4.3BSD-UWisc/man/cat2/fork.2

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



NAME
     fork - create a new process

SYNOPSIS
     pid = fork()
     int pid;

DESCRIPTION
     _F_o_r_k causes creation of a new process.  The new process
     (child process) is an exact copy of the calling process
     except for the following:

          The child process has a unique process ID.

          The child process has a different parent process ID
          (i.e., the process ID of the parent process).

          The child process has its own copy of the parent's
          descriptors.  These descriptors reference the same
          underlying objects, so that, for instance, file
          pointers in file objects are shared between the child
          and the parent, so that an _l_s_e_e_k(2) on a descriptor in
          the child process can affect a subsequent _r_e_a_d or _w_r_i_t_e
          by the parent.  This descriptor copying is also used by
          the shell to establish standard input and output for
          newly created processes as well as to set up pipes.

          The child processes resource utilizations are set to 0;
          see _s_e_t_r_l_i_m_i_t(2).

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 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 configuration-
                    dependent.

     [EAGAIN]       The system-imposed limit MAXUPRC
                    (<_s_y_s/_p_a_r_a_m._h>) on the total number of
                    processes under execution by a single user
                    would be exceeded.

     [ENOMEM]       There is insufficient swap space for the new



Printed 12/27/86          May 22, 1986                          1






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



                    process.

SEE ALSO
     execve(2), wait(2)



















































Printed 12/27/86          May 22, 1986                          2