centos系统升级，boot目录剩余空间只剩几兆，需要进行清理。
清理流程如下：
查看已安装的kernel
[root@localhost ~]# rpm -qa|grep kernel kernel-headers-3.10.0-1160.45.1.el7.x86_64 abrt-addon-kerneloops-2.1.11-60.el7.centos.x86_64 kernel-devel-3.10.0-1160.21.1.el7.x86_64 kernel-3.10.0-1160.21.1.el7.x86_64 kernel-tools-libs-3.10.0-1160.45.1.el7.x86_64 kernel-3.10.0-1160.45.1.el7.x86_64 kernel-devel-3.10.0-1160.45.1.el7.x86_64 kernel-tools-3.10.0-1160.45.1.el7.x86_64
卸载kernel
[root@localhost ~]# rpm -e kernel-3.10.0-1160.21.1.el7.x86_64 kernel-devel-3.10.0-1160.21.1.el7.x86_64
再次查看已安装的kernel
[root@localhost ~]# rpm -qa|grep kernel kernel-headers-3.10.0-1160.45.1.el7.x86_64 abrt-addon-kerneloops-2.1.11-60.el7.centos.x86_64 kernel-tools-libs-3.10.0-1160.45.1.el7.x86_64 kernel-3.10.0-1160.45.1.el7.x86_64 kernel-devel-3.10.0-1160.45.1.el7.x86_64 kernel-tools-3.10.0-1160.45.1.el7.x86_64
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