How to startd the AVD manager without starting android studio
It is just the android avd command, where the android shell script is in the tools/ directory of your SDK installation.

Or go to the directory and 

cd ~/Android/Sdk/tools/bin/ 
./avdmanager


Documentation can be found (deprecated) but it works for me
https://developer.android.com/studio/tools/help/android.html

I hope it will be useful