The way to run the emulator from the console (I assume that you installed it before, using Android Studio) is:

run

cd ~/Android/Sdk/tools/bin && ./avdmanager list avd

OR

cd ~/Android/Sdk/tools && ./emulator -list-avds

You will get the list od your virtual installed devices. In my case it was:

Available Android Virtual Devices:
Name: Galaxy_Nexus_API_17
Device: Galaxy Nexus (Google)
Path: /home/piotr/.android/avd/Galaxy_Nexus_API_17.avd
Target: Google APIs (Google Inc.)
Based on: Android 4.2 (Jelly Bean) Tag/ABI: google_apis/x86
Skin: galaxy_nexus
Sdcard: /home/piotr/.android/avd/Galaxy_Nexus_API_17.avd/sdcard.img

Copy name of the device you want to run and then

cd ~/Android/Sdk/tools && ./emulator -avd NAME_OF_YOUR_DEVICE

in my case:

cd ~/Android/Sdk/tools && ./emulator -avd Nexus_5X_API_23