Modules

LPIC-1LINUX

TL;DR

lsmod | grep <module> -> listing modules

modinfo <module> -> info about a module

sudo modprobe <module> / sudo modprobe -r <module> -> temporary change (disappears at reboot)

/lib/modules/$(uname -r) -> modules warehouse, modules that could be loaded

/proc/modules -> where the lsmod command looks, volatile FS

/sys/module -> echo 1 | sudo tee /sys/module/usbcore/parameters/usbfs_memory_mb, volatile FS, can modify the parameters of a module immediately

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1 Main commands

  • Check if it's already there: lsmod | grep <module>

  • Get info about the module: modinfo <module>

  • Load the module: sudo modprobe <module>

  • Verify it created a device: Check /proc/modules first. Then if you want to double check, verify that this created entries in /sys/module/<module>

  • Remove it cleanly: sudo modprobe -r <module>

2 Commands mainly used by developers

  • insmode: loads a module using the full path and the file ending in .ko. It does not handle dependencies.

  • rmmode: it is also a "dummy" command, it removes a module but not its dependencies.

Warning: forcing a rmmode command, is something you could do, but it can cause a "kernel panic". The author is not responsible of the damage to your system with this command or any command listed.

3 Making a change permanent

modprobe is a temporary change (it disappears after reboot). To make it permanent you need to create a .conf file under /etc/modprobe.d/ .

4 Location of modules

There are three different locations where you will find the modules, each one has a different purpose:

  1. /lib/modules/$(uname -r): This is the "warehouse". The files are stored in the hard drive. It shows what modules could be loaded.

  2. /proc/modules: this is a file with a list of all the modules. This is where lsmod looks to get its information. Like everything in /proc, this lives in memory only. This, with the lsmod command, is the place where you look to verify a module is loaded.

  3. /sys/module/: under this directory there are more directories with the modules and its parameters. Parameters can be modified instantly. No need to reload the module. Changes made in /sys are volatile, they are wiped after reboot.

    Example: echo 1 | sudo tee /sys/module/usbcore/parameters/usbfs_memory_mb

5 Checking the logs

dmesg | grep -i <module_name>

To know more about different types of modules, take a look at Static vs. Dynamic Modules.

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