I always find myself constantly Googling the list of unix status codes (typically defined in sysexits.h).
0 # successful termination 64 # base value for error messages 64 # command line usage error 65 # data format error 66 # cannot open input 67 # addressee unknown 68 # host name unknown 69 # service unavailable 70 # internal software error 71 # system error (e.g., can't fork) 72 # critical OS file missing 73 # can't create (user) output file 74 # input/output error 75 # temp failure; user is invited to retry 76 # remote error in protocol 77 # permission denied 78 # configuration error