Summary

Processes are instances of executable programs that are run and managed by the operating system. Programs make use of predefined functions to implement their tasks. Some of these predefined functions are actually system calls. System calls request the kernel to directly perform a task for the process. Other predefined functions are library functions. Library functions, which may indirectly contain system calls, also perform tasks for the process, but in a less intrusive manner. The object code for system calls and library functions is stored in object code format in library files. The object code for system calls and library functions is included, on an as-needed basis, when a program is compiled.

When a system call or library function fails, the external variable errno can be examined to determine the reason for failure. The library functions perror or strerror can be used to generate a descriptive error message.

Executing programs are placed in system memory. The executable code and constant data for the program are placed in a region known as the text segment. The initialized and uninitialized program data is placed in the data segment. The program stack segment is used to handle automatic program variables and function call data. In addition, the system will keep process-specific information and system call data in the user area ( u area) of memory.

Processes are generated by the fork system call. A newly generated process inherits the majority of its state information from its parent.