Ubuntu – Why does Ubuntu need two kernels

aptkernelpackage-management

My computer has rather low disk space. For this reason every so often I need to run sudo apt autoremove to remove old kernels and headers and stuff.

Not that long ago, I noticed that it has kept 4.4.0.77 as well as 4.4.0.78. I have run autoremove twice since noticing, but it still is there. I only use the latest kernel, and I don't think any of my software depends on that particular version, but when I tried to remove it, it wanted to remove linux-image-generic. That sounds important, so I didn't, but why does it depend on an outdated kernel version?

Best Answer

Ubuntu does not need two kernels. It keeps one "backup" kernel in case you can't boot with the latest one.

You can safely remove the older kernel if you are sure you won't need it.

And you probably tried to remove the latest one if linux-image-generic was to be removed. It depends on the latest kernel only.

Related Solutions

Ubuntu – Why is it unsafe to delete old kernels

Removing old kernels is not inherently unsafe, but if you remove all your kernels and reboot, you'll be left at an angry Grub screen. Fixing that takes significant know-how (like that but with an apt-get install linux-generic at the end).

The first time you do this is quite thrilling but the people looking to clean up their Grub menu or recover some disk space aren't looking for thrills.

The danger comes from users copy-pasting a block of code that —unbeknownst to them and without acknowledging the risks— doesn't apply. There are many examples of detecting old kernels and few are perfect. Even my latest effort still has its pitfalls. And we're talking about an issue that can be fixed; many posts on Ask Ubuntu could lead to permanent data loss if used incorrectly.

We try to safeguard against damage by signposting the risk to make users conscious of potential problems. In the best case scenarios, the user will be prepared and equipped to deal with a problem and in the worst case, at least they can't complain that they weren't warned.

Ubuntu – Autoremove does not remove old headers

autoremove will remove any package that:

is auto installed
is not included in APT::NeverAutoRemove APT configuration
don't have any dependents

Here is the debuging steps we followed

Checked auto/manual installation
```
aptitude search '^linux* ?installed'
```
Checked currently declared versions under APT::NeverAutoRemove
```
cat /etc/apt/apt.conf.d/01autoremove-kernels
```

Checked dependency

apt-cache rdepends linux-headers-4.4.0-38-generic

brings nothing but

sudo apt-get -o Debug::pkgAutoRemove=1 -s autoremove 2> debug-autoremove.txt

...
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-43-lowlatency:amd64 4.4.0-43.63
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-43-generic:amd64 4.4.0-43.63
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-42-lowlatency:amd64 4.4.0-42.62
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-42-generic:amd64 4.4.0-42.62
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-38-lowlatency:amd64 4.4.0-38.57
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-38-generic:amd64 4.4.0-38.57
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-36-lowlatency:amd64 4.4.0-36.55
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-36-generic:amd64 4.4.0-36.55
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-34-lowlatency:amd64 4.4.0-34.53
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-34-generic:amd64 4.4.0-34.53
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-31-lowlatency:amd64 4.4.0-31.50
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-31-generic:amd64 4.4.0-31.50
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-28-lowlatency:amd64 4.4.0-28.47
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-28-generic:amd64 4.4.0-28.47
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-24-lowlatency:amd64 4.4.0-24.43
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-24-generic:amd64 4.4.0-24.43
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-22-lowlatency:amd64 4.4.0-22.40
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-22-generic:amd64 4.4.0-22.40
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-21-lowlatency:amd64 4.4.0-21.37
Following dep: virtualbox-5.0:amd64 5.0.20-106931~Ubuntu~wily Recommends linux-headers:amd64 , provided by linux-headers-4.4.0-21-generic:amd64 4.4.0-21.37
...

So it's a dependency issue through the virtual package linux-headers

I'm in doubt here, It seems to me as bug.

Either in autoremove function, it can't deal with virtual package dependency.
Or in virtualbox package, that may need another way to declare dependency to Linux headers.

Best Answer

Related Solutions

Ubuntu – Why is it unsafe to delete old kernels

Ubuntu – Autoremove does not remove old headers

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