How do I prevent a kernel module from loading automatically?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux

Issue

  • How do I prevent a kernel module from loading automatically?
  • How to disable a kernel module?
  • How to disable a specific device driver?

Resolution

  • In order to prevent kernel modules loading during boot, the module name must be added to a configuration file for the "modprobe" utility. This file must reside in /etc/modprobe.d .
  • Ensure the module is not configured to get loaded in either /etc/modprobe.conf, /etc/modprobe.d/*, /etc/rc.modules, or /etc/sysconfig/modules/* before making the following modifications.
  • Due to differences between the various versions of RHEL, be sure to follow the appropriate steps for your system's version below:
  • Unloading kernel modules at the early stages of the boot

Shared Initial Steps for Red Hat Enterprise Linux 5, 6, 7, 8 and 9

Kernel modules can be loaded directly, loaded as a dependency from another module, or during the boot process -- because of this, we need to take several measures to keep the module from being loaded.

  • [ step1 ] First we unload the module from the running system if it is loaded.

    # modprobe -r module_name                                                      #step1

  • [ step2 ] To prevent a module from being loaded directly you add the blacklist line to a configuration file specific to the system configuration -- for example /etc/modprobe.d/local-dontload.conf.

    This alone will not prevent a module being loaded if it is a required or an optional dependency of another module. Some kernel modules will attempt to load optional modules on demand, which we mitigate in the step3.

    # echo "blacklist module_name" >> /etc/modprobe.d/local-dontload.conf            #step2

  • [ step3 ] The install line simply causes /bin/false to be run instead of installing a module. (The same can be achieved by using /bin/true.)

    The next time the loading of the module is attempted, the /bin/false will be executed instead. This will prevent the module from being loaded on-demand. If the excluded module is required for other specific hardware, there might be unexpected side effects.

    # echo "install module_name /bin/false" >> /etc/modprobe.d/local-dontload.conf   #step3

  • Now continue with the relevant steps for your system's version of RHEL:

Finishing Steps for Red Hat Enterprise Linux 8 and 9 only.

  • [ step4 ] Make a backup copy of your initramfs.

    # cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak

  • [ step5 ] If the kernel module is part of the initramfs (use lsinitrd /boot/initramfs-$(uname -r).img|grep module-name.ko to verify), then you should rebuild your initial ramdisk image, omitting the module to be avoided (see How to rebuild the initial ramdisk image in Red Hat Enterprise Linux for more information).

    # dracut --omit-drivers module_name -f

    Optional: To make this persistent across future kernel upgrades and initramfs rebuilds, add the driver to omit to dracut's permanent configuration:

    # MODNAME="module_name"; echo "omit_dracutmodules+=\" $MODNAME \"" >> /etc/dracut.conf.d/omit-$MODNAME.conf

    To remove the persistent configuration, delete the /etc/dracut.conf.d/omit-module_name.conf file and rebuild the initramfs.

  • [ step6 ] Get the current kernel command line parameters.

    # grubby --info DEFAULT
# grubby --info ALL (To view changes in all available kernels)

  • [ step7 ] Append module_name.blacklist=1 rd.driver.blacklist=module_name at the end of the output found in #step 6. (For RHEL 8 and RHEL 9, grubby utility is actually the recommended method for altering these variables. Refer How to manually modify the boot parameter in grub before the system boots for more information).

    # grubby --args  "<module_name.blacklist=1 rd.driver.blacklist=module_name>" --update-kernel ALL
# grubby --update-kernel=ALL --remove-args="<PARAMETER_TO_REMOVE>" (incase if we wish to remove the added parameters later)

  • [ step8 ] Make a backup copy of the kdump initramfs.

    # cp /boot/initramfs-$(uname -r)kdump.img /boot/initramfs-$(uname -r)kdump.img.$(date +%m-%d-%H%M%S).bak

  • [ step9 ] Append rd.driver.blacklist=module_name to the KDUMP_COMMANDLINE_APPEND setting in /etc/sysconfig/kdump. This will cause it to be omitted from the kdump initramfs.

    # sed -i '/^KDUMP_COMMANDLINE_APPEND=/s/"$/ rd.driver.blacklist=module_name"/' /etc/sysconfig/kdump

  • [ step10 ] Restart the kdump service to pick up the changes to kdump's initrd.

    # kdumpctl restart

  • [ step11 ] Rebuild the kdump initial ramdisk image.

    # mkdumprd -f /boot/initramfs-$(uname -r)kdump.img

  • [ step12 ] Reboot the system for changes to reflect.

    # reboot

Finishing Steps for Red Hat Enterprise Linux 7 only

  • [ step4 ] Make a backup copy of your initramfs.

    # cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak

  • [ step5 ] If the kernel module is part of the initramfs (boot configuration), rebuild your initial ramdisk image, omitting the module to be avoided (see How to rebuild the initial ramdisk image in Red Hat Enterprise Linux for more information).

    # dracut --omit-drivers module_name -f

    Optional: To make this persistent across future kernel upgrades and initramfs rebuilds, add the driver to omit to dracut's permanent configuration:

    # MODNAME="module_name"; echo "omit_dracutmodules+=\" $MODNAME \"" >> /etc/dracut.conf.d/omit-$MODNAME.conf

    To remove the persistent configuration, delete the /etc/dracut.conf.d/omit-module_name.conf file and rebuild the initramfs.

  • [ step6 ] Append module_name.blacklist to the kernel cmdline. We give it an invalid parameter of blacklist and set it to 1 as a way to preclude the kernel from loading it. Here we also set rd.driver.blacklist as another method of preventing it from being loaded.

    # sed -i '/^GRUB_CMDLINE_LINUX=/s/"$/ module_name.blacklist=1 rd.driver.blacklist=module_name"/' /etc/default/grub

  • [ step7 ] Reinstall grub2 to put the kernel cmdline changes into effect. If your system uses UEFI, the path must be changed to /boot/efi/EFI/redhat/grub.cfg

    # grub2-mkconfig -o /boot/grub2/grub.cfg

  • [ step8 ] Make a backup copy of the kdump initramfs.

    # cp /boot/initramfs-$(uname -r)kdump.img /boot/initramfs-$(uname -r)kdump.img.$(date +%m-%d-%H%M%S).bak

  • [ step9 ] Append rd.driver.blacklist=module_name to the KDUMP_COMMANDLINE_APPEND setting in /etc/sysconfig/kdump. This will cause it to be omitted from the kdump initramfs.

    # sed -i '/^KDUMP_COMMANDLINE_APPEND=/s/"$/ rd.driver.blacklist=module_name"/' /etc/sysconfig/kdump

  • [ step10 ] Restart the kdump service to pick up the changes to kdump's initrd.

    # kdumpctl restart

  • [ step11 ] Rebuild the kdump initial ramdisk image.

    # mkdumprd -f /boot/initramfs-$(uname -r)kdump.img

  • [ step12 ] Reboot the system at a convenient time to have the changes take effect.

    # reboot

Finishing Steps for Red Hat Enterprise Linux 6 only

  • [ step4 ] Make a backup copy of your initramfs.

    # cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak

  • [ step5 ] If the kernel module is part of the initramfs (boot configuration), rebuild your initial ramdisk image, omitting the module to be avoided (see How to rebuild the initial ramdisk image in Red Hat Enterprise Linux for more information).

    # dracut --omit-drivers module_name -f

    Optional: To make this persistent across future kernel upgrades and initramfs rebuilds, add the driver to omit to dracut's permanent configuration:

    # MODNAME="module_name"; echo "omit_dracutmodules+=\"$MODNAME\"" >> /etc/dracut.conf

    To remove the persistent configuration, delete the omit_dracutmodules line from /etc/dracut.conf and rebuild the initramfs.

  • [ step6 ] Append module_name.blacklist to the kernel cmdline. We give it an invalid parameter of blacklist and set it to 1 as a way to preclude the kernel from loading it.

    # sed -i '/\s*kernel \/vmlinuz/s/$/ module_name.blacklist=1/' /boot/grub/grub.conf

  • [ step7 ] Edit kdump's configuration file: mark it there as excluded from being loaded by kdump.

    # echo "blacklist module_name" >> /etc/kdump.conf

  • [ step8 ] Restart the kdump service to pick up the changes to kdump's initrd.

    # service kdump restart

  • [ step9 ] Reboot the system at a convenient time to have the changes take effect.

    # reboot

Continued Steps for Red Hat Enterprise Linux 5 only

  • [ step4 ] Make a backup copy of your initrd.

    # cp /boot/initrd-$(uname -r).img /boot/initrd-$(uname -r).img.$(date +%m-%d-%H%M%S).bak

  • [ step5 ] If the kernel module is part of the initrd (boot configuration), rebuild your initial ramdisk image. Use the --builtin=module_name flag to mkinitrd to have it skip the module in question.

    # mkinitrd -v --builtin=module_name

  • [ step6 ] Append module_name.blacklist to the kernel cmdline. We give it an invalid parameter of blacklist and set it to 1 as a way to preclude the kernel from loading it.

    # sed -i '/\s*kernel \/vmlinuz/s/$/ module_name.blacklist=1/' /boot/grub/grub.conf

  • [ step7 ] Reboot the system at a convenient time to have the changes take effect.

    # reboot

Kernel modules can be loaded directly, loaded as a dependency from another module, or during the boot process -- because of this, we need to take several measures to keep the module from being loaded.

Red Hat Enterprise Linux 4

  • Add the following line to /etc/modprobe.conf:

    alias <module name> off

  • If the kernel module is part of the initrd (boot configuration), the initrd should be regenerated. Boot the affected kernel and run the following command to regenerate the affected kernel initrd.

    # mkinitrd /boot/initrd-$(uname -r).img $(uname -r)

Remove Module Temporarily

  • It is possible to remove any currently-loaded module by running:

    # modprobe -r <module name>

Various reasons can prevent unloading of the module.

  • If a running process uses the module, then terminate the process before unloading the module.
  • If a second module uses the module we try to unload, then the second module needs to be unloaded first.

Loading Modules

The procedure for loading modules is available in the product documentation at:

Unloading kernel modules at the early stages of the boot

If the server is getting crashed/panicked on boot due to 3rd party module then it can be unloaded in the early stage of the boot process using the below steps:

[ step1 ] Reboot the server and wait until the GRUB menu appears, now press any key to interrupt the default timeout value. Select the kernel to boot into using the up/down key and once selected, press the e key.

[ step2 ] Scroll to the line starting with:
- linux16 or linuxefi (on UEFI systems) if RHEL 7
- linux if RHEL 8 or RHEL 9

[ step3 ] Append the following to that line:

module_blacklist=<module_name>
  • Where the <module_name> is the name of the module that is causing the issue here. For example, if “abc” module is causing the issue then the parameter will be:
module_blacklist=abc
  • Multiple modules can be specified as a comma-separated list.

[ step4 ] Press CTRL+x to accept the changes and to boot the system with the temporary kernel parameter changes.

[ step5 ] Once the system gets booted successfully disable the module permanently using the above mentioned steps for the respective RHEL version and engage the respective module vendor for further investigation.

  • Note: The kernel parameter module_blacklist is only available from RHEL 7.3 and above.

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