Re: [ptxdist] systemd: Using second offline update service beside rc-once in PTXDIST

[Michael Olbrich <m.olbrich@pengutronix.de>]

Hi,

On Thu, Jun 01, 2017 at 02:51:46PM +0000, Schenk, Gavin wrote:
> before continuing to hack ptxdist and rc-once, I would appreciate some
> feedback from the gurus.
>  
> I want to use systemd.offline-updated as introduced here and already used in PTXDIST by rc-once:
> https://www.freedesktop.org/software/systemd/man/systemd.offline-updates.html#
> 
> In my use case, I have to do some data-migration stuff on an already
> delivered target. The data-migration has some deep impacts on the targets
> storages and I want to ensure no other stuff is running on the machine.
> Additionally I would like to provide my customers some gui when transforming
> the targets data. As the migration is done via shell scripts I use pv and
> dialog. To be able to use dialog a VT on the framebuffer I have to do some
> settings in the service file e.g.:
> 
> ...
> StandardOutput=tty
> StandardInput=tty
> TTYPath=/dev/tty1
> TTYReset=yes
> TTYVHangup=yes
> ...
> 
> One of my problems is, that rc-once does not check where /system-update
> points to, as suggested. My idea is to install a second update-service that
> does the migration stuff instead of hacking rc-once service file and do it
> there. Running both in parallel is a bad idea!
>  
> What do you think about using readlink in systemd-rc-once and just exit
> without error if /system-update does point to another location than
> /etc/rc-once?
> Another idea is to add a second service that doesn´t check /system-update
> either and use a after directive in its service file?
> Is this something we want a common solution for?

I think checking the link target for /system-update is a good solution.
This will keep things separated. But make sure the check is correct:
Currently /usr/sbin/enable-rc-once uses 'etc/rc.once.d' as link target and
/usr/lib/systemd/systemd-rc-once uses '/etc/rc.once.d' (in the fallback
case). I think that should be fixed, but both versions should be accepted
by systemd-rc-once.

Regards,
Michael

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