services: Add and use shepherd-signal-action.

* gnu/services/shepherd.scm (shepherd-signal-action): New procedure.

* gnu/services/audio.scm (mpd-shepherd-service): Use it for actions.
* gnu/services/base.scm (syslog-shepherd-service):
* gnu/services/base.scm (dnsmasq-shepherd-service):
* gnu/services/file-sharing.scm (transmission-daemon-shepherd-service):
* gnu/services/monitoring.scm (vnstat-shepherd-service):
* gnu/services/mail.scm (rspamd-shepherd-service):

* doc/guix.texi (shepherd-signal-action): Document it.

Change-Id: Ief5e00c7d430ec4aa28c3ef11d0ef9897793b45f
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Merges: #6097

1 files changed, 23 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index b0ab0c1db5b..9924f4771f2 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -50488,6 +50488,29 @@ cat $(herd configuration tor)
 This can come in as a handy debugging tool!
 @end deffn
 
+@deffn {Procedure} shepherd-signal-action name signal @
+[#:documentation `Send signal @var{signal} to the running service`] @
+[#:message `Service has been asked to perform @var{name}`]
+Return a shepherd action with @var{name} to send @var{signal} to the
+running process. The optional @var{documentation} and @var{message} can be used
+to customize the documentation and output message.
+
+Many daemons perform special actions after receiving a specific signal.
+
+For example the @command{syslogd} logger will reread its configuration file
+after receiving @code{SIGHUP}.
+
+After adding
+@lisp
+(shepherd-signal-action 'reload SIGHUP))
+@end lisp
+
+the @code{reload} action will be available and can be used with
+@example
+herd reload syslogd
+@end example
+@end deffn
+
 @defvar shepherd-root-service-type
 The service type for the Shepherd ``root service''---i.e., PID@tie{}1.