1.查看自己机器的内核版本 uname -r
2.产看机器上已经安装的内核版本 rpm -qa | grep kernel
3.删除自己不想用的版本 dnf remove （旧的版本号，去上面复制好了）
<---------------------------------------------------------------------------------------------->
[root@fedora bin]# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.20.6-200.fc29.x86_64
Found initrd image: /boot/initramfs-4.20.6-200.fc29.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-d9e9c1557ec74b7092c163ccbe56a6fc
Found initrd image: /boot/initramfs-0-rescue-d9e9c1557ec74b7092c163ccbe56a6fc.img
Found Korora 26 (Bloat) on /dev/mapper/korora-root