The UNIX system provides basic functionality to build and execute programs. Your COBOL system exploits this and provides additional COBOL-specific functionality. The Linker is used to create programs in an operating system executable format.
A linked program is a subprogram that is held in object form in one of the following:
Any program, subprogram or support routine can be linked into these file types.
The procedural code of the linked file types is shared between multiple concurrent users. The procedural code of callable shared objects and shared libraries is also shared between multiple applications.
To run a COBOL application you must first invoke a standard UNIX system executable file. This is loaded by the system loader and control is passed to the main entry point. The application starts to run and control passes explicitly to called subprograms or implicitly to run-time support routines. See the chapter COBOL System Interface (Cob) for details on how you specify the main entry point.
An executable file that requires the first entry point to be specified at run time is generally known as an executable run-time system (RTS). An executable file that has the first entry point built-in at link time is generally known as an executable application. The default executable RTS is:
To link the programs in your application use the Cob utility. Cob can be used to link a program to the various system or language support routines, and, if necessary, to any called subroutines that are needed at run time.
See the chapter Linking to System Executables for more details.