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EugeneTheJeep
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PostPosted: Thu Jan 04, 2018 10:00 pm    Post subject: kernel downgrade and configuration Reply with quote

Hey all,

I want to downgrade my kernel, and was wondering if it's safe to use make olddefconfig using a .config file from a newer kernel version. I really don't want to go through everything manually. Is this advisable? Otherwise, is there another way to do it automatically?

Thanks for any help
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LIsLinuxIsSogood
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PostPosted: Fri Jan 05, 2018 11:36 am    Post subject: Reply with quote

Not sure if you've solved the issue, but something like this should work if you want to go about this a more bare bones linux solution:
1. Downgrade kernel and then build using either genkernel or with another sort of plain kernel (make defconfig)
2. Then using these text editing tools grep, awk or sed along with diff command you can probably find all the differences between the files and replace the missing settings from within the the old file.

Does that make sense? If not, then you can probably still go the route you mentioned which is i suppose to copy the kernel configuration into the folder where the linux kernel Makefile is stored and then make olddefconfig???


EDIT: I changed the instruction in #1 to include the instruction for default config (make defconfig)
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John R. Graham
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PostPosted: Fri Jan 05, 2018 12:06 pm    Post subject: Reply with quote

"make oldconfig" on recent versions is usually safe, though. That's what I'd try first.

- John
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EugeneTheJeep
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PostPosted: Fri Jan 05, 2018 2:13 pm    Post subject: Reply with quote

LlsLinuxIsSoGood,

Quote:
Does that make sense? If not, then you can probably still go the route you mentioned which is i suppose to copy the kernel configuration into the folder where the linux kernel Makefile is stored and then make olddefconfig???


Correct, when I upgrade I always copy .config from the old source folder to the new one and then run makeolddefconfig. My understanding is that it merges your old manual configuration with default settings of any configuration options added to the new kernel. Is this correct?

John R. Graham

I want to downgrade from 4.14.8 to 4.9.72. I had upgraded to 4.14.7 while it was briefly marked stable, then it was removed, so I upgraded again to 4.14.8, but I prefer to run the latest stable kernel.
I'm a noob, so is it safe to say that these are recent enough that make oldconfig would be generally safe? They seem to be minor revisions released in relatively rapid succession, so my gut tells me yes, but I just want to make sure.

Otherwise, should I just stay at 4.14.8? I really haven't noticed anything different at all... seems pretty stable to me
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John R. Graham
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PostPosted: Fri Jan 05, 2018 4:21 pm    Post subject: Reply with quote

EugeneTheJeep wrote:
... I'm a noob, so is it safe to say that these are recent enough that make oldconfig would be generally safe? They seem to be minor revisions released in relatively rapid succession, so my gut tells me yes, but I just want to make sure.
In this case, yes, definitely, as this is exactly what I did. I'm currently running on the resultant kernel.

- John
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Frautoincnam
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PostPosted: Fri Jan 05, 2018 9:25 pm    Post subject: Reply with quote

EugeneTheJeep wrote:
I want to downgrade from 4.14.8 to 4.9.72. I had upgraded to 4.14.7 while it was briefly marked stable, then it was removed, so I upgraded again to 4.14.8, but I prefer to run the latest stable kernel.

I always save config with the kernel :
Code:
$ ls -tl /boot/*4.1{2,4}*
-rw-r--r-- 1 root root   92162 21 déc.  12:36 /boot/config-4.14.8-gentoo-r1
-rw-r--r-- 1 root root 5853648 21 déc.  12:36 /boot/kernel-4.14.8-gentoo-r1
-rw-r--r-- 1 root root 5620176  3 déc.  18:15 /boot/kernel-4.12.12-gentoo
-rw-r--r-- 1 root root   91002 15 sept. 21:57 /boot/config-4.12.12-gentoo
-rw-r--r-- 1 root root   90965 14 août  18:25 /boot/config-4.12.5-gentoo
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LIsLinuxIsSogood
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PostPosted: Fri Jan 05, 2018 10:49 pm    Post subject: Reply with quote

Quote:
Otherwise, should I just stay at 4.14.8? I really haven't noticed anything different at all... seems pretty stable to me


I think the answer on this would be it depends. What purpose is the machine being used for?

If it isn't a huge risk that is involved, then it is probably safe enough to expect that it should work through those potential panics or whatever and not completely hang or stall.

Personally my own preference to avoid this is to not be updating the kernel every time that the new sources are available. For one it is a large download which sort of seems like it could just be taking up precious disk space if you know what I mean. And I basically like to test and then keep just the upgrades of a single kernel every few motnhs, and then like Frautoincnam said the old ones can be reused in the case of any problems or if the system becomes inaccessible, incompatible or downright difficult to use with the kernel you are currently on.
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