fork, vfork - create a child process
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 pending
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.
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.
fork cannot allocate sufficient memory to copy the
parent's page tables and allocate a task structure for
fork failed to allocate the necessary kernel structures
because memory is tight.
Under Linux, vfork is merely an alias for fork.
The fork call conforms to SVr4, SVID, POSIX, X/OPEN, BSD
clone(2), execve(2), wait(2)