fork(2)                                                   fork(2)



NAME
     fork - creates a new process

SYNOPSIS
     #include <sys/types.h>
     pid_t fork()

DESCRIPTION
     fork causes creation of a new process.  The new process, or
     child process, is an exact copy of the calling process or
     parent process.  The child process inherits the following
     attributes from the parent process:

        environment
        close-on-exec flag (see exec(2))
        signal-handling settings (such as SIG_DFL, SIG_IGN,
        function address)
        set-user-ID mode bit
        set-group-ID mode bit
        process compatibility flags (see setcompat(2))
        profiling on/off status
        access groups (see getgroups(2))
        nice value (see nice(2))
        all attached shared-memory segments (see shmop(2))
        process group ID
        tty group ID (see exit(2) and signal(3))
        trace flag (see ptrace(2) request 0)
        time left until an alarm clock signal (see alarm(2))
        current working directory
        root directory
        file-mode-creation mask (see umask(2))
        file size limit (see ulimit(2))
        phys regions (see phys(2))

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

        The child process has a unique process ID.

        The child process has a different parent process ID (that
        is, the process ID of the parent process).

        The child process has its own copy of the parent's file
        descriptors.  Each of the child's file descriptors shares
        a common file pointer with the corresponding file
        descriptor of the parent.  The child process also has its
        own copy of the parent's open directory streams.  The
        child and parent share directory stream positioning.

        The set of signals pending for the child process is
        cleared.




January 1992                                                    1

fork(2)                                                   fork(2)



        All semadj values are cleared (see semop(2)).

        Process locks, text locks, and data locks are not
        inherited by the child (see plock(2)).

        The child process's utime, stime, cutime, and cstime are
        set to 0 (see times(2)).  The time left until an alarm
        clock signal is reset to 0.

STATUS MESSAGES AND VALUES
     On 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.  Otherwise, a value of -1 is
     returned to the parent process, no child process is created,
     and errno is set to indicate the error.

     The fork command will fail and no child process will be
     created if one or more of the following is true:


     EAGAIN
          The system-imposed limit on the total number of
          processes under execution was exceeded.

     EAGAIN
          The system-imposed limit on the total number of
          processes under execution by a single user was
          exceeded.

     EAGAIN
          The system has temporarily exhausted its available
          memory or swap space.

SEE ALSO
     exec(2), nice(2), physf1(2), plock(2), ptrace(2), semop(2),
     setcompat(2), shmop(2), times(2), wait(2), wait3(2N),
     signal(3)


















2                                                    January 1992