You are quite right.
But sometimes the messages coming up are not always very helpful or for “normal” users incomprehensible.
And often, when one post a topic of such warnings, you get the answer from the cracks: “You can ignore it.It’s just a warning” 
.
I got this Warning too, when upgrading to M2. So I looked into “services/addons.cfg”
And what I saw was this:
# The installation package of this openHAB instance
# Note: This is only regarded at the VERY FIRST START of openHAB
# Note: If you want to specify your add-ons yourself through entries below, set the package to "minimal"
# as otherwise your definition might be in conflict with what the installation package defines.
#
# Optional. If not set, the dashboard (https://<yourserver>:8080/) will ask you to choose a package.
#
# Valid options:
# - minimal : Installation only with dashboard, but no UIs or other add-ons. Use this for custom setups.
# - simple : Setup for using openHAB purely through UIs - you need to expect MANY constraints in functionality!
# - standard : Default setup for normal users, best for textual setup
# - expert : Setup for expert users, especially for people migrating from openHAB 1.x
# - demo : A demo setup which includes UIs, a few bindings, config files etc.
#
# See https://www.openhab.org/docs/configuration/packages.html for a detailed explanation of these packages.
#
#package = minimal
# Access Remote Add-on Repository
# Defines whether the remote openHAB add-on repository should be used for browsing and installing add-ons.
# This not only makes latest snapshots of add-ons available, it is also required for the installation of
# any legacy 1.x add-on. (default is true)
#
#remote = true
# Include legacy 1.x bindings. If set to true, it also allows the installation of 1.x bindings for which there is
# already a 2.x version available (requires remote repo access, see above). (default is false)
#
#legacy = true
# A comma-separated list of bindings to install (e.g. "binding = sonos,knx,zwave")
#binding =
# A comma-separated list of UIs to install (e.g. "ui = basic,paper")
#ui =
# A comma-separated list of persistence services to install (e.g. "persistence = rrd4j,jpa")
#persistence =
# A comma-separated list of actions to install (e.g. "action = mail,pushover")
#action =
# A comma-separated list of transformation services to install (e.g. "transformation = map,jsonpath")
#transformation =
# A comma-separated list of voice services to install (e.g. "voice = marytts,freetts")
#voice =
# A comma-separated list of miscellaneous services to install (e.g. "misc = myopenhab")
#misc =
As you can see, every line is commented out, means never used by the system. But I also found a solution in another topic here. So I looked into
openHAB-share\openhab2-userdata\config\org\openhab\addons.config
:org.apache.felix.configadmin.revision:=L"2"
action="mqtt"
binding="ntp,samsungtv,sonos,exec,network,astro,mqtt1,avmfritz,http1,openweathermap,homematic"
felix.fileinstall.filename="file:/var/lib/openhab2/etc/org.openhab.addons.cfg"
legacy=B"true"
misc=
package="expert"
persistence="mapdb"
remote=B"true"
service.pid="org.openhab.addons"
transformation=",regex,exec,map,jsonpath,javascript,scale"
ui="paper,basic,restdocs"
and found there the place to change.
But after upgrading I’m fighting with some other problems too.
The first one seems to be no problem as it’s an INFO on OH-Start, but I’d never had this before and I do not understand what is meant:
// Infomeldung beim Start M2 für Paper UI
2019-08-13 13:36:11.906 [INFO ] [org.openhab.ui.paper ] - FrameworkEvent INFO - org.openhab.ui.paper
org.osgi.framework.BundleException: The bundle class path entry "patch/" could not be found for the bundle "osgi.identity; type="osgi.bundle"; version:Version="2.5.0.M2"; osgi.identity="org.openhab.ui.paper""
at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.findClassPathEntry(ClasspathManager.java:174) ~[?:?]
at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.buildClasspath(ClasspathManager.java:152) ~[?:?]
at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.<init>(ClasspathManager.java:81) ~[?:?]
at org.eclipse.osgi.internal.loader.EquinoxClassLoader.<init>(EquinoxClassLoader.java:43) ~[?:?]
at org.eclipse.osgi.internal.loader.BundleLoader.createClassLoaderPrivledged(BundleLoader.java:316) ~[?:?]
at org.eclipse.osgi.internal.loader.BundleLoader.getModuleClassLoader(BundleLoader.java:233) ~[?:?]
at org.eclipse.osgi.internal.loader.BundleLoader.searchHooks(BundleLoader.java:503) ~[?:?]
at org.eclipse.osgi.internal.loader.BundleLoader.findResource(BundleLoader.java:600) ~[?:?]
at org.eclipse.osgi.internal.loader.buddy.DependentPolicy.loadResource(DependentPolicy.java:82) ~[?:?]
at org.eclipse.osgi.internal.loader.buddy.PolicyHandler.doBuddyResourceLoading(PolicyHandler.java:157) ~[?:?]
at org.eclipse.osgi.internal.loader.BundleLoader.findResource(BundleLoader.java:649) ~[?:?]
at org.eclipse.osgi.internal.loader.buddy.DependentPolicy.loadResource(DependentPolicy.java:82) ~[?:?]
at org.eclipse.osgi.internal.loader.buddy.PolicyHandler.doBuddyResourceLoading(PolicyHandler.java:157) ~[?:?]
at org.eclipse.osgi.internal.loader.BundleLoader.findResource(BundleLoader.java:649) ~[?:?]
at org.eclipse.osgi.internal.loader.ModuleClassLoader.getResource(ModuleClassLoader.java:200) ~[?:?]
at org.eclipse.osgi.internal.framework.EquinoxBundle.getResource(EquinoxBundle.java:532) ~[?:?]
at org.apache.servicemix.specs.activation.Activator.register(Activator.java:58) ~[?:?]
at org.apache.servicemix.specs.locator.Activator.start(Activator.java:70) ~[?:?]
at org.apache.servicemix.specs.activation.Activator.start(Activator.java:46) ~[?:?]
at org.eclipse.osgi.internal.framework.BundleContextImpl$3.run(BundleContextImpl.java:779) ~[?:?]
at org.eclipse.osgi.internal.framework.BundleContextImpl$3.run(BundleContextImpl.java:1) ~[?:?]
at java.security.AccessController.doPrivileged(Native Method) ~[?:?]
at org.eclipse.osgi.internal.framework.BundleContextImpl.startActivator(BundleContextImpl.java:772) ~[?:?]
at org.eclipse.osgi.internal.framework.BundleContextImpl.start(BundleContextImpl.java:729) [?:?]
at org.eclipse.osgi.internal.framework.EquinoxBundle.startWorker0(EquinoxBundle.java:933) ~[?:?]
at org.eclipse.osgi.internal.framework.EquinoxBundle$EquinoxModule.startWorker(EquinoxBundle.java:309) ~[?:?]
at org.eclipse.osgi.container.Module.doStart(Module.java:581) ~[?:?]
at org.eclipse.osgi.container.Module.start(Module.java:449) ~[?:?]
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.incStartLevel(ModuleContainer.java:1634) ~[?:?]
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.incStartLevel(ModuleContainer.java:1614) ~[?:?]
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.doContainerStartLevel(ModuleContainer.java:1585) ~[?:?]
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.dispatchEvent(ModuleContainer.java:1528) ~[?:?]
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.dispatchEvent(ModuleContainer.java:1) ~[?:?]
at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230) [?:?]
at org.eclipse.osgi.framework.eventmgr.EventManager$EventThread.run(EventManager.java:340) [?:?]
2019-08-13 13:36:18.678 [INFO ] [.core.internal.i18n.I18nProviderImpl] - Time zone set to 'Europe/Berlin'.
------------------------------------------------------------------------------------------------------------------------------------------
I have a made a workaround for it, in the karaf-console
openhab> log:set warn org.openhab.ui.paper
setting the log to WARN. But now all Infos are suppressed (not the best way).
Even in the karaf-console I get this
openhab> bundle:list | grep -i paper
253 x Active x 80 x 2.5.0.M2 x openHAB UI :: Bundles :: Paper UI
openhab>
So I’m asking me what this INFO in the start-sequence stands for. I don’t know 
. Do you ?
Cheers,
Peter
You have eyes like an eagle. I was just to lazy to enter the path, so I made it by copy and paste out of my editor (from the windows-side via samba-share).
. I always made my updates and upgrades via openhabian-config and never found a hint to upgrade OS and how to do it. I only know that Buster is the OS for RPi4, but not for RPi3 