Hi,
Sebastian Wiesner wrote on 28/12/2021 00:04:
Hello,
I've experimented with homectl today, and noticed two issues when
creating LUKS-lookback-backed home areas on top of a btrfs filesystem:
1) homectl resize doesn't work reliably on btrfs: It looks as if on
btrfs resizing a home area requires more free space on the underlying
btrfs filesystem than I expected. I assumed that resizing from X to Y
only requires Y-X extra free space on the underlying device, but on
btrfs it seems to require Y free space, i.e. it looks as if homectl
attempts to allocate the entire home area anew.
I've found https://github.com/systemd/systemd/issues/19398 which looks
like the problem, but went nowhere.
2) homectl creates loopback files which have COW-enabled. As far as I
understand btrfs it's not recommended to enable COW for large files
which frequently get updated in-place which as far as I see it would
include the backing loopback files for LUKS home areas.
Shouldn't homectl explicitly disable COW for new home areas if the
underlying file system is btrfs?
I can work around 2) by setting -C on /home/ but I haven't figured out
a solution for 1)
Is LUKS on btrfs supported by homectl? Or should I rather use e.g.
ext4 as underlying file system for /home/?
I'm migrating to a similar setup with a new laptop so would be
interested in guidance/recommendations on this too if it's available.
Reddit/other google results seem a little dated.
Managed to get it working on Fedora 35 install with a little PAM
fighting and selinux tweaks.
Col