1.终端运行uname -a 查看当前使用内核，别面错误卸载正在使用的内核
2.使用dpkg --get-selections | grep linux查看已经安装的内核，其中linux-image开头的是内核
gexueyuan@gexueyuan-Ubuntu:~$ dpkg --get-selections | grep linux
libselinux1 install linux-firmware install linux-generic-pae install linux-headers-2.6.38-10 install linux-headers-2.6.38-10-generic-pae install linux-headers-2.6.38-11 install linux-headers-2.6.38-11-generic-pae install linux-headers-2.6.38-12 install linux-headers-2.6.38-12-generic-pae install linux-headers-2.6.38-8 install linux-headers-2.6.38-8-generic-pae install linux-headers-generic-pae install linux-image-2.6.38-10-generic-pae deinstall linux-image-2.6.38-11-generic-pae deinstall linux-image-2.6.38-12-generic-pae install linux-image-2.6.38-8-generic-pae deinstall linux-image-generic-pae install linux-libc-dev install linux-sound-base install pptp-linux install syslinux install syslinux-common install util-linux install
3.卸载相应内核：sudo apt-get remove linux-image-2.6.38-XX-generic-pae
4.更新grub2：sudo update-grub2
注：暴力删除---查看了下grub2的脚本/etc/grub.d/10_linux ，发现启动界面是通过解析/boot目录下的引导镜像和内核镜像生成的，所以只要删除位于/boot下的内核和启动镜像，就可以删除不需要的内核（效果正在查看）
一个删除不用内核的脚本命令：
dpkg -l 'linux-*' | sed '/^ii/!d;/'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d;s/^[^ ]* [^ ]* \([^ ]*\).*/\1/;/[0-9]/!d' | xargs sudo apt-get -y purge
经过测试，很厉害！！