Basically these bugs:
Happening here on Kubuntu 15.04 even when editor is set to build for Linux (not Android)
I was having this happen as well. When starting Play Mode currently for the first time after launch I normally have to launch a terminal and run “adb kill-server” then run “adb devices”(or similar to start the the process again). One odd thing is the first “adb devices” command if performed quickly tends to trigger a adb process launch failure then the second seems fine.
I also don’t know what started this issue as mine was working fine without doing this for weeks. Then I started messing around with Unity Remote and built one Android application, so I’m not exactly sure which of these triggered the issue initially.