fork()

FORK(2)             Linux Programmer's Manual             FORK(2)

NAME
       fork, vfork - create a child process

SYNOPSIS
       #include <unistd.h>

       pid_t fork(void);
       pid_t vfork(void);

DESCRIPTION
       fork  creates a child process that differs from the parent
       process only in its PID and PPID, and  in  the  fact  that
       resource  utilizations are set to 0.  File locks and pend-
       ing signals are not inherited.

       Under  Linux,  fork  is  implemented  using  copy-on-write
       pages,  so  the  only penalty incurred by fork is the time
       and memory required to duplicate the parent's page tables,
       and to create a unique task structure for the child.

RETURN VALUE
       On  success,  the  PID of the child process is returned in
       the parent's thread of execution, and a 0 is  returned  in
       the child's thread of execution.  On failure, a -1 will be
       returned in the parent's context, no child process will be
       created, and errno will be set appropriately.