Introduction.


The initial scenario is a computer with several Operative Systems installed, all of them working fine.

Normally the default OS should be the last one installed, and you can choose in the boot OS selector which operative system you wanna use.

In our Mistika configurations this should be CentOS 7.2.


The boot OS selector is the text screen that appear after the BIOS startup.


In a computer with three Operative systems (Centos 7.2 + SUSE 11 SP3 + Windows-10) the boot OS selector could be something like this:


CentOS Linux (3.10.0-327.e17.x86_64) 7 (Core)

CentOS Linux (0-rescue-049a2b2f83d04d028aff8a59c75167c1) 7 (Core)

SUSE Linux Enterprise Desktop 11 (x86_64) (on /dev/sda2)

Advanced options for SUSE Linux Enterprise Desktop 11 (x86_64) (on /dev/sda2)

Windows Recovery Environment (loader) (on /dev/sda4)


The default boot selector numbered sequentially. This means:


0.- CentOS Linux (3.10.0-327.e17.x86_64) 7 (Core)

1.- CentOS Linux (0-rescue-049a2b2f83d04d028aff8a59c75167c1) 7 (Core)

2.- SUSE Linux Enterprise Desktop 11 (x86_64) (on /dev/sda2)

3.- Advanced options for SUSE Linux Enterprise Desktop 11 (x86_64) (on /dev/sda2)

4.- Windows Recovery Environment (loader) (on /dev/sda4)


The default operative system is by default 0.


Procedure to change the default boot O.S. in system with multiple O.S.


This procedure it should be done from the CentOS Operative System which is the "manager" of the boot process.


All these commands should be executed from a console as root.


Which Operative System is the default?

Type grub2-editenv list


To change the Default Operative System use this command.

grub2-set-default <Number of the Operative System to be default>


Reboot the system and confirm works well.


In any case you can start the system choosing manually which OS you wish to use.