How to guarantee one process precedes another at startup?

[Ralf Mardorf]

On Sun, 19 Jul 2020 18:53:40 +0100, Chris Green wrote:
>I run the minidlna daemon to provide DLNA services on my system.  I
>also run mp3fs to convert much of my music from flac to mp3 'on the
>fly' as it were.
>
>The minidlna daemon us started in the normal way and has an entry in
>/etc/init.d but mp3fs is started from /etc/rc.local.  Unfortunately
>this means that minidlna gets started before mp3fs and that means it
>doesn't see the files created by mp3fs.

The 'normal' way would be to start it by a systemd unit.

>How can I guarantee that minidlna waits for mp3fs?  I want to do this
>'properly' if I can.  Obviously I *could* just remove minidlna from
>/etc/init.d and put it in /etc/rc.local after mp3fs but that feels
>like a bit of a bodge.  Is there a better way?

How should mp3fs get started by either an init script or a systemd unit?
IIUC fuse does this on demand. IOW you need to ensure that the fuse
(bridge) module isn't blacklisted (I'm aware that the terms
'blacklisted' and 'slave' became a taboo a few days ago, but actually
it's still the correct term). IIUC you either need a /lib/udev/rules.d/
file or an entry in /etc/modprobe{,.d/foo}.

Arch Linux packages provide udev rules:

$ pacman -Qo /usr/lib/udev/rules.d/99-fuse*rules
/usr/lib/udev/rules.d/99-fuse.rules is owned by fuse2 2.9.9-4
/usr/lib/udev/rules.d/99-fuse3.rules is owned by fuse3 3.9.2-1

The Ubuntu path should be /lib/udev/rules.d/ without /user. Each distro
has got it's individual Linux Standard Base (LSB).