Introduction to grub 2

GRUB 2 Destination

​ BIOS-based

​ /boot/grub2/grub.cfg

​ UEFI

​ /boot/efi/EFI/redhat/grub.cfg

Menu Entries in grub.cfg

Example
menuentry 'Red Hat Enterprise Linux Server' --class red --class gnu-linux --class gnu --class os
$menuentry_id_option 'gnulinux-simple-c60731dc-9046-4000-9182-64bdcce08616' {
    load_video
    set gfxpayload=keep
    insmod gzio
    insmod part_msdos
    insmod xfs
    set root='hd0,msdos1'
    if [ x$feature_platform_search_hint = xy ]; then
        search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hintbaremetal=ahci0,msdos1 --hint='hd0,msdos1' 19d9e294-65f8-4e37-8e73-d41d6daa6e58
    else
        search --no-floppy --fs-uuid --set=root 19d9e294-65f8-4e37-8e73-d41d6daa6e58
    fi
    echo 'Loading Linux 3.8.0-0.40.el7.x86_64 ...'
    linux16 /vmlinuz-3.8.0-0.40.el7.x86_64 root=/dev/mapper/rhel-root ro rd.md=0 rd.dm=0 rd.lvm.lv=rhel/swap crashkernel=auto rd.luks=0 vconsole.keymap=us rd.lvm.lv=rhel/root rhgb quiet
    echo 'Loading initial ramdisk ...'
    initrd /initramfs-3.8.0-0.40.el7.x86_64.img
}

linux on 64-bit IBM POWER Series, linux16 on x86_64 BIOS-based systems, and linuxefi on UEFI-based systems.

The initrd directives followed by the path to the kernel and the initramfs image respectively.

Configuring GRUB 2 to Require a Password only for Modifying Entries

  1. Run the grub2-setpassword command as root:

    ~]# grub2-setpassword

  2. Enter and confirm the password:

    Enter password:
    Confirm password:

Following this procedure creates a /boot/grub2/user.cfg file that contains the hash of the password. The user for this password, root, is defined in the /boot/grub2/grub.cfg file. With this change, modifying a boot entry during booting requires you to specify the root user name and your password.

Changing the Default Boot Entry

GRUB 2 supports using a numeric value as the key for the saved entry directive to change the default order in which the operating systems are loaded. To specify which operating system should be loaded first, pass its number to the grub2-set-default command. For example:

~]# grub2-set-default 2

To force a system to always use a particular menu entry, use the menu entry name as the key to the GRUB_DEFAULT directive in the /etc/default/grub file. To list the available menu entries, run the following command as root:

~]# awk -F\' '$1=="menuentry " {print $2}' /etc/grub2.cfg

Rebuilding the grub.cfg file

Changes to /etc/default/grub require rebuilding the grub.cfg file as follows:
On BIOS-based machines, issue the following command as root:

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

On UEFI-based machines, issue the following command as root:

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