How do I permanently modify the kernel command line in RHEL 8?

Environment

• Red Hat Enterprise Linux 8
• GRUB2 boot loader

Issue

• The boot loader Grand Unified Boot Loader (GRUB2) in RHEL 8 differs from the GRUB2 in RHEL 7.
• How do I modify the kernel command line (and, thus, kernel boot parameters) in Red Hat Enterprise Linux 8?

Resolution

Method 1: Using grub2-editenv

• grub2-editenv command can be used to update the /boot/grub2/grubenv file:

  • RHEL 8:

1. List the kernel parameters from the kernelopts variable:

    # grub2-editenv - list | grep kernelopts
   

2. The following commands can be used to add/remove/modify the kernel command line parameters:

      # grub2-editenv - set "$(grub2-editenv - list | grep kernelopts) <NEW_PARAMETER>"
   
      OR
   
      # grub2-editenv - set "kernelopts=root=/dev/mapper/rhel-root ro crashkernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet"
   

3. Verify the newly added output:

   # grub2-editenv - list | grep kernelopts
   

4. Reboot the system to apply the changes:

   # systemctl reboot
   

Note: If you have to abort the changes then you can unset the kernelopts with the following command:

# grub2-editenv - unset kernelopts

Note: The older method of modification of kernel command line from file /etc/default/grub followed by the rebuilding of grub (grub2-mkconfig) is still possible. However, it is recommended to use the ways mentioned in this solution for modifying the kernel command line on RHEL 8.

Method 2: Using grubby

1. For checking details of default kernel:

# grubby --info DEFAULT

2. For adding parameters on all kernels:

# grubby --update-kernel=ALL --args="argA argB"

3. For removing parameters on all kernels:

# grubby --update-kernel=ALL --remove-args="argA argB"

4. Reboot the system to apply the changes:

# reboot

Documentation

• The RHEL 8 documentation for modifying kernel command line parameters.

Additional Links for reference:

• To make a persistent change to the kernel command line in RHEL9 and RHEL10, see: How to modify the kernel command-line in Red Hat Enterprise Linux 9 and 10

• To make a persistent change to the kernel command line in RHEL5 and RHEL6, see: How do I permanently modify the kernel command line in RHEL5 and RHEL6?

• To make a persistent change to the kernel command line in RHEL7, see: How do I permanently modify the kernel command line in RHEL7?

• To make a one-time, non-persistent change at boot, see: How to manually modify the boot parameter in grub before the system boots

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