vfork(2) [ultrix man page]

vfork(2)							System Calls Manual							  vfork(2)

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

Syntax
       pid = vfork()
       int pid;

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

       The system call returns a value of zero (0) in the child's context and, later, the pid of the child in the parent's context.

       The system call can normally be used just like It does not work, however, to return while running in the childs context from the  procedure
       which  called because the eventual return from would then return to a nonexistent stack frame.  Be careful, also, to call _exit rather than
       exit if you cannot call because exit will flush and close standard I/O channels and thereby cause problems in the parent process's standard
       I/O data structures.  Even with it is wrong to call exit, because buffered data would then be flushed twice.

Restrictions
       To avoid a possible deadlock situation, processes which are children in the middle of a are never sent SIGTTOU or SIGTTIN signals.  Rather,
       output or ioctls are allowed, and input attempts result in an end-of-file indication.

Diagnostics
       Same as for

See Also
       execve(2), fork(2), sigvec(2), wait(2)

																	  vfork(2)

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

NAME

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

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     pid_t
     vfork(void);

DESCRIPTION

     The vfork system call creates a new process that does not have a new virtual address space, but rather shares address space with the parent,
     thus avoiding potentially expensive copy-on-write operations normally associated with creating a new process.  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 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(2) rather than exit(3) if you can't execve(2), since exit(3) will flush and close standard I/O channels, and thereby mess
     up the standard I/O data structures in the parent process.  (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).

ERRORS

     Same as for fork(2).

SEE ALSO

     execve(2), fork(2), sigaction(2), wait(2)

HISTORY

     The vfork() function call appeared in 3.0BSD.  In 4.4BSD, the semantics were changed to only suspend the parent.  The original semantics were
     reintroduced in NetBSD 1.4.

BUGS

     Users should not depend on the memory sharing semantics of vfork() as other ways of speeding up the fork process may be developed in the
     future.

     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
								  January 3, 1998							       BSD