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 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:
-
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 Control-U (kill); #,
DEL and back space (erase); carriage return and line
feed (end of line).
-
Optionally deduces the baud rate from the CONNECT
messages produced by Hayes(tm)-compatible modems.
-
Optionally does not hang up when it is given an
already opened line (useful for call-back
applications).
-
Optionally does not display the contents of the
/etc/issue file.
-
Optionally displays an alternative issue file
instead of /etc/issue.
-
Optionally does not ask for a login name.
-
Optionally invokes a non-standard login program
instead of /bin/login.
-
Optionally turns on hard-ware flow control
-
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 character (Ctrl-@) can also be used
for baud rate switching.
- term
-
The value to be used for the TERM environment
variable. 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 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 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.
−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.
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:
For a directly connected terminal without proper carriage
detect wiring: (try this if your terminal just sleeps instead
of giving you a password: prompt.)
For a old style dial-in line with a 9600/2400/1200 baud
modem:
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.)
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 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:
displays as
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
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
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.
