[arch-general] Automatically stop systemd service

[Robbie Smith]

On 29/03/13 00:39, Leonid Isaev wrote:
> On Thu, 28 Mar 2013 18:23:03 +1100
> Robbie Smith <zoqaeski at gmail.com> wrote:
>
>> TL;DR: More toying with mobile broadband and systemd; would like help
>> automatically stopping service depending on device availability.
>>
>> [...]
>>
>> What I cannot figure out how to do is automatically stop the service if
>> the device is unplugged, similar to how ifplugd works for wired ethernet
>> interfaces.
>
> How about "BindsTo=" from man 5 systemd.unit? For example,
> "BindsTo=sys-subsystem-net-devices-wap.device".
>
That looks like the right starting point. “PartOf=” seems like it’s 
intended to control units, not devices.

There’s a slight problem though: not only are the device names quite 
verbose[*], they aren’t persistent. Only the lowest-numbered USB serial 
port will communicate with the device; usually this is /dev/ttyUSB0 but 
sometimes it’s not. I have no idea what the other two or three do, and I 
couldn’t find documentation on minicom (or similar) to be able to probe 
them.

The new Linux persistent naming rules don’t apply to these devices, and 
udev rules seem so arcane I could never figure out how to write a rule 
that would give a consistent name to the accessible port.

[*] There do appear to be aliases to their names in /dev/, so this 
probably isn’t an issue.