Re: systemd.setenv and a mount.unit

[Goffredo Baroncelli <kreijack@inwind.it>]

On 2014-11-19 23:48, Jakob Schürz wrote:
> Hi there!
> 
> Another challenge... I'm using btrfs. So i make snapshots from my
> system. And in a script, I make a symlink (for example:
> @system.CURRENT and @system.LAST) for the current and the last
> snapshot.

Interesting, I was unaware that I could mount a subvolume passing
a "soft" link.

> 
> So i want to add 2 entries in grub2 from which i can boot into the
> current and the last snapshot.
> 
> I tried to pass an environmental variable with
> systemd.setenv=BOOTSNAP=@system.CURRENT, and i have a mount-unit
> containing the option
> 
> Options=defaults,nofail,subvol=archive-local/@system.$BOOTSNAP
> 
> but it doesn't work. If i change $BOOTSNAP to CURRENT, the mount
> works. So i made a test.service, containing only StartExec=/bin/echo
> $BOOTSNAP I get the value @system.CURRENT in the logs...

This is more a systemd related question. However it seems that ExecStart 
supports "...basic environment variable substitution..."; but the mount unit
doesn't. This explain your difficulties. Anyway I suggest you to contact the 
systemd developers to get further support; maybe that this could be a add as
TODO item.

> How can I do this mounts?

For the boot, I used the "rootflags=" command line options. This 
usually is interpreted by the initrd/initramfs as option to pass
to the mount command. In my case I have:

	rootflags=subvol=debian

so, the subvol=debian option is passed to mount. When grub-mkconfig
generates the grub menu entries, does so.


> jakob
BR
G.Baroncelli

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