mgetty

Remote Serial Console HOWTO
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# 6.4. mgetty

mgetty is a modem-aware getty. It supports modems with the Hayes AT command set and is especially designed for supporting modems that are used to send faxes and to dial out as well as dial in. These features are not required for a serial console.

mgetty does not require the traditional `/etc/gettydefs` file. As a result mgetty is invoked from `/etc/inittab` without supplying an entry in `/etc/gettydefs`.

Figure 6-7. `/etc/inittab` entry for mgetty

    co:2345:respawn:/sbin/mgetty ttyS0

mgetty is configured using the file `/etc/mgetty+sendfax/mgetty.config`. It should contain an entry for the port used by the serial console.

Figure 6-8. mgetty configuration file `mgetty.config`

    port ttyS0
     speed 9600
     direct yes
     data-only yes
     toggle-dtr yes
     need-dsr yes
     port-owner root
     port-group root
     port-mode 600
     login-prompt @ \P login:\040
     login-time 60
     term vt102

All the options are documented in the PostScript file `/usr/share/doc/mgetty…/mgetty.ps`.

We set `direct`, `data-only`, `need-dsr` and `toggle-dtr` so that the RS-232 control lines are used correctly for a dumb modem.

`port-owner`, `port-group` and `port-mode` set the serial device to be accessible only by the root user. Modem applications, which normally use the uucp group, cannot now accidentally use the serial console.

`login-prompt` shows the machine (`@`) and serial port (`\P`) being used. The text `\040` is simply the octal code for a space after `login:`.

`term vt102` gives the make and model of the terminal most likely to dial in. This sets the `TERM` environment variable, which you can change if you are dialling in from another terminal type.

The remaining configuration files, `/etc/mgetty+sendfax/dialin.config` and `/etc/mgetty+sendfax/login.config`, do not need to be altered.

If you wish to alter the suggested configuration then note that mgetty's `blocking` and `toggle-dtr` parameters do not co-exist well.

If you have difficulties, activate debugging by adding `debug 8` to `mgetty.config`. mgetty's actions are then visible in the file `/var/log/mgetty.log.ttyS0`.

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