bsd man page for vfork

VFORK(2)							System Calls Manual							  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.  Vfork differs
       from  fork  in  that  the child borrows the parent's memory and thread of control until a call to execve(2) 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 childs  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.

4th Berkeley Distribution					   June 30, 1985							  VFORK(2)