service_mgr: detect systemd, even offline

[jamescassell]

SUMMARY

Currently, systemd is only detected as the service manager if systemd is actually running. This also adds a check that will detect systemd ever if it is not currently running, such as during a container bulid.

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

service_mgr

ADDITIONAL INFORMATION

[jamescassell]

@bcoca if I were to remove this section, would you be okay merging it? This would leave only the SUSE family of distros out in the cold. All other systemd-based distros I tried have /sbin/init as a symlink to systemd. Same for debian jessie when in systemd mode. If you switch it to sysVinit mode, /sbin/init is no longer a symlink to systemd but is instead the SysV binary.

I could find no non-systemd distro where systemctl is an available package and /sbin/init is missing... If you can identify such a distro, I can look to see how to handle it.

FWIW, the linux service_mgr code has been unmodified since you originally introduced it, except for a small tweak for openrc.

[bcoca]

off top of my head, gentoo (i used it w/o systemd, but with systemctl installed), but mostly i would just look at previous tickets that posed the issue (i installed systemctl on my workstation just to test this).

IIRC the most common case was using a container for a distro that defaults to systemd, while the host is not using systemd.

[jamescassell]

Thanks for checking. I've removed these lines. I've found that OpenSUSE and friends have an optional systemd-sysvinit package that provides this symlink. (Their initrd has /init symlinked to /usr/lib/systemd/systemd, so no technical need for /sbin/init to be symlinked given that they're using an initrd.)

[samdoran]

This issue has been discussed extensively in several IRC meetings and we are reluctantly going to merge this.

There a lot of potential unknown issues this autodetection could introduce. While this change is helpful in the use case described above, it very well may break other use cases. We just don't know. This is why we added the use parameter to the service module, allowing playbook authors to specify the service manager rather than relying on the automatic detection.

That's still the approach we favor over improving the autodetection, but @jamescassell has advocated heavily for this change and is willing to help with the fallout.

rebuild_merge