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Looking into Linux modules
The lsmod command can tell you which kernel modules are currently loaded on your system, along with some interesting details about their use.
What are Linux modules?
Kernel modules are chunks of code that are loaded and unloaded into the kernel as needed, thus extending the functionality of the kernel without requiring a reboot. In fact, unless users inquire about modules using commands like lsmod , they won't likely know that anything has changed.
One important thing to understand is that there are lots of modules that will be in use on your Linux system at all times and that a lot of details are available if you're tempted to dive into the details.
One of the prime ways that lsmod is used is to examine modules when a system isn't working properly. However, most of the time, modules load as needed and users don't need to be aware of how they are working.
[ Also see:Must-know Linux Commands ]
Listing modules
The easiest way to list modules is with the lsmod command. While this command provides a lot of detail, this is the most user-friendly output.
$ lsmod
Module Size Used by
snd_hda_codec_realtek 114688 1
snd_hda_codec_generic 77824 1 snd_hda_codec_realtek
ledtrig_audio 16384 2 snd_hda_codec_generic,snd_hda_codec_realtek
snd_hda_codec_hdmi 53248 1
snd_hda_intel 40960 2
snd_hda_codec 131072 4 snd_hda_codec_generic,snd_hda_codec_hdmi,snd_hda_intel
,snd_hda_codec_realtek
snd_hda_core 86016 5 snd_hda_codec_generic,snd_hda_codec_hdmi,snd_hda_intel
,snd_hda_codec,snd_hda_codec_realtek
snd_hwdep 20480 1 snd_hda_codec
snd_pcm 102400 4 snd_hda_codec_hdmi,snd_hda_intel,snd_hda_codec,snd_hda
_core
snd_seq_midi 20480 0
snd_seq_midi_event 16384 1 snd_seq_midi
dcdbas 20480 0
snd_rawmidi 36864 1 snd_seq_midi
snd_seq 69632 2 snd_seq_midi,snd_seq_midi_event
coretemp 20480 0
snd_seq_device 16384 3 snd_seq,snd_seq_midi,snd_rawmidi
snd_timer 36864 2 snd_seq,snd_pcm
kvm_intel 241664 0
kvm 626688 1 kvm_intel
radeon 1454080 10
irqbypass 16384 1 kvm
joydev 24576 0
input_leds 16384 0
ttm 102400 1 radeon
drm_kms_helper 180224 1 radeon
drm 475136 13 drm_kms_helper,radeon,ttm
snd 81920 15 snd_hda_codec_generic,snd_seq,snd_seq_device,snd_hda
_codec_hdmi,snd_hwdep,snd_hda_intel,snd_hda_codec,snd
_hda_codec_realtek,snd_timer,snd_pcm,snd_rawmidi
i2c_algo_bit 16384 1 radeon
fb_sys_fops 16384 1 drm_kms_helper
syscopyarea 16384 1 drm_kms_helper
serio_raw 20480 0
sysfillrect 16384 1 drm_kms_helper
sysimgblt 16384 1 drm_kms_helper
soundcore 16384 1 snd
mac_hid 16384 0
sch_fq_codel 20480 2
parport_pc 40960 0
ppdev 24576 0
lp 20480 0
parport 53248 3 parport_pc,lp,ppdev
ip_tables 28672 0
x_tables 40960 1 ip_tables
autofs4 45056 2
raid10 57344 0
raid456 155648 0
async_raid6_recov 24576 1 raid456
async_memcpy 20480 2 raid456,async_raid6_recov
async_pq 24576 2 raid456,async_raid6_recov
async_xor 20480 3 async_pq,raid456,async_raid6_recov
async_tx 20480 5 async_pq,async_memcpy,async_xor,raid456,async_raid6_re
cov
xor 24576 1 async_xor
raid6_pq 114688 3 async_pq,raid456,async_raid6_recov
libcrc32c 16384 1 raid456
raid1 45056 0
raid0 24576 0
multipath 20480 0
linear 20480 0
hid_generic 16384 0
psmouse 151552 0
i2c_i801 32768 0
pata_acpi 16384 0
lpc_ich 24576 0
usbhid 53248 0
hid 126976 2 usbhid,hid_generic
e1000e 245760 0
floppy 81920 0
In the output above:
- "Module" shows the name of each module
- "Size" shows the module size (not how much memory it is using)
- "Used by" shows each module's usage count and the referring modules
Clearly, that's a lot of modules. The number of modules loaded will depend on your system and distribution and what's running. We can count them like this:
$ lsmod | wc -l
67
To see the number of modules available on the system (not just running), try this command:
$ modprobe -c | wc -l
41272
Other commands for examining modules
Linux provides several commands for listing, loading and unloading, examining, and checking the status of modules.
- depmod -- generates modules.dep and map files
- insmod -- a simple program to insert a module into the Linux Kernel
- lsmod -- show the status of modules in the Linux Kernel
- modinfo -- show information about a Linux Kernel module
- modprobe -- add and remove modules from the Linux Kernel
- rmmod -- a simple program to remove a module from the Linux Kernel
Listing modules that are built in
As mentioned above, the lsmod command is the most convenient command for listing modules. There are, however, other ways to examine them. The modules.builtin file lists all modules that are built into the kernel and is used by modprobe when trying to load one of these modules. Note that $(uname -r) in the commands below provides the name of the kernel release.
$ more /lib/modules/$(uname -r)/modules.builtin | head -10
kernel/arch/x86/crypto/crc32c-intel.ko
kernel/arch/x86/events/intel/intel-uncore.ko
kernel/arch/x86/platform/intel/iosf_mbi.ko
kernel/mm/zpool.ko
kernel/mm/zbud.ko
kernel/mm/zsmalloc.ko
kernel/fs/binfmt_script.ko
kernel/fs/mbcache.ko
kernel/fs/configfs/configfs.ko
kernel/fs/crypto/fscrypto.ko
You can get some additional detail on a module by using the modinfo command, though nothing that qualifies as an easy explanation of what service the module provides. The omitted details from the output below include a lengthy signature.
$ modinfo floppy | head -16
filename: /lib/modules/5.0.0-13-generic/kernel/drivers/block/floppy.ko
alias: block-major-2-*
license: GPL
author: Alain L. Knaff
srcversion: EBEAA26742DF61790588FD9
alias: acpi*:PNP0700:*
alias: pnp:dPNP0700*
depends:
retpoline: Y
intree: Y
name: floppy
vermagic: 5.0.0-13-generic SMP mod_unload
sig_id: PKCS#7
signer:
sig_key:
sig_hashalgo: md4
You can load or unload a module using the modprobe command. Using a command like the one below, you can locate the kernel object associated with a particular module:
$ find /lib/modules/$(uname -r) -name floppy*
/lib/modules/5.0.0-13-generic/kernel/drivers/block/floppy.ko
If you needed to load the module, you could use a command like this one:
$ sudo modprobe floppy
Wrap-up
Clearly the loading and unloading of modules is a big deal. It makes Linux systems considerably more flexible and efficient than if they ran with a one-size-fits-all kernel. It also means you can make significant changes — including adding hardware — without rebooting.
[ Two-Minute Linux Tips:Learn how to master a host of Linux commands in these 2-minute video tutorials ]
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作者：Sandra Henry-Stocker 选题：lujun9972 译者：译者ID 校对：校对者ID