CentOS7开机启动界面显示多个内核选项
正常情况下，有两个启动项，一个是“正常启动”，另一个是“救援模式启动”（rescue）。
如果启动项多于2个，说明当前系统有旧内核未删除。原因是CentOS更新后不会自动删除旧内核。
默认以新内核启动，可以在启动选项中临时选择，也可以修改配置永久指定。
修改默认启动的内核
[root@CentOS-7 ~]# uname -r # 查看当前内核版本
3.10.0-693.5.2.el7.x86_64
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# cat /boot/grub2/grub.cfg |grep "menuentry " # 查看所有可用内核
menuentry 'CentOS Linux (3.10.0-693.5.2.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-327.el7.x86_64-advanced-88ae7d3d-ffaf-4402-9d44-56b6845789e4' {
menuentry 'CentOS Linux (3.10.0-327.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-327.el7.x86_64-advanced-88ae7d3d-ffaf-4402-9d44-56b6845789e4' {
menuentry 'CentOS Linux (0-rescue-8405cda22c0b421db40478edcf9c1fb2) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-8405cda22c0b421db40478edcf9c1fb2-advanced-88ae7d3d-ffaf-4402-9d44-56b6845789e4' {
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# grub2-set-default 'CentOS Linux (3.10.0-327.el7.x86_64) 7 (Core)'
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# grub2-editenv list # 查看内核修改结果
saved_entry=CentOS Linux (3.10.0-327.el7.x86_64) 7 (Core)
[root@CentOS-7 ~]#
删除无用内核
[root@CentOS-7 ~]# uname -r # 查看当前内核版本
3.10.0-693.5.2.el7.x86_64
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# rpm -qa |grep kernel-[0-9] # 查看全部内核包
kernel-3.10.0-693.5.2.el7.x86_64
kernel-3.10.0-327.el7.x86_64
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# yum remove kernel-3.10.0-327.el7.x86_64 # 删除指定的无用内核
Loaded plugins: fastestmirror, langpacks
Resolving Dependencies
--> Running transaction check
---> Package kernel.x86_64 0:3.10.0-327.el7 will be erased
--> Finished Dependency Resolution
Dependencies Resolved
=============================================================================================================================================================
Package Arch Version Repository Size
=============================================================================================================================================================
Removing:
kernel x86_64 3.10.0-327.el7 @anaconda 136 M
Transaction Summary
=============================================================================================================================================================
Remove 1 Package
Installed size: 136 M
Is this ok [y/N]: y
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Erasing : kernel-3.10.0-327.el7.x86_64 1/1
Verifying : kernel-3.10.0-327.el7.x86_64 1/1
Removed:
kernel.x86_64 0:3.10.0-327.el7
Complete!
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# rpm -qa |grep kernel-[0-9] # 查看全部内核包
kernel-3.10.0-693.5.2.el7.x86_64
[root@CentOS-7 ~]#
[root@CentOS-7 ~]# cat /boot/grub2/grub.cfg |grep "menuentry "
menuentry 'CentOS Linux (3.10.0-693.5.2.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-327.el7.x86_64-advanced-88ae7d3d-ffaf-4402-9d44-56b6845789e4' {
menuentry 'CentOS Linux (0-rescue-8405cda22c0b421db40478edcf9c1fb2) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-8405cda22c0b421db40478edcf9c1fb2-advanced-88ae7d3d-ffaf-4402-9d44-56b6845789e4' {
[root@CentOS-7 ~]#
来自：https://www.cnblogs.com/anliven/p/7944842.html