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paradigm-X
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PostPosted: Thu Sep 19, 2013 7:23 pm    Post subject: kernel upgrade and installation after Xen Reply with quote

Let me know, as it is not clear to me, whether this post belongs in another place because it seems to touch on more than one topic here. Basically, I want to upgrade, or at least rebuild, a Gentoo OS kernel on a PC. However, the situation is not exactly straightforward, and I do not have a great deal of experience doing so or working with Gentoo itself.

Recently, I had installed a minimal Gentoo OS by following the handbook online. Then I installed Xen once again by following the online instructions at Gentoo sites, wiki, etc. I eventually succeeded and it appears to be running fine now. In following the instructions, my system was left with two different kernels. The original kernel, which I can refer to here as kernel_1, still works just as it did before, except that the symbolic link from the plain "Linux" directory now points to the second kernel, i.e., kernel_2, which is incidentally a different version. The kernel_2 is now set to run as dom0, and it has the link from "Linux" directory pointing to it. Additionally, I have configured my boot-loader, Syslinux, to allow me to boot into either the original kernel, such that I am operating just as I was previously, or into the Xen environment, which uses the kernel_2.

What I would like to do at this point is continue using either system separately, but I also now want to upgrade the kernel_1 OS. Is there any reason I cannot change the link from where it was left pointing to kernel_2 and now point it back at kernel_1 while I then proceed to upgrade kernel_1? Would changing the link or upgrading the original kernel break the Xen system? The degree of separation between them is not perfectly clear to me at this point. These two systems do seem to share some components on this disk, but I did not find any clear guidance, nor do I understand adequately based on my limited experience with Gentoo and Xen, to what extent changes made to won would affect the other.
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NeddySeagoon
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PostPosted: Thu Sep 19, 2013 7:36 pm    Post subject: Reply with quote

paradigm-X,

Welcome to Gentoo

The /usr/src/linux symbolic link is used by external kernel modules to find the kernel to build against.
Its a name that never changes, used to point to a kernel directory that has a version number in it.

The modules from kernel_1 will go into /lib/modules/<kernel_1>, while those from kernel_2 will go into/lib/modules/<kernel_2> provided the versioning at the top of the kernel Makefile is different.
From the top of /usr/src/linux/Makefile
Code:
VERSION = 3
PATCHLEVEL = 10
SUBLEVEL = 10
EXTRAVERSION = -gentoo


Nothing else builds against the kernel. A stable set of kernel headers for everything else to use is provided by the kernel-headers package.

Look in /lib/modules/ and be sure you have a set of modules for both of your kernels and you are all set to update as your propose.
If you do not use any packages the provide kernel modules, you do not need the /usr/src/linux symlink at all.
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Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
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paradigm-X
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PostPosted: Fri Sep 20, 2013 9:43 pm    Post subject: Reply with quote

Thanks for the fast response, NeddySeagoon. I changed the link and rebuilt the kernel successfully. I appreciate your explanation too. There is a lot to learn with Gentoo, and I am amazed about how each step in any direction along the way leads to a new set of circumstances to consider. Every day is a new day. Fortunately, its complexity is made less burdensome by an abundance of excellent documentation, active community involvement and knowledgeable support resources. Take care.
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