VFORK(2)                             BSD                              VFORK(2)



NAME
     vfork - spawn new process in a virtual memory efficient way

SYNOPSIS
     pid = vfork()
     int pid;

DESCRIPTION
     vfork can be used to create new processes without fully copying the
     address space of the old process, which is horrendously inefficient in a
     paged environment.  It is useful when the purpose of fork(2) would have
     been to create a new system context for an execve(2).  vfork differs from
     fork in that the child borrows the parent's memory and thread of control
     until a call to execve or an exit (either by a call to exit(2) or
     abnormally.)  The parent process is suspended while the child is using
     its resources.

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

     vfork can normally be used just like fork. It does not work, however, to
     return while running in the child's context from the procedure that
     called vfork since the eventual return from vfork would then return to a
     no longer existent stack frame.  Be careful, also, to call _exit rather
     than exit if you can't execve, since exit will flush and close standard
     I/O channels, and thereby mess up the parent processes standard I/O data
     structures.  (Even with fork, it is wrong to call exit since buffered
     data would then be flushed twice.)

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

DIAGNOSTICS
     Same as for fork.

BUGS
     This system call will be eliminated when proper system sharing mechanisms
     are implemented. Users should not depend on the memory sharing semantics
     of vfork as it will, in that case, be made synonymous to fork.

     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 ioctls are allowed and input attempts result in an end-of-file
     indication.