Ubuntu系统默认会自动更新内核，这样更新次数过多的话就会有大量的旧内核占用硬盘空间，尤其对于我这种硬盘只有512G的笔记本用户来说，硬盘资源就更加宝贵了，所以需要清理一些不需要的东西以释放磁盘空间。或者是多余的内核对生产环境来说存在不稳定因素，有时候重启后进入不到系统提示：not syncing : VFS: Unable to mount root解决办法就是开机的时候选择高级模式，选择之前的低版本的内核，这时候我们也需要手动删除内核。
当然如果只是做磁盘清理使用apt autoremove命令也能做得到。

一、查看当前的内核

root@linux:~# uname -a
Linux linux 4.15.0-96-generic #97-Ubuntu SMP Wed Apr 1 03:25:46 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

二、查看当前系统中所有内核

root@linux:~# dpkg --get-selections |grep linux
console-setup-linux                install
libselinux1:amd64                install
linux-base                    install
linux-firmware                    install
linux-generic                    install
linux-headers-4.15.0-72                install
linux-headers-4.15.0-72-generic            install
linux-headers-4.15.0-91                install
linux-headers-4.15.0-91-generic            install
linux-headers-4.15.0-96                install
linux-headers-4.15.0-96-generic            install
linux-headers-4.15.0-97                install
linux-headers-4.15.0-97-generic            install
linux-headers-generic                install
linux-image-4.15.0-54-generic            deinstall
linux-image-4.15.0-55-generic            deinstall
linux-image-4.15.0-58-generic            deinstall
linux-image-4.15.0-60-generic            deinstall
linux-image-4.15.0-62-generic            deinstall
linux-image-4.15.0-64-generic            deinstall
linux-image-4.15.0-65-generic            deinstall
linux-image-4.15.0-66-generic            deinstall
linux-image-4.15.0-70-generic            deinstall
linux-image-4.15.0-72-generic            install
linux-image-4.15.0-74-generic            deinstall
linux-image-4.15.0-76-generic            deinstall
linux-image-4.15.0-88-generic            deinstall
linux-image-4.15.0-91-generic            install
linux-image-4.15.0-96-generic            install
linux-image-4.15.0-97-generic            install
linux-image-generic                install
linux-modules-4.15.0-54-generic            deinstall
linux-modules-4.15.0-55-generic            deinstall
linux-modules-4.15.0-58-generic            deinstall
linux-modules-4.15.0-60-generic            deinstall
linux-modules-4.15.0-62-generic            deinstall
linux-modules-4.15.0-64-generic            deinstall
linux-modules-4.15.0-65-generic            deinstall
linux-modules-4.15.0-66-generic            deinstall
linux-modules-4.15.0-70-generic            deinstall
linux-modules-4.15.0-72-generic            install
linux-modules-4.15.0-74-generic            deinstall
linux-modules-4.15.0-76-generic            deinstall
linux-modules-4.15.0-88-generic            deinstall
linux-modules-4.15.0-91-generic            install
linux-modules-4.15.0-96-generic            install
linux-modules-4.15.0-97-generic            install
linux-modules-extra-4.15.0-54-generic        deinstall
linux-modules-extra-4.15.0-55-generic        deinstall
linux-modules-extra-4.15.0-58-generic        deinstall
linux-modules-extra-4.15.0-60-generic        deinstall
linux-modules-extra-4.15.0-62-generic        deinstall
linux-modules-extra-4.15.0-64-generic        deinstall
linux-modules-extra-4.15.0-65-generic        deinstall
linux-modules-extra-4.15.0-66-generic        deinstall
linux-modules-extra-4.15.0-70-generic        deinstall
linux-modules-extra-4.15.0-72-generic        install
linux-modules-extra-4.15.0-74-generic        deinstall
linux-modules-extra-4.15.0-76-generic        deinstall
linux-modules-extra-4.15.0-88-generic        deinstall
linux-modules-extra-4.15.0-91-generic        install
linux-modules-extra-4.15.0-96-generic        install
linux-modules-extra-4.15.0-97-generic        install
selinux-utils                                install
util-linux                                   install

命令运行结果中后面的选项为install且不是当前正在使用的内核就可以删除。

三、移除多余的内核

root@linux:~# sudo apt-get remove linux-headers-4.15.0-70 linux-headers-4.15.0-70-generic linux-image-4.15.0-70-generic linux-modules-4.15.0-70-generic linux-modules-extra-4.15.0-70-generic

这样删除后会还会在列表中显示存在，不过是状态显示为已经卸载，如果想不显示彻底清除的话执行以下命令：

root@linux:~# sudo apt-get purge linux-headers-4.15.0-74 linux-headers-4.15.0-74-generic linux-image-4.15.0-74-generic linux-modules-4.15.0-74-generic linux-modules-extra-4.15.0-74-generic

卸载之后进行检查：

root@linux:~# dpkg --get-selections |grep linux
console-setup-linux                install
libselinux1:amd64                install
linux-base                    install
linux-firmware                    install
linux-headers-4.15.0-96                install
linux-headers-4.15.0-96-generic            install
linux-image-4.15.0-54-generic            deinstall
linux-image-4.15.0-55-generic            deinstall
linux-image-4.15.0-58-generic            deinstall
linux-image-4.15.0-60-generic            deinstall
linux-image-4.15.0-62-generic            deinstall
linux-image-4.15.0-64-generic            deinstall
linux-image-4.15.0-65-generic            deinstall
linux-image-4.15.0-66-generic            deinstall
linux-image-4.15.0-70-generic            deinstall
linux-image-4.15.0-72-generic            deinstall
linux-image-4.15.0-74-generic            deinstall
linux-image-4.15.0-76-generic            deinstall
linux-image-4.15.0-88-generic            deinstall
linux-image-4.15.0-91-generic            deinstall
linux-image-4.15.0-96-generic            install
linux-image-4.15.0-97-generic            deinstall
linux-modules-4.15.0-54-generic            deinstall
linux-modules-4.15.0-55-generic            deinstall
linux-modules-4.15.0-58-generic            deinstall
linux-modules-4.15.0-60-generic            deinstall
linux-modules-4.15.0-62-generic            deinstall
linux-modules-4.15.0-64-generic            deinstall
linux-modules-4.15.0-65-generic            deinstall
linux-modules-4.15.0-66-generic            deinstall
linux-modules-4.15.0-70-generic            deinstall
linux-modules-4.15.0-72-generic            deinstall
linux-modules-4.15.0-74-generic            deinstall
linux-modules-4.15.0-76-generic            deinstall
linux-modules-4.15.0-88-generic            deinstall
linux-modules-4.15.0-91-generic            deinstall
linux-modules-4.15.0-96-generic            install
linux-modules-4.15.0-97-generic            deinstall
linux-modules-extra-4.15.0-54-generic        deinstall
linux-modules-extra-4.15.0-55-generic        deinstall
linux-modules-extra-4.15.0-58-generic        deinstall
linux-modules-extra-4.15.0-60-generic        deinstall
linux-modules-extra-4.15.0-62-generic        deinstall
linux-modules-extra-4.15.0-64-generic        deinstall
linux-modules-extra-4.15.0-65-generic        deinstall
linux-modules-extra-4.15.0-66-generic        deinstall
linux-modules-extra-4.15.0-70-generic        deinstall
linux-modules-extra-4.15.0-72-generic        deinstall
linux-modules-extra-4.15.0-74-generic        deinstall
linux-modules-extra-4.15.0-76-generic        deinstall
linux-modules-extra-4.15.0-88-generic        deinstall
linux-modules-extra-4.15.0-91-generic        deinstall
linux-modules-extra-4.15.0-96-generic        install
linux-modules-extra-4.15.0-97-generic        deinstall
selinux-utils                   　　　　　　　 install
util-linux                    　　　　　　　　 install

状态为deinstall即为已经卸载。

四、更新系统引导

删除内核后需要更新grup移除失效的启动项：

root@linux:~# sudo update-grub　　#根据情况选择grub/grub2