use journal namespace

packaging/deb/conffiles

@@ -1 +1,2 @@
 /etc/default/terractl
+/etc/systemd/journald@terraria.conf

packaging/deb/postinst

@@ -8,6 +8,17 @@ case "$1" in
         if [ -d /run/systemd/system ]; then
             systemctl daemon-reload || true
         fi
+        # Let the terraria group read the servers' journal (LogNamespace=terraria)
+        terractl journal-access || true
+        # Servers running from before 0.0.11 still log to the system journal until
+        # restarted, so 'terractl attach' and 'cmd' can't show their output yet.
+        if [ -n "$2" ] && dpkg --compare-versions "$2" lt 0.0.11 && [ -d /run/systemd/system ]; then
+            running=$(systemctl list-units --plain --no-legend --state=active 'terraria@*.service' | awk '{print $1}')
+            if [ -n "$running" ]; then
+                echo "Restart running Terraria servers so they use their new journal:"
+                for unit in $running; do echo "  sudo systemctl restart $unit"; done
+            fi
+        fi
         # Running instances are not restarted; they pick up changes on their next start.
         ;;
 esac