vfork(2)                         UNIX System V                         vfork(2)


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

SYNOPSIS
      #include <unistd.h>

      pidt 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.

DIAGNOSTICS
      Upon successful completion, vfork returns a value of 0 to the child
      process and 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 the global variable errno is set to
      indicate the error.

      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.  This limit is
                     determined when the system is generated.

      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.

SEE ALSO
      exec(2), exit(2), fork(2), ioctl(2), wait(2)



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vfork(2)                         UNIX System V                         vfork(2)


NOTES
      This system call 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.







































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