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?
