[systemd-devel] minimal required units

[Aaron_Wright at selinc.com]

Andrei Borzenkov <arvidjaar at gmail.com> wrote on 03/11/2015 08:47:43 PM:

> From: Andrei Borzenkov <arvidjaar at gmail.com>
> To: Aaron_Wright at selinc.com
> Cc: systemd-devel at lists.freedesktop.org
> Date: 03/11/2015 08:47 PM
> Subject: Re: [systemd-devel] minimal required units
> 
> В Wed, 11 Mar 2015 12:02:29 -0700
> Aaron_Wright at selinc.com пишет:
> 
> > I'm trying to make an embedded device, and I would like to start with 
the 
> > minimal setup as possible. Are there some units that are required by 
> > systemd?
> > I ask because systemd is complaining about a missing rescue.target 
unit, 
> 
> When does it do it?

It was doing this because my default unit was not set correctly. But that 
isn't really the question. The question is, what units are required by 
systemd? How can I figure that out? It seems like rescue.target, 
local-fs.target, and local-fs-pre.target are required, but I've only 
discovered that after trial and error. I know the systemd.special man page 
lists a ton of special units, but it seems that not all of them are 
required. Right? Well, which ones are? I feel like I need to look through 
the code to see when a hardcoded unit is referenced, like rescue.target 
was, that I don't know about.

My device doesn't have many of the same requirements of a full desktop or 
server Linux, so I'm trying to strip out things from systemd, unit wise, 
that I don't want or need. I've customized sysinit.target and basic.target 
to just reference the units I want. And that seems to be going smooth, but 
it appears there are other units, that I didn't know about that are 
required, but that aren't documented as such (that I could find). This 
scares me a bit.
 
> 
> > but I don't list rescue.target as a dependency of any other unit.
> > However, grep tells me that /usr/lib/systemd/systemd contains the 
> > "rescue.target" string, which worries me. Is there a list of all the 
units 
> > that are required, even though no other unit lists them?

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