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