• If you’re not seeing hardware show up, then implement the modules.
  • Linux Kernel is Monolithic - in RAM it has everything there.
  • Dynamic Kernel Modules can load in modules as required. This is powered by DKMS (Dynamic Kernel Module System).
    • If it hits hardware, then great and it keeps the module. If it does not hit hardware, it then unloads the unnused module.
      • Allows the system to have as much free RAM as possible to play with.
  • Distros take the Kernel, GNU Utils, X/Wayland and to add various modules and hardware support.
    • Some distros only include Open Source drivers.
    • Proprietary wireless drivers such as Intel can be taken by some distros and still loaded.
  • Useful command is lsmod
    • List modules that are loaded on the system.
      • IT WILL NOT LIST THE ONES THAT ARE NOT LOADED.
    • It will output the name of the module, the Size of the module and what other modules are depending on it (specified by the Used by column).
    • For example rfcomm stands for Radio Frequency Communications and is likely the WiFi driver, bluetooth etc.
  • Next command is modinfoand we can get more information by runnng modinfo <module name>
  • All of the modules are running in Kernel Space.
  • For example with modinfo zstd_compress, you can see exactly where the file is stored: 
    filename:       /lib/modules/5.15.0-91-generic/kernel/lib/zstd/zstd_compress.ko
  • Kernel modules have an extension of .ko
  • We can check further in /lib/modules if we want to change the files or replace them. These would go into /lib/modules
  • During boot and hardware discovery, if the hardware is there it loads it and if it is not there, it unloads it.
  • When you compile a Kernel, you can place modules into the Kernel and say There are going to run.
    • You can speed up your boot time and hardware detection by doing that.
  • Whenever hardware changes on your system, we can see this in dmesg. For example if you have bluetooth, in dmesg you see Registered procol family <number> and HCI device and connection manager initiallized. That would also load usbcore, for if it is a USB bluetooth adapter. btusbis the interface driver.
    • When hardware is added, it looks for the appropriate module at the time.
  • We can temporarily load a module.
    • Ideally should check vendor documentation on which module is required.
  • To install a module, we run the command sudo insmod <module_file>
    • An example is deploying a system to AWS, where they have ENA (Elastic Network Adapters).
    • Example: sudo insmod /lib/modules/5.15.0-91-generic/kernel/drivers/net/ethernet/amazon/ena/ena.ko
      • Then check with lsmond | grep <name>
        • Was it assigned a device name by udev (this runs in the background).
  • Can then remove the mod with sudo rmmod <module_name>
  • For lsmod, insmod and rmmod, there is a command that replaces all of those called modprobe.
    • sudo modprobe -a <module_name> (the -a is to add a module).
    • To remove the module, we do sudo modprobe -r <module_name>
  • The module name rarely matches the device name.
  • Worth checking if the module has loaded in dmesg and grepping the output.
  • If you know what type of hardware you are looking for, you can check the bus it is on.
    • lsusb for the USB bus.
    • lspci for the PCI card.
      • If you see an unknown device, the device is missing a module.
        • Virtual devices are also tricky to spot.
  • We also have lsdev, which lists all of the devices. Good way to check that the module did its job and the device is online.
    • Need to install procinfo if there is no output from the above.
  • Ethernet adapter used to be called eth0, but then they renamed it based on the bus. –> ens. So you see an adapter called enp0s10, which is Ethernet, Bus Number and Slot Number.
  • MAC –> Media Access Control
  • Can overwrite the names provided to devices.
    • Using the device’s identifier, you can create a udev rule based on that and specify what the name is.
    • An example of a udev rule is in /etc/udev, you will see a udev.conf file. However, we want the directory called rules.d, where we can create our own rules. hwdb.d is the hardware database directory.
    • Recommended to not modify in hwbd.d. If there are any updates, that is then overwritten.
    • We can create a new rule in rules.d, we can use sudoedit
      • With network adapters, the vendor may have a preferred name. The files are run in order, based on their filename.
        • For example sudoedit 70-persistent-ipoib.rules. The prior is the Ubuntu naming scheme.
          • Inside the above file, we can specify the rules to overwrite the behaviour: 
            # This is the network subsystem that is being overwritten
# ACTION is when new hardware is being added to the system
# DRIVERS is where we specify the particular driver if we were keying off that. ?* allows us to not care what the driver is and so any network driver is loaded
# ATTR is the attribute used to identify the card. type is 1, because we only have 1 MAC Address on the adapter
# Kernel is the name it is assigned by default
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="MAC_ADDRESS", ATTR{type}=="1", KERNEL=="ens666", NAME=="eth0"
  • Now when the Kernel sees the above adapter, it will be called ens666by the Kernel itself, but known as eth0 to the users.
  • The above change will not take effect until a reboot is called.
    • To force it to be loaded with a reboot, we can do sudo udevadm control --reload-rules && udevadm trigger
    • udevadm is udev admin

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