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 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.
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
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 (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 custom messages to be dis
played 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 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.
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 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 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 character before sending the
/etc/issue (or other) file and the login prompt.
Very useful in connection with the -I option.
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 consist
of a backslash (\) immediately followed by one of the let
ters 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.
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 combi
nation with a multiple 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 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
Peter Orbaek <poe@daimi.aau.dk>
Linux port and more options. Still maintains the code.
Eric Rasmussen <ear@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
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