Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 318 — #344

The hotplug system is not only used for devices that can be inserted and

removed during operation, but also for all devices only detected after the

kernel has been booted. These devices are entered in the sysfs ﬁle sys-

tem, which is mounted under /sys. Until the kernel has been booted, only

devices that are absolutely necessary, such as bus system, boot disks, or

keyboard, are initialized.

The most important hotplug functions are conﬁgured in two ﬁles. The ﬁrst

of these, /etc/sysconfig/hotplug, contains variables that inﬂuence

the behavior of hotplug and coldplug. Every variable is explained by a

comment. The second ﬁle, /proc/sys/kernel/hotplug, contains the

name of the executable program called by the kernel.

14.1 Devices and Interfaces

As well as devices, the hotplug system also administers interfaces. A device

is either linked to a bus or an interface. An interface links devices to each

other or to an application.

Devices entered in the sysfs ﬁle are found under /sys/devices. In-

terfaces are located under /sys/class or /sys/block. All interfaces

should have a link to the related device in the sysfs ﬁle, but there are al-

ways some drivers that do not automatically add this link.

Typical examples of devices and interfaces include the following:

PCI Network Card A device linked to the PCI bus (/sys/devices/

pci0000:00/0000:00:1e.0/0000:02:00.0) that has a network

interface used by network services or linked to a virtual network de-

vice, such as a tunnel or VLAN. (/sys/class/net/eth0)

PCI SCSI Controller A device (/sys/devices/pci0000:20/0000:

20:01.1) that makes several physical interfaces available in the form

of a bus (/sys/class/scsi_host/host1).

SCSI Hard Disk A device (/sys/devices/pci0000:20/0000:20:

01.1/host1/1:0:0:0) with several interfaces (/sys/block/

sda*).

14.2 Hotplug Events

Every device and every interface has an associated hotplug event, which

is processed by the relevant hotplug agent. Hotplug events are triggered

318 14.1. Devices and Interfaces