Detecting the init system in use

[Mike Pontillo]

On Wed, Dec 13, 2017 at 9:57 AM, Robie Basak <robie.basak at ubuntu.com> wrote:

> 1) Fix systemd on Trusty so that testing for /run/systemd/system works
> again. This will probably need to remove /run/systemd/system correctly
> on postinst as part of the fix. This will unbreak MAAS and snapd working
> together.
>
> 2) Come up with and agree on some other universal way for testing for
> systemd and make that work everywhere. Then we can SRU that test to MAAS
> in Trusty, and fix any other packages in Trusty affected by the
> behaviour change of the original test.
>
> 3) Accept that on Trusty the general case is now broken, and make the
> official test be something like the following. This will need to be
> SRU'd to MAAS in Trusty, and we'll need to fix any other packages in
> Trusty affected by the behaviour change of the original test.
>
>    if Trusty: upstart
>    else if [ -d /run/systemd/system ]: systemd
>    else [existing checks for other init systems]
>
> Are there any other options? Please discuss as you wish. My purpose in
> starting this thread is to record consensus once we have it, so the
> archive of this thread can be used to be consistent in how we handle
> fixing this.


We discussed this from the MAAS angle recently, and one of the options the
team came up with was to check what binary the `/proc/1/exe`link points to.
Unfortunately, you can't do that without elevated privileges, but we could
ship a simple setuid/setcap utility to do so. I've got a quick
proof-of-concept here, if that's an option:

    https://github.com/mpontillo/which-init-system

That said, MAAS 1.9 is intended to run on Trusty, and 2.0 through 2.3 are
intended to run on Xenial. Due to other dependencies that changed between
Trusty and Xenial, I don't think it would be practical to support MAAS on a
"Frankenstein" Trusty system that has been upgraded to Xenial but not
rebooted.

So that's somewhat a combination of (2) and (3). I think it's difficult to
predict if the benefit of doing (1) is worth the effort.

Regards,
Mike
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.ubuntu.com/archives/ubuntu-devel/attachments/20171213/78b7c9e7/attachment.html>