CentOS7修改內核啟動順序：
1.首先查看當前系統有幾個內核
cat /boot/grub2/grub.cfg |grep menuentry
2.查看當前默認內核
grub2-editenv list
3.更改默認啟動內核
grub2-set-default 'CentOS Linux (3.10.0-514.26.2.el7.x86_64) 7 (Core)'
4.重啟機器生效