/var dataset requires legacy mount on systemd based distros.

[gotwf]

When separating out /var and NOT using legacy mounts, journald writes to /var before zfs has initiated/mounted it. Hence, zfs will subsequently be unable to mount /var, as it now contains existing data. Note that I've not tested this very thoroughly, and it has been some years since I used zfs (so maybe I'm out in left field here....) but that sure looks to be what is happening.

[ryao]

systemd will need something like 3f1cc17 to address this.

[mailinglists35]

is this still an issue, right? I've just tried to migrate /var to zfs on centos7 but it does not get mounted in initrd process. if this is no longer an issue, what is the correct approach to migrate just /var from ext4 to zfs?

[sylveon]

I do not have this issue, but then my initrd mounts the /var partition before systemd even gets a chance to start.

[mailinglists35]

do you mind sharing your setup? i tried installing zfs-dracut and rebuilding initrd but systemd kicks in the initrd before zfs-import-cache

[rlaager]

A systemd generator (see issue #4898) was merged in PR #7329, so I think this is resolved in master, but not yet a release.

[mailinglists35]

@rlaager thank you. @behlendorf is this planned for being included in a 0.7.x update or will be later in 0.8.0?

[behlendorf]

@mailinglists35 it's planned for 0.8.0.

[zh99998]

does it work now?
I still can't mount /var without legacy mount.

debian buster, zfs 0.8.2

[rlaager]

@zh99998 Yes, but you have to be using the zfs-mount-generator, which is not enabled by default.

See step 5.8 here, starting with mkdir /etc/zfs/zfs-list.cache:
https://github.com/zfsonlinux/zfs/wiki/Debian-Buster-Root-on-ZFS