This command sets the file type of the given file (the full filename must be supplied) to zero. The reason for this command is that certain assemblers and tools set the file type to 1 (executable file) even though the file cannot be started as a job. Since commands like EX or EXEC check the file type to decide whether a file can be executed, they will try to start such a file and crash the system in most cases. A simple UNJOB prevents this in the long term.
v1.00 of this command did not work on most QL ROM versions, giving a bad parameter error.
Each file has a file type which can be found with the FTYP and FILE_TYPE functions or directly by looking at the file header (HEADR). It is also possible to set the file type by rewriting the whole file header with HEADS; alternatively, UNJOB does the same.