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AGETTY(8) AGETTY(8)
NAME
agetty - alternative Linux getty
SYNOPSIS
agetty [-ihLmnw] [-f issue_file] [-l login_program] [-I init] [-t timeout] [-H
login_host] port baud_rate,... [term]
agetty [-ihLmnw] [-f issue_file] [-l login_program] [-I init] [-t timeout] [-H
login_host] baud_rate,... port [term]
DESCRIPTION
agetty opens a tty port, prompts for a login name and invokes the /bin/login com-
mand. 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 parity, and 8-bit characters
with no parity. The following special characters are recognized: @ and Con-
trol-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 applications).
o Optionally does not display the contents of the /etc/issue file.
o Optionally displays an alternative issue file instead of /etc/issue.
o Optionally does not ask for a login name.
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 established.
Under System V, a "-" port argument should be preceded 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 charac-
ter (Ctrl-@) can also be used for baud rate switching.
term The value to be used for the TERM environment variable. This overrides what-
ever 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 (or other) before writing the
login prompt. Terminals or communications 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.
-f issue_file
Display the contents of issue_file instead of /etc/issue. This allows cus-
tom messages to be displayed on different terminals. The -i option will
override this option.
-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 characters may
be sent by writing their octal code preceded 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).
-H login_host
Write the specified login_host into the utmp file. (Normally, no login host
is given, since agetty is used for local hardwired connections and consoles.
However, this option can be useful for identifying terminal concentrators
and the like.
-m Try to extract the baud rate the CONNECT status message produced by
Hayes(tm)-compatible modems. These status messages are of the form:
"<junk><speed><junk>". agetty assumes that the modem emits its status mes-
sage 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 com-
mand line.
-n Do not prompt the user for a login name. This can be used in connection with
-l option to invoke a non-standard login process such as a BBS system. Note
that with the -n option, agetty gets no input from user who logs in and
therefore won’t be able to figure out parity, character size, and newline
processing of the connection. It defaults to space parity, 7 bit characters,
and ASCII CR (13) end-of-line character. Beware that the program that
agetty starts (usually /bin/login) is run as root.
-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 a local line with no need for carrier detect. This can
be useful when you have a 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 char-
acter before sending the /etc/issue (or other) file and the login prompt.
Very useful in connection with the -I option.
EXAMPLES
This section shows examples for the process field of an entry in the /etc/inittab
file. You’ll have to prepend appropriate values for the other fields. See
inittab(5) for more details.
For a hard-wired line or a console tty:
/sbin/agetty 9600 ttyS1
For a directly connected terminal without proper carriage detect wiring: (try this
if your terminal just sleeps instead of giving you a password: prompt.)
/sbin/agetty -L 9600 ttyS1 vt100
For a old style dial-in line with a 9600/2400/1200 baud modem:
/sbin/agetty -mt60 ttyS1 9600,2400,1200
For a Hayes modem with a fixed 115200 bps interface to the machine: (the example
init string turns off modem echo and result codes, makes modem/computer DCD track
modem/modem DCD, makes a DTR drop cause a dis-connection and turn on auto-answer
after 1 ring.)
/sbin/agetty -w -I ’ATE0Q1&D2&C1S0=1\015’ 115200 ttyS1
ISSUE ESCAPES
The issue-file (/etc/issue or the file set with the -f option) may contain certain
escape codes to display the system name, date and time etc. All escape codes con-
sist 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.
/dev/console, problem reports (if syslog(3) is not used).
/etc/inittab, init(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 combination with a mul-
tiple baud rate command-line argument, so that BREAK processing is enabled.
The text in the /etc/issue file (or other) 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 diagnostics 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 AT wzv.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 AT daimi.dk>
Linux port and more options. Still maintains the code.
Eric Rasmussen <ear AT usfirst.org>
Added -f option to display custom login messages on different terminals.
CREATION DATE
Sat Nov 25 22:51:05 MET 1989
LAST MODIFICATION
96/07/20
AGETTY(8)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2008-08-30 04:48 @38.103.63.61 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)