vfork(2)                   DG/UX 4.30                    vfork(2)



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

     SYNOPSIS
          int     vfork   ( )

     PARAMETERS
          None.

     DESCRIPTION
          Vfork creates a new process in the same way that fork(2)
          does except that the new process (the child) shares the
          address space of the parent rather than being given his own
          address space that is a copy of the parent's.  The vfork
          call does not return in the parent process until the child
          does an exec, an _exit, or terminates abnormally.  The vfork
          call does return in the child process, whereupon it is
          expected the child will call exec very soon.

          Vfork can normally be used just like fork, except after the
          vfork call the child must be careful about modifying the
          user address space and any per-process state since the
          changes will be reflected in the parent when he continues.
          It does not work, for example, for the child process to
          return from the procedure which called vfork because the
          parent would return to a no-longer-existent stack frame.

          If the following process attributes are changed by the
          child, those changes will be visible to the parent:

          ⊕    The shared memory segments (see shmat and shmdt).

          ⊕    The unshared data segment as a result of changing the
               break value (see brk and sbrk).

          ⊕    The text or data segment locks (see plock).

     ACCESS CONTROL
          No access checking is performed.

     RETURN VALUE
          Upon successful completion, vfork returns a value of 0 to
          the child process and (later) returns the process ID of the
          child process to the parent process. Otherwise a value of -1
          is returned to the parent process, no child process is
          created, and errno is set to indicate the error.

     EXCEPTIONS
          Vfork will fail and no child process will be created if one
          or more of the following are true:

          EAGAIN         The system-imposed limit on the total number



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     vfork(2)                   DG/UX 4.30                    vfork(2)



                         of processes under execution would be
                         exceeded.

          EAGAIN         The calling process is not a superuser and
                         there already exists
                         cf_pm_max_processes_per_real_user_id
                         processes with the same real user id as the
                         calling process.

          ENOMEM         The process requires more space than the
                         system is able to supply.

     SEE ALSO
          exec(2), fork(2), nice(2), plock(2), ptrace(2), semop(2),
          signal(2), sigset(2), times(2), ulimit(2), umask(2),
          wait(2).

     NOTES
          To avoid a possible deadlock, child processes 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.

     STANDARDS
          When using m88kbcs as the Software Development Environment
          target, the vfork function will be an incomplete emulation
          of Berkeley semantics.   This emulation does not support the
          virtual fork capability but is simply a call to fork.



























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