fork(2)                                                   fork(2)



     NAME
          fork - create 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, func-
             tion 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.




     April, 1990                                                     1

     fork(2)                                                   fork(2)



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

             Process locks, text locks, and data locks are not inher-
             ited 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.

     RETURN VALUE
          On successful completion, fork returns a value of 0 to the
          child process and returns the process ID of the child pro-
          cess to the parent process.  Otherwise, a value of -1 is re-
          turned to the parent process, no child process is created,
          and errno is set to indicate 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 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), phys(2), plock(2), ptrace(2), semop(2),
          setcompat(2), shmop(2), times(2), wait(2), wait3(2N), sig-
          nal(3).




















     2                                                     April, 1990