guix.texi

@subsection Defining Services

The @code{(gnu services @dots{})} modules define several procedures that allow
users to declare the operating system's services (@pxref{Using the
Configuration System}).  These procedures are @emph{monadic
procedures}---i.e., procedures that return a monadic value in the store
monad (@pxref{The Store Monad}).  Examples of such procedures include:

@table @code
@item mingetty-service
return the definition of a service that runs @command{mingetty} to
offer a login service on the given console tty;

@item nscd-service
return a definition for libc's name service cache daemon (nscd);

@item guix-service
return a definition for a service that runs @command{guix-daemon}
(@pxref{Invoking guix-daemon}).
@end table

@cindex service definition
The monadic value returned by those procedures is a @dfn{service
definition}---a structure as returned by the @code{service} form.
Service definitions specifies the inputs the service depends on, and an
expression to start and stop the service.  Behind the scenes, service
definitions are ``translated'' into the form suitable for the
configuration file of dmd, the init system (@pxref{Services,,, dmd, GNU
dmd Manual}).

As an example, here is what the @code{nscd-service} procedure looks
like:

@lisp
(define (nscd-service)
  (mlet %store-monad ((nscd (package-file glibc "sbin/nscd")))
    (return (service
             (documentation "Run libc's name service cache daemon.")
             (provision '(nscd))
             (start `(make-forkexec-constructor ,nscd "-f" "/dev/null"
                                                "--foreground"))
             (stop  `(make-kill-destructor))

             (respawn? #f)
             (inputs `(("glibc" ,glibc)))))))
@end lisp

@noindent
The @code{inputs} field specifies that this service depends on the
@var{glibc} package---the package that contains the @command{nscd}
program.  The @code{start} and @code{stop} fields are expressions that
make use of dmd's facilities to start and stop processes (@pxref{Service
De- and Constructors,,, dmd, GNU dmd Manual}).  The @code{provision}
field specifies the name under which this service is known to dmd, and
@code{documentation} specifies on-line documentation.  Thus, the
commands @command{deco start ncsd}, @command{deco stop nscd}, and
@command{deco doc nscd} will do what you would expect (@pxref{Invoking
deco,,, dmd, GNU dmd Manual}).


@c *********************************************************************
@node Contributing
@chapter Contributing

This project is a cooperative effort, and we need your help to make it
grow!  Please get in touch with us on @email{guix-devel@@gnu.org} and
@code{#guix} on the Freenode IRC network.  We welcome ideas, bug
reports, patches, and anything that may be helpful to the project.  We
particularly welcome help on packaging (@pxref{Packaging Guidelines}).

Please see the
@url{http://git.savannah.gnu.org/cgit/guix.git/tree/HACKING,
@file{HACKING} file} that comes with the Guix source code for practical
details about contributions.


@c *********************************************************************
@node Acknowledgments
@chapter Acknowledgments

Guix is based on the Nix package manager, which was designed and
implemented by Eelco Dolstra.  Nix pioneered functional package
management, and promoted unprecedented features, such as transactional
package upgrades and rollbacks, per-user profiles, and referentially
transparent build processes.  Without this work, Guix would not exist.

The Nix-based software distributions, Nixpkgs and NixOS, have also been
an inspiration for Guix.

@c *********************************************************************
@node GNU Free Documentation License
@appendix GNU Free Documentation License

@include fdl-1.3.texi

@c *********************************************************************
@node Concept Index
@unnumbered Concept Index
@printindex cp

@node Function Index
@unnumbered Function Index
@printindex fn

@bye

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