As in the above monks said
The fork system call in Unix creates a new process. The new process inherits various properties from its parent (Environmental variables, File descriptors, etc - see the manual page for details). After a successful fork call, two copies of the original code will be running. In the original process (the parent) the return value of fork will be the process ID of the child. In the new child process the return value of fork will be 0.
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