Some return codes do not reach the application. For example, EM_BUFSIZE (203) is detected and corrected by CLI without the application’s intervention. Or again, the EM_NODATA (211) and EM_DATAHERE (212) return codes are alternates, but CLI filters out EM_DATAHERE; the application must therefore test for EM_DATAHERE by testing for the absence of EM_NODATA.
At times, application programs may print, to stderr, messages that have the word net/oserr and a number code. The code shown is generated by MOSI and the message is formatted by MTDP.