Make R exit with non-zero status code

It’s an argument to quit(). See ?quit.

Arguments:

status: the (numerical) error status to be returned to the operating
        system, where relevant.  Conventionally ‘0’ indicates
        successful completion.

Details:

 Some error statuses are used by R itself.  The default error
 handler for non-interactive use effectively calls ‘q("no", 1,
 FALSE)’ and returns error code 1.  Error status 2 is used for R
 ‘suicide’, that is a catastrophic failure, and other small numbers
 are used by specific ports for initialization failures.  It is
 recommended that users choose statuses of 10 or more.