[systemd-devel] [PATCH] man: add instruction on clearing file descriptors

[Mantas Mikulėnas]

I'm not sure if it's more portable. I recall FreeBSD only exposing 0–2 in
its /dev/fd by default unless you mounted a separate virtual filesystem
there. NetBSD seems to always have 64 devnodes no matter how many fds.

I don't think there's a *good* portable method (which is why closerange()
is being added) and besides that I'm not sure if that is even in scope for
this systemd-centric manpage...the whole idea is that under systemd, a
daemon shouldn't need that.

On Mon, Dec 7, 2020, 19:30 Petar Kapriš <petarkapris at 420blaze.it> wrote:

> In the daemon.7 manpage, I added an instruction on closing open file
> descriptors, an important step in daemon startup, showing an option to
> close them using the files in /dev/fd (a more portable alternative
> across systems to using /proc/self/fd)
> ---
>  man/daemon.xml | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/man/daemon.xml b/man/daemon.xml
> index db95d2f75b..4bae6ebb82 100644
> --- a/man/daemon.xml
> +++ b/man/daemon.xml
> @@ -47,12 +47,13 @@
>          <listitem><para>Close all open file descriptors except
>          standard input, output, and error (i.e. the first three file
>          descriptors 0, 1, 2). This ensures that no accidentally passed
> -        file descriptor stays around in the daemon process. On Linux,
> -        this is best implemented by iterating through
> -        <filename>/proc/self/fd</filename>, with a fallback of
> -        iterating from file descriptor 3 to the value returned by
> +        file descriptor stays around in the daemon process.  On most
> +        modern systems, this is best implemented by iterating through
> +        <filename>/dev/fd</filename>, or
> +        <filename>/proc/self/fd</filename> on Linux, with a fallback
> +        of iterating from file descriptor 3 to the value returned by
>          <function>getrlimit()</function> for
> -        <constant>RLIMIT_NOFILE</constant>. </para></listitem>
> +        <constant>RLIMIT_NOFILE</constant>.  </para></listitem>
>
>          <listitem><para>Reset all signal handlers to their default.
>          This is best done by iterating through the available signals
> --
> 2.29.2
>
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