当boot提示空间不足时，一般是因为ubuntu自动更新了内核导致，解决方法就是删除旧的不用的内核
df -l 查看磁盘状态
文件系统 1K-块 已用 可用 已用% 挂载点
udev 3935352 0 3935352 0% /dev
tmpfs 793124 9680 783444 2% /run
/dev/sda7 39752296 32944260 4765668 88% /
tmpfs 3965604 352 3965252 1% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 3965604 0 3965604 0% /sys/fs/cgroup
/dev/sda5 184307 112584 58104 66% /boot
/dev/sda2 101589 19418 82171 20% /boot/efi
tmpfs 793124 68 793056 1% /run/user/1000
uname -a 查看当前使用的内核是4.10.35
Linux guolin-ThinkPad-T470 4.10.0-35-generic #39~16.04.1-Ubuntu SMP Wed Sep 13 09:02:42 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
dpkg --get-selections|grep linux
console-setup-linux install
libselinux1:amd64 install
linux-base install
linux-firmware install
linux-generic-hwe-16.04 install
linux-headers-4.10.0-28 install
linux-headers-4.10.0-28-generic install
linux-headers-4.10.0-35 install
linux-headers-4.10.0-35-generic install
linux-headers-generic-hwe-16.04 install
linux-image-4.10.0-35-generic install
linux-image-extra-4.10.0-28-generic deinstall
linux-image-extra-4.10.0-35-generic install
linux-image-generic-hwe-16.04 install
linux-libc-dev:amd64 install
linux-signed-image-4.10.0-28-generic deinstall
linux-signed-image-4.10.0-35-generic install
linux-sound-base install
pptp-linux install
syslinux install
syslinux-common install
syslinux-legacy install
util-linux install
sudo apt-get remove linux-image4.10.0-28-generic
过程中可能会出错，这时再运行
sudo apt-get autoremove
最后的效果，
/dev/sda5 184307 112584 58104 66% /boot
