I discovered that the MPD service (among others) had died for no apparent reason.
My Raspberry Pi just sat there running overnight, doing nothing. I had stopped, not paused, the music.
To make sure this won't happen again, I edited the mpd.service file that I found in /etc/systemd/system/multi-user.target.wants, and added "Restart=always" to the "[Service]" section:
[root@runeaudio multi-user.target.wants]# cat mpd.service
[Unit]
Description=Music Player Daemon
After=network.target sound.target
[Service]
ExecStart=/usr/bin/mpd --no-daemon
Restart=always
[Install]
WantedBy=multi-user.target
This is followed by the command 'systemctl daemon-reload'.
This makes MPD start within a few seconds of any kind of failure, even if you stop the service yourself. Changes to MPD from the webUI should still work, as that does a restart of the service.
If you for some reason really want to keep MPD stopped, replace "Restart=always" with "Restart=on-failure". With this option, MPD will not restart if you do a clean exit with 'systemctl stop mpd'.
(The other services that seem to have failed may not work at all. They're logrotate.service and shadow.service.)
