There are a number of factors involved in 'hotplugging' and HAL is only one of them. When a new device is added, e.g. a USB drive is plugged in, the following occurs (roughly):
* The kernel becomes aware of a new device and registers it in /sys. * Udev creates a device node (e.g. /dev/sdb1), and loads the
drivers/modules needed. * The HAL daemon is notified by D-Bus and adds the device and what it can find out about it to its database. * The addition of the new device is broadcast by HAL over D-Bus to whatever programs are subscribing, e.g. Thunar, which shows it as an icon in the shortcuts side panel, or Metacity/Nautilus which will add an icon to the desktop. * Another program listening may be a volume manager, such as thunar-volman or AutoFS, configured to automatically create mount points and mount certain types of drives, start Rhythmbox whenever an iPod is connected, etc.
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