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1.1 root 1: .\" @(#)acucntrl.8c 6.2 (Berkeley) 7/29/85
2: .\"
3: .TH acucntrl 8C "July 29, 1985"
4: .UC 6
5: .SH NAME
6: acucntrl \- turn around tty line between dialin and dialout
7: .SH SYNOPSIS
8: .B /usr/lib/uucp/acucntrl
9: keyword ttyline
10: .SH DESCRIPTION
11: .PP
12: .I Acucntrl
13: turns around terminal line, enabling it to be used for both dialin and dialout.
14: On dialin a terminal line is assumed to have modem control enabled and a getty
15: process in existence waiting for logins. On dialout modem control is disabled
16: and there is no getty process.
17: .PP
18: This program must be run setuid to root.
19: .PP
20: .I keyword
21: is chosen from the list:
22: .I disable
23: or
24: .IR dialout ,
25: to condition a line for dialout;
26: and
27: .I enable
28: or
29: .IR dialin ,
30: to condition a line for dialin.
31: .PP
32: When the line is conditioned for dialing out, the login name of the real uid
33: of the process is placed in /etc/utmp in capitals.
34: This declares that the line is in use and acts as an additional locking
35: mechanism.
36: .I Acucntrl
37: will refuse to act if the /etc/utmp entry for the line is not null,
38: is not the the user's login name (capitalized or not),
39: and if the process is not running as the superuser.
40: The last condition is to allow the superuser to clear the state of the line.
41: .PP
42: Turning modem control on or off is handled by poking into /dev/kmem.
43: It is currently implemented for dz, dh, and dmf lines.
44: .PP
45: Under 4.2 BSD the program will also refuse to disable a line if carrier is
46: sensed on it. This is to avoid the dead period where someone has just dialed
47: in and made the connection but has not yet logged in.
48: .PP
49: .I Ttyline
50: can be either of the form tty* or /dev/tty*.
51: Enabling/disabling a line whose name does not begin with ttyd? is prohibited
52: unless the real uid of the process is 0 or if the login name corresponding to
53: the real uid is uucp. This is a security precaution.
54: .PP
55: Steps taken when disabling
56: .RI ( i . e .
57: setup for dialing out)
58: .IP 1)
59: check input arguments
60: .IP 2)
61: look in /etc/utmp to check that the line is not in use by another user
62: .IP 3)
63: disable modem control on line
64: .IP 4)
65: check for carrier on device
66: .IP 5)
67: change owner of device to real uid
68: .IP 6)
69: edit /etc/ttys, changing the first character of the appropriate line to 0
70: .IP 7)
71: send a hangup to process 1 to poke init to disable getty
72: .IP 8)
73: post uid name in capitals in /etc/utmp to let world know device has been grabbed
74: .IP 9)
75: make sure that DTR is on
76: .PP
77: Steps taken when enabling
78: .RI ( i . e .
79: setup for dialin)
80: .IP 1)
81: check input arguments
82: .IP 2)
83: look in /etc/utmp to check that the line is not in use by another user
84: .IP 3)
85: make sure modem control on line is disabled
86: .IP 4)
87: turn off DTR to make sure line is hung up
88: .IP 5)
89: condition line: clear exclusive use and set hangup on close modes
90: .IP 6)
91: turn on modem control
92: .IP 7)
93: edit /etc/ttys, changing the first character of the appropriate line to 1
94: .IP 8)
95: send a hangup to process 1 to poke init to enable getty
96: .IP 9)
97: clear uid name for /etc/utmp
98: .SH HISTORY
99: .PP
100: First written by Allan Wilkes (fisher!allan)
101: .PP
102: Modified June 8,1983 by W.Sebok (astrovax!wls) to poke the kernel rather
103: than use a kernel hack to turn on/off modem control, using a subroutine
104: stolen from a program written by Tsutomu Shimomura {astrovax,escher}!tsutomu
105: .PP
106: Worked over many times by W.Sebok
107: .RI ( i . e .
108: hacked to death)
109: .SH FILES
110: /dev/kmem, /vmunix, /etc/ttys, /etc/utmp, /dev/tty*
111: .SH BUGS
112: .PP
113: Sensing carrier requires the 4.2 BSD TIOCMGET ioctl call. Unfortunately this
114: ioctl is not implemented in the vanilla 4.2 BSD dh driver even though the
115: dz and dmf drivers use an emulation of the DH11's modem control bits. This
116: has been fixed here.
117: .PP
118: Some time (currently 2 seconds) is required between disabling modem control
119: and opening the device. This is probably because of a race with getty whose
120: open is finally being allowed to complete. This time interval may not be
121: enough on a loaded system. Because of this problem and the above problem with
122: the dh driver there is deliberately no error message given when the TIOCMGET
123: ioctl fails.
124: .PP
125: Previously there was similar synchronization problem with the init process.
126: When dialins are disabled the capitalized name of the process cannot be posted
127: into /etc/utmp until init has finished clearing /etc/utmp. However one does
128: not know how long that will take, and, on a loaded system, it can take quite
129: a while. This was solved by the strategy of 1) posting the name, 2) poking
130: init, 3) going into a loop where the process repeatedly waits a second and
131: checks whether the entry has been cleared from /etc/utmp, and 4) posting the
132: name again.
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