Fork is an operation whereby a process creates a copy of itself. It is usually a system call, implemented in the kernel. Fork is the primary (and historically, only) method of process creation on Unix-like operation. In multitasking operating systems, processes (running programs) need a way to create new processes, e.g. to run other programs.Fork and its variants are typically the only way of doing so in Unix-like systems.
For a process to start the execution of a different program, it first forks to create a copy of itself. Then, the copy, called the “child process”, calls the exec system call to overlay itself with the other program: it ceases execution of its former program in favor of the other systems.The child process has an exact copy of all the memory segments of the parent process, though if copy-on-write semantics are implemented, the physical memory need not be actually copied. Instead, virtual memory pages in both processes may refer to the same pages of physical memory until one of them writes to such a page: then it is copied. This optimization is important in the common case where fork is used in conjunction with exec to execute a new program: typically, the child process performs only a small set of actions before it ceases execution of its program in favour of the program to be started, and it requires very few, if any, of its parent’s data structures.

When a process calls fork, it is deemed the parent process, and the newly created process, its child. After the fork, both processes not only run the same program, but they resume execution as though both had called the system call. They can then inspect the call’s return value to determine their status, child or parent, and act accordingly.
Communication
The child process inherits the standard streams from its parent, along with the rest of the environment. For interprocess communication, the parent process will often create a pipe or several pipes, and then after forking the processes will close the ends of the pipes that they don’t need.