[kwlug-disc] Why would an LTS install non-LTS kernels?

[Khalid Baheyeldin]

Thanks for that link. That explains what I have been seeing that
various servers get different kernels depending on the HWE installed.

I have finally moved everything to 14.04 (no more 12.04). On servers,
there is less 'exotic' hardware and therefore there are seldom any
surprises.

On the desktop, it is another matter.

Per the schedule that is in the link you provided, 14.04 will have 5
years of kernel 3.13, so I am good staying with that, until the time
comes for moving to 16.04.

Perhaps I will try the Xenial 16.04 kernel (4.x, due in August).

On Tue, Mar 15, 2016 at 7:09 PM, Darcy Casselman <dscassel at gmail.com> wrote:
> The LTS point releases ship updated kernels for hardware enablement.  The
> process is described here: https://wiki.ubuntu.com/Kernel/LTSEnablementStack
>
> Generally I'd expect that things that work shouldn't stop working.  But I
> know from experience that that assumption is naive.  It's software.  Stuff
> breaks.  Also, it's the kernel, and they do strange things sometimes.
>
> Darcy.
>
> On Tue, Mar 15, 2016 at 5:03 PM, Khalid Baheyeldin <kb at 2bits.com> wrote:
>>
>> Finally got around to the task of reinstalling my laptop, using the
>> warranty replaced SSD disk from OCZ.
>>
>> After installing Kubuntu 14.04, guvcview would not work with the built
>> in webcam, but another USB webcam (actually a microscope of sorts).
>> Both would give a black screen (no video).
>>
>> The USB webcam is supported by uvc (supposedly).
>>
>> usb 2-2: New USB device found, idVendor=1871, idProduct=7670
>> usb 2-2: New USB device strings: Mfr=2, Product=3, SerialNumber=0
>> usb 2-2: Product: USB2.0 UVC PC Camera
>> usb 2-2: Manufacturer: GenesysLogic Technology Co., Ltd.
>>
>>
>> Both were working fine with guvcview on the previous install (Ubuntu
>> Server 14.04, then KDE Plasma Desktop on top, so should not be much
>> different).
>>
>> A lengthy investigation ensued, using programs like Cheese, vlc,
>> qtv4l2 test, ...etc. Some of them (e.g. Cheese) would work with the
>> built in web cam, but not the USB webcam. Others (e.g. vlc) could work
>> with the USB video, but NOT using the uvcvideo driver (e.g. v4l).
>>
>> So there was something with the uvcvideo kernel module for the USB
>> webcam with an error like this:
>>
>> kernel: [  100.912205] uvcvideo: Failed to query (GET_DEF) UVC control
>> 11 on unit 3: -32 (exp. 1).
>>
>> The reason I say uvc was the culprit is that other applications using
>> other drivers do work.
>>
>> Luckily, I have the old disk lying around in the state it was in
>> before I removed it from the laptop. I probed around, and found that
>> the new Kubuntu install has a 3.19 kernel, while the old one Ubuntu
>> Server LTS was 3.13.
>>
>> So, I installed the Trusty generic image:
>>
>> $ sudo aptitude install linux-image-generic-lts-trusty
>>
>> And purged the vivid ones:
>>
>> $ sudo aptitude purge linux-generic-lts-vivid
>> linux-image-generic-lts-vivid linux-image-3.19.0-56-generic
>> linux-image-3.19.0-25-generic linux-image-extra-3.19.0-25-generic
>> linux-image-extra-3.19.0-56-generic
>>
>> After a reboot, both webcams work fine, as things were before.
>>
>> There is still the same error in dmesg, but things work as I want them
>> too.
>>
>> So, the big questions are:
>>
>> 1. Why would something that works stop working in a point release of
>> the kernel (remember that most devices have drivers written once, and
>> then not touched at all).
>>
>> 2. Why would an LTS release install a non-LTS kernel?
>> --
>> Khalid M. Baheyeldin
>> 2bits.com, Inc.
>> Fast Reliable Drupal
>> Drupal optimization, development, customization and consulting.
>> Simplicity is prerequisite for reliability. --  Edsger W.Dijkstra
>> Simplicity is the ultimate sophistication. --   Leonardo da Vinci
>> For every complex problem, there is an answer that is clear, simple,
>> and wrong." -- H.L. Mencken
>>
>>
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>
>
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-- 
Khalid M. Baheyeldin
2bits.com, Inc.
Fast Reliable Drupal
Drupal optimization, development, customization and consulting.
Simplicity is prerequisite for reliability. --  Edsger W.Dijkstra
Simplicity is the ultimate sophistication. --   Leonardo da Vinci
For every complex problem, there is an answer that is clear, simple,
and wrong." -- H.L. Mencken