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doc: Add example showing how to customize 'nscd-service'.

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* doc/guix.texi (Name Service Switch): Add link to nss-mdns.  Add
  example show how to pass #:name-services to 'nscd-service'.
  (Base Services): Add link from 'nscd-service' to the above.
* gnu/services/base.scm (nscd-service): Update docstring accordingly.
This commit is contained in:
Ludovic Courtès 2015-04-12 22:34:47 +02:00
parent 99af4996ea
commit 4c9050c63d
2 changed files with 36 additions and 4 deletions
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38
doc/guix.texi
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@ -4531,7 +4531,8 @@ the ``message of the day''.
Return a service that runs libc's name service cache daemon (nscd) with
the given @var{config}---an @code{<nscd-configuration>} object.
Optionally, @code{#:name-services} is a list of packages that provide
name service switch (NSS) modules needed by nscd.
name service switch (NSS) modules needed by nscd. @xref{Name Service
Switch}, for an example.
@end deffn
@defvr {Scheme Variable} %nscd-default-configuration
@ -4898,9 +4899,12 @@ next method in the list. The NSS configuration is given in the
@code{name-service-switch} field of @code{operating-system} declarations
(@pxref{operating-system Reference, @code{name-service-switch}}).
@c See <http://0pointer.de/lennart/projects/nss-mdns/>.
@cindex nss-mdns
@cindex .local, host name lookup
As an example, the declaration below configures the NSS to use the
@code{nss-mdns} back-end for host name lookups:
@uref{http://0pointer.de/lennart/projects/nss-mdns/, @code{nss-mdns}
back-end}, which supports host name lookups over multicast DNS (mDNS)
for host names ending in @code{.local}:
@example
(name-service-switch
@ -4926,6 +4930,34 @@ As an example, the declaration below configures the NSS to use the
(name "mdns")))))
@end example
Note that, in this case, in addition to setting the
@code{name-service-switch} of the @code{operating-system} declaration,
@code{nscd-service} must be told where to find the @code{nss-mdns}
shared library (@pxref{Base Services, @code{nscd-service}}). Since the
@code{nscd} service is part of @var{%base-services}, you may want to
customize it by adding this snippet in the operating system
configuration file:
@example
(use-modules (guix) (gnu))
(define %my-base-services
;; Replace the default nscd service with one that knows
;; about nss-mdns.
(map (lambda (mservice)
;; "Bind" the MSERVICE monadic value to inspect it.
(mlet %store-monad ((service mservice))
(if (member 'nscd (service-provision service))
(nscd-service (nscd-configuration)
#:name-services (list nss-mdns))
mservice)))
%base-services))
@end example
@noindent
@dots{} and then refer to @var{%my-base-services} instead of
@var{%base-services} in the @code{operating-system} declaration.
The reference for name service switch configuration is given below. It
is a direct mapping of the C library's configuration file format, so
please refer to the C library manual for more information (@pxref{NSS

2
gnu/services/base.scm
View file

@ -499,7 +499,7 @@ (define* (nscd-service #:optional (config %nscd-default-configuration)
"Return a service that runs libc's name service cache daemon (nscd) with the
given @var{config}---an @code{<nscd-configuration>} object. Optionally,
@code{#:name-services} is a list of packages that provide name service switch
(NSS) modules needed by nscd."
(NSS) modules needed by nscd. @xref{Name Service Switch}, for an example."
(mlet %store-monad ((nscd.conf (nscd.conf-file config)))
(return (service
(documentation "Run libc's name service cache daemon (nscd).")