That'll make it easier to identify what are the obsolete packages in the
output. The openmetrics output is not needed during investigation.

howto/upgrades.md

@@ -129,7 +129,7 @@ following two commands:
     apt list "?obsolete"
     # The following will mainly print the same list as above, but there might be
     # some more in its list.
-    DEBUG=1 /usr/share/prometheus-node-exporter-collectors/apt_info.py
+    DEBUG=1 /usr/share/prometheus-node-exporter-collectors/apt_info.py >/dev/null
 
 Check the state of each package with `apt policy $package` to determine what
 needs to be done with it. If most cases, the packages can just be purged, but