How to modify the kernel command-line in Red Hat Enterprise Linux 9 and 10

Solution Verified - Updated 30 Jul 2025

Environment

Red Hat Enterprise Linux (RHEL) 9
Red Hat Enterprise Linux (RHEL) 10
grub2

Issue

How to modify the boot parameter in RHEL 9 and RHEL 10

grub2-editenv - list command output is not showing kernelopts option to update kernel commandline.

# grub2-editenv - list
saved_entry=d7a9453a54b34038ab12deddd44484e6-5.14.0-39.el9.aarch64
boot_success=0

Resolution

Solution 1 - Update the kernel command-line via `grubby`

Verify the current arguments

# grubby --info DEFAULT
index=0
kernel="/boot/vmlinuz-5.14.0-39.el9.aarch64"
args="ro crashkernel=2G-:448M rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap"
root="/dev/mapper/rhel-root"
initrd="/boot/initramfs-5.14.0-39.el9.aarch64.img"
title="Red Hat Enterprise Linux (5.14.0-39.el9.aarch64) 9.0 (Plow)"
id="d7a9453a54b34038ab12deddd44484e6-5.14.0-39.el9.aarch64"

Add the command-line parameters with option to update the current kernel or all kernel

# grubby --update-kernel=/boot/vmlinuz-$(uname -r) --args="<NEW_PARAMETER>"

# grubby --update-kernel=ALL --args="<NEW_PARAMETER>"

# grubby --args <NEW_PARAMETER> --update-kernel DEFAULT

Similarly we may remove any kernel command-line parameters with below option
```
# grubby --update-kernel=ALL --remove-args="<PARAMETER_TO_REMOVE>"
```
Reboot the system for changes to reflect
```
# systemctl reboot
```

Solution 2 - Edit `/etc/default/grub` and rebuild the menu

Edit /etc/default/grub file and update the kernel command-line parameter on line GRUB_CMDLINE_LINUX and save it
```
GRUB_CMDLINE_LINUX="crashkernel=2G-:448M rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap"  
```
Rebuild the menu files
- In Red Hat Enterprise Linux 9.0, 9.1 and 9.2:
```
# grub2-mkconfig -o /boot/grub2/grub.cfg
```
- In Red Hat Enterprise Linux 9.3 and later:
```
# grub2-mkconfig -o /boot/grub2/grub.cfg --update-bls-cmdline
```
NOTE: The /boot/efi/EFI/redhat/grub.cfg file, which GRUB previously used on UEFI systems, is now a stub that redirects to /boot/grub2/grub.cfg, which contains the real GRUB configuration. In RHEL 9 grub2-mkconfig should not be used with /boot/efi/EFI/redhat/grub.cfg as an output file. See the "Root Cause" section below for more details.

NOTE: If /boot/efi/EFI/redhat/grub.cfg gets overwritten, then it is possible to restore its initial content by re-installing the package grub2-common. See the "Diagnostic Steps" section below for more details on the expected content of this file.
Reboot the system to apply the changed kernel command line.
```
# systemctl reboot
```

NOTE If you are changing the name of your root VG, please reference: grub2-mkconfig command shows "/usr/sbin/grub2-probe: error: failed to get canonical path of `/dev/mapper/rhel-root'." error message after renaming root lv.

Root Cause

By default, the kernel command-line parameters, for RHEL 8 using the GRUB2 bootloader, were defined in the kernelopts variable of the /boot/grub2/grubenv file for all kernel boot entries.
The file /boot/grub2/grubenv can easily get corrupted. As all boot entries in RHEL 8 use the same variable for the kernel command-line, if this file gets corrupted then none of the boot entries will be able to get correct kernel command-line options. This creates a single point of failure for all boot entries. Especially if the root parameter is not set correctly, all entries will fail to boot.
Storing the kernel command line parameters in the grubenv file as a kernelopts variable is deprecated in RHEL 9.
In RHEL 9 configuration files for the GRUB boot loader are stored in the /boot/grub2/ directory on all supported CPU architectures. There is no longer a different configuration file for UEFI systems. Also the symbolic links in /etc are pointing to /boot/grub2/grub.cfg. More information is available in the Red Hat Enterprise Linux 9.0 relase notes.
In RHEL 9 the file /boot/grub2/grub.cfg contains a default kernel command line as a fall-back option, for the case individual boot loader entries are missing kernel command line options. Every boot entry is saved in a Boot Loader Specification (BLS) snippet (in /boot/loader/entries) and can contain a kernel command line definition overriding the one in /boot/grub2/grub.cfg.
In RHEL 9.3 and later, the grub2-mkconfig utility works differently than in RHEL 9.2 or older:
If the GRUB_ENABLE_BLSCFG parameter is true, running the grub2-mkconfig -o /path/to/grub.cfg command applies changes from /etc/default/grub only to grub.cfg without updating the BLS snippets that are used to dynamically generate the boot menu during boot.
To update also BLS snippets, use the --update-bls-cmdline option of grub2-mkconfig or the grubby tool.
For more information, see: New default behavior of grub2-mkconfig with BLS and the man grubby page.

Diagnostic Steps

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It is possible to review boot loader entries with:
```
grubby --info=ALL
```
According to the Content from uapi-group.org is not included.Boot Loader Specification, snippets used for creating grub entries during boot can be found in /boot/loader/entries.
These files can be reviewed with a text editor for confirming options, but, under normal contitions, they should not be edited manually. grubby can be used to update these entries.
On UEFI systems, the file /boot/efi/EFI/redhat/grub.cfg should contain minimal configuration to redirect to /boot/grub2/grub.cfg, similar to the following:
```
    search --no-floppy --fs-uuid --set=dev <filesystem UUID of /boot>
    set prefix=($dev)/grub2

    export $prefix
    configfile $prefix/grub.cfg
```
If the file has different content, then it has been overwritten and needs to be recreated by re-installing the grub2-common package (which contains a scriptlet to generate /boot/efi/EFI/redhat/grub.cfg).

SBR

Shells

Product(s)

Red Hat Enterprise Linux

Components

grub

Category

Configure

Tags

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