How to make root-fs larger when RuntimeSize is configured?

[fwilhe2]

Hi, this might be my missing experience when working with systemd-repart but I could not figure out how to resolve this.

What I want is pretty simple: I'm building a dev vm using mkosi and I need a larger root-fs for building software inside the VM.

I fund the RuntimeSize parameter and setting that properly enlarges the disk image when booting the VM as expected, but the root fs is not enlarged, so I get a ESP and a root partition which only take up a small fraction of the disk. I could manually resize the partition but I think this should not be needed.

My question is: How can I configure mkosi so that given a RuntimeSize of 30Gig, my root partition takes up all remaining space? I'm fine when this is happening on first boot, but it should be automated.

I've tried configuring repart but that did not bring the expected result.

What's the most simple way to do this?

[DaanDeMeyer]

Put the following in mkosi.extra/usr/lib/repart.d/10-root.conf:

[Partition]
Type=root

That should be sufficient (you might need a somewhat recent systemd as I remember a recent bugfix for this).

Although for dev vms using mkosi I would skip the disk output completely and just use the directory output instead which will use virtiofs so there will be no need to select a size in the first place.

[fwilhe2]

Thanks, I'll try that out.

Btw, my host system is Fedora 39, and I'm building a VM for Debian Testing. I'm using mkosi from the Fedora repo which is currently at version 19, running with systemd 254 (254.7-1.fc39).

[Cornelicorn]

The commit from that MR is only in 255 yet, sadly, so you would need to try sid for Debian.

[fwilhe2]

Does that refer to the host or the system built by mkosi? Changing testing to sid should be fine.

[DaanDeMeyer]

@fwilhe2 The system built by mkosi, so you can change that to sid and it should resize the filesystem as well

[fwilhe2]

Yes, can confirm it works with sid.

Will look into the directory option, too.

Thanks for the support 💯