grub-mkconfig fails with ZFS when /etc/fstab was touched: find: ‘mount: (hint) your fstab has been modified, but systemd still uses[…]/tmp/zfsmnt.2a85H0/boot’: No such file or directory

[Louis Sautier]

Hello,
If /etc/fstab is newer than /run/systemd/systemd-units-load, mount emits a hint to STDOUT.
This causes the following mount call to return a message which is later interpreted as a path:
https://git.launchpad.net/~ubuntu-core-dev/grub/+git/ubuntu/tree/debian/patches/ubuntu-zfs-enhance-support.patch?h=debian/2.12-5ubuntu5.3#n180
https://git.launchpad.net/~ubuntu-core-dev/grub/+git/ubuntu/tree/debian/patches/ubuntu-zfs-enhance-support.patch?h=debian/2.12-5ubuntu5.3#n472
To reproduce:
* Install Ubuntu 25.04 with a /boot and a / dataset:
  root@test:~# zfs list
  NAME USED AVAIL REFER MOUNTPOINT
  zp0 2.73G 212G 24K none
  zp0/zd0 118M 906M 118M /boot
  zp0/zd1 2.61G 212G 2.61G /
* Run "touch /etc/fstab"

root@test:~# grub-mkconfig
Sourcing file `/etc/default/grub'
Generating grub configuration file ...
[…]
### BEGIN /etc/grub.d/10_linux_zfs ###
find: ‘mount: (hint) your fstab has been modified, but systemd still uses\n the old version; use 'systemctl daemon-reload' to reload.\n/tmp/zfsmnt.f2yDJq/boot’: No such file or directory
### END /etc/grub.d/10_linux_zfs ###
[…]

util-linux's upstream might change mount's behavior to skip the hint when STDOUT is not a TTY, see https://github.com/util-linux/util-linux/issues/3558#issuecomment-2854381281

In the meantime, I think it might be prudent to discard output from all mount calls from /etc/grub.d/10_linux_zfs, or to use upstream's 10_linux for ZFS too.

[Louis Sautier (lesbraz)]

Could you please backport this util-linux patch to fix the bug? https://github.com/util-linux/util-linux/commit/cdc8b265bff5ee1ebd496aa1d6211e4ba120f766