The main reason is that after upgrading the kernel several times, the old version of the kernel was not uninstalled and took up too much space, but in fact, the new version of the kernel is used now, and the old version is useless, so just uninstall it.
Proceed as follows:
1 First check the currently used kernel version uname -a and get the output similar to the following:
fourfire@fourfire:~$ uname -a
Linux fourfire 3.16.0-45-generic #60~14.04.1-Ubuntu SMP Fri Jul 24 21:16:23 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
2 To check how many versions of the kernel are currently installed, use the dpkg command (the full name is debain package, the dpkg command for the software management system dedicated to the Debian operating system is a bit low-level, and the apt-get command is based on dpkg): dpkg --get-selections |grep linux-image , the output is similar to the following:
fourfire@fourfire:~$ dpkg --get-selections |grep linux-image
linux-image-3.16.0-44-genericinstall
linux-image-3.16.0-45-genericinstall
linux-image-extra-3.16.0-44-genericinstall
linux-image-extra-3.16.0-45-genericinstall
linux-image-generic-lts-utopicinstall
3 As can be seen from the above, linux-image-3.16.0-44-generic is a useless version and can be deleted. Use the apt-get command to delete it
sudo apt-get purge linux-image-3.16.0-44-generic The related linux-image-extra-3.16.0-44-generic will also be deleted. Be careful not to use the version you are using such as linux- image-3.16.0-45-generic was deleted. In addition, to be on the safe side, it is also good to keep 1 or 2 old versions such as linux-image-3.16.0-44-generic for backup. Generally, 3 or 4 old versions are accumulated before there is insufficient space.