我正在 Ubuntu 16.04 上安装 CUDA Toolkit，在支持的发行版表中写着内核必须是“4.4”。当我运行：
uname -r
我得到了“4.10.0-42-generic”。我尝试安装它，但失败并显示以下消息：
It is likely that 4.10.0-42-generic belongs to a chroot's host
Building initial module for 4.10.0-42-generic
Done.
bbswitch:
Running module version sanity check.
- Original module
- No original module exists within this kernel
- Installation
- Installing to /lib/modules/4.10.0-42-generic/updates/dkms/
depmod....
DKMS: install completed.
Setting up nvidia-prime (0.8.2) ...
Setting up vdpau-driver-all:amd64 (1.1.1-3ubuntu1) ...
Processing triggers for libc-bin (2.23-0ubuntu9) ...
Processing triggers for initramfs-tools (0.122ubuntu8.9) ...
update-initramfs: Generating /boot/initrd.img-4.10.0-42-generic
Processing triggers for shim-signed (1.32~16.04.1+0.9+1474479173.6c180c6-1ubuntu1) ...
Errors were encountered while processing:
linux-image-4.4.0-21-lowlatency
E: Sub-process /usr/bin/dpkg returned an error code (1)
那么，我怎样才能恢复到该版本的内核？
注意：“我有一个专门用于启动文件的目录“/boot”，其大小为 250 MB，现在它已“占用 80%”。