我运行了 apt-get update、apt-get upgrade，然后运行了 apt-get dist-ipgrade，dist-upgrade 结束时出现了一些错误：
Setting up linux-image-extra-3.13.0-139-generic (3.13.0-139.188) ...
run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.13.0-139-generic /boot/vmlinuz-3.13.0-139-generic
run-parts: executing /etc/kernel/postinst.d/initramfs-tools 3.13.0-139-generic / boot/vmlinuz-3.13.0-139-generic
update-initramfs: Generating /boot/initrd.img-3.13.0-139-generic
gzip: stdout: No space left on device
E: mkinitramfs failure cpio 141 gzip 1
update-initramfs: failed for /boot/initrd.img-3.13.0-139-generic with 1.
run-parts: /etc/kernel/postinst.d/initramfs-tools exited with return code 1
dpkg: error processing package linux-image-extra-3.13.0-139-generic (--configure ):
subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of linux-image-generic:
linux-image-generic depends on linux-image-extra-3.13.0-139-generic; however:
Package linux-image-extra-3.13.0-139-generic is not configured yet.
dpkg: error processing package linux-image-generic (--configure):
dependency problems - leaving unconfigured
Setting up linux-headers-3.13.0-139 (3.13.0-139.188) ...
Setting up linux-headers-3.13.0-139-generic (3.13.0-139.188) ...
Setting up linux-headers-generic (3.13.0.139.148) ...
dpkg: dependency problems prevent configuration of linux-generic:
linux-generic depends on linux-image-generic (= 3.13.0.139.148); however:
Package linux-image-generic is not configured yet.
dpkg: error processing package linux-generic (--configure):
dependency problems - leaving unconfigured
Errors were encountered while processing:
linux-image-extra-3.13.0-139-generic
linux-image-generic
linux-generic
E: Sub-process /usr/bin/dpkg returned an error code (1)
我清理了 /boot，并认为重新运行 apt-get dist-upgrade 应该可以完成。这次 dist-upgrade 似乎认为没有什么可做的：
sudo apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
我现在想知道系统处于什么状态。似乎有一个部分安装的内核，并且 dist-update 无法判断它不完整。