Add systemd instantiated service file and per-session environment files

Currently the management scripts allow for only a single instance of the
minecraft server to be run, but it's actually not hard at all to support
multiple instances. This commit makes the following changes:

  - Adds a new systemd service file, `[email protected]`, which
    is an instantiated variant that overrides `SERVER_ROOT` and
    `SESSION_NAME`
  - Modifies `minecraftd.sh` to support sourcing an `environment` file
    from `SERVER_ROOT`, in addition to the existing system-wide file
    `/etc/conf.d/GAME`.
  - Instantiated versions of the minecraftd-backup service and timer.

The one potentially unsafe assumption I'm making is that the
`MAIN_EXECUTABLE` lives in the original compile-time `SERVER_ROOT`,
which I know is the case for at least papermc and spigot. For
installations where this is not the case, the environment file can
override `SERVER_START_CMD`.

The intended use case for this change is fairly common: using the same
package to run multiple instances of a minecraft server on a single
host. This would commonly be seen with, for example, multi-server
bungeecord deployments.

Makefile

@@ -10,7 +10,7 @@ datarootdir = $(prefix)/share
 mandir = $(prefix)/share/man
 man1dir = $(mandir)/man1
 
-SOURCES = minecraftd.sh.in minecraftd.conf.in minecraftd.service.in minecraftd.sysusers.in minecraftd.tmpfiles.in minecraftd-backup.service.in minecraftd-backup.timer.in
+SOURCES = minecraftd.sh.in minecraftd.conf.in minecraftd.service.in minecraftd@.service.in minecraftd.sysusers.in minecraftd.tmpfiles.in minecraftd-backup.service.in minecraftd-backup@.service.in minecraftd-backup.timer.in minecraftd-backup@.timer.in
 OBJECTS = $(SOURCES:.in=)
 
 GAME = minecraft
@@ -92,6 +92,9 @@ install:
 	$(INSTALL_DATA) -D minecraftd.service        "$(DESTDIR)$(libdir)/systemd/system/$(INAME).service"
 	$(INSTALL_DATA) -D minecraftd-backup.service "$(DESTDIR)$(libdir)/systemd/system/$(INAME)-backup.service"
 	$(INSTALL_DATA) -D minecraftd-backup.timer   "$(DESTDIR)$(libdir)/systemd/system/$(INAME)-backup.timer"
+	$(INSTALL_DATA) -D [email protected]        "$(DESTDIR)$(libdir)/systemd/system/$(INAME)@.service"
+	$(INSTALL_DATA) -D [email protected] "$(DESTDIR)$(libdir)/systemd/system/$(INAME)[email protected]"
+	$(INSTALL_DATA) -D [email protected]   "$(DESTDIR)$(libdir)/systemd/system/$(INAME)[email protected]"
 	$(INSTALL_DATA) -D minecraftd.sysusers       "$(DESTDIR)$(libdir)/sysusers.d/$(INAME).conf"
 	$(INSTALL_DATA) -D minecraftd.tmpfiles       "$(DESTDIR)$(libdir)/tmpfiles.d/$(INAME).conf"
 

minecraftd-backup@.service.in

@@ -0,0 +1,15 @@
+[Unit]
+Description=@GAME@ Server World Backup
+After=local-fs.target
+
+[Service]
+Type=oneshot
+Environment=SERVER_ROOT=@SERVER_ROOT@/servers/%i
+Environment=BACKUP_DEST=@SERVER_ROOT@/servers/%i/backup
+Environment=SESSION_NAME=@GAME@-%i
+ExecStart=/usr/bin/@INAME@ backup
+User=@GAME_USER@
+Group=@GAME_USER@
+
+[Install]
+WantedBy=multi-user.target

minecraftd-backup@.timer.in

@@ -0,0 +1,10 @@
+[Unit]
+Description=Daily @GAME@ Server Backup
+
+[Timer]
+OnCalendar=daily
+AccuracySec=5min
+Persistent=true
+
+[Install]
+WantedBy=multi-user.target

minecraftd.sh.in

@@ -33,7 +33,11 @@ declare -r GAME="@GAME@"
 [[ -n "${GAME_COMMAND_DUMP}" ]] && declare -r GAME_COMMAND_DUMP=${GAME_COMMAND_DUMP} || GAME_COMMAND_DUMP="@GAME_COMMAND_DUMP@"
 
 # Variables passed over the command line will always override the one from a config file
-source /etc/conf.d/"${GAME}" 2>/dev/null || >&2 echo "Could not source /etc/conf.d/${GAME}"
+for path in "/etc/conf.d/${GAME}" "${SERVER_ROOT}/environment"; do
+	if test -r "$path"; then
+		source "$path" || (echo "Could not source ${path}" >&2)
+	fi
+done
 
 # Preserve the content of IDLE_SERVER without making it readonly
 [[ -n ${tmp_IDLE_SERVER} ]] && IDLE_SERVER=${tmp_IDLE_SERVER}

minecraftd@.service.in

@@ -0,0 +1,20 @@
+[Unit]
+Description=@GAME@ Server - %i instance
+After=local-fs.target network.target multi-user.target
+
+[Service]
+Type=forking
+Environment=SERVER_ROOT=@SERVER_ROOT@/servers/%i
+Environment=BACKUP_DEST=@SERVER_ROOT@/servers/%i/backup
+Environment=SESSION_NAME=@GAME@-%i
+Environment=MAIN_EXECUTABLE=../../@MAIN_EXECUTABLE@
+# create the "servers" directory followed by the instance directory
+ExecStartPre=/bin/bash -c "/bin/test -d @SERVER_ROOT@/servers || /bin/install -d -m 0750 -o @GAME_USER@ -g @GAME_USER@ @SERVER_ROOT@/servers"
+ExecStartPre=/bin/bash -c "/bin/test -d @SERVER_ROOT@/servers/%i || /bin/install -d -m 0750 -o @GAME_USER@ -g @GAME_USER@ @SERVER_ROOT@/servers/%i"
+ExecStart=/usr/bin/@INAME@ start
+ExecStop=/usr/bin/@INAME@ stop
+User=@GAME_USER@
+Group=@GAME_USER@
+
+[Install]
+WantedBy=multi-user.target