agetty
Hurricane Electric Internet Services
NAME
agetty - alternative Linux getty
SYNOPSIS
agetty [-ihLmw] [-l login_program] [-I init] [-t timeout] port baud_rate,... [term]
agetty [-ihLmw] [-l login_program] [-I init] [-t timeout] baud_rate,... port [term]
DESCRIPTION
agetty opens a tty port, prompts for a login name and
invokes the /bin/login command. It is normally invoked by
init(8).
agetty has several non-standard features that are useful
for hard-wired and for dial-in lines:
o Adapts the tty settings to parity bits and to
erase, kill, end-of-line and uppercase characters
when it reads a login name. The program can handle
7-bit characters with even, odd, none or space par-
ity, and 8-bit characters with no parity. The fol-
lowing special characters are recognized: @ and
Control-U (kill); #, DEL and back space (erase);
carriage return and line feed (end of line).
o Optionally deduces the baud rate from the CONNECT
messages produced by Hayes(tm)-compatible modems.
o Optionally does not hang up when it is given an
already opened line (useful for call-back applica-
tions).
o Optionally does not display the contents of the
/etc/issue file (System V only).
o Optionally invokes a non-standard login program
instead of /bin/login.
o Optionally turns on hard-ware flow control
o Optionally forces the line to be local with no need
for carrier detect.
This program does not use the /etc/gettydefs (System V) or
/etc/gettytab (SunOS 4) files.
ARGUMENTS
port A path name relative to the /dev directory. If a
"-" is specified, agetty assumes that its standard
input is already connected to a tty port and that a
connection to a remote user has already been estab-
lished.
Under System V, a "-" port argument should be pre-
ceded by a "--".
baud_rate,...
A comma-separated list of one or more baud rates.
Each time agetty receives a BREAK character it
advances through the list, which is treated as if
it were circular.
Baud rates should be specified in descending order,
so that the null character (Ctrl-@) can also be
used for baud rate switching.
term The value to be used for the TERM environment vari-
able. This overrides whatever init(8) may have set,
and is inherited by login and the shell.
OPTIONS
-h Enable hardware (RTS/CTS) flow control. It is left
up to the application to disable software
(XON/XOFF) flow protocol where appropriate.
-i Do not display the contents of /etc/issue before
writing the login prompt. Terminals or communica-
tions hardware may become confused when receiving
lots of text at the wrong baud rate; dial-up
scripts may fail if the login prompt is preceded by
too much text.
-I initstring
Set an initial string to be sent to the tty or
modem before sending anything else. This may be
used to initialize a modem. Non printable charac-
ters may be sent by writing their octal code pre-
ceded by a backslash (\). For example to send a
linefeed character (ASCII 10, octal 012) write
\012.
-l login_program
Invoke the specified login_program instead of
/bin/login. This allows the use of a non-standard
login program (for example, one that asks for a
dial-up password or that uses a different password
file).
-m Try to extract the baud rate the connect status
message produced by some Hayes(tm)-compatible
modems. These status messages are of the form:
"<junk><speed><junk>". agetty assumes that the
modem emits its status message at the same speed as
specified with (the first) baud_rate value on the
command line.
Since the -m feature may fail on heavily-loaded
systems, you still should enable BREAK processing
by enumerating all expected baud rates on the
command line.
-t timeout
Terminate if no user name could be read within
timeout seconds. This option should probably not be
used with hard-wired lines.
-L Force the line to be local line with no need for
carrier detect. This can be useful when you have
locally attached terminal where the serial line
does not set the carrier detect signal.
-w Wait for the user or the modem to send a carriage-
return or a linefeed character before sending the
/etc/issue file and the login prompt.
EXAMPLES
This section shows sample entries for the /etc/inittab file.
For a hard-wired line:
tty1:con80x60:/sbin/agetty 9600 tty1
For a dial-in line with a 9600/2400/1200 baud modem:
ttyS1:dumb:/sbin/agetty -mt60 ttyS1 9600,2400,1200
These examples assume you use the simpleinit(8) init program for Linux.
If you use a SysV like init (does /etc/inittab mention "respawn"?), refer
to the appropriate manual page.
ISSUE ESCAPES
The /etc/issue file may contain certain escape codes to
display the system name, date and time etc. All escape
codes consist of a backslash (\) immediately followed by
one of the letters explained below.
b Insert the baudrate of the current line.
d Insert the current date.
s Insert the system name, the name of the operating
system.
l Insert the name of the current tty line.
m Insert the architecture identifier of the machine,
eg. i486
n Insert the nodename of the machine, also known as
the hostname.
o Insert the domainname of the machine.
r Insert the release number of the OS, eg. 1.1.9.
t Insert the current time.
u Insert the number of current users logged in.
U Insert the string "1 user" or "<n> users" where <n>
is the number of current users logged in.
v Insert the version of the OS, eg. the build-date
etc.
Example: On my system, the following /etc/issue file:
This is \n.\o (\s \m \r) \t
displays as
This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
FILES
/var/run/utmp, the system status file.
/etc/issue, printed before the login prompt (System V only).
/dev/console, problem reports (if syslog(3) is not used).
/etc/inittab (Linux simpleinit(8) configuration file).
BUGS
The baud-rate detection feature (the -m option) requires
that agetty be scheduled soon enough after completion of a
dial-in call (within 30 ms with modems that talk at 2400
baud). For robustness, always use the -m option in combi-
nation with a multiple baud rate command-line argument, so
that BREAK processing is enabled.
The text in the /etc/issue file and the login prompt are
always output with 7-bit characters and space parity.
The baud-rate detection feature (the -m option) requires
that the modem emits its status message after raising the
DCD line.
DIAGNOSTICS
Depending on how the program was configured, all diagnos-
tics are written to the console device or reported via the
syslog(3) facility. Error messages are produced if the
port argument does not specify a terminal device; if there
is no utmp entry for the current process (System V only);
and so on.
AUTHOR(S)
W.Z. Venema <wietse@wzv.win.tue.nl>
Eindhoven University of Technology
Department of Mathematics and Computer Science
Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
Peter Orbaek <poe@daimi.aau.dk>
Linux port.
CREATION DATE
Sat Nov 25 22:51:05 MET 1989
LAST MODIFICATION
91/09/01 23:22:00
VERSION/RELEASE
1.29
Hurricane Electric Internet Services
Copyright (C) 1998
Hurricane Electric.
All Rights Reserved.