ERROR(5) File Formats Manual ERROR(5)

error - return an error

size[4] Rerror tag[2] ename[s]

The Rerror message (there is no Terror) is used to return an error string describing the failure of a transaction. It replaces the corresponding reply message that would accompany a successful call; its tag is that of the failing request.

By convention, clients may truncate error messages after Sys->ERRMAX-1 bytes.