Setting CentOS 7 boot order

Get current boot order

grub2-editenv list

saved_entry=CentOS Linux 7 (Core), with Linux 3.10.0-229.4.2.el7.x86_64

List all the menu entries that will be displayed at system boot

grep "^menuentry" /boot/grub2/grub.cfg | cut -d "'" -f2

0 : CentOS Linux 7 (Core), with Linux 3.10.0-229.14.1.el7.x86_64
1 : CentOS Linux 7 (Core), with Linux 3.10.0-229.4.2.el7.x86_64
2 : CentOS Linux 7 (Core), with Linux 3.10.0-229.el7.x86_64
3 : CentOS Linux 7 (Core), with Linux 0-rescue-605f01abef434fb98dd1309e774b72ba

Set the default boot entry

grub2-set-default 0

grub2-editenv list
saved_entry=0

Reboot the machine.