How to list all the namespaces? Right now, to list all the settings of System namespace I can do:

platform-tools/adb shell settings list system


To list all the settings from Global namespace I can do

platform-tools/adb shell settings list global


But I want to explore all the settings from all the namespaces currently installed, and for that I need to list all the available namespaces, so how do I do I get this list?
There are only three namespaces available: system, secure and global.

The settings command prints this information if you execute it without parameter:

adb shell settings

usage:  settings [--user &lt;USER_ID&gt; | current] [--cm] get namespace key
        settings [--user &lt;USER_ID&gt; | current] [--cm] put namespace key value
        settings [--user &lt;USER_ID&gt; | current] [--cm] delete namespace key
        settings [--user &lt;USER_ID&gt; | current] [--cm] list namespace

'namespace' is one of {system, secure, global}, case-insensitive
If '--user &lt;USER_ID&gt; | current' is not given, the operations are performed on the system user.
If '--cm' is given, the operations are performed on the CMSettings provider.



  'namespace' is one of {system, secure, global}, case-insensitive


Alternatively if you don't belive the settings help page you can see it in the AOSP source code. The settings command is implemented in the Java class com.android.commands.settings.SettingsCmd where you can see that exactly those three namespaces are accepted.