[gentoo-user] Changing CPU and motherboard

[gentoo-user] Changing CPU and motherboard

[whiteman808]

Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
not, what steps should be done on the existing Gentoo installation? Do I
need to do these operations from chroot?

Re: [gentoo-user] Changing CPU and motherboard

[Jay Faulkner]

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On 6/28/2025 9:38 AM, whiteman808 wrote:
> Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
> not, what steps should be done on the existing Gentoo installation? Do I
> need to do these operations from chroot?

I'm assuming this is amd64->amd64.

So the main thing to worry about is CPU compatibility, and your CFLAGS. 
If you're using -march=native, there's a chance your system won't work 
as compiled. This isn't always true, but these days it's no longer a 
guarantee that a newer CPU will have all the features of the old.


What I usually do in this case is:

- set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch 
generic target works) -- 
https://wiki.gentoo.org/wiki/Safe_CFLAGS#Generic_psABI_levels can help 
with this. - Ensure my system is fully updated, and `emerge 
--depclean`'d. - emerge -e @world # this will rebuild your entire system.


You can *significantly* reduce the pain of this by using the binary 
package host.


-JayF

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Re: [gentoo-user] Changing CPU and motherboard

[Michael]

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On Saturday, 28 June 2025 18:33:24 British Summer Time Jay Faulkner wrote:
> On 6/28/2025 9:38 AM, whiteman808 wrote:
> > Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
> > not, what steps should be done on the existing Gentoo installation? Do I
> > need to do these operations from chroot?
> 
> I'm assuming this is amd64->amd64.
> 
> So the main thing to worry about is CPU compatibility, and your CFLAGS.
> If you're using -march=native, there's a chance your system won't work
> as compiled. This isn't always true, but these days it's no longer a
> guarantee that a newer CPU will have all the features of the old.
> 
> 
> What I usually do in this case is:
> 
> - set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch
> generic target works) --
> https://wiki.gentoo.org/wiki/Safe_CFLAGS#Generic_psABI_levels can help
> with this. - Ensure my system is fully updated, and `emerge
> --depclean`'d. - emerge -e @world # this will rebuild your entire system.
> 
> 
> You can *significantly* reduce the pain of this by using the binary
> package host.
> 
> 
> -JayF

If you have compiled a bespoke kernel strictly specified for the CPU/MoBo 
hardware the system is running on and them move it to a different CPU/MoBo 
hardware, you will find the kernel may not boot at all, or it may boot but 
fail to initialise some hardware, e.g. NICs, graphics card, etc., because it 
is missing specific drivers and firmware.  Using more generic settings will 
get you a bigger kernel which can boot more hardware than the original.

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Re: [gentoo-user] Changing CPU and motherboard

[whiteman808]

On 28 Jun 2025, 10:33:24, Jay Faulkner wrote:
> On 6/28/2025 9:38 AM, whiteman808 wrote:
> > Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
> > not, what steps should be done on the existing Gentoo installation? Do I
> > need to do these operations from chroot?
> 
> I'm assuming this is amd64->amd64.
> 
> So the main thing to worry about is CPU compatibility, and your CFLAGS. If
> you're using -march=native, there's a chance your system won't work as
> compiled. This isn't always true, but these days it's no longer a guarantee
> that a newer CPU will have all the features of the old.
> 
> 
> What I usually do in this case is:
> 
> - set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch
> generic target works) --
> https://wiki.gentoo.org/wiki/Safe_CFLAGS#Generic_psABI_levels can help with
> this. - Ensure my system is fully updated, and `emerge --depclean`'d. -
> emerge -e @world # this will rebuild your entire system.
> 
> 
> You can *significantly* reduce the pain of this by using the binary package
> host.
> 
> 
> -JayF
Should I execute `emerge -e @world` inside chroot on some livecd?

Re: [gentoo-user] Changing CPU and motherboard

[Jay Faulkner]

On 6/28/2025 12:10 PM, whiteman808 wrote:
> On 28 Jun 2025, 10:33:24, Jay Faulkner wrote:
>> On 6/28/2025 9:38 AM, whiteman808 wrote:
>>> Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
>>> not, what steps should be done on the existing Gentoo installation? Do I
>>> need to do these operations from chroot?
>> I'm assuming this is amd64->amd64.
>>
>> So the main thing to worry about is CPU compatibility, and your CFLAGS. If
>> you're using -march=native, there's a chance your system won't work as
>> compiled. This isn't always true, but these days it's no longer a guarantee
>> that a newer CPU will have all the features of the old.
>>
>>
>> What I usually do in this case is:
>>
>> - set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch
>> generic target works) --
>> https://wiki.gentoo.org/wiki/Safe_CFLAGS#Generic_psABI_levels can help with
>> this. - Ensure my system is fully updated, and `emerge --depclean`'d. -
>> emerge -e @world # this will rebuild your entire system.
>>
>>
>> You can *significantly* reduce the pain of this by using the binary package
>> host.
>>
>>
>> -JayF
> Should I execute `emerge -e @world` inside chroot on some livecd?

As long as you pick a target that overlaps your current and future CPU, 
you should be able to perform 100% of the steps on the "before" PC.


-JayF

Re: [gentoo-user] Changing CPU and motherboard

[Dale]

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Jay Faulkner wrote:
> On 6/28/2025 9:38 AM, whiteman808 wrote:
>> Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
>> not, what steps should be done on the existing Gentoo installation? Do I
>> need to do these operations from chroot?
>
> I'm assuming this is amd64->amd64.
>
> So the main thing to worry about is CPU compatibility, and your
> CFLAGS. If you're using -march=native, there's a chance your system
> won't work as compiled. This isn't always true, but these days it's no
> longer a guarantee that a newer CPU will have all the features of the old.
>
>
> What I usually do in this case is:
>
> - set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch
> generic target works) --
> https://wiki.gentoo.org/wiki/Safe_CFLAGS#Generic_psABI_levels can help
> with this. - Ensure my system is fully updated, and `emerge
> --depclean`'d. - emerge -e @world # this will rebuild your entire system.
>
>
> You can *significantly* reduce the pain of this by using the binary
> package host.
>
>
> -JayF
>


Follow Jay's advice on the march setting in make.conf.  You want a
setting that is compatible with both CPUs as Jay mentioned.  Do a emerge
-e world.  Also, --depclean as well. 

When you install the new CPU.  You will need a kernel.  Your current one
may work, may not.  If it does, I'd stick to a console with no GUI
running.  Method below may be faster since you only have to recompile
once if you want to switch the march setting back to native.

A somewhat shorter method, after you install new CPU, boot another boot
media, Gentoo Live CD, Knoppix or whatever your system can boot with and
you like.  Then mount your partitions as needed for the OS, chroot in,
emerge -e world.  It should see the new CPU and change all the
settings.  Since the boot media is handling the boot, it doesn't matter
what your version of OS is as long as the Arch is the same.  Don't
forget to build a new kernel as well.  The command lspci -k can be a
really awesome friend.  Also, you can leave the MARCH set to native
setting and this way you only compile once.

If you can make it without the computer a bit, I'd boot from other media
and rebuild only once.  Oh, don't forget to change the CPU flags if you
have it set.  The command cpuid2cpuflags is good for that.  If you don't
have it, package is the same name.  You can unmerge it when done if you
want. 

Just another idea.  There are likely several ways to accomplish this. 
Biggest thing is the kernel. 

Dale

:-)  :-) 

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Re: [gentoo-user] Changing CPU and motherboard

[whiteman808]

On 28 Jun 2025, 14:32:57, Dale wrote:
> Jay Faulkner wrote:
> 
>     On 6/28/2025 9:38 AM, whiteman808 wrote:
> 
>         Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
>         not, what steps should be done on the existing Gentoo installation? Do I
>         need to do these operations from chroot?
> 
>     I'm assuming this is amd64->amd64.
> 
>     So the main thing to worry about is CPU compatibility, and your CFLAGS. If
>     you're using -march=native, there's a chance your system won't work as
>     compiled. This isn't always true, but these days it's no longer a guarantee
>     that a newer CPU will have all the features of the old.
> 
> 
>     What I usually do in this case is:
> 
>     - set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch
>     generic target works) -- https://wiki.gentoo.org/wiki/Safe_CFLAGS#
>     Generic_psABI_levels can help with this. - Ensure my system is fully
>     updated, and `emerge --depclean`'d. - emerge -e @world # this will rebuild
>     your entire system.
> 
> 
>     You can *significantly* reduce the pain of this by using the binary package
>     host.
> 
> 
>     -JayF
> 
> 
> 
> Follow Jay's advice on the march setting in make.conf.  You want a setting that
> is compatible with both CPUs as Jay mentioned.  Do a emerge -e world.  Also,
> --depclean as well. 
> 
> When you install the new CPU.  You will need a kernel.  Your current one may
> work, may not.  If it does, I'd stick to a console with no GUI running.  Method
> below may be faster since you only have to recompile once if you want to switch
> the march setting back to native.
> 
> A somewhat shorter method, after you install new CPU, boot another boot media,
> Gentoo Live CD, Knoppix or whatever your system can boot with and you like. 
> Then mount your partitions as needed for the OS, chroot in, emerge -e world. 
> It should see the new CPU and change all the settings.  Since the boot media is
> handling the boot, it doesn't matter what your version of OS is as long as the
> Arch is the same.  Don't forget to build a new kernel as well.  The command
> lspci -k can be a really awesome friend.  Also, you can leave the MARCH set to
> native setting and this way you only compile once.
> 
> If you can make it without the computer a bit, I'd boot from other media and
> rebuild only once.  Oh, don't forget to change the CPU flags if you have it
> set.  The command cpuid2cpuflags is good for that.  If you don't have it,
> package is the same name.  You can unmerge it when done if you want. 
> 
> Just another idea.  There are likely several ways to accomplish this.  Biggest
> thing is the kernel. 
> 
> Dale
> 
> :-)  :-) 
Does portage need to be able to execute some files already present on
the system if I compile new software or recompile entire system using
emerge -e? If yes, what if old CPU features and flags are entirely
incompatible and not subset of the new CPU settings if I compile using
livecd? How portage handles these cases?

Re: [gentoo-user] Changing CPU and motherboard

[Dale]

whiteman808 wrote:
> On 28 Jun 2025, 14:32:57, Dale wrote:
>> Jay Faulkner wrote:
>>
>>     On 6/28/2025 9:38 AM, whiteman808 wrote:
>>
>>         Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
>>         not, what steps should be done on the existing Gentoo installation? Do I
>>         need to do these operations from chroot?
>>
>>     I'm assuming this is amd64->amd64.
>>
>>     So the main thing to worry about is CPU compatibility, and your CFLAGS. If
>>     you're using -march=native, there's a chance your system won't work as
>>     compiled. This isn't always true, but these days it's no longer a guarantee
>>     that a newer CPU will have all the features of the old.
>>
>>
>>     What I usually do in this case is:
>>
>>     - set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch
>>     generic target works) -- https://wiki.gentoo.org/wiki/Safe_CFLAGS#
>>     Generic_psABI_levels can help with this. - Ensure my system is fully
>>     updated, and `emerge --depclean`'d. - emerge -e @world # this will rebuild
>>     your entire system.
>>
>>
>>     You can *significantly* reduce the pain of this by using the binary package
>>     host.
>>
>>
>>     -JayF
>>
>>
>>
>> Follow Jay's advice on the march setting in make.conf.  You want a setting that
>> is compatible with both CPUs as Jay mentioned.  Do a emerge -e world.  Also,
>> --depclean as well. 
>>
>> When you install the new CPU.  You will need a kernel.  Your current one may
>> work, may not.  If it does, I'd stick to a console with no GUI running.  Method
>> below may be faster since you only have to recompile once if you want to switch
>> the march setting back to native.
>>
>> A somewhat shorter method, after you install new CPU, boot another boot media,
>> Gentoo Live CD, Knoppix or whatever your system can boot with and you like. 
>> Then mount your partitions as needed for the OS, chroot in, emerge -e world. 
>> It should see the new CPU and change all the settings.  Since the boot media is
>> handling the boot, it doesn't matter what your version of OS is as long as the
>> Arch is the same.  Don't forget to build a new kernel as well.  The command
>> lspci -k can be a really awesome friend.  Also, you can leave the MARCH set to
>> native setting and this way you only compile once.
>>
>> If you can make it without the computer a bit, I'd boot from other media and
>> rebuild only once.  Oh, don't forget to change the CPU flags if you have it
>> set.  The command cpuid2cpuflags is good for that.  If you don't have it,
>> package is the same name.  You can unmerge it when done if you want. 
>>
>> Just another idea.  There are likely several ways to accomplish this.  Biggest
>> thing is the kernel. 
>>
>> Dale
>>
>> :-)  :-) 
> Does portage need to be able to execute some files already present on
> the system if I compile new software or recompile entire system using
> emerge -e? If yes, what if old CPU features and flags are entirely
> incompatible and not subset of the new CPU settings if I compile using
> livecd? How portage handles these cases?
>
>


I've never ran into that but given the changes software, especially
emerge, has made, it could possibly make a difference.  What you could
do is set march to a common setting for both CPUs and then do a emerge
-e portage.  That should rebuild everything emerge depends on and emerge
itself.  What I would do, I'd try it first.  I'd expect emerge to work
fine.  I checked on my system, portage doesn't even have CPU flags or
anything that I could see.  Of course, python would be the important
one.  I checked the python here and it doesn't have CPU flags either. 
Given that info, I'd say it is a 99% chance it would work fine.  If you
live somewhere where electricity is pricey, I'd certainly try it first. 
Just chroot in and do a emerge -ae world.  I'd think if there was a
problem, it would say something.  If it does fail, then revert.  I'd
think booting from other media would eliminate most all issues tho. 

Me tho, I'd install the CPU and try booting.  I'd just stick to a
console, no GUI.  Run emerge -ae world and go take a nap, go to work or
whatever.  Make sure to include --resume tho.  If something fails, it
will keep trying.  If anything does fail, it will spit out a list.  Try
them on their own.  If you don't have --oneshot set, make sure to
oneshot those so your world file doesn't get full of unwanted entries. 

Someone else may have more info on that question.  I just think it will
work and at least worth a try.  Save a lot of time for sure if it does
work. 

Dale

:-)  :-) 

Re: [gentoo-user] Changing CPU and motherboard

[Michael]

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On Saturday, 28 June 2025 21:10:59 British Summer Time Dale wrote:

> Me tho, I'd install the CPU and try booting.  I'd just stick to a
> console, no GUI.  Run emerge -ae world and go take a nap, go to work or
> whatever.  Make sure to include --resume tho.  If something fails, it
> will keep trying.

I think you meant to write:   '--keep-going y'


> If anything does fail, it will spit out a list.  Try
> them on their own.  If you don't have --oneshot set, make sure to
> oneshot those so your world file doesn't get full of unwanted entries. 
> 
> Someone else may have more info on that question.  I just think it will
> work and at least worth a try.  Save a lot of time for sure if it does
> work. 
> 
> Dale
> 
> :-)  :-) 


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Re: [gentoo-user] Changing CPU and motherboard

[Dale]

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Michael wrote:
> On Saturday, 28 June 2025 21:10:59 British Summer Time Dale wrote:
>
>> Me tho, I'd install the CPU and try booting.  I'd just stick to a
>> console, no GUI.  Run emerge -ae world and go take a nap, go to work or
>> whatever.  Make sure to include --resume tho.  If something fails, it
>> will keep trying.
> I think you meant to write:   '--keep-going y'
>
>
>> If anything does fail, it will spit out a list.  Try
>> them on their own.  If you don't have --oneshot set, make sure to
>> oneshot those so your world file doesn't get full of unwanted entries. 
>>
>> Someone else may have more info on that question.  I just think it will
>> work and at least worth a try.  Save a lot of time for sure if it does
>> work. 
>>
>> Dale
>>
>> :-)  :-) 


You may be right.  I have that set in make.conf, as are most settings I
always want used.  Sometimes I forget which one.  ;-) 

Dale

:-)  :-) 

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Re: [gentoo-user] Changing CPU and motherboard

[whiteman808]

How does situation look in binary-based distros like Debian, Arch? Is
rsyncing old Debian or Arch installation to PC with new processor or
motherboard and configuring hardware-specific stuff sufficient?

Re: [gentoo-user] Changing CPU and motherboard

[Dale]

whiteman808 wrote:
> How does situation look in binary-based distros like Debian, Arch? Is
> rsyncing old Debian or Arch installation to PC with new processor or
> motherboard and configuring hardware-specific stuff sufficient?
>
>


I haven't used those in ages.  Unless something has changed, they are
always ready for pretty much any hardware.  When you install those, they
are set to a common setting for pretty much any CPU in that arch. 
Basically and amd64 install should work with any amd64 CPU.  This is why
some run Gentoo.  In some cases having settings specific to a CPU can
result in code running faster. 

If you have a install of one of those, I'd think you could swap CPUs and
it not matter.  If you add a new network card, I think it sees it on
boot up, loads the module(s) that makes it work and then you just
configure it to use DHCP or whatever.  Heck, it may activate itself as
well. 

Again, it's been ages since I even booted one of those. 

Dale

:-)  :-) 

Re: [gentoo-user] Changing CPU and motherboard

[Frank Steinmetzger]

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Am Sat, Jun 28, 2025 at 07:39:03PM -0500 schrieb Dale:
> whiteman808 wrote:
> > How does situation look in binary-based distros like Debian, Arch? Is
> > rsyncing old Debian or Arch installation to PC with new processor or
> > motherboard and configuring hardware-specific stuff sufficient?
> >
> >
> 
> 
> I haven't used those in ages.  Unless something has changed, they are
> always ready for pretty much any hardware.  When you install those, they
> are set to a common setting for pretty much any CPU in that arch. 
> Basically and amd64 install should work with any amd64 CPU.  This is why
> some run Gentoo.  In some cases having settings specific to a CPU can
> result in code running faster. 

I just read about using a binary distro with a more modern baseline. One 
post said that a lot of software already has built-in support for that. So 
even if you use a well-hung distro like debian whose baseline is, say v2, 
then there is still userland software that detects the hardware and 
dynamically loads proper code paths, like blender, ffmpeg etc.

-- 
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Please do not share anything from, with or about me on any social network.

Rather to have a good position than a good job.

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Re: [gentoo-user] Changing CPU and motherboard

[Jay Faulkner]

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On 6/28/2025 4:04 PM, whiteman808 wrote:
> How does situation look in binary-based distros like Debian, Arch? Is
> rsyncing old Debian or Arch installation to PC with new processor or
> motherboard and configuring hardware-specific stuff sufficient?


These distributions target a generic architecture, like x86-64-v2 or 
x86-64-v3. Following my instructions earlier on getting a more generic 
CFLAGS setup and using binary packages will get you to the same place 
with Gentoo.

-JayF

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[gentoo-user] Re: Changing CPU and motherboard

[Grant Edwards]

On 2025-06-28, whiteman808 <whiteman808@paraboletancza.org> wrote:

> How does situation look in binary-based distros like Debian, Arch? Is
> rsyncing old Debian or Arch installation to PC with new processor or
> motherboard and configuring hardware-specific stuff sufficient?

I don't know what you mean by "resyncing".

If you just swap in new hardware for a distro like that, it's quite
possible that the initrd/ramdisk image used during early boot isn't
going to contain the right drivers for the new hardware — and the
system won't boot.

--
Grant

Re: [gentoo-user] Changing CPU and motherboard

[Frank Steinmetzger]

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Am Sat, Jun 28, 2025 at 10:33:24AM -0700 schrieb Jay Faulkner:
> On 6/28/2025 9:38 AM, whiteman808 wrote:
> > Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
> > not, what steps should be done on the existing Gentoo installation? Do I
> > need to do these operations from chroot?
> 
> I'm assuming this is amd64->amd64.
> 
> So the main thing to worry about is CPU compatibility, and your CFLAGS. If
> you're using -march=native, there's a chance your system won't work as
> compiled. This isn't always true, but these days it's no longer a guarantee
> that a newer CPU will have all the features of the old.
> 
> 
> What I usually do in this case is:
> 
> - set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch
> generic target works) --
> https://wiki.gentoo.org/wiki/Safe_CFLAGS#Generic_psABI_levels can help with
> this. - Ensure my system is fully updated, and `emerge --depclean`'d. -
> emerge -e @world # this will rebuild your entire system.


I see no point in rebuilding the system on the old machine with with a 
generic -march, just to migrate it to a new machine where you rebuild it 
again with -march=native. So if you do run march=native and it doesn’t just 
boot, I would build from scratch and migrate my settings. It’s more efficient.

-- 
Grüße | Greetings | Salut | Qapla’
Please do not share anything from, with or about me on any social network.

The Bible says to work for six days and rest on the seventh.
But where is it written that we shall start fresh on the eigth?

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Re: [gentoo-user] Changing CPU and motherboard

[Michael]

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On Sunday, 29 June 2025 03:19:59 British Summer Time Frank Steinmetzger wrote:
> Am Sat, Jun 28, 2025 at 10:33:24AM -0700 schrieb Jay Faulkner:
> > On 6/28/2025 9:38 AM, whiteman808 wrote:
> > > Is it necessary to reinstall Gentoo if I change CPU or motherboard? If
> > > not, what steps should be done on the existing Gentoo installation? Do I
> > > need to do these operations from chroot?
> > 
> > I'm assuming this is amd64->amd64.
> > 
> > So the main thing to worry about is CPU compatibility, and your CFLAGS. If
> > you're using -march=native, there's a chance your system won't work as
> > compiled. This isn't always true, but these days it's no longer a
> > guarantee
> > that a newer CPU will have all the features of the old.
> > 
> > 
> > What I usually do in this case is:
> > 
> > - set -march=x86-64-v3 (or whatever lowest-common-denominator CPU arch
> > generic target works) --
> > https://wiki.gentoo.org/wiki/Safe_CFLAGS#Generic_psABI_levels can help
> > with
> > this. - Ensure my system is fully updated, and `emerge --depclean`'d. -
> > emerge -e @world # this will rebuild your entire system.
> 
> I see no point in rebuilding the system on the old machine with with a
> generic -march, just to migrate it to a new machine where you rebuild it
> again with -march=native. So if you do run march=native and it doesn’t just
> boot, I would build from scratch and migrate my settings. It’s more
> efficient.

+1 ^^^

When moving a Gentoo system from one hardware platform to another your need to 
check and adjust if necessary:

1. The CPU architecture and compiler flags.
2. The CPU microcode.
3. The NICs drivers and firmware.
4. The graphics drivers and firmware.
5. The drivers for any change in MoBo bus(es), partition types and 
filesystems.
6. The drivers and firmware for any peripherals.

Unless I've missed anything, after you build the new kernel with the above in 
mind you should be able to boot with it.  You can rebuild @world on the PC 
which runs faster.

If you're using the Gentoo Distribution Kernel and Binhost packages, the 
migration could be much easier due to the generic choices of the precompiled 
software.

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[gentoo-user] Re: Changing CPU and motherboard

[Grant Edwards]

On 2025-06-29, Michael <confabulate@kintzios.com> wrote:

> When moving a Gentoo system from one hardware platform to another your need to 
> check and adjust if necessary:
>
> 1. The CPU architecture and compiler flags.
> 2. The CPU microcode.
> 3. The NICs drivers and firmware.
> 4. The graphics drivers and firmware.
> 5. The drivers for any change in MoBo bus(es), partition types and 
> filesystems.
> 6. The drivers and firmware for any peripherals.
>
> Unless I've missed anything, after you build the new kernel with the above in 
> mind you should be able to boot with it.

IFF all of the user-space binaries required for that were build with
CFLAGS settings that work with the new hardware.

> You can rebuild @world on the PC which runs faster.

[gentoo-user] Re: Changing CPU and motherboard

[Grant Edwards]

On 2025-06-29, Frank Steinmetzger <Warp_7@gmx.de> wrote:

> I see no point in rebuilding the system on the old machine with with a 
> generic -march, just to migrate it to a new machine where you rebuild it 
> again with -march=native. So if you do run march=native and it doesn’t just 
> boot, I would build from scratch and migrate my settings. It’s more efficient.

Yep, that's what I always do.  It will probably take less time/effort
that trying to rebuild the old system two or three times.

Re: [gentoo-user] Changing CPU and motherboard

[Steven Lembark]

On Sat, 28 Jun 2025 10:33:24 -0700
Jay Faulkner <jayf@gentoo.org> wrote:

> On 6/28/2025 9:38 AM, whiteman808 wrote:
> > Is it necessary to reinstall Gentoo if I change CPU or motherboard?
> > If not, what steps should be done on the existing Gentoo
> > installation? Do I need to do these operations from chroot?

You don't say if the kernel is compiled locally or if you use 
something like '-march=native' compiling everything. 

If you do then the simplest fix is (assuming you don't have it 
all glommed onto one partition) is just do a fresh install on 
a new /root + /var LV and mount the old stuff. The baseline 
stage3, mount your existing non-stage LV's, build a kernel,
then "emerge @world" isn't that much hands-on time.

If you are using a generic kernel with separate LV's then just
skip compiling a new kernel.

If you are using a single partition for all of it then consider
this an excellent time to use LV's for managing it going forward.

-- 
Steven Lembark
Workhorse Computing
lembark@wrkhors.com
+1 888 359 3508

Re: [gentoo-user] Changing CPU and motherboard

[Jay Faulkner]

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On 7/1/2025 9:22 AM, Steven Lembark wrote:
> On Sat, 28 Jun 2025 10:33:24 -0700
> Jay Faulkner<jayf@gentoo.org> wrote:
>
>> On 6/28/2025 9:38 AM, whiteman808 wrote:
>>> Is it necessary to reinstall Gentoo if I change CPU or motherboard?
>>> If not, what steps should be done on the existing Gentoo
>>> installation? Do I need to do these operations from chroot?
> You don't say if the kernel is compiled locally or if you use
> something like '-march=native' compiling everything.
>
> If you do then the simplest fix is (assuming you don't have it
> all glommed onto one partition) is just do a fresh install on
> a new /root + /var LV and mount the old stuff. The baseline
> stage3, mount your existing non-stage LV's, build a kernel,
> then "emerge @world" isn't that much hands-on time.

Honestly, I think this is overkill given you can:

1) emerge gentoo-kernel-bin (for a starting point kernel that will work 
on both devices) 2) update make.conf and emerge -e @world (or read docs 
and get some certainty you don't need to for your CPU upgrade) 3) hooray 
it works on both systems \o/

I always think that anytime with gentoo you do a reinstall instead of 
working through the process, you're giving up a chance to understand how 
stuff really works just a little bit better ... which is a lot of the 
point of running it for me personally :).

-JayF

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[gentoo-user] Re: Changing CPU and motherboard

[Grant Edwards]

On 2025-06-28, whiteman808 <whiteman808@paraboletancza.org> wrote:

> Is it necessary to reinstall Gentoo if I change CPU or motherboard?

Do you configure your kernels specifically to match the devices available on your motherboard?

If yes, then you'll probably have to at least re-compile your kernel.

If your CFLAGS was set up specifically for your old CPU, then you may have to recomile everything.

> If not, what steps should be done on the existing Gentoo
> installation? Do I need to do these operations from chroot?

It's not possible to say without more details.