I’m using KM 7.2.1. I believe that I upgraded my Mac from the most recent previous version of El Capitan. I know that Keyboard Maestro was working fine under El Capitan until recently.
When I tried to restart, I discovered that KM was running and prevented reboot. Several tries to force quit failed. Finally, I had to force restart by holding down the on key.
Did you use the force-quit dialog or the Activity Monitor?
The next step is to gird your loins and use the Terminal:
If you’re unfamiliar with the Terminal it’s a bit scary when you first do this, but if it works it’s better than a forced-shutdown. (Only very rarely have I seen a kill command fail on OSX.)
Searching for the process:
ps auxc | egrep -i "key"
Result:
myUserName 212 0.2 1.1 2615472 88512 ?? S 6:17AM 0:19.89 Keyboard Maestro Engine
myUserName 272 0.0 0.0 2471156 3956 ?? S 6:17AM 0:00.03 CloudKeychainProxy
myUserName 247 0.0 0.2 2534616 17624 ?? S 6:17AM 0:00.12 Keychain Circle Notification
myUserName 1243 0.0 1.1 3789456 89764 ?? S 8:12AM 0:05.09 Keyboard Maestro
That gives me the process names and ID numbers.
From there:
killall lets you use the process name.
NOTE – quotes are needed due to spaces in the process name.
killall 'Keyboard Maestro Engine'
kill uses the PID (Process ID) of the process:
kill -9 212
-9 is the baddest of the kill codes:
9 KILL (non-catchable, non-ignorable kill)
See “man kill” and “man killall” in the Terminal for the man (manual) pages.
The StackOverflow article has some fairly comprehensive information.