2.9BSD/usr/man/cat2/fork.2

FORK(2)             UNIX Programmer's Manual              FORK(2)

NAME
     fork  -  spawn new process

SYNOPSIS
     fork()

DESCRIPTION
     _F_o_r_k is one of two ways new processes are created.  The new
     process's core image is a copy of that of the caller of
     _f_o_r_k.  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 pro-
     cess ID is used by _w_a_i_t(2).

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

RETURN VALUE
     Upon successful completion, _f_o_r_k returns a value of 0 to the
     child process and returns the process ID of the child pro-
     cess to the parent process.  Otherwise, a value of -1 is
     returned to the parent process, no child process is created,
     and the global variable _e_r_r_n_o is set to indicate the error.

ERRORS
     _F_o_r_k will fail and no child process will be created if:

     [EAGAIN]            The system-imposed limit on the total
                         number of processes under execution
                         would be exceeded.

     [EAGAIN]            The system-imposed liimit on the total
                         number of processes under execution by a
                         single user would be exceeded.

SEE ALSO
     execve(2), vfork(2), exec(3)

ASSEMBLER
     (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 pro-
     cess could not be created.

Printed 5/26/83                                                 1