31.3. Loading a Module

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To load a kernel module, run the modprobe <module_name> command as root. For example, to load the wacom module, run:
~]# modprobe wacom
By default, modprobe attempts to load the module from the /lib/modules/<kernel_version>/kernel/drivers/ directory. In this directory, each type of module has its own subdirectory, such as net/ and scsi/, for network and SCSI interface drivers respectively.
Some modules have dependencies, which are other kernel modules that must be loaded before the module in question can be loaded. A list of module dependencies is generated and maintained by the depmod program that is run automatically whenever a kernel or driver package is installed on the system. The depmod program keeps the list of dependencies in the /lib/modules/<kernel_version>/modules.dep file. The modprobe command always reads the modules.dep file when performing operations. When you ask modprobe to load a specific kernel module, it first examines the dependencies of that module, if there are any, and loads them if they are not already loaded into the kernel. modprobe resolves dependencies recursively: If necessary, it loads all dependencies of dependencies, and so on, thus ensuring that all dependencies are always met.
You can use the -v (or --verbose) option to cause modprobe to display detailed information about what it is doing, which may include loading module dependencies. The following is an example of loading the Fibre Channel over Ethernet module verbosely:

Example 31.3. modprobe -v shows module dependencies as they are loaded

~]# modprobe -v fcoe
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/scsi_tgt.ko
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/scsi_transport_fc.ko
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/libfc/libfc.ko
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/fcoe/libfcoe.ko
insmod /lib/modules/2.6.32-71.el6.x86_64/kernel/drivers/scsi/fcoe/fcoe.ko
This example shows that modprobe loaded the scsi_tgt, scsi_transport_fc, libfc and libfcoe modules as dependencies before finally loading fcoe. Also note that modprobe used the more primitive insmod command to insert the modules into the running kernel.


Although the insmod command can also be used to load kernel modules, it does not resolve dependencies. Because of this, you should always load modules using modprobe instead.
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