Chapter 18. The Hotplug System / 18.3. Hotplug Agents | ||||
|---|---|---|---|---|
 | 18.2. Hotplug Events | 18.4. Automatic Module Loading |  | |
Chapter 18. The Hotplug System / 18.3. Hotplug Agents | ||||
|---|---|---|---|---|
| 18.2. Hotplug Events | 18.4. Automatic Module Loading | | |
A hotplug agent is an executable program that performs suitable
actions for an event. The agents for device events are located
in /etc/hotplug.d/event
name and
/etc/hotplug.d/default. All programs in these
directories that have the suffix .hotplug are
executed in alphabetical order.
To ensure that events of a particular kind are ignored, remove the
executable bits from the respective hotplug agents. Alternatively,
change the suffix .hotplug to something else.
Usually, device agents load kernel modules, but
occasionally they also call additional commands.
In SUSE LINUX, this is handled by /sbin/hwup or
/sbin/hwdown. These programs search for a configuration
suitable for the device in the directory
/etc/sysconfig/hardware and apply it. To prevent
a certain device from being initialized, create a suitable configuration
file with the start mode manual or
off. If
/sbin/hwup does not find any configuration, modules are
automatically loaded by the agent. In this case some agents automatically
generate configuration files for hwup. This makes the
agent faster the next time it runs. For more information, see
Section 18.4, “Automatic Module Loading”.
More information about
/sbin/hwup is available in the file
/usr/share/doc/packages/sysconfig/README and
in the manual page man hwup.
Before interface agents are called, udev usually generates a device node the system can access. udev enables the assignment of persistent names to interfaces. See Chapter 19, Dynamic Device Nodes with udev for details. Subsequently, the individual agents set up the interfaces. The procedures for some interfaces are described below.
Network interfaces are initialized with
/sbin/ifup and deactivated with
/sbin/ifdown. Details are provided
in the file /usr/share/doc/packages/sysconfig/README
and in the manual page man ifup.
If a computer has several network devices with different drivers,
the designations of the interface can change if another driver
is loaded faster while the system is booting. For this
reason, SUSE LINUX manages events for PCI network devices
by means of a queue. This feature can be disabled with the
variable HOTPLUG_PCI_QUEUE_NIC_EVENTS=no
in the file /etc/sysconfig/hotplug.
The best solution, however, is to use persistent interface
designations. You can specify the names of the individual interfaces in the
configuration files. Details about this method are available
in the file /usr/share/doc/packages/sysconfig/README.
Since SUSE LINUX 9.3, udev also deals with network interfaces,
although these are not
device nodes. This allows use of persistent interface names in a more
standardized manner.
Interfaces to storage devices must be mounted
to be able to access them. This can be fully automated
or preconfigured. The configuration takes place in the
variables HOTPLUG_DO_MOUNT,
HOTPLUG_MOUNT_TYPE, and
HOTPLUG_MOUNT_SYNC in
/etc/sysconfig/hotplug
and in the file /etc/fstab.
A fully automated operation can be activated by setting
the variable
HOTPLUG_DO_MOUNT=yes. Deactivate it by
setting the variable to no.
Use the variable HOTPLUG_MOUNT_TYPE
to switch between two modes: subfs or fstab.
In the HOTPLUG_MOUNT_TYPE=subfs mode,
a subdirectory is created in the directory /media.
The name of the subdirectory is derived from the device
properties. When the medium is accessed, it is automatically
mounted and unmounted by submountd. Devices in
this mode can easily be removed when they are no longer accessed.
In the HOTPLUG_MOUNT_TYPE=fstab mode, storage
devices are mounted in the conventional way by means of a
suitable entry in the file /etc/fstab.
The variable HOTPLUG_MOUNT_SYNC can be set
to enable access in synchronous or asynchronous mode. In the
asynchronous mode, write access is faster, because the results
are buffered. However, careless removal of the data medium
can result in incomplete writing of data. In the synchronous
mode, all data is written immediately, but the access takes
longer. The device must be unmounted manually with
umount.
The use of persistent device names is recommended, because traditional device names may change depending on the initialization sequence. Details about persistent device names is available in Chapter 19, Dynamic Device Nodes with udev.
