Add interpreter adaptation for service, with documentation

dist/arch/PKGBUILD

@@ -39,7 +39,6 @@ package() {
     cp -r lib locale sql vendor www CHANGELOG UPGRADING README.md arsse.php "$pkgdir/usr/share/webapps/arsse"
     cp -r manual/* "$pkgdir/usr/share/doc/arsse"
     cp LICENSE AUTHORS "$pkgdir/usr/share/licenses/arsse"
-    cp dist/systemd/* "$pkgdir/usr/lib/systemd/system"
     cp dist/sysuser.conf "$pkgdir/usr/lib/sysusers.d/arsse.conf"
     cp dist/tmpfiles.conf "$pkgdir/usr/lib/tmpfiles.d/arsse.conf"
     cp dist/php-fpm.conf "$pkgdir/etc/php/php-fpm.d/arsse.conf"
@@ -58,4 +57,6 @@ package() {
     install -Dm755 dist/arch/arsse "$pkgdir/usr/bin/arsse"
     cp dist/arch/nginx-arsse-fcgi.conf "$pkgdir/etc/webapps/arsse/nginx/arsse-fcgi.conf"
     cp dist/arch/apache-arsse-fcgi.conf "$pkgdir/etc/webapps/arsse/apache/arsse-fcgi.conf"
+    cp dist/arch/*.service "$pkgdir/usr/lib/systemd/system"
+    cp dist/arch/systemd-environment "$pkgdir/etc/webapps/arsse/systemd-environment"
 }

dist/arch/arsse-fetch.service

@@ -0,0 +1,37 @@
+[Unit]
+Description=The Arsse newsfeed fetching service
+Documentation=https://thearsse.com/manual/
+PartOf=arsse.service
+
+[Install]
+WantedBy=multi-user.target
+
+[Service]
+User=arsse
+Group=arsse
+Type=simple
+WorkingDirectory=/usr/share/webapps/arsse
+EnvironmentFile=/etc/webapps/arsse/systemd-environment
+ExecStart=/usr/bin/arsse daemon
+
+ProtectProc=invisible
+NoNewPrivileges=true
+ProtectSystem=full
+ProtectHome=true
+StateDirectory=arsse
+ConfigurationDirectory=arsse
+PrivateTmp=true
+PrivateDevices=true
+RestrictSUIDSGID=true
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=arsse
+Restart=on-failure
+RestartPreventStatus=
+
+# These directives can be used for extra security, but are disabled for now for compatibility
+
+#ReadOnlyPaths=/
+#ReadWriePaths=/var/lib/arsse
+#NoExecPaths=/
+#ExecPaths=/usr/bin/php

dist/arch/arsse.service

@@ -0,0 +1,13 @@
+[Unit]
+Description=The Arsse newsfeed management service
+Documentation=https://thearsse.com/manual/
+Requires=arsse-fetch.service
+Wants=php-fpm.service php-legacy-fpm.service
+
+[Install]
+WantedBy=multi-user.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=true
+ExecStart=/usr/bin/true

dist/arch/systemd-environment

@@ -0,0 +1 @@
+ARSSE_PHP=/usr/bin/php

docs/en/020_Getting_Started/020_Download_and_Installation/010_On_Arch_Linux.md

@@ -35,6 +35,23 @@ LoadModule proxy_fcgi_module modules/mod_proxy_fcgi.so
 
 No additional set-up is required for Nginx.
 
+# Using an alternative PHP interpreter
+
+The above instructions assume you will be using the `php` package as your PHP interpreter. If you wish to use `php-legacy` (which is always one feature version behind, for compatibility) a few configuration tweaks are required. The follwoing commands are a short summary:
+
+```sh
+# Enable the necessary PHP extensions; curl is optional but recommended; pdo_sqlite may be used instead of sqlite3, but this is not recommended
+sudo sed -i -e 's/^;\(extension=\(curl\|iconv\|intl\|sqlite3\)\)$/\1/' /etc/php-legacy/php.ini
+# Modify the system service's environment
+sudo sed -i -e 's/^ARSSE_PHP=.*/ARSSE_PHP=\/usr\/bin\/php-legacy/' /etc/webapps/arsse/systemd-environment
+# Modify the PAM environment for the administrative CLI
+echo "export ARSSE_PHP=/usr/bin/php-legacy" | sudo tee -a /etc/profile.d/arsse >/dev/null
+# Modify the Nginx and Apache HTTPD configurations
+sudo sed -i -se 's/\/run\/php-fpm\//\/run\/php-fpm-legacy\//' /etc/webapps/arsse/apache/arsse-fcgi.conf /etc/webapps/arsse/nginx/arsse-fcgi.conf
+```
+
+The above procedure can also be applied to use another PHP version from AUR if so desired.
+
 # Next steps
 
 If using a database other than SQLite, you will likely want to [set it up](/en/Getting_Started/Database_Setup) before doing anything else.