Chapter 45. General Parameters and Modules

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This chapter is provided to illustrate some of the possible parameters available for common hardware device drivers [9], which under Red Hat Enterprise Linux are called kernel modules. In most cases, the default parameters do work. However, there may be times when extra module parameters are necessary for a device to function properly or to override the module's default parameters for the device.
During installation, Red Hat Enterprise Linux uses a limited subset of device drivers to create a stable installation environment. Although the installation program supports installation on many different types of hardware, some drivers (including those for SCSI adapters and network adapters) are not included in the installation kernel. Rather, they must be loaded as modules by the user at boot time.
Once installation is completed, support exists for a large number of devices through kernel modules.


Red Hat provides a large number of unsupported device drivers in groups of packages called kernel-smp-unsupported-<kernel-version> and kernel-hugemem-unsupported-<kernel-version> . Replace <kernel-version> with the version of the kernel installed on the system. These packages are not installed by the Red Hat Enterprise Linux installation program, and the modules provided are not supported by Red Hat, Inc.

45.1. Kernel Module Utilities

A group of commands for managing kernel modules is available if the module-init-tools package is installed. Use these commands to determine if a module has been loaded successfully or when trying different modules for a piece of new hardware.
The command /sbin/lsmod displays a list of currently loaded modules. For example:
Module                  Size  Used by
tun                    11585  1
autofs4                21573  1
hidp                   16193  2
rfcomm                 37849  0
l2cap                  23873  10 hidp,rfcomm
bluetooth              50085  5 hidp,rfcomm,l2cap
sunrpc                153725  1
dm_mirror              29073  0
dm_mod                 57433  1 dm_mirror
video                  17221  0
sbs                    16257  0
i2c_ec                  5569  1 sbs
container               4801  0
button                  7249  0
battery                10565  0
asus_acpi              16857  0
ac                      5701  0
ipv6                  246113  12
lp                     13065  0
parport_pc             27493  1
parport                37001  2 lp,parport_pc
uhci_hcd               23885  0
floppy                 57317  1
sg                     34653  0
snd_ens1371            26721  1
gameport               16073  1 snd_ens1371
snd_rawmidi            24897  1 snd_ens1371
snd_ac97_codec         91360  1 snd_ens1371
snd_ac97_bus            2753  1 snd_ac97_codec
snd_seq_dummy           4293  0
snd_seq_oss            32705  0
serio_raw               7493  0
snd_seq_midi_event      8001  1 snd_seq_oss
snd_seq                51633  5 snd_seq_dummy,snd_seq_oss,snd_seq_midi_event
snd_seq_device          8781  4 snd_rawmidi,snd_seq_dummy,snd_seq_oss,snd_seq
snd_pcm_oss            42849  0
snd_mixer_oss          16833  1 snd_pcm_oss
snd_pcm                76485  3 snd_ens1371,snd_ac97_codec,snd_pcm_oss
snd_timer              23237  2 snd_seq,snd_pcm
snd                    52933  12 snd_ens1371,snd_rawmidi,snd_ac97_codec,snd_seq_oss,snd_seq,snd_seq_device,snd_pcm_oss,snd_mixer_oss,snd_pcm,snd_timer
soundcore              10145  1 snd
i2c_piix4               8909  0
ide_cd                 38625  3
snd_page_alloc         10569  1 snd_pcm
i2c_core               21697  2 i2c_ec,i2c_piix4
pcnet32                34117  0
cdrom                  34913  1 ide_cd
mii                     5825  1 pcnet32
pcspkr                  3521  0
ext3                  129737  2
jbd                    58473  1 ext3
mptspi                 17353  3
scsi_transport_spi     25025  1 mptspi
mptscsih               23361  1 mptspi
sd_mod                 20929  16
scsi_mod              134121  5 sg,mptspi,scsi_transport_spi,mptscsih,sd_mod
mptbase                52193  2 mptspi,mptscsih
For each line, the first column is the name of the module, the second column is the size of the module, and the third column is the use count.
The /sbin/lsmod output is less verbose and easier to read than the output from viewing /proc/modules.
To load a kernel module, use the /sbin/modprobe command followed by the kernel module name. By default, modprobe attempts to load the module from the /lib/modules/<kernel-version>/kernel/drivers/ subdirectories. There is a subdirectory for each type of module, such as the net/ subdirectory for network interface drivers. Some kernel modules have module dependencies, meaning that other modules must be loaded first for it to load. The /sbin/modprobe command checks for these dependencies and loads the module dependencies before loading the specified module.
For example, the command
modprobe e100
loads any module dependencies and then the e100 module.
To print to the screen all commands as /sbin/modprobe executes them, use the -v option. For example:
modprobe -v e100
Output similar to the following is displayed:
insmod /lib/modules/2.6.9-5.EL/kernel/drivers/net/e100.ko
Using /lib/modules/2.6.9-5.EL/kernel/drivers/net/e100.ko
Symbol version prefix 'smp_'
The /sbin/insmod command also exists to load kernel modules; however, it does not resolve dependencies. Thus, it is recommended that the /sbin/modprobe command be used.
To unload kernel modules, use the /sbin/rmmod command followed by the module name. The rmmod utility only unloads modules that are not in use and that are not a dependency of other modules in use.
For example, the command
rmmod e100
unloads the e100 kernel module.
Another useful kernel module utility is modinfo. Use the command /sbin/modinfo to display information about a kernel module. The general syntax is:
modinfo [options] <module>
Options include -d, which displays a brief description of the module, and -p, which lists the parameters the module supports. For a complete list of options, refer to the modinfo man page (man modinfo).

[9] A driver is software which enables Linux to use a particular hardware device. Without a driver, the kernel cannot communicate with attached devices.
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