A kernel module is a program which can loaded into or unloaded from the kernel upon demand, without necessarily recompiling it (the kernel) or rebooting the system, and is intended to enhance the functionality of the kernel.

In general software terms, modules are more or less like plugins to a software such as WordPress. Plugins provide means to extend software functionality, without them, developers would have to build a single massive software with all functionalities integrated in a package. If new functionalities are needed, they would have to be added in new versions of a software.

Likewise without modules, the kernel would have to be built with all functionalities integrated directly into the kernel image. This would mean having bigger kernels, and system administrators would need to recompile the kernel every time a new functionality is needed.

A simple example of a module is a device driver – which enables the kernel to access a hardware component/device connected to the system.

Suggested Read: How to Find Out What Version of Linux You Are Running

List All Loaded Kernel Modules in Linux

In Linux, all modules end with the .ko extension, and they are normally loaded automatically as the hardware is detected at system boot. However a system administrator can manage the modules using certain commands.

To list all currently loaded modules in Linux, we can use the lsmod (list modules) command which reads the contents of /proc/modules like this.

# lsmod

Module                  Size  Used by
rfcomm                 69632  2
pci_stub               16384  1
vboxpci                24576  0
vboxnetadp             28672  0
vboxnetflt             28672  0
vboxdrv               454656  3 vboxnetadp,vboxnetflt,vboxpci
bnep                   20480  2
rtsx_usb_ms            20480  0
memstick               20480  1 rtsx_usb_ms
btusb                  45056  0
uvcvideo               90112  0
btrtl                  16384  1 btusb
btbcm                  16384  1 btusb
videobuf2_vmalloc      16384  1 uvcvideo
btintel                16384  1 btusb
videobuf2_memops       16384  1 videobuf2_vmalloc
bluetooth             520192  29 bnep,btbcm,btrtl,btusb,rfcomm,btintel
videobuf2_v4l2         28672  1 uvcvideo
videobuf2_core         36864  2 uvcvideo,videobuf2_v4l2
v4l2_common            16384  1 videobuf2_v4l2
videodev              176128  4 uvcvideo,v4l2_common,videobuf2_core,videobuf2_v4l2
intel_rapl             20480  0
x86_pkg_temp_thermal    16384  0
media                  24576  2 uvcvideo,videodev
....

How to Load and Unload (Remove) Kernel Modules in Linux

To load a kernel module, we can use the insmod (insert module) command. Here, we have to specify the full path of the module. The command below will insert the speedstep-lib.ko module.

# insmod /lib/modules/4.4.0-21-generic/kernel/drivers/cpufreq/speedstep-lib.ko 

To unload a kernel module, we use the rmmod (remove module) command. The following example will unload or remove the speedstep-lib.ko module.

# rmmod /lib/modules/4.4.0-21-generic/kernel/drivers/cpufreq/speedstep-lib.ko 

How to Manage Kernel Modules Using modprobe Command

modprobe is an intelligent command for listing, inserting as well as removing modules from the kernel. It searches in the module directory /lib/modules/$(uname -r) for all the modules and related files, but excludes alternative configuration files in the /etc/modprobe.d directory.

Here, you don’t need the absolute path of a module; this is the advantage of using modprobe over the previous commands.

To insert a module, simply provide its name as follows.

# modprobe speedstep-lib

To remove a module, use the -r flag like this.

# modprobe -r speedstep-lib

Note: Under modprobe, automatic underscore conversion is performed, so there is no difference between _ and – while entering module names.

For more usage info and options, read through the modprobe man page.

# man modprobe

Source: https://www.tecmint.com/load-and-unload-kernel-modules-in-linux/

ow do I add or remove hardware device driver (module) from running Linux kernel?

Linux systems comes with the modprobe command, to add and remove modules from the Linux Kernel. Please note that:

=> Under MS-Windows you use term device driver for modules.

=> Under Linux you use term modules for device drivers.

=> The Linux kernel has a modular design.

=> At boot time, only a minimal resident kernel is loaded into memory.

=> If you add new hardware you need to add driver i.e. modules.

=> The modprobe command intelligently adds or removes a module from the Linux kernel

=> Usually, all Linux kernel modules (drivers) are stored in the module directory located that /lib/modules/$(uname -r) directory. To see current modules, type:
$ ls /lib/modules/$(uname -r)
Output:

build                modules.ccwmap       modules.order
initrd               modules.dep          modules.pcimap
kernel               modules.dep.bin      modules.seriomap
misc                 modules.devname      modules.softdep
modules.alias        modules.ieee1394map  modules.symbols
modules.alias.bin    modules.inputmap     modules.symbols.bin
modules.builtin      modules.isapnpmap    modules.usbmap
modules.builtin.bin  modules.ofmap        updates

Use the following command to list all drivers for various devices:
$ ls /lib/modules/$(uname -r)/kernel/drivers/
Sample outputs:

Task: Add a Module (driver) Called foo

Type the following command as root user:
# modprobe foo
In this example, I am loading a module called i8k, enter:
# modprobe -v i8k
Sample outputs:

insmod /lib/modules/3.5.0-30-generic/kernel/drivers/char/i8k.ko

Find out info about loaded module

You need to use the modinfo command to see information about a Linux Kernel module. The syntax is:
# modinfo -v {module-name-here}
# modinfo i8k
Sample outputs:

Task: List all loaded modules

Use the lsmod command to show the status of modules in the Linux Kernel:
# lsmod
Sample outputs:

Module                  Size  Used by
smbfs                  75465  0
md5                     5953  1
ipv6                  284193  10
ipt_TOS                 4033  2
iptable_mangle          4545  1
ip_conntrack_ftp       74801  0
ip_conntrack_irc       74033  0
ipt_REJECT              8897  43
ipt_LOG                 8513  2
ipt_limit               4033  6
iptable_filter          4673  1
ipt_multiport           3521  4
ipt_state               3393  16
ip_conntrack           54297  3 ip_conntrack_ftp,ip_conntrack_irc,ipt_state
ip_tables              21825  8 ipt_TOS,iptable_mangle,ipt_REJECT,ipt_LOG,ipt_limit,iptable_filter,ipt_multiport,ipt_state
i2c_dev                13889  0
i2c_core               28865  1 i2c_dev
dm_mirror              32721  0
dm_mod                 68609  1 dm_mirror
button                  9313  0
battery                11465  0
ac                      6985  0
ohci_hcd               24529  0
ehci_hcd               33989  0
tg3                   109381  0
floppy                 66065  0
ext3                  137937  2
jbd                    69105  1 ext3
sata_svw               10053  3
libata                 78345  1 sata_svw
sd_mod                 19393  4
scsi_mod              141457  2 libata,sd_mod

Task: Remove a module called foo

Pass the -r option to modprobe command to remove a module, type:
# modprobe -r foo
You can also use the rmmod command, which is simple program to remove a module from the Linux Kernel:
# rmmod foo

Recommended readings

• man pages – modinfo, lsmod, insmod, and modprobe

Source: https://www.cyberciti.biz/faq/add-remove-list-linux-kernel-modules/