[systemd-devel] minimal required units

Aaron_Wright at selinc.com Aaron_Wright at selinc.com
Thu Mar 12 13:49:38 PDT 2015

Andrei Borzenkov <arvidjaar at gmail.com> wrote on 03/12/2015 12:18:15 PM:

> From: Andrei Borzenkov <arvidjaar at gmail.com>
> To: Aaron_Wright at selinc.com
> Cc: systemd-devel at lists.freedesktop.org
> Date: 03/12/2015 12:18 PM
> Subject: Re: [systemd-devel] minimal required units
> В Thu, 12 Mar 2015 11:09:57 -0700
> Aaron_Wright at selinc.com пишет:
> > 
> > I feel like there needs to be a list of required units to get base 
> > functionality out of systemd. So that embedded guys like me can build 
up a 
> > system from scratch, instead of starting from full blown desktop 
> > and guessing at what can be taken out.
> > 
> sysinit.target is supposed to get you minimal working system (more or
> less what you got with single user in the past). It could be considered
> as starting point. Most embedded systems I have seen were running
> something very close to single user anyway.

Right now, I'm starting with the basic.target. Gets me a few more features 
than sysinit.target, such as timers, which I feel I can use in my product 
to replace cron.

> > My question is mainly about whether the list of actual required units 
> > known, or if it is something that requires investigation (digging 
> > a bunch of code).
> > 
> Did you see bootup(7)?

Yes, I've read that a few times, and I love the diagram. It seems to 
suggest to me that I can use basic.target as a good synchronization point, 
and then add my units after that, which makes sense to me.

If I include at least all of the units leading up to basic.target, would 
that cover the units required by systemd? Though, that would include lots 
of things I don't need, such as cryptsetup.target, swap.target, mqueue, 
configfs, debugfs, etc.

I'm concerned because I left out local-fs.target to begin with, as I don't 
need systemd to mount anything, but that seemed to cause systemd to 
unmount everything other than / and the kernel file systems. So I got bit 
by there not being any documentation that says, "local-fs.target is 
Required". Unless, I'm missing something.

PS - Thanks for pointing me at information. I'm still getting up to speed 
on systemd.
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