4.3 Changing the Default Boot Option
When the system starts, the boot options screen will appear and wait 5 seconds for the user to make an operating system choice. If no selection has been made before the timeout elapses, the default operating system will be started. On a newly configured system, the default operating system will be the standard (non-rescue) RHEL 8 image. This default can, however, be changed from within RHEL.
A range of boot configuration options (including the 5 second timeout and the boot RHGB settings outlined in “Installing RHEL 8 on a Clean Disk Drive”) are declared in the /etc/default/grub file which reads as follows on a new installation:
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=”crashkernel=auto resume=/dev/mapper/cl-swap rd.lvm.lv=cl/root...