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doc: Add “Inspecting Services” section.

* doc/guix.texi (Inspecting Services): New subsection.

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Ludovic Courtès 2024-02-21 15:47:40 +01:00
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@ -17536,6 +17536,61 @@ Alternatively, the @code{modify-services} macro can be used:
(delete avahi-service-type))
@end lisp
@unnumberedsubsec Inspecting Services
@cindex troubleshooting, for system services
@cindex inspecting system services
@cindex system services, inspecting
As you work on your system configuration, you might wonder why some
system service doesn't show up or why the system is not as you expected.
There are several ways to inspect and troubleshoot problems.
@cindex dependency graph, of Shepherd services
First, you can inspect the dependency graph of Shepherd services like
so:
@example
guix system shepherd-graph /etc/config.scm | \
guix shell xdot -- xdot -
@end example
This lets you visualize the Shepherd services as defined in
@file{/etc/config.scm}. Each box is a service as would be shown by
@command{sudo herd status} on the running system, and each arrow denotes
a dependency (in the sense that if service @var{A} depends on @var{B},
then @var{B} must be started before @var{A}).
@cindex extension graph, of services
Not all ``services'' are Shepherd services though, since Guix System
uses a broader definition of the term (@pxref{Services}). To visualize
system services and their relations at a higher level, run:
@example
guix system extension-graph /etc/config.scm | \
guix shell xdot -- xdot -
@end example
This lets you view the @dfn{service extension graph}: how services
``extend'' each other, for instance by contributing to their
configuration. @xref{Service Composition}, to understand the meaning of
this graph.
Last, you may also find it useful to inspect your system configuration
at the REPL (@pxref{Using Guix Interactively}). Here is an example
session:
@example
$ guix repl
scheme@@(guix-user)> ,use (gnu)
scheme@@(guix-user)> (define os (load "config.scm"))
scheme@@(guix-user)> ,pp (map service-kind (operating-system-services os))
$1 = (#<service-type localed cabba93>
@dots{})
@end example
@xref{Service Reference}, to learn about the Scheme interface to
manipulate and inspect services.
@unnumberedsubsec Instantiating the System
@cindex system instantiation