I tried to upgrade Geth to 1.4.6, now I get fatal error "Error starting protocol stack datadir already used"

Question

I tried to upgrade Geth to 1.4.6, now I get this error, why and how can I fix it?

Fatal: Error starting protocol stack: datadir already used

OS: Ubuntu 15.10

Note: Chaindata is being symlinked to an external SD card, not sure if that is relevant

Answer 1

Seems you already have a Geth instance running in the background that has the database locked.

Answer 2

Check for running geth instaces using ps.

 ~ $ ps aux | grep geth
user     10382  6.2  0.4 643660 66508 pts/0    Sl+  10:17   0:00 geth
user     10408  0.0  0.0  13164  2288 pts/1    S+   10:17   0:00 grep --color=auto geth

Kill it softly.

 ~ $ killall geth

If the issue persists, and geth is not wanting to be killed softly, look up the process ID from ps (above, here: 10382), and kill it hard:

 ~ $ kill -9 10382

Now you can launch geth again. However, you could also just geth attach to check if geth is running.