Remove redundant linux kernel after Centos upgrade

1. View the current kernel

[root@ou grub2]# uname -a
Linux ou 3.10.0-693.21.1.el7.x86_64 #1 SMP Wed Mar 7 19:03:37 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

2. View all kernel information

[root@ou grub2]# rpm -qa|grep kernel
kernel-devel-3.10.0-693.17.1.el7.x86_64
abrt-addon-kerneloops-2.1.11-48.el7.centos.x86_64
kernel-headers-3.10.0-693.21.1.el7.x86_64
kernel-3.10.0-693.17.1.el7.x86_64
kernel-3.10.0-693.21.1.el7.x86_64
kernel-devel-3.10.0-693.21.1.el7.x86_64
[root@ou grub2]# 

3. Delete the old version of the kernel information

[root@ou grub2]# yum remove kernel-3.10.0-693.17.1.el7.x86_64 

Enter and select Yes.

[root@ou grub2]# yum remove kernel-devel-3.10.0-693.17.1.el7.x86_64 

Enter and select Yes.

4. View the deleted kernel

[root@ou grub2]# rpm -qa|grep kernel
abrt-addon-kerneloops-2.1.11-48.el7.centos.x86_64
kernel-headers-3.10.0-693.21.1.el7.x86_64
kernel-3.10.0-693.21.1.el7.x86_64
kernel-devel-3.10.0-693.21.1.el7.x86_64
[root@ou grub2]# 

5. Restart the system to view the modified startup items.