FORK(2)                                                                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 pro‐
       cess and returns the process ID of the child process to the parent pro‐
       cess.   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 indi‐
       cate 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  pro‐
                      cesses 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 process.

SEE ALSO
       execve(2), wait(2)



3rd Berkeley Distribution        May 22, 1986                          FORK(2)