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agetty - alternative Linux getty 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]
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 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).
- 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 (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.
- 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.
- -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 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.
- -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).
- -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.
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.
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
/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).
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 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.
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. 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.
Sat Nov 25 22:51:05 MET 1989
91/09/01 23:22:00
1.29
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