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+.\" Copyright (c) 1985, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"	@(#)acucntrl.8	8.2 (Berkeley) 12/11/93
+.\"
+.TH ACUCNTRL 8 "December 11, 1993"
+.UC 6
+.SH NAME
+acucntrl \- turn around tty line between dialin and dialout
+.SH SYNOPSIS
+.B /usr/lib/uucp/acucntrl
+keyword ttyline
+.SH DESCRIPTION
+.PP
+.I Acucntrl
+turns around the terminal line,
+enabling it to be used for both dialin and dialout.
+On dialin a terminal line is assumed to have  modem control enabled and a getty
+process in existence waiting for logins.  On dialout modem control is disabled
+and there is no getty process.
+.PP
+This program must be run setuid to root.
+.PP
+.I keyword
+is chosen from the list:
+.I disable
+or
+.IR dialout ,
+to condition a line for dialout;
+and
+.I enable
+or
+.IR dialin ,
+to condition a line for dialin.
+.PP
+When the line is conditioned for dialing out, the login name of the real uid
+of the process is placed in /etc/utmp in capitals.
+This declares that the line is in use and acts as an additional locking
+mechanism.
+.I Acucntrl
+will refuse to act if the /etc/utmp entry for the line is not null,
+is not the the user's login name (capitalized or not),
+and if the process is not running as the superuser.
+The last condition is to allow the superuser to clear the state of the line.
+.PP
+Turning modem control on or off is handled by poking into /dev/kmem.
+It is currently implemented for dz, dh, and dmf lines.
+.PP
+Under 4.2 BSD the program will also refuse to disable a line if carrier is
+sensed on it.  This is to avoid the dead period where someone has just dialed
+in and made the connection but has not yet logged in.
+.PP
+.I Ttyline
+can be either of the form tty* or /dev/tty*.
+Enabling/disabling a line whose name does not begin with ttyd? is prohibited
+unless the real uid of the process is 0 or if the login name corresponding to
+the real uid is uucp.  This is a security precaution.
+.PP 
+Steps taken when disabling
+.RI ( i . e .
+setup for dialing out)
+.IP 1)
+check input arguments
+.IP 2)
+look in /etc/utmp to check that the line is not in use by another user
+.IP 3)
+disable modem control on line
+.IP 4)
+check for carrier on device
+.IP 5)
+change owner of device to real uid
+.IP 6)
+edit /etc/ttys,  changing the first character of the appropriate line to 0
+.IP 7)
+send a hangup to process 1 to poke init to disable getty
+.IP 8)
+post uid name in capitals in /etc/utmp to let world know device has been grabbed
+.IP 9)
+make sure that DTR is on
+.PP
+Steps taken when enabling
+.RI ( i . e .
+setup for dialing in)
+.IP 1)
+check input arguments
+.IP 2)
+look in /etc/utmp to check that the line is not in use by another user
+.IP 3)
+make sure modem control on line is disabled
+.IP 4)
+turn off DTR to make sure line is hung up
+.IP 5)
+condition line: clear exclusive use and set hangup on close modes
+.IP 6)
+turn on modem control
+.IP 7)
+edit /etc/ttys,  changing the first character of the appropriate line to 1
+.IP 8)
+send a hangup to process 1 to poke init to enable getty
+.IP 9)
+clear uid name for /etc/utmp
+.SH HISTORY
+.PP
+First written by Allan Wilkes (fisher!allan)
+.PP
+Modified June 8,1983 by W.Sebok (astrovax!wls) to poke the kernel rather
+than use a kernel hack to turn on/off modem control, using a subroutine
+stolen from a program written by Tsutomu Shimomura {astrovax,escher}!tsutomu
+.PP
+Worked over many times by W.Sebok
+.RI ( i . e .
+hacked to death)
+.SH FILES
+/dev/kmem, /vmunix, /etc/ttys, /etc/utmp, /dev/tty*
+.SH BUGS
+.PP
+Sensing carrier requires the 4.2 BSD TIOCMGET ioctl call.  Unfortunately this
+ioctl is not implemented in the vanilla 4.2 BSD dh driver even though the
+dz and dmf drivers use an emulation of the DH11's modem control bits. This
+has been fixed here.
+.PP
+Some time (currently 2 seconds) is required between disabling modem control
+and opening the device.  This is probably because of a race with getty whose
+open is finally being allowed to complete.  This time interval may not be
+enough on a loaded system.  Because of this problem and the above problem with
+the dh driver there is deliberately no error message given when the TIOCMGET
+ioctl fails.
+.PP
+Previously there were similar synchronization problems with the init process.
+When dialins are disabled the capitalized name of the process cannot be posted
+into /etc/utmp until init has finished clearing /etc/utmp.  However one does
+not know how long that will take, and, on a loaded system,  it can take quite
+a while.  This was solved by the strategy of 1) posting the name, 2) poking
+init, 3) going into a loop where the process repeatedly waits a second and
+checks whether the entry has been cleared from /etc/utmp, and 4) posting the
+name again.