[systemd-devel] [PATCH v3] systemd.service(5): add some simple examples

[Christian Seiler]

Am 27.01.2015 um 21:45 schrieb Lennart Poettering:
> On Tue, 27.01.15 17:45, Christian Seiler (christian at iwakd.de) wrote:
>> +                        <para>Note that systemd assumes here that the
>> +                        program will continue running in the foreground
>> +                        as long as it's active. If the program
> 
> I think "foreground" vs. "background" here is probably something to
> avoid. These are services after all, and hence kinda "background" in
> all cases. I am not sure how to explain this better though... Maybe
> clarify that the program does not fork on its own, and that the
> process systemd starts stays running until the very end of the
> daemon, or so.

Yes, you are completely right. I've kept the use of 'background' at some
places, but specifically avoided foreground, since that is really,
really misleading. I've also rephrased the paragraph in question. I hope
that's better.

>> +                        <para>Note that systemd will consider the unit
>> +                        to be in the state 'starting' until the program
>> +                        has terminated, so ordered dependencies will
>> +                        wait for the program to finish before starting
>> +                        themselves. The unit will revert to the
>> +                        'inactive' state after the execution is
>> +                        done. That means another request to start the
>> +                        unit will perform the action again.</para>
> 
> It might be worth also mentioning here that the the unit this way will
> never actually be "active". It will go directly from "activating" to
> "inactive", which might be surprising!

Thanks for the pointer, done!

Now I also mentioned something about multiple ExecStart= for oneshot
units, which might be useful there.

>> +                        <para>Similarly to the oneshot services, there
>> +                        are sometimes units that need to execute a
>> +                        program to set up something and then execute
>> +                        another to shut it down, but no process remains
>> +                        active while they are considered
>> +                        'started'. Network configuration can sometimes
>> +                        fall into this category.</para>
> 
> Another reason to use RemainAfterExit= are services that shall not
> execute again and again when they are pulled in, but only the first
> time...

Mentioned that, thanks!

>> <varname>RemainAfterExit=</varname><option>dbus</option>
> 
> Typo. Should be Type=, not RemainAfterExit=

*hehe* fixed.

>> +                <example>
>> +                        <title>Deferred (idle) services</title>
> 
> Hmm, I wonder if we maybe should remove this part. Idle services are
> kinda exotic, and I figure people might be tempted to misuse them. I
> think this might be something to document at the description of Type=,
> but not push people towards using this beyond that.

When I started writing this, I didn't just want to copy the getty
service (people can look that up anyway), so I decided to come up with
something else. However, once I wrote that unit, I realized that this
could have easily just been a Type=oneshot, RemainAfterExit=yes,
After=multi-user.target unit and have the same effect, and be a lot more
consistent with the rest of the way of doing things...

Type=idle is basically really just for gettys or something extremely
similar (like other interactive apps on VTs) that also get automatically
restarted.

Since these examples are supposed to provide a starting point for people
on how to write services, I've removed the section completely, and I
think this kind of special internal thing should remain in the reference
documentation.

v3 attached, I also fixed one or two other minor typos I noticed.

Christian

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