VFORK(2)                  OpenBSD Programmer's Manual                 VFORK(2)

NAME
     vfork - spawn new process and block parent

SYNOPSIS
     #include <unistd.h>

     pid_t
     vfork(void);

DESCRIPTION
     vfork() was originally used to create new processes without fully copying
     the address space of the old process, which is horrendously inefficient
     in a paged environment.  It was useful when the purpose of fork(2) would
     have been to create a new system context for an execve(2).  Since fork(2)
     is now efficient, even in the above case, the need for vfork() has
     diminished.  vfork() differs from fork(2) in that the parent is suspended
     until the child makes a call to execve(2) or an exit (either by a call to
     _exit(2) or abnormally).  In addition, fork handlers established using
     pthread_atfork(3) are not called when a multithreaded program calls
     vfork().

     vfork() returns 0 in the child's context and (later) the PID of the child
     in the parent's context.

RETURN VALUES
     Same as for fork(2).

SEE ALSO
     execve(2), fork(2), sigaction(2), wait(2)

HISTORY
     The vfork() function call appeared in 2.9BSD.

BUGS
     To avoid a possible deadlock situation, processes that are children in
     the middle of a vfork() are never sent SIGTTOU or SIGTTIN signals;
     rather, output or ioctl(2) calls are allowed and input attempts result in
     an end-of-file indication.

OpenBSD 4.9                     April 24, 2008                     OpenBSD 4.9