[bug#43921] [PATCH v3 2/2] Add User Service example.

["Jan (janneke) Nieuwenhuizen" <janneke@gnu.org>]

* modules/shepherd/support.scm: Export %user-cache-dir, %user-config-dir,
%user-runtime-dir.
* doc/shepherd.texi (User Service examples): Use them in new subsection with
example.

Co-authored-by: Efraim Flashner <efraim@flashner.co.il>
---
 doc/shepherd.texi            | 79 ++++++++++++++++++++++++++++++++++--
 modules/shepherd/support.scm |  4 ++
 2 files changed, 79 insertions(+), 4 deletions(-)

diff --git a/doc/shepherd.texi b/doc/shepherd.texi
index 7c9a739..15d00f1 100644
--- a/doc/shepherd.texi
+++ b/doc/shepherd.texi
@@ -13,6 +13,7 @@ Copyright @copyright{} @value{OLD-YEARS} Wolfgang J@"ahrling@*
 Copyright @copyright{} @value{NEW-YEARS} Ludovic Courtès@*
 Copyright @copyright{} 2020 Brice Waegeneire@*
 Copyright @copyright{} 2020 Oleg Pykhalov
+Copyright @copyright{} 2020 Jan (janneke) Nieuwenhuizen@*
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -146,10 +147,11 @@ configuration file.  When it is started with superuser privileges, it
 tries to use @code{/etc/shepherd.scm}.  When started as normal user, it
 looks for a file called @code{$XDG_CONFIG_HOME/shepherd/init.scm}.  If
 the @code{XDG_CONFIG_HOME} environment variable is not defined,
-@code{$HOME/.config/shepherd/init.scm} is used instead.  With the option
-@code{--config} (or, for short, @code{-c}), you can specify where to
-look instead.  So if you want to start @command{shepherd} with an
-alternative file, use one of the following commands:
+@code{$HOME/.config/shepherd/init.scm} is used instead (@pxref{User
+Service examples}).  With the option @code{--config} (or, for short,
+@code{-c}), you can specify where to look instead.  So if you want to
+start @command{shepherd} with an alternative file, use one of the
+following commands:
 
 @example
 shepherd --config=/etc/shepherd.scm.old
@@ -1025,6 +1027,75 @@ also specifies some more initial values for the slots:
                    (restart (...)))))
 @end lisp
 
+@menu
+* User Service examples::
+@end menu
+
+@node User Service examples
+@subsection User Service examples
+
+For starters, use a toplevel @code{$XDG_CONFIG_HOME/shepherd/init.scm}
+that looks like this:
+
+@lisp
+;;; Commentary:
+;;;
+;;; Add to your ~/.bash_profile:
+;;;
+;;; if [[ ! -S ${XDG_RUNTIME_DIR-$HOME/.cache}/shepherd/socket ]]; then
+;;;     shepherd
+;;; fi
+;;;
+;;; Code:
+
+(use-modules (shepherd service)
+             ((ice-9 ftw) #:select (scandir)))
+
+;; Load all the files in the directory 'init.d' with a suffix '.scm'.
+(for-each
+  (lambda (file)
+    (load (string-append "init.d/" file)))
+  (scandir (string-append (dirname (current-filename)) "/init.d")
+           (lambda (file)
+             (string-suffix? ".scm" file))))
+
+;; Send shepherd into the background
+(action 'shepherd 'daemonize)
+@end lisp
+
+Then, individual user services can be put in
+@code{$XDG_CONFIG_HOME/shepherd/init.d/}, e.g., for ssh-agent
+
+@lisp
+;;; Commentary:
+;;;
+;;; Add to your ~/.bash_profile:
+;;;
+;;; SSH_AUTH_SOCK=${XDG_RUNTIME_DIR-$HOME/.cache}/ssh-agent/socket
+;;; export SSH_AUTH_SOCK
+;;;
+;;; Code:
+
+(use-modules (shepherd support))
+
+(define ssh-agent
+  (make <service>
+    #:provides '(ssh-agent)
+    #:docstring "Run `ssh-agent'"
+    #:start (let ((socket-dir (string-append %user-runtime-dir "/ssh-agent")))
+              (unless (file-exists? socket-dir)
+                (mkdir-p socket-dir)
+                (chmod socket-dir #o700))
+              (make-forkexec-constructor
+               `("ssh-agent" "-D" "-a" ,(string-append socket-dir "/socket"))
+               #:log-file (string-append %user-cache-dir "/ssh-agent.log")))
+    #:stop (make-kill-destructor)
+    #:respawn? #t))
+(register-services ssh-agent)
+
+(start ssh-agent)
+@end lisp
+
 @c @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
 
 @node The root and unknown services
diff --git a/modules/shepherd/support.scm b/modules/shepherd/support.scm
index fe64a05..bf34ada 100644
--- a/modules/shepherd/support.scm
+++ b/modules/shepherd/support.scm
@@ -61,6 +61,10 @@
             persistency
             persistency-state-file
 
+            %user-cache-dir
+            %user-config-dir
+            %user-runtime-dir
+
             verify-dir))
 
 (define-syntax-rule (if-2.0 subsequent alternate)
-- 
Jan Nieuwenhuizen <janneke@gnu.org> | GNU LilyPond http://lilypond.org
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