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Unix Version 7 - man page for fork (v7 section 2)

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FORK(2) 										  FORK(2)

       fork  -	spawn new process

       fork( )

       Fork is the only way new processes are created.	The new process's core image is a copy of
       that of the caller of fork.  The only distinction is the fact that the value  returned  in
       the  old  (parent)  process  contains the process ID of the new (child) process, while the
       value returned in the child is 0.  Process ID's range from 1 to 30,000.	This  process  ID
       is used by wait(2).

       Files  open before the fork are shared, and have a common read-write pointer.  In particu-
       lar, this is the way that standard input and output files are passed and  also  how  pipes
       are set up.

       wait(2), exec(2)

       Returns	-1  and fails to create a process if: there is inadequate swap space, the user is
       not super-user and has too many processes, or the system's process table  is  full.   Only
       the super-user can take the last process-table slot.

       (fork = 2.)
       sys fork
       (new process return)
       (old process return, new process ID in r0)

       The  return  locations in the old and new process differ by one word.  The C-bit is set in
       the old process if a new process could not be created.

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