For each kernel module loaded, display its name, size, use count and a list of other referring modules. This command yields the same information as is available in /proc/modules. On a particular laptop, for instance, the command /sbin/lsmod reports:

Module      Size   Used by
serial_cb   1120   1
tulip_cb    31968  2
cb_enabler  2512   4 [serial_cb tulip_cb]
ds          6384   2 [cb_enabler]
i82365      22384  2
pcmcia_core 50080  0 [cb_enabler ds i82365]

The format is name, size, use count, list of referring modules. If the module controls its own unloading via a “can_unload” routine, then the user count displayed by lsmod is always -1, irrespective of the real use count.

Insert a module into the running kernel. The module is located automatically and inserted. You must be logged in as superuser to insert modules. It is generally recommended to use modprobe instead, since insmod only gives very general error codes and modprobe is more specific about errors. Also, you need to pass the complete filename to insmod , where modprobe will work with just the module name.

# insmod sym53c8xx.ko
# echo $?
0

# insmod snd-ens1371.ko
insmod: error inserting 'snd-ens1371.ko': -1 Unknown symbol in module
# echo $?
1

Unless a module is in use or referred to by another module, the module is removed from the running kernel. You must be logged in as the superuser to remove modules.

# rmmod snd_ac97_codec
ERROR: Module snd_ac97_codec is in use by snd_ens1371
# echo $?
1

# rmmod snd_ens1371
# rmmod ac97_codec
# echo $?
0

Like insmod, modprobe is used to insert modules. However, modprobe has the ability to load single modules, modules and their prerequisites, or all modules stored in a specific directory. The modprobe command can also remove modules when combined with the -r option. It also is more specific in it's error messages than insmod.

A module is inserted with optional symbol=value parameters such as irq=5 or dma=3 . This can be done on the command line or by specifying options in the module configuration file as will be explained later on. If the module is dependent upon other modules, they will be loaded first. The modprobe command determines prerequisite relationships between modules by reading modules.dep at the top of the module directory hierarchy, for instance /lib/modules/2.6.31/modules.dep. You must be logged in as the superuser to insert modules.

# modprobe snd_ens1371
# echo $?
0
# lsmod
Module                  Size  Used by
snd_ens1371            20704  0
snd_rawmidi            22448  1 snd_ens1371
snd_seq_device          7436  1 snd_rawmidi
snd_ac97_codec        112280  1 snd_ens1371
ac97_bus                1992  1 snd_ac97_codec
snd_pcm                72016  2 snd_ens1371,snd_ac97_codec
snd_timer              21256  1 snd_pcm
snd                    62392  6 snd_ens1371,snd_rawmidi,snd_seq_device,snd_ac97_codec,snd_pcm,snd_timer
soundcore               7952  1 snd
snd_page_alloc          9528  1 snd_pcm

Display information about a module from its module-object-file. Some modules contain no information at all, some have a short one-line description, others have a fairly descriptive message.

# modinfo snd_ens1371
filename:       /lib/modules/2.6.31/kernel/sound/pci/snd-ens1371.ko
description:    Ensoniq/Creative AudioPCI ES1371+
license:        GPL
author:         Jaroslav Kysela <perex@perex.cz>, Thomas Sailer <sailer@ife.ee.ethz.ch>
alias:          pci:v00001102d00008938sv*sd*bc*sc*i*
alias:          pci:v00001274d00005880sv*sd*bc*sc*i*
alias:          pci:v00001274d00001371sv*sd*bc*sc*i*
depends:        snd-pcm,snd,snd-rawmidi,snd-ac97-codec
vermagic:       2.6.31-gentoo-r10 SMP mod_unload modversions
parm:           index:Index value for Ensoniq AudioPCI soundcard. (array of int)
parm:           id:ID string for Ensoniq AudioPCI soundcard. (array of charp)
parm:           enable:Enable Ensoniq AudioPCI soundcard. (array of bool)
parm:           spdif:S/PDIF output (-1 = none, 0 = auto, 1 = force). (array of int)
parm:           lineio:Line In to Rear Out (0 = auto, 1 = force). (array of int)

The command modprobe can determine module dependencies and install prerequisite modules automatically. To do this, modprobe scans the first column of /lib/modules/kernel-version/modules.dep to find the module it is to install. Lines in modules.dep are in the following form:

module_name.o: dependency1 dependency2 ...

Below is an example for thermal and processor modules (which are part of the ACPI layer):

/lib/modules/2.6.31/kernel/drivers/acpi/thermal.ko: \
    /lib/modules/2.6.31/kernel/drivers/thermal/thermal_sys.ko
/lib/modules/2.6.31/kernel/drivers/acpi/processor.ko: \
    /lib/modules/2.6.31/kernel/drivers/thermal/thermal_sys.ko

Here both the processor and thermal module depend on the thermal_sys module.

All of the modules available on the system are listed in the modules.dep file and are referred to with their full path and filenames, including their .ko extension. Those that are not dependent on other modules are listed, but without dependencies. Dependencies that are listed are inserted into the kernel by modprobe first, and after they have been successfully inserted, the subject module itself can be loaded.

The modules.dep file must be kept current to ensure the correct operation of modprobe. If module dependencies were to change without a corresponding modification to modules.dep, then modprobe would fail because a dependency would be missed. As a result, modules.dep needs to be (re)created each time the system is booted. Most distributions will do this by executing depmod -a automatically when the system isbooted.

This procedure is also necessary after any change in module dependencies.