How do I blacklist a kernel module to prevent it from loading automatically?

Environment

• Red Hat Enterprise Linux 4, 5, 6, 7, 8

Issue

• How do I blacklist a kernel module to prevent it 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 into the blacklist file.

• Ensure the module is not configured to load either in /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, please be sure to follow the appropriate steps for your system's version below:

  • The shared steps for RHEL 5, 6, 7, 8 followed by the specific steps for each version
  • The steps for RHEL 4

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

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.

Raw

# modprobe -r module_name                                                      #step1

echo "blacklist module_name" >> /etc/modprobe.d/local-blacklist.conf           #step2
echo "install module_name /bin/false" >> /etc/modprobe.d/local-blacklist.conf  #step3

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

• [step2 above] 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-blacklist.conf.

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

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

  • This change will take effect the next time that the module is attempted to load. There may be unexpected side effects if a module is blacklisted that is required for other specific hardware.

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

  • Finishing Steps for RHEL 8
  • Finishing Steps for RHEL 7
  • Finishing Steps for RHEL 6
  • Finishing Steps for RHEL 5

---

Finishing Steps for Red Hat Enterprise Linux 8 only.

Raw

# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak                       #step4

# dracut --omit-drivers module_name -f                                                                               #step5

# grub2-editenv - list | grep kernelopts                                                                             #step6

# grub2-editenv - set kernelopts="<> module_name.blacklist=1 rd.driver.blacklist=module_name"                        #step7

# cp /boot/initramfs-$(uname -r)kdump.img /boot/initramfs-$(uname -r)kdump.img.$(date +%m-%d-%H%M%S).bak             #step8

# sed -i '/^KDUMP_COMMANDLINE_APPEND=/s/"$/ rd.driver.blacklist=module_name"/' /etc/sysconfig/kdump                  #step9

# kdumpctl restart                                                                                                   #step10

# mkdumprd -f /boot/initramfs-$(uname -r)kdump.img                                                                   #step11

# reboot                                                                                                             #step12

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

• [step5 above] 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).

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

• [step7 above] Append module_name.blacklist=1 rd.driver.blacklist=module_name at the end of the output found in #step 6. (For RHEl 8, grub2-editenv 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).

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

• [step9 above] 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.

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

• [step11 above] Rebuild the kdump initial ramdisk image.

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

---

Finishing Steps for Red Hat Enterprise Linux 7 only

Raw

# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak                       #step4

# dracut --omit-drivers module_name -f                                                                               #step5

# sed -i '/^GRUB_CMDLINE_LINUX=/s/"$/ module_name.blacklist=1 rd.driver.blacklist=module_name"/' /etc/default/grub   #step6

# grub2-mkconfig -o /boot/grub2/grub.cfg                                                                             #step7

# cp /boot/initramfs-$(uname -r)kdump.img /boot/initramfs-$(uname -r)kdump.img.$(date +%m-%d-%H%M%S).bak             #step8

# sed -i '/^KDUMP_COMMANDLINE_APPEND=/s/"$/ rd.driver.blacklist=module_name"/' /etc/sysconfig/kdump                  #step9

# kdumpctl restart                                                                                                   #step10

# mkdumprd -f /boot/initramfs-$(uname -r)kdump.img                                                                   #step11

# reboot                                                                                                             #step12

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

• [step5 above] 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).

• [step6 above] 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.

• [step7 above] 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

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

• [step9 above] 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.

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

• [step11 above] Rebuild the kdump initial ramdisk image.

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

---

Finishing Steps for Red Hat Enterprise Linux 6 only

Raw

# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date +%m-%d-%H%M%S).bak   #step4

# dracut --omit-drivers module_name -f                                                           #step5

# sed -i '/\s*kernel \/vmlinuz/s/$/ module_name.blacklist=1/' /boot/grub/grub.conf               #step6

# echo "blacklist module_name" >> /etc/kdump.conf                                                #step7

# service kdump restart                                                                          #step8

# reboot                                                                                         #step9

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

• [step5 above] 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).

• [step6 above] 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.

• [step7 above] Blacklist the kernel module in kdump's configuration file.

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

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

---

Continued Steps for Red Hat Enterprise Linux 5 only

Raw

# cp /boot/initrd-$(uname -r).img /boot/initrd-$(uname -r).img.$(date +%m-%d-%H%M%S).bak   #step4

# mkinitrd -v --builtin=module_name                                                        #step5

# sed -i '/\s*kernel \/vmlinuz/s/$/ module_name.blacklist=1/' /boot/grub/grub.conf         #step6

# reboot                                                                                   #step7

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.

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

• [step5 above] 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.

• [step6 above] 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.

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

---

Red Hat Enterprise Linux 4

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

  Raw

    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.

  Raw

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

Remove Module Temporarily

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

  Raw

    # modprobe -r <module name>
  

If the module can not be unloaded. A process or another module may still be using the module, terminate the process and unload the module using the module that is being removed.