vfork(2)                          SDK R4.11                         vfork(2)


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

SYNOPSIS
       #include <sys/types.h>

       pidt   vfork ()

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
       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 address space 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).

       Vfork cannot be used by multi-threaded processes since it is possible
       for other threads in the parent process that are not involved in the
       vfork call to alter the process address space.  This could cause
       undesirable affects to the child process that is expecting the parent
       to be stopped.

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.

DIAGNOSTICS
       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 of processes
                 under execution would be exceeded.

       EAGAIN    The calling process is not, on a generic DG/UX system, a
                 superuser, or, does not, on a system with DG/UX information
                 security, have appropriate privilege, and there already
                 exists cf_pm_max_processes_per_real_user_id processes with
                 the same real user id as the calling process.  For systems
                 with DG/UX information security, appropriate privilege is
                 defined as having one or more specific capabilities enabled
                 in the effective capability set of the calling process.
                 See capdefaults(5) for the default capability for this
                 system call.

       On a generic DG/UX system, appropriate privilege means that the
       process has an effective UID of root.

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

       EINVAL The process is multi-threaded.

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),
       appropriateprivilege(5), capdefaults(5).

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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