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NAME

     vfork — create a new process without copying the address space

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     pid_t
     vfork(void);

DESCRIPTION

     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 twice.)

RETURN VALUES

     Same as for fork(2).

SEE ALSO

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

HISTORY

     The vfork() system 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.