fork(2)                             CLIX                             fork(2)



  NAME

    fork - Creates a new process

  LIBRARY

    Standard C Library (libc.a)

  SYNOPSIS

    #include <sys/types.h>

    pid_t fork(
      void );

  DESCRIPTION

    The fork() function creates a new process (child process) that is
    identical to the calling process (parent process).

    The child process inherits the following attributes from the parent
    process:

    ⊕  Environment

    ⊕  Close on exec flags (described in the exec() functions)

    ⊕  Signal handling settings (that is, SIG_DFL, SIG_IGN, SIG_HOLD
       referenced in signal.h, function address)

    ⊕  Set-user-ID mode bit

    ⊕  Set-group-ID mode bit

    ⊕  Profiling on/off status

    ⊕  Nice value (see the nice() function)

    ⊕  Process group ID

    ⊕  Session ID

    ⊕  tty group ID (described in the exit() function)

    ⊕  Current directory

    ⊕  Root directory

    ⊕  File mode creation mask (described in the umask() function)

    ⊕  File size limit (described in the ulimit() function)



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  fork(2)                             CLIX                             fork(2)



    ⊕  Attached shared memory segments (described in the shmop() function)

    ⊕  Attached mapped file segments

    ⊕  The child process inherits all mapped regions with the same protection
       and sharing mode as in the parent process.

    The child process differs from the parent process in the following ways:

    ⊕  The child process has a unique process ID and does not match any active
       process group ID.

    ⊕  The parent process ID of the child process matches the process ID of
       the parent.

    ⊕  The child process has its own copy of the parent process's file
       descriptors.  However, each of the child's file descriptors shares a
       common file pointer with the corresponding file descriptor of the
       parent process.

    ⊕  All semadj values are cleared.  (Information about semadj values can be
       found in the semop() function.)

    ⊕  Process locks, text locks, and data locks are not inherited by the
       child process.  (Information about locks can be found in the plock()
       function.)

    ⊕  The child process's utime(), stime(), cutime(), and cstime() functions
       are set to 0.

    ⊕  Any pending alarms are cleared in the child process.

    ⊕  Any signals pending for the parent process are cleared for the child
       process.

  EXAMPLES

    To create a new process:

    int fork_retval;
    fork_retval = fork();

    switch(fork_retval)

            case -1:
                    perror("Fork failed");
                    return(-1);

            case 0:
                    /* Child */
                    ...



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  fork(2)                             CLIX                             fork(2)



            default:
                    /* Parent, fork_retval is child's process ID */
                    ...


  RETURN VALUES

    Upon successful completion, fork() returns a value of 0 to the child
    process and returns the process ID of the child process to the parent
    process.  If fork() fails, a value of -1 is returned to the parent
    process, no child process is created, and the global variable errno is set
    to indicate the error.

  ERRORS

    The fork() function fails if one or more of the following are true:

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

    [EAGAIN]   The system-imposed limit on the total number of processes
               executing for a single user would be exceeded.

    [EAGAIN]   The total amount of system memory available when reading
               through raw input/output is temporarily insufficient.

  RELATED INFORMATION

    Functions:  exec(2), exit(2), times(2), plock(2), nice(2), ptrace(2),
    semop(2), shmop(2), sigaction(2), signal(2), sigset(2), ulimit(2),
    umask(2), wait(2), waitpid(2)























  2/94 - Intergraph Corporation                                              3