This function returns the exit value (aka return code) of a process that was running. Used by run() and runShellCommand() to return the status of the process that the user has launched. exitValue() returns a 0 if the process is has completed correctly. If an error occurred during the process the exit value will different than 0. There isn't a standard definition for the return code, it depends on the process. Refer to the documentation of the process to know what the code means.