1、查看内核启动顺序

[root@master2 ~]# awk -F\' '$1=="menuentry " {print $2}' /etc/grub2.cfg
CentOS Linux (5.15.11-1.el7.elrepo.x86_64) 7 (Core)
CentOS Linux (3.10.0-1160.49.1.el7.x86_64) 7 (Core)
CentOS Linux (3.10.0-862.el7.x86_64) 7 (Core)
CentOS Linux (0-rescue-9b68e42b0645407f9473f6ecafdab81e) 7 (Core)

2、修改内核配置文件

[root@master2 ~]# cat /etc/default/grub 
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=0                                                    # 已经修改好的，默认是saved，修改成数字0
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet"
GRUB_DISABLE_RECOVERY="true"

3、接下来运行下面的命令来重新创建内核配置

[root@master2 ~]# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.15.11-1.el7.elrepo.x86_64
Found initrd image: /boot/initramfs-5.15.11-1.el7.elrepo.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-1160.49.1.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-1160.49.1.el7.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-862.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-862.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-9b68e42b0645407f9473f6ecafdab81e
Found initrd image: /boot/initramfs-0-rescue-9b68e42b0645407f9473f6ecafdab81e.img
done

4、重启并查看内核是否是刚升级完的内核

[root@master2 ~]# uname -r 
5.15.11-1.el7.elrepo.x86_64