fork(2)                          UNIX System V                          fork(2)


NAME
      fork - create a new process

SYNOPSIS
      #include <sys/types.h>
      #include <unistd.h>

      pid_t fork(void);

DESCRIPTION
      fork causes creation of a new process.  The new process (child process)
      is an exact copy of the calling process (parent process).  This means the
      child process inherits the following attributes from the parent process:

            real user ID, real group ID, effective user ID, effective group ID
            environment
            close-on-exec flag [see exec(2)]
            signal handling settings (i.e., SIG_DFL, SIG_IGN, SIG_HOLD,
            function address)
            supplementary group IDs
            set-user-ID mode bit
            set-group-ID mode bit
            profiling on/off status
            nice value [see nice(2)]
            scheduler class [see priocntl(2)]
            all attached shared memory segments [see shmop(2)]
            process group ID
            session ID [see exit(2)]
            current working directory
            root directory
            file mode creation mask [see umask(2)]
            resource limits [see getrlimit(2)]
            controlling terminal

      Scheduling priority and any per-process scheduling parameters that are
      specific to a given scheduling class may or may not be inherited
      according to the policy of that particular class [see priocntl(2)].

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

            The child process has a unique process ID which does not match any
            active process group 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 file descriptors
            and directory streams.  Each of the child's file descriptors shares
            a common file pointer with the corresponding file descriptor of the
            parent.




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fork(2)                          UNIX System V                          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 tms structure is cleared:  tms_utime, stime,
            cutime, and cstime are set to 0 [see times(2)].

            The time left until an alarm clock signal is reset to 0.

            The set of signals pending for the child process is initialized to
            the empty set.

      Record locks set by the parent process are not inherited by the child
      process [see fcntl(2)].

      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 processes
                     under execution by a single user would be exceeded.

      EAGAIN         Total amount of system memory available when reading via
                     raw I/O is temporarily insufficient.

      ENOMEM         There is not enough swap space.

SEE ALSO
      alarm(2), exec(2), fcntl(2), getrlimit(2), nice(2), plock(2),
      priocntl(2), ptrace(2), semop(2), shmop(2), signal(2), times(2),
      umask(2), wait(2), system(3S).

DIAGNOSTICS
      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.  Otherwise, a value of (pid_t)-1 is returned to the parent
      process, no child process is created, and errno is set to indicate the
      error.
















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