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Debian GNU/Linux Reference Guide
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10.8.2 Triggering network configuration – hotplug

For hot-plug support install the hotplug package.

Networking hardware can be hot plugged either at boot time or after a card (e.g., a PCMCIA card) is inserted into the machine or after a utility such as discover runs and loads necessary driver modules.

When the kernel detects new hardware it initializes the driver for the hardware and then runs the hotplug program to configure it. Later if the hardware is removed then the kernel runs hotplug again with different environment variable settings. In Debian, when hotplug is called it runs scripts in /etc/hotplug/ and /etc/hotplug.d/. See hotplug(8) for details.

Newly inserted network hardware is configured by the script /etc/hotplug/net.agent. [ 62] Suppose your PCMCIA network card has been inserted resulting in interface eth0 becoming available for use. /etc/hotplug/net.agent does the following [63] :

     ifup eth0=hotplug

Unless you have added a logical interface definition or mapping named hotplug to /etc/network/interfaces, this command will do nothing. To make it so that the command will configure eth0, add the following stanza to /etc/network/interfaces:

     mapping hotplug
             script echo

As explained in High level network configuration using ifupdown logical interface definitions, Section 10.6.2 this will map the command shown above so that it is equivalent to the following:

     ifup eth0=eth0

(Do not include a mapping stanza like this if you are using ifplugd or waproamd instances started by hotplug to control the interface.)

If you want only eth0 and no other interfaces to be brought up on hot plug then use grep instead of echo as follows:

     mapping hotplug
             script grep
             map eth0

See Automatic network configuration using ifupdown, Section 10.6.3 and /usr/share/doc/hotplug/README.Debian for more tips.

Debian GNU/Linux Reference Guide
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