Re: reconfiguring

[Carlo Zancanaro]

On Tue, Feb 13 2018, Leo Famulari wrote:
> > That’s a misunderstanding.  All of the things in the “services” 
> > field of
> > your operating-system configuration are “system services”, so 
> > all of
> > them get updated.
>
> But, it doesn't try to stop and restart those services in case 
> of any
> relevant changes, right? Doesn't that require a reboot?

The "system services" aren't services in the sense of being 
started/stopped. They are an extensible way to modify the system, 
such that one "service" can depend on another for its behaviour. 
For example, the `etc-service-type` is responsible for putting 
files in /etc, and so other services can "extend" it with files 
that they want placed in /etc. The concept of "starting" and 
"stopping" these services isn't really meaningful, because they 
just specify the state of the system. These services have an 
effect when you reconfigure.

One of the things that a "system service" can do is to register a 
Shepherd service. This is a process which will be invoked by 
Shepherd (pid 1), and can be started/stopped with the `herd` 
command. Reconfigure will not register any new Shepherd services, 
if doing so would involve starting an already-running service. So, 
for instance, you probably have a `guix-daemon` process running on 
your system. Reconfiguring your system will not upgrade (and thus 
restart) your `guix-daemon`. You need to reboot to have the new, 
updated, `guix-daemon` process. (Ideally you would only have to 
stop/start the Shepherd service manually to have the updated 
version, but at the moment doing so will just restart the old 
version.)

Hopefully that explanation is helpful. I also hope it's correct.

Carlo

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