MFC:

MFC:
  o Implement the stop_boot subroutine [1]. This subroutine can be used by
    scripts in rc.d to stop rc(8) from booting into multi-user mode when
    a critical or severe error condition is encountered.

  o Modify scripts in etc/rc.d that already implemented this functionality
    independently.

  o Document it.

  [1] - This subroutine was implemented in FreeBSD in rc.d/fsck. I moved it
        to rc.subr(8). Our version differs slightly in that it takes an
        optional argument to stop the boot even if "autoboot" is not set.

  Obtained from: NetBSD