bug#39708: nfs-service-type broken: rpc.mountd respawns too quickly

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

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Ludovic Courtès <ludo@gnu.org> writes:

> Hi,
>
> Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:
>
>> The rpc.mountd service, one of the required services for
>> nfs-service-type, respawns the process quickly until disabled.
>
> Does /var/log/messages contain hints?  Is rpc.statd running?
> Could it be that all these services need to depend on ‘loopback’?
>
> No answers, but a lot of questions.  :-)
>
> Ludo’.

OK, I've managed to find the problem.  rpc.mountd daemonizes itself upon
starting by default, which is not supported by Shepherd (at least not
its `make-forkexec-constructor' procedure).  I had to pass the
'--foreground' option to workaround this limitation (c.f.: commit
5fdc5b2d57d2e7ab04dbaf9c85e7f34eebe81495).

It'd be interesting to see what systemd does when a service is hinted as
forking in its configuration file.  We should also document that
limitation in the Shepherd info manual (see attached patch for
Shepherd).

Maxim

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From 8f84ce9abe12b49340befbeee663896d226bb869 Mon Sep 17 00:00:00 2001
From: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Date: Sun, 8 Mar 2020 00:34:36 -0500
Subject: [PATCH] doc: Note that make-forkexec-constructor requires a
 non-forking process.

This merits to be documented as it can be confusing, as demonstrated by
<https://bugs.gnu.org/39708>.
---
 doc/shepherd.texi | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/doc/shepherd.texi b/doc/shepherd.texi
index fbd1a3f..a0ac11b 100644
--- a/doc/shepherd.texi
+++ b/doc/shepherd.texi
@@ -898,12 +898,14 @@ execution of the @var{command} was successful, @code{#t} if not.
   [#:directory (default-service-directory)] @
   [#:environment-variables (default-environment-variables)]
 Return a procedure that forks a child process, closes all file
-descriptors except the standard output and standard error descriptors, sets
-the current directory to @var{directory}, changes the environment to
-@var{environment-variables} (using the @code{environ} procedure), sets the
-current user to @var{user} and the current group to @var{group} unless they
-are @code{#f}, and executes @var{command} (a list of strings.)  The result of
-the procedure will be the PID of the child process.
+descriptors except the standard output and standard error descriptors,
+sets the current directory to @var{directory}, changes the environment
+to @var{environment-variables} (using the @code{environ} procedure),
+sets the current user to @var{user} and the current group to @var{group}
+unless they are @code{#f}, and executes @var{command} (a list of
+strings.)  The result of the procedure will be the PID of the child
+process.  The child process must not fork (daemonize) itself for this to
+work correctly.
 
 When @var{pid-file} is true, it must be the name of a PID file
 associated with the process being launched; the return value is the PID
-- 
2.25.0


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