improved systemd service log

hosts/yodaNas/host-specific.nix

@@ -35,8 +35,20 @@
     ];
     script = ''
       set -eu -o pipefail
-      /jc-config/docker-compose pull
-      /jc-config/docker-compose up -d --wait
+
+      # We use
+      #   2> >(sed 's/^/<3> /' >&2)
+      # to prefix each line of stderr with
+      #   "<3> "
+      # Source: https://superuser.com/a/882025/919675
+      #
+      # With this prefix, the stderr output is treated as error messages by systemd.
+      # See https://www.freedesktop.org/software/systemd/man/latest/sd-daemon.html
+      # They can be viewed with
+      #   journalctl -b -u Jinja-Compose.service
+
+      /jc-config/docker-compose pull         2> >(sed 's/^/<3> /' >&2)
+      /jc-config/docker-compose up -d --wait 2> >(sed 's/^/<3> /' >&2)
     '';
   };
 }