Re: Running VDR from systemd on Raspberry Pi OS

Sun, Dec 25, 2022 at 01:10:51PM +0100, Udo Richter wrote:
>On 24.12.22 10:33, Marko Mäkelä wrote:
>>then
>>   sudo service vdr stop
>>   sudo umount /video
>>   sudo udisksctl power-off -b /dev/sda
>>fi
>>
>>The first step appears to terminate the shell script, because the shell
>>is a subprocess of VDR. So, the storage will remain mounted and powered
>>on. I guess that we need to launch a separate "vdr-shutdown" service
>>that would take care of the remaining steps. Has someone already
>>implemented something like this?
>
>Maybe you can prevent that by backgrounding and setting some bash trap's
>on SIGINT or SIGKILL.

All these steps depend on each other: VDR must be stopped before the 
video directory can be unmounted, and actually any pending writes should 
be durably submitted before the device is powered off. That would make 
any asynchronous invocation a little more challenging.

I did not test it carefully yet, but I understood from the systemd 
documentation that the following might work as intended (umount as soon 
as all file handles are closed by VDR):

sudo systemd-umount /video
sudo service vdr stop

I just learned about "man systemd.mount" via this question on automating 
backups to USB storage: https://unix.stackexchange.com/questions/89881/

>However, I'd say the most clean way is to include the unmount and 
>udiskctrl into the vdr shutdown itself, so these commands run within 
>the vdr service after the vdr process stops. That way you just have to 
>fire the service stop and are done.

Do you mean implementing that as part of VDR plugin?

>Or if you want to go full systemd, you can probably do a service that 
>does the mount/unmount/poweroff on start/stop, and then add that as 
>requirement to the vdr service.

A simple change to the shutdown script would be to have it execute 
something like "sudo shutdown -h now" (or whatever invocation systemd 
prefers). That will umount and power off the USB storage just fine.

I think that I might actually go down that route, because currently the 
Raspberry Pi runs no other services than VDR. Except for the -s script, 
the vdr.service file that I posted yesterday already works for me.

I did not find any systemd integration with udisksctl, other than as 
part of an implicit poweroff service.

I could also avoid defining a shutdown script at all, and instead define 
a command script for invoking shutdown. That could be invoked when there 
are no timed recordings coming up for a while. I would have to remember 
to power up the system manually for the next timed recording. This would 
allow the power button on the remote control to be mapped to a "suspend" 
function that would make VDR stop the video output and stop polling the 
tuner. The USB SSD could remain powered on; I do not think it will 
consume much power when not being accessed.

	Marko

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