After Installing OEL7.6 boot loader comes with 3 options.  You need to choose the options to can login your system every boot.

linux.jpg

If you want to fix default boot you need to follow below steps:

  1. Display the menu entries that are defined in the configuration file, for example: 
    # grep '^menuentry' /boot/grub2/grub.cfg menuentry 'Oracle Linux Everything, with Linux 3.10.0-123.el7.x86_64' ... { menuentry 'Oracle Linux Everything, with Linux 3.8.13-35.2.1.el7uek.x86_64' ... { menuentry 'Oracle Linux Everything, with Linux 0-rescue-052e316f566e4a45a3391cff21b4174b' ... {

    In this example for a BIOS-based system, the configuration file is /boot/grub2/grub.cfg, which contains menu entries 0, 1, and 2 that correspond to the RHCK, UEK, and the rescue kernel respectively.

    – 0 refer first line
    – 1 refer second line
    – 2 refer third line

  2. Enter the following commands to make the UEK (entry 1) the default boot kernel: 
    # grub2-set-default 1 # grub2-mkconfig -o /boot/grub2/grub.cfg

     

    Reference:https://docs.oracle.com/cd/E52668_01/E54669/html/ol7-grub2_bootloader.html