Kernel confusion

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cleanman2
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Kernel confusion

Post by cleanman2 »

Running Mint 20.3
In preparation to remove some old kernels I looked at update manager-->view-->kernels. I see kernels listed from top to bottom as:
5.15
5.13
5.11
5.8
5.4

The active kernel is 5.4.0-125 which is listed as superseded. There is version 5.4.0-126 which is supported until April 2025 and is available to install.

Kernels 5.1, 5.8, and 5.13 are listed as end of life.

Kernel 5.15 shows 4 sub-versions as superseded and version 5.15.0-48 as supported until April 2025 and is installable.

Each time the software updater offers me a chance to update I do so including kernels. If version 5.4 is the oldest and 5.15 is the newest I don't understand why I a still running version 5.4 and why versions between 5.4 and 5.15 are all at end of life?

I know it is recommended that you keep a couple of older kernels just in case. So which of the above kernels can I delete?

If 5.15 is newer why is one of the 5.15 versions not installed?

My system is running fine and I am not looking to "fix" something by installing a new kernel. After seeing the results above I got curious and wanted to understand the kernel versioning system

Regards, Jim
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spamegg
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Re: Kernel confusion

Post by spamegg »

There are short-term kernels supported for about 1 year, after that they will reach "end of life." The purpose of these kernels is usually to support new hardware that the long-term kernel at the time does not fully support.

Then there is the whole LTS (Long Term Support) factor. Each Ubuntu LTS (and Mint) release comes with a fixed long-term kernel for 5 years. This is why it might look "outdated" but it's not that simple. Newer kernels can sometimes introduce new bugs, or break existing functionality (regressions). So the long-term "outdated" kernel tries to provide a more stable experience for those who don't have very new hardware.

On Mint 19/Ubuntu 18.04 the 5-year long-term kernel series was 4.15.

If you are on the 5.4 series kernel, that means you are using Mint 20/Ubuntu 20.04.

Mint 21/Ubuntu 22.04 comes with the 5.15 series kernel.

So if we take a look at the timeline:

Code: Select all

                2018->2020->2022
Ubuntu/Mint LTS 4.15->5.4->5.15 (latest kernel is already 5.19 or something)
                     ^    ^ 
                     |    |
                  lots of other         
                 kernels released      
Ubuntu also has other short-term OS releases like 21.10 etc. They temporarily (about 1 year) come with those newer but short-term kernels for people who really want it. Mint Update Manager allows access to these kernels.

There are many other kernel version numbers in-between two long-term series. This is because the upstream Linux kernel developers keep releasing new versions, but they don't interfere with distro LTS decisions.

Then Debian/Ubuntu can take those kernels and modify them, add more support, etc. and make their own decisions. They might decide: "OK, for our next long term support release, let's use 5.4 series kernel." This will go for 5 years but the upstream Linux kernel developers aren't going to sit around doing nothing in that timeframe. They will keep releasing new kernels, and it's up to each distribution to decide how slowly/quickly they want to "catch up", weighing in the balance of trying to support a broad selection of users/hardware while at the same time trying to provide a stable experience.

On Mint, normally you just stay on the "outdated" LTS kernel that is supported for the 5 years, unless you have a specific reason to use a newer kernel (like very new hardware, or performance related issues, etc.)
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JerryF
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Re: Kernel confusion

Post by JerryF »

As an example, I am using Mint 20.3. The kernel series started with 5.4.x and I still use that series.

It is possible to install higher-numbered kernels such as the 5.15.x series but that may not be prudent. If the 5.4.x series is working fine for you then stick with it.
cleanman2
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Re: Kernel confusion

Post by cleanman2 »

Thanks @spamegg and JerryF. My machine is running fine and I am not looking to update the kernel. When I watch what the update manager is installing and I see that kernels are being installed I mistakenly thought that they were also being made the active kernel.

Sometimes when update manager is running and kernels are involved it takes forever to finish because it seems to loop through each kernel and their sub-versions. I want to shorten the time an update takes.

I see advice that if you delete kernels you should always keep the active one and a couple of others to fall back on. When they give that advice are they saying to keep the active kernel and a couple of its sub versions or are they saying to keep the active kernel and all of its sub versions and another kernel version and all of its sub versions?

Does it make sense for me to:
1) Delete all of 5.13, 5.11 & 5.8 all of which have reached end of life.
2) Keep 5.4.0-124 (installed & superseded), 5.4.0-125 (active & superseded) and 5.4.0-126 (supported until apr 2025)
3) Keep 5.15,0-48, 5.15.0-46 & 5.15.0-43 just in case.

Thanks, Jim
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JerryF
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Re: Kernel confusion

Post by JerryF »

In my opinion, I would delete those end-of-life kernels and keep 1 to 2 earlier kernels within the series you're using (5.4.x)
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Pjotr
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Re: Kernel confusion

Post by Pjotr »

JerryF wrote:
Mon Sep 26, 2022 7:54 am
In my opinion, I would delete those end-of-life kernels and keep 1 to 2 earlier kernels within the series you're using (5.4.x)
Good advice.
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kc1di
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Re: Kernel confusion

Post by kc1di »

Usually the only kernel actually installed is the Long term one that came with your system either 5.4 -xxx or 5.15-xxx depending upon which version of Mint your using. It's best in most cases to stick with those. When update manager updates the kernel it normally will only update the one install on the system to a updated version of that Kernel. It will not normally install another version. Unless there is an over riding need for some security feature not provided by the same kernel.

It is best not to install the short term kernels again unless there is some over riding need for a function that the current kernel will not provide.
IE newer hardware.

I keep the kernel in use and that last version of that kernel and delete all others
Last edited by kc1di on Mon Sep 26, 2022 7:31 pm, edited 1 time in total.
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JerryF
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Re: Kernel confusion

Post by JerryF »

I also think the confusion for some users is that just because the kernels for all the series are listed from Update Manager, example: 5.4.x, 5.8.x, 5.11.x, 5.15.x, doesn't mean they are installed.

Only when it actually says Installed is it installed.

Now, in order to have the most recent, installed kernel active, a reboot/restart must be done. A kernel only can be active when booted.

In my case, we have two computers. Both have auto updates set for Update Manager. My laptop always gets turned off, so the most recent kernel gets loaded. My partner's desktop always goes into suspend mode so doesn't always have the latest kernel loaded. I check his every so often and reboot it so that his computer is running the latest kernel.
colinp1234
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Re: Kernel confusion

Post by colinp1234 »

Excellent thread. Very clear explanation on how the numbering system on kernels work and what they mean. Thanks for this.
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Pjotr
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Re: Kernel confusion

Post by Pjotr »

JerryF wrote:
Mon Sep 26, 2022 10:16 am
My partner's desktop always goes into suspend mode so doesn't always have the latest kernel loaded. I check his every so often and reboot it so that his computer is running the latest kernel.
Tread careful there.... That may cause a threat to domestic peace. :lol:
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JerryF
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Re: Kernel confusion

Post by JerryF »

Pjotr wrote:
Mon Sep 26, 2022 11:21 am
JerryF wrote:
Mon Sep 26, 2022 10:16 am
My partner's desktop always goes into suspend mode so doesn't always have the latest kernel loaded. I check his every so often and reboot it so that his computer is running the latest kernel.
Tread careful there.... That may cause a threat to domestic peace. :lol:
I'm also his computer guy (he's technically disabled) so what I say, goes!
cleanman2
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Re: Kernel confusion

Post by cleanman2 »

Ok thanks to all that responded. I will delete the kernels as outlined in the replies.

thanks, Jim
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JerryF
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Re: Kernel confusion

Post by JerryF »

To mark your problem as solved, please edit your ORIGINAL post and add [SOLVED] to the beginning of the Subject Line. It helps other members.
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