How to recreate the missing /etc/default/grub file in Red Hat Enterprise Linux ?

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux 10
  • Red Hat Enterprise Linux 9
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 7
  • GRUB2 Bootloader

Issue

  • The /etc/default/grub file is missing.
  • The system is up and running, how can one recreate it?

Resolution

  • Manually create a file at the /etc/default/grub location with the following content:

    GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
#GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="root=/dev/mapper/volgroup_lv_root rd.lvm.lv=vg_<volgroup>/<lvm_1> rd.lvm.lv=vg_<volgroup>/<lvm_1> custom_parameter_1 custom_parameter_2"
GRUB_DISABLE_RECOVERY="true"
GRUB_THEME="/boot/grub2/themes/system/theme.txt"

  • In the created /etc/default/grub file, change the arguments list for GRUB_CMDLINE_LINUX. The list can be obtained from /proc/cmdline (or from /boot/grub2/grub.cfg if it was not recreated).

    • Note: if the argument list is not available, the LVM names can be passed via command line with the custom kernel parameters as required.

  • Ensure the file owner and group is root and the modes are set to 0644 (-rw-r--r--).

  • Once run, take a backup of the existing grub configuration file:

    • For BIOS-based systems:

      # cp -v /boot/grub2/grub.cfg /boot/grub2/grub.cfg.backup

    • For UEFI-based systems:

      # cp -v /boot/efi/EFI/redhat/grub.cfg /boot/efi/EFI/redhat/grub.cfg.backup

  • Recreate the grub.cfg configuration file:

    • In case of BIOS: 

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

    • In case of EFI:

      • For RHEL 9.2 and older:

        # grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

      • For RHEL 9.3 and later:

        # grub2-mkconfig -o /boot/grub2/grub.cfg --update-bls-cmdline

      • Note: The /boot/efi/EFI/redhat/grub.cfg file, which GRUB2 previously used on UEFI systems, is now a stub that redirects to /boot/grub2/grub.cfg, which contains the real GRUB2 configuration. In RHEL 9 grub2-mkconfig should not be used with /boot/efi/EFI/redhat/grub.cfg as an output file.

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