1.查询系统内核有几个

[root@master ~]# cat /boot/grub2/grub.cfg | grep menuentry
if [ x"${feature_menuentry_id}" = xy ]; then
  menuentry_id_option="--id"
  menuentry_id_option=""
export menuentry_id_option
menuentry 'CentOS Linux (5.15.2-1.el7.elrepo.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-862.el7.x86_64-advanced-044ef4fd-d7d8-4bf9-a1e3-6dca6e5b350a' {
menuentry 'CentOS Linux (3.10.0-1160.45.1.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-862.el7.x86_64-advanced-044ef4fd-d7d8-4bf9-a1e3-6dca6e5b350a' {
menuentry 'CentOS Linux (3.10.0-862.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-862.el7.x86_64-advanced-044ef4fd-d7d8-4bf9-a1e3-6dca6e5b350a' {
menuentry 'CentOS Linux (0-rescue-f299d39bce71487f81342ecbdd3bfc4b) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-f299d39bce71487f81342ecbdd3bfc4b-advanced-044ef4fd-d7d8-4bf9-a1e3-6dca6e5b350a' {

2.修改系统默认启动内核

[root@master ~]# grub2-set-default 'CentOS Linux (5.15.2-1.el7.elrepo.x86_64) 7 (Core)'

3.查看默认内核版本

[root@master ~]# grub2-editenv list
saved_entry=CentOS Linux (5.15.2-1.el7.elrepo.x86_64) 7 (Core)