4.3BSD - /usr/man/cat2/fork.0

FORK(2)                                                                FORK(2)


NAME
       fork - create a new process

SYNOPSIS
       pid = fork()
       int pid;

DESCRIPTION
       Fork 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 lseek(2) on a descriptor  in  the
            child process can affect a subsequent read or write 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  setr���
            limit(2).

RETURN VALUE
       Upon successful completion, fork 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 errno is set to indi‐
       cate the error.

ERRORS
       Fork  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 (<sys/param.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)