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     vfork — create a new process without copying the address space


     Standard C Library (libc, -lc)


     #include <unistd.h>



     The vfork() system call 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).
     The vfork() system call differs from fork(2) 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.

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

     The vfork() system call can normally be used just like fork(2).  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(2) rather than exit(3) if you cannot execve(2), since
     exit(3) will flush and close standard I/O channels, and thereby mess up
     the parent processes standard I/O data structures.  (Even with fork(2) it
     is wrong to call exit(3) since buffered data would then be flushed


     Same as for fork(2).


     execve(2), _exit(2), fork(2), rfork(2), sigvec(2), wait(2), exit(3)


     The vfork() system call appeared in 2.9BSD.


     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.