3.10. Preventing kernel modules from being automatically loaded at system boot time

Procedure

1. List modules loaded to the currently running kernel by using the lsmod command:

   $ lsmod
   Module                  Size  Used by
   tls                   131072  0
   uinput                 20480  1
   snd_seq_dummy          16384  0
   snd_hrtimer            16384  1
   …

   In the output, identify the module you want to prevent from getting loaded.

   • Alternatively, identify an unloaded kernel module you want to prevent from potentially loading in the /lib/modules/<KERNEL-VERSION>/kernel/<SUBSYSTEM>/ directory, for example:

     $ ls /lib/modules/6.12.0-55.9.1.el10_0.x86_64/kernel/crypto/
     ansi_cprng.ko.xz        chacha20poly1305.ko.xz  md4.ko.xz               serpent_generic.ko.xz
     anubis.ko.xz            cmac.ko.xz…

2. Create a configuration file serving as a denylist:

   # touch /etc/modprobe.d/denylist.conf

3. In a text editor of your choice, combine the names of modules you want to exclude from automatic loading to the kernel with the blacklist configuration command, for example:

   # Prevents <KERNEL-MODULE-1> from being loaded
   blacklist <MODULE-NAME-1>
   install <MODULE-NAME-1> /bin/false
   
   # Prevents <KERNEL-MODULE-2> from being loaded
   blacklist <MODULE-NAME-2>
   install <MODULE-NAME-2> /bin/false
   …

   Because the blacklist command does not prevent the module from getting loaded as a dependency for another kernel module that is not in a denylist, you must also define the install line. In this case, the system runs /bin/false instead of installing the module. The lines starting with a hash sign are comments you can use to make the file more readable.

   注意

   When entering the name of a kernel module, do not append the .ko.xz extension to the end of the name. Kernel module names do not have extensions; their corresponding files do.

4. Create a backup copy of the current initial RAM disk image before rebuilding:

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

   • Alternatively, create a backup copy of an initial RAM disk image which corresponds to the kernel version for which you want to prevent kernel modules from automatic loading:

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

5. Generate a new initial RAM disk image to apply the changes:

   # dracut -f -v

   • If you build an initial RAM disk image for a different kernel version than your system currently uses, specify both target initramfs and kernel version:

     # dracut -f -v /boot/initramfs-<TARGET-VERSION>.img <CORRESPONDING-TARGET-KERNEL-VERSION>

6. Restart the system:

   $ reboot

   重要

   The changes described in this procedure will take effect and persist after rebooting the system. If you incorrectly list a key kernel module in the denylist, you can switch the system to an unstable or non-operational state.