the VG is going to be and we've had a few bugs like this in the past but I thought they were mostly fixed. The .crash file from /var/crash would be great help in figuring out what is going on.

[Conny Molin (connymolin)]

No, encryption haven’t been enabled. Just a plain vanilla vm with a single disk (hw ver 13, paravirtual scsi controller, thin provisioned disk residing on a Netapp flash SAN).

I’ve worked around it already so I don’t have a .crash file at the time of this writing. It’s easily reproduced though so I’ll deploy a new vm in the morning and get you that file.

Anything else you know you might need to aid in this investigation?

[Conny Molin (connymolin)]

Attached is the .crash log.

[Conny Molin (connymolin)]

I took a few screenshots as well if they are of interest.

[Michael Hudson-Doyle (mwhudson)]

Thanks for the crash file and sorry for the slow response. From the crash file:

   Volume group "ubuntu-vg" has insufficient free space (6271 extents): 6272 required.

We are only off by one! I think the lesson here is that we need to be more careful about LV sizes, this code is basically assuming one can take the size of the VG, divide it by two and create two LVs of that size but that's not really true, you can only create LVs whose size is a multiple of the extent size, which is by default 4MiB (and subiquity does not allow controlling this).

[Michael Hudson-Doyle (mwhudson)]

https://github.com/canonical/subiquity/pull/1068