Comment # 56 on bug 906900 from Thomas Blume

(In reply to Andrei Borzenkov from comment #55)
> 
> Why "su -" needs logind session in the first place? This seems to work in
> Arch without it; what are the real reasons to have pam_systemd for su?

According to the (OpenSUSE) manpage 'su -' is the same like 'su --login', which
is the command to create a login session.
If this is different on Arch, there seems to be a difference in the su package,
not in systemd.

> Anyway, here is test package for systemd that should fix it on systemd side. 
> It sets KillMode=none for scope units started from within sysvinit scripts. 
> Change is suprisingly small (all infrastructure was there already).

Already tried this.
Unfortunately, it doesn't help, since the processes are killed directly at
session logout, not by a timeout (see comment#24).