init system

Remote Serial Console HOWTO
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# 6.1. init system

The file `/etc/inittab` contains the background programs that used to keep the system running. One of these programs is one getty process per serial port.

Figure 6-3. getty is started by init, based upon an entry in `/etc/inittab`

    co:2345:respawn:/sbin/getty ttyS0 CON9600 vt102

Each field in `inittab` is separated by a colon and contains:

`co`

  Arbitrary entry for `inittab`. As long as this entry doesn't appear anywhere else in `inittab`, you're okay. We named this entry `co` because it's for the console.

  Red Hat Linux 7.3 has a program called kudzu which configures the system when it is booted. kudzu treats an `inittab` entry of `co` specially, setting it for the attached monitor and keyboard or the serial console. Hardcoding the value of `co` prevents this behaviour.

`2345`

  Run levels where this entry gets started. Run levels 2, 3, 4 and 5 can be used for an operational system, getty should not be used in other run levels. The serial console still works in run level 1 (or single user mode) even without a getty.

`respawn`

  Re-run the program if it dies. We want this to happen so that a new `login` prompt will appear when you log out of the console.

`/sbin/getty ttyS0 CON9600 vt102`

  The command to run. In this case, we're telling getty to connect to `/dev/ttyS0` using the settings for `CON9600` which exists in `/etc/gettydefs`. This entry represents a terminal running at 9600bps. Initially assume that the terminal is a later-model VT100.

After changing `/etc/inittab` restart init with

    telinit q

An alternative is to send the hangup signal to init with the command kill -HUP 1. This is not recommended: if you make a typing mistake and actually kill init then your system will suddenly halt.

| Comments in `inittab` and Red Hat's kudzu
| kudzu uses the `#` line comment to activate and deactivate the gettys for the attached monitor and keyboard and for the serial port. To prevent a genuine comment from becoming confused with a line saved by kudzu use `##` at the start of a line of genuine comments.

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