I got the following error messages when I pushed an app of Liberty for Java into Bluemix.

[Console]
an instance of the app crashed: failed to start exit status: -1, CRASHED

[cf events *APPNAME*]
index: 1, reason: CRASHED, exit\_description: failed to start, exit\_status: -1
index: 2, reason: CRASHED, exit\_description: failed to start, exit\_status: -1

a) Is there exit status code list? I can not find it.
b) This error, exit status = -1, sometimes occurred. What is it? How should I investigate this cause?