Composefs backend: /var unmount fails (at first)

[rlees85]

I think this is a systemd shortcoming but one the project should be aware of. I tried to start a discussion here: #2333 and after messing with it a lot came to the conclusion there is an issue.

When using composefs, systemd fails to unmount /var (I think it later successfully unmounts it during the shutdown/ramdisk phase).

On standard Silverblue installed with bootc it works fine.

I believe its because systemd is not aware of /var so much when using pure composefs.

with Ostree

$ cat /run/systemd/generator/var.mount 
##
# Automatically generated by ostree-system-generator
##

[Unit]
Documentation=man:ostree(1)
DefaultDependencies=no
ConditionKernelCommandLine=!systemd.volatile
After=local-fs-pre.target sysroot.mount
Before=local-fs.target

[Mount]
Where=/var
What=/sysroot/ostree/deploy/default/var
Options=bind,slave,shared

With composefs (pure)

$ systemctl status var.mount
● var.mount - /var
     Loaded: loaded (/proc/self/mountinfo)
     Active: active (mounted) since Mon 2026-07-27 13:05:52 BST; 5min ago
 Invocation: 2f58249fc3cb42b5a7a3082a8853152d
      Where: /var
       What: /dev/vda2

With composefs it has to learn about the mount retrospectively from /proc/self/mountinfo whereas something has generated the mount already for ostree.

Workaround

Create: /etc/systemd/system/systemd-journal-flush.service.d/override.conf

[Unit]
Requires=var.mount

Most other workarounds for general /var not unmounting properly dont seem to work.