Programming Jabber

Starting and stopping the script

The dialup connection is set up using the Point-to-Point Protocol daemon pppd. This uses a program such as chat to talk to the modem and get it to dial the ISP. The pppd mechanism affords us an ideal way to start and stop a script on the respective connection and disconnection of the line. When the connection has been made, the script /etc/ppp/ip-up is invoked and passed a number of connection-related parameters. Similarly /etc/ppp/ip-down is invoked when the connection is closed.

Some implementations of pppd also offer /etc/ppp/ip-up.local and /etc/ppp/ip-down.local, which should be used in place of the ip-up and ip-down scripts if they exist. These .local versions are intended to separate out system-specific connection-related activities from general connection-related activities, in a similar way to how the rc.local file allows system-specific startup activities to be defined in the /etc/rc.d/ Unix System V set of runlevel directories.

So what we want to do is start HostAlive with ip-up[.local] and stop it with ip-down[.local]. What these starter and stopper scripts might look like is shown in Example 8-4 and Example 8-5. They are simply shell scripts that share the process ID (PID) of the Jabber script via a temporary file. The starter starts the Jabber script and writes the PID of that script to a file. The stopper kills the script using the PID.

Example 8-4. An ip-up starter script

#!/bin/sh # Change to working directory cd /jabber/java/ ...