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<chapt id="modules">
<heading>Managing the kernel modules</heading>
<p>
Linux device drivers come in the form of kernel modules - object
files which may be loaded into the running kernel to extend its
functionality. The list of currently loaded kernel modules can be
obtained using the <tt>lsmod</tt> command, modules may be loaded
using <tt>modprobe</tt>, and removed using <tt>modprobe -r</tt>.
The <tt>depmod</tt> command may be used to regenerate the list of
available modules (after installation of the new modules, for
example), even though it is pretty unlikely that you will ever
need to invoke it by hand.
</p>
<p>
Normally, the devices are detected and neccessary kernel modules
are loaded by <tt>udev</tt> during boot time. Occasionally, one
may need finer control over the loading of kernel modules, for
example to pass the additional parameters to the module, force
loading of some modules on startup, or prevent certain module(s)
from being loaded.
</p>
<p>
If some modules are not loaded automatically by <tt>udev</tt>, but
you would like them to be loaded during boot, it is possible to force
it by listing the names of the modules in <tt>/etc/modules</tt>.
This will be scanned for the names of
the modules (one name per line), which will then be loaded using
<tt>modprobe</tt>. You can also specify the arguments for the modules.
For example, a typical <tt>/etc/modules</tt> might look like that
<example>
loop max_int=32
sbp2
</example>
To find out what parameters are accepted by a given module, you can
use the <tt>modinfo</tt> command, for example:
<example>
# modinfo loop
filename: /lib/modules/3.2.0-2-686-pae/kernel/drivers/block/loop.ko
alias: devname:loop-control
alias: char-major-10-237
alias: block-major-7-*
license: GPL
depends:
intree: Y
vermagic: 3.2.0-2-686-pae SMP mod_unload modversions 686
parm: max_loop:Maximum number of loop devices (int)
parm: max_part:Maximum number of partitions per loop device (int)
</example>
</p>
<p>
To add custom arguments to the modules loaded by <tt>udev</tt>
early in the boot process, you need to create a custom
configuration file for <tt>modprobe</tt>, which <tt>udev</tt>
uses to load the modules. For example, to pass an
<tt>atapi_enabled=1</tt> argument to the <tt>libata</tt> kernel
module, create <tt>/etc/modprobe.d/local</tt> file with a
following line:
<example>
options libata atapi_enabled=1
</example>
You can choose arbitrary names for the configuration files in
<tt>/etc/modprobe.d</tt> and put multiple <tt>options</tt> lines in
the same file.
</p>
<p>
Sometimes two different modules claim support for the same
device, usually because two slightly different versions of the
device exist, requiring different kernel modules to operate. In
such situation <tt>udev</tt> loads both kernel modules, with
unpredictable results. To avoid this problem, you can prevent
any module (let's say, <tt>tulip</tt>) from loading by creating
an arbitrarily named file, containing a line
<example>
blacklist tulip
</example>
in <tt>/etc/modprobe.d</tt> directory. See the <tt>modprobe</tt>
manual page (<tt>man modprobe</tt>) for much more information on
configuring and using modprobe.
</p>
</chapt>
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