How to access data partition created with repart?

[danielbisar]

Host: Debian 12
mkosi v0.20.2 (git) + #2347
Target: Ubuntu focal

Lets say i have a mkosi.repart/20-data.conf with the following content:

[Partition]
Type=linux-generic
Format=ext4
SizeMinBytes=1G
SizeMaxBytes=1G

On boot the partition is also shown in the overview before systemd starts.

This is just the start of a more complex setup. So there are a few questions:

• there is no fstab?

• context: system booted with "mkosi boot": how do i mount the additional partition (lsblk show loop5 -> loop5p3), if i try mount -o loop loop5p3 /mnt it says permission denied; and I guess i should probably create some systemd mount files?

• mount does not seem to have it mounted

• access to internet does not work in mkosi.postinst, event though [Packages] -> WithNetwork=yes is set.

[DaanDeMeyer]

there is no fstab?

I am adding fstab support in systemd/systemd#30636. Until that lands, you have to write /etc/fstab yourself (which is complicated unless you use fixed UUIDS)

context: system booted with "mkosi boot": how do i mount the additional partition (lsblk show loop5 -> loop5p3), if i try mount -o loop loop5p3 /mnt it says permission denied; and I guess i should probably create some systemd mount files?

You cannot mount additional partitions from within a systemd-nspawn containers. These have to be mounted on the host and passed into the container. Maybe systemd-nspawn should look at fstab, but this is something related to systemd, not mkosi, so I'd suggest opening an issue in the systemd repo.

mount does not seem to have it mounted

There's no fstab, and systemd-nspawn doesn't automatically mount generic data partitions

access to internet does not work in mkosi.postinst, event though [Packages] -> WithNetwork=yes is set.

I'll need a lot more information that that to be able to debug this

[danielbisar]

Ok, thatnk you. I guess I missunderstood the concept a bit.

What I came up with is the following:

30-data.conf

[Partition]
Type=linux-generic
Format=ext4
CopyFiles=/data:/
SizeMinBytes=1G
SzeMaxBytes=1G

1. I create the data partition after the root, makes the order of loopback devices created more logical (1 = efi, 2 = root, 3 = data). I am wondering, since I thought that creating a the conf file like I had, that the content of /data will be deployed into the new partition and the content of the /data folder inside the root will be empty afterwards; the order root vs data doesn't seem to matter for that)
2. create the image with mkosi
3. on the host: create loop devices for each partition with `kpartx -av ./image.raw`
4. mount the root partition and delete the content of /data
5. mount the other partitions (in this case: /efi and /data)
6. boot using systemd-nspawn -b --directory=./my_root
7. umount via relative paths ./my_root/data, .../efi, ../
8. kpartx -dv ./image.raw

I am writing you this for two reasons:

1. I am suspecting I am doing something wrong OR there might be a bug in mkosi or both....
2. Maybe you didn't know about this kpartx thing; isn't without sudo, but at least a way

I probably will implement some kind of script that will parse the output of kpartx and automount at least for simple cases like (root, efi, additional parts) for our CI.