VFORK(2)                COMMAND REFERENCE                VFORK(2)



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

SYNOPSIS
     pid = vfork()
     int pid;

DESCRIPTION
     Vfork is identical to fork(2).  It is provided here for
     compatibility with other systems.  On those systems, vfork
     creates new processes without copying the address space of
     the old process, borrowing 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).

     Here, with both vfork and fork the address space is not
     copied; data and stack are made copy-on-access so neither
     the parent nor the child can modify the other's memory.  The
     new process is created without the overhead of copying the
     whole process.

     Vfork returns 0 in pid in the child's context and (later) in
     pid the pid of the child in the parent's context.

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, NPROC, would be
                  exceeded.

     [EAGAIN]     The system-imposed limit on the total number of
                  processes under execution by a single user,
                  MAXUPRC, defined in <sys/param.h>, would be
                  exceeded.

     [ENOMEM]     Insufficient space exists in the swap area for
                  the child process.

RETURN VALUE
     Upon successful completion, vfork returns a value of 0 in
     pid to the child process and returns the process ID of the
     child process in pid 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.

SEE ALSO
     execve(2), fork(2), and wait(2).





Printed 4/6/89                                                  1

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