Your output shows three different kernels, each of which has an associated initrd file:
vmlinuz-3.13.0-24-generic
vmlinuz-3.13.0-74-generic
vmlinuz-3.13.0-76-generic
These are three kernels in the 3.13.0 series, with Ubuntu-specific sub-versions of 24, 74, and 76. This type of configuration is perfectly normal. Ordinarily, an Ubuntu installation drops a starting kernel on the computer. As time goes on, though, the kernel may be updated to fix bugs or add features, so your normal software update process will install whatever update is currently available. This process continues. Left unchecked, you can end up with dozens of kernels installed, which can cause problems if you've got a separate /boot
partition that's too small. This issue is documented in a couple of bug reports:
If you type sudo apt-get autoremove
as part of your software-update process, the number of installed kernels will normally be limited to a maximum of three, so problems should not occur unless your /boot
partition is significantly smaller than the default of ~250MB.
Keeping multiple kernels installed is a useful precaution. Although kernel updates are often introduced to fix bugs, they sometimes unintentionally create new bugs. In extreme cases, a kernel bug can prevent the OS from booting. Although this problem is rare, keeping the last-booted kernel installed guarantees you'll have a way to boot the computer should such a problem occur. You'll need to select the older, working kernel in the boot manager (typically GRUB), but at least that possibility exists.
Note also that you can install separate signed kernels, in addition to the standard unsigned kernels. The signed kernels have the same filenames as their unsigned counterparts, but with .efi.signed
appended. Signed kernels are needed to boot from some boot loaders (such as rEFInd or Fedora's GRUB) when Secure Boot is active. Ubuntu should set itself up to install signed kernels if the installer detects that Secure Boot is active. Thus, you could end up with six kernels (and three matching initrd files, which are not signed), even if you regularly run sudo apt-get autoremove
.