vfork(2)                                                    vfork(2)


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

       SYNOPSIS
             #include <unistd.h>
             pid_t vfork(void);

       DESCRIPTION
             vfork can be used to create new processes without fully
             copying the address space of the old process.  It is useful
             when the purpose of fork 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 or an exit (either by a call to exit 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 process
             ID (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 which 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 cannot 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.

          Return Values
             On success, vfork returns 0 to the child process and returns
             the process ID of the child process to the parent process.  On
             failure, vfork returns -1, sets errno to identify the error,
             and no child process is created.

          Errors
             In the following conditions, vfork fails and sets errno to:

             EAGAIN         The system-imposed limit on the total number of
                            processes under execution would be exceeded.
                            This limit is determined when the system is
                            generated.





                           Copyright 1994 Novell, Inc.               Page 1

      vfork(2)                                                    vfork(2)


            EAGAIN         The system-imposed limit on the total number of
                           processes under execution by a single user
                           would be exceeded.  This limit is determined
                           when the system is generated.

            ENOMEM         There is insufficient swap space for the new
                           process.

      REFERENCES
            exec(2), exit(2), fork(2), ioctl(2), wait(2)

      NOTICES
            vfork will be eliminated in a future release.  System
            implementation changes are making the efficiency gain of vfork
            over fork smaller.  The memory sharing semantics of vfork can
            be obtained through other mechanisms.

            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 EOF indication.

            On some systems, the implementation of vfork causes the parent
            to inherit register values from the child.  This can create
            problems for certain optimizing compilers if unistd.h is not
            included in the source calling vfork.

         Considerations for Lightweight Processes
            vfork will fail if the process has more than one LWP.



















                          Copyright 1994 Novell, Inc.               Page 2