How to re-create the missing /etc/default/grub file in Red Hat Enterprise Linux ?

Environment

• Red Hat Enterprise Linux 7
• Red Hat Enterprise Linux 8
• Red Hat Enterprise Linux 9

Issue

• The /etc/default/grub file is missing from the system.
• The system is up and running, how can one re-create it?

Resolution

1. 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"
   

2. In the created /etc/default/grub file, change the arguments list for GRUB_CMDLINE_LINUX. You can either fetch the list from /proc/cmdline or from /boot/grub2/grub.cfg if not re-created. If you are unable to fetch the arguments list, you can mention all lvm names on the command line with the custom kernel parameters as required.

3. Ensure the following:

   • The owner and group for this file is root.
   • The file permissions are set to -rw-r--r--.

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

   • In case of BIOS:

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

   • In case of EFI:

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

5. Re-create the grub configuration file:

   • In case of BIOS:

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

   • In case of EFI:

     • In Red Hat Enterprise Linux 7,8,9.0,9.1 and 9.2:

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

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