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VFORK(2)                    BSD System Calls Manual                   VFORK(2)

NAME
     vfork -- spawn new process and block parent

SYNOPSIS
     #include <&lt;unistd.h>&gt;

     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 dimin-
     ished.  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 with the additional seman-
     tics that the child process ran in the memory of the parent until it
     called execve(2) or exited.  That sharing of memory was removed in
     4.4BSD, leaving just the semantics of blocking the parent until the child
     calls execve(2) or exits.  On many other systems the original behavior
     has been restored, making this interface particularly unportable.

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.

BSD                             April 29, 2017                             BSD