The transport control program tp collects all return codes that occur when a tp command is executed. From all of these single return codes, a combined return code is calculated that tp outputs as a result at the end the command. During an import, for example, all return codes for individual import steps are handled. If a special return code does not occur, then the combined return code at the end is the maximum of individual return codes that occur. In addition to the value of the return code, tp also gives a short description of this return code. You can display this short description using the command explainrc.

Normally, all return codes that occur originate from individual transport steps. Since these individual return codes can only have the following values 0, 4, 6, 8, 12, 13, 14, 16, the combined return code also has one of these values. However, if a general error occurs, a single return code over 200 is generated. For example, this could arise if tp cannot establish a connection to the database. The maximum return code for all single transport steps is output in a separate message before specifying the combined returned code. In this case, the combined return code is always the return code of the general error message.