How do I remove a particular module from initramfs in Red Hat Enterprise Linux 6 and 7?

Environment

• Red Hat Enterprise Linux (RHEL) 6
• Red Hat Enterprise Linux (RHEL) 7
• dracut (the tool that generates initramfs images in RHEL6 and 7)

Issue

• Requirement to remove a module from initrd image in order to avoid it loading at boot time.
• In some cases, a SAN disk may get labelled as "/dev/sda", before the local disk does.

Resolution

There are three alternative methods to avoid a particular kernel module being loaded at boot time in RHEL 6 and RHEL7

• In order to remove / disable a kernel module at boot time, omit the module (in the following example the lpfc driver) and rebuild the initrd.

  # mv /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r)-old.img
  # dracut --omit-drivers lpfc /boot/initramfs-$(uname -r).img
  

• Add the module to the omit_drivers+="" line in /etc/dracut.conf. Specify a space-separated list of kernel modules to omit from the initramfs. Uncomment the line if required and then rebuild the initrd file. For example:

  # grep ^omit_drivers /etc/dracut.conf
  omit_drivers+="lpfc"
  
  # mv /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r)-old.img
  # dracut /boot/initramfs-$(uname -r).img $(uname -r)
  

NOTE: The value specified in omit_drivers can be an regular expression string.

• Add the rdblacklist boot parameter to the vmlinuz kernel command line in /boot/grub/grub.conf:

  • For example, append the following line to the vmlinuz line(s) in /boot/grub/grub.conf:

    rdblacklist=lpfc
    

  • An example:

    # grep vmlinuz /boot/grub/grub.conf 
          kernel /vmlinuz-version ro root=/dev/sda2 rdblacklist=lpfc
    

NOTE: In RHEL7, rdblacklist= is deprecated by rd.driver.blacklist=, but it still works for compatibility.

Root Cause

dracut provides a method for manually excluding kernel modules from the initrd file: the --omit-drivers options explained here.

Please note that this is different from omitting dracut modules themselves: see omit_dracutmodules in dracut.conf(5) (or the -o / --omit command line option for ``dracut(8)` to exclude dracut modules from the initramfs. As an example:

• --omit-drivers dm-multipath will exclude dm-multipath.ko from the initrd
• --omit multipath will generate an intird which does not include the code that loads dm-multipath and activates multipathd

More information about omitting kernel modules from dracut are available at the dracut(8) and dracut.conf(5) man pages, and at This content is not included.at the following site.

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