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Comment by fredsted | Hacker News Reader

Doesn't `apt-get autoremove` remove those old kernels? Not that it's a solution; it should of course be done automatically! Here's what I get when using it:

    > apt-get autoremove
    Reading package lists... Done
    Building dependency tree
    Reading state information... Done
    The following packages will be REMOVED:
      linux-headers-3.19.0-79 linux-headers-3.19.0-79-generic
      linux-image-3.19.0-78-generic linux-image-3.19.0-79-generic
      linux-image-extra-3.19.0-78-generic linux-image-extra-3.19.0-79-generic
    0 upgraded, 0 newly installed, 24 to remove and 39 not upgraded.
    After this operation, 1,732 MB disk space will be freed.
    Do you want to continue? [Y/n]

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Whenever a kernel is updated autoremove should be called immediately afterwards. It should be called before the restart now / restart later dialog box of update-notifier appears.

Currently, Ubuntu installs a new kernel and update-notifier tells the user a reboot is needed. The autoremove notification only appears when using the terminal which explains why users are running into this issue. Also, update-notifier informs the user another reboot is needed after autoremove is run.

To avoid this mess I’ve commented out the lines of /etc/apt/apt.conf.d/99update-notifier and wrote my own updater using bash and zenity and incorporated needsrestart. It’s not pretty but it works.

Care to share it? Maybe it could help others...

I thought about sharing it but like I said it’s not pretty. It involves editing sudoers and holding back config updates for sudoers and update-notifier-common which might cause problems in the future if you’re not aware. I’d much rather see Canonical address it properly.

absolutely not, automatically running auto remove may lead to bad things; on occasion autoremove flags other more useful packages for removal.

For example I'm using LVM with my installation on my Ubuntu laptop and after updating the kernel and running "apt autoremove" it removed the LVM package leaving me scratching my head shortly on reboot as to why it wouldn't find my root filesystem (frankly i have no idea how it became "unneeded").

A more sensible approach is how Red Hat do it with YUM/DNF, that is, to allow a certain number of the same packages to be installed, "installonly_limit" in yum.conf. Doing this means that when a new kernel gets installed the oldest is removed to keep the the system at the limit specified.

On my RHEL/CentOS machines I tend to narrowly provision /boot to around 250-500MB. set "installonly_limit" to 2 and the system will keep the most recent kernel and one back. it works for me.

I see you’re point, though I too use LVM and haven’t seen that happen... weird. I could have been more exact with my response as autoremove does more than just remove old kernels. Anyway, it would be nice to see Canonical resolve this.

>Doesn't `apt-get autoremove` remove those old kernels?

Of course it doesn't! Why would you assume such a silly thing? /s https://askubuntu.com/questions/563483/why-doesnt-apt-get-au...

> It's better to err on the side of saving too many kernels than saving too few

But Muh Freedoms! I hate to be subject to one man's opinion of things /s

It's also kind of a garbage argument.

People who know they have broken kernels don't keep upgrading them, they stop and fix them.

People who don't know they have broken kernels also don't know they can boot with an older kernel, so they get nothing from the "backup".

We want to leave some time for people to realize their kernel is broken, so keeping three is probably just fine. Honestly, it would probably be adequate to just bump the oldest one off the queue whenever a newer one is requested. If you've got a tiny boot partition, maybe that means only two revisions. If you've got a huge boot partition it could be 20.

But just keeping them all and making people manually uninstall them gains you nothing, it's user-hostile for no reason.

Yes, it does remove old kernels. Read the very link you posted.

I confirm that it doesn't autoremove. I had to empty /boot on some servers lately.

Anyway sometimes one wants to keep old kernels. I have an old laptop that runs OK with a 3.something kernel and has wierd video sync problems with any newer ones. Ubuntu 16.04 keeps running with that old kernel so I keep booting from that, maybe once or twice per year.

However the proper solution would be pinning a package and autoremoving the others.

Except, it would be nice to keep a few of the (recent) older kernels, in case things go awry with the new update.

I agree.

I'm running Ubuntu 16.10 currently. A kernel upgrade hosed my setup yesterday, and having an older kernel available saved my butt. I was able to do another `apt-get update` and things eventually worked with the latest kernel.

This already happens: apt autoremove won't remove the package for the running kernel. It'll clean up "old" (N-1 and lower) kernels, but installing kernel N+1 won't allow kernel N to be deleted as long as kernel N is still executing.

Once you reboot/kexec into the N+1 kernel, it'll let you remove the N (now N-1) kernel, bringing you down to one. But at that point you've proven the new kernel works—at least well enough to get to a shell you can run apt autoremove from.

This is why autoremove isn't so auto: if it happened automatically after reboot, it might be running on a now-wedged system (e.g. one that can't bring up the display manager), removing the last-known-good kernel and leaving you with only the broken one.

I think the right middle-ground solution would just be for installing kernel updates to touch a file, and for Desktop Environments to notice that file and trigger a dialog prompt of "you've just rebooted into a new kernel. Everything good?"—where answering "yes" runs apt autoremove. On a wedged system, you can't answer the prompt, so the system won't drop the old kernel. (In other words, just copy the "your display settings were changed. Can you read this?" prompt. It's a great design!)

Wouldn't a good solution then be to run autoremove before installing a new kernel?

That way, you have kernel N running, first autoremove wipes kernels N-1 and older, then it installs kernel N+1, so that when you reboot into N+1, you'll always have known-good kernel N if it doesn't work.

It's a very similar solution to how a good programmer solves an off-by-one error, doing a shift/rotate shuffle on a for/while loop.

What happens when you have a high-uptime system where you repeatedly "apt dist-upgrade" and end up installing packages for kernels N+1, N+2, N+3, etc., all without rebooting into any of them?

I agree that if the user manually runs an apt [dist-]upgrade—or really any manual apt command—that that's a good time to do apt maintenance work. (Homebrew does maintenance work whenever you invoke it and there haven't been any complaints so far.) But kernels usually get installed automatically, so it can't just run then.

Now, if there was a specific concept of a "last-known good kernel" (imagine, say, the grub package generating+installing a virtual package when you run grub-install, that depends on whatever kernel you specified as your recovery kernel, ensuring it remains around), then your approach could work—you'd always have two kernels, the LKG for a recovery boot, and the newest for a regular boot.

Exactly what happens on Fedora.

Fedora/RHEL yum has a much better solution: installonly_limit, defaulting to 3. Kernels which have been updated will only be kept up to this depth. The excess are automatically trimmed during update.

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