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majoron
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PostPosted: Mon Nov 12, 2018 2:09 pm    Post subject: [solved] New kernel does not boot Reply with quote

Hi,
I have a new PC and I'm having troubles to find a proper kernel config: the kernel does not boot. But I don't know why. It only powers off the computer. There must be some options that prevent the kernel from even being loaded, but no idea of what can it be.

I have tried to run the kernel with kexec, but the kernel provided by the Gentoo installation CD does not allow me to run kexec :?

Any ideas?

BR
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Last edited by majoron on Wed Nov 14, 2018 11:56 am; edited 1 time in total
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NeddySeagoon
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PostPosted: Mon Nov 12, 2018 3:10 pm    Post subject: Reply with quote

majoron,

Please start with SystemRescueCD. Its Gentoo based.
Either on a CD or a USB stick.

Is this a computer you assembled yourself?
Has it ever done anything except power off ?
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Cuong Nguyen
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PostPosted: Mon Nov 12, 2018 4:10 pm    Post subject: Reply with quote

NeddySeagon,

Is it OK to build new kernel and initramfs with genkernel --all-ramdisk-modules --firmware to make sure vmlinuz will load any modules that not binary compiled into the kernel?
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NeddySeagoon
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PostPosted: Mon Nov 12, 2018 4:24 pm    Post subject: Reply with quote

Cuong Nguyen,

Yes.

You will get a big bloated initrd but that won't matter.

genkernel does not build every module in the kernel. It has its own .config file that it uses.
I don't know if it supports NVMe yet, so NVMe users should use the --menuconfig option to check.
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Cuong Nguyen
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PostPosted: Mon Nov 12, 2018 7:03 pm    Post subject: Reply with quote

NeddySeagoon wrote:
Cuong Nguyen,

Yes.

You will get a big bloated initrd but that won't matter.

genkernel does not build every module in the kernel. It has its own .config file that it uses.
I don't know if it supports NVMe yet, so NVMe users should use the --menuconfig option to check.


Thank you NeddySeagoon

I am still a bit confused to decide whether to put modules into the kernel or just as loadable? What is the rule of thumb here? Can you give some recommendations? I usually borrow kernel config from binary distro like Arch and follow Gentoo Wiki to set configs for special needs like aufs, lvm over luks. Arch Linux puts most of the modules as on disk loadable just like "make allmodconfig".

Is there any tool to debug kernel loading process? Sometimes I got booting stucks and don't know why, so I just opt to release compiler optimizations like march=native to march=x86-64, making lots for trial and error, getting lost along the path.
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NeddySeagoon
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PostPosted: Mon Nov 12, 2018 7:42 pm    Post subject: Reply with quote

Cuong Nguyen,

My rules of thumb are to build everything needed to boot, into the kernel.
That way, either no initrd is required, or if you need user space tools to a assemble raid and start LVM, like I do, the initrd does not contain any kernel modules.
That means that the initrd need not be rebuilt for kernel updates. Its just like firmware.

Next everything needed after boot should be a loadable module. This isn't hard and fast.
e.g. I could make amdgpu as a module but I like an early console, so I have amdgpu and its 20 firmware files built into the kernel.

Anything you always use can be built in too, even things you load with module parameters.
Module parameters can be passed on the kernel command line. Modules are much better than built in for parameter trial and error.

Lastly, things you won't need, turn off. Good use of the menu system in the kernel config tools will save a lot of time.
When you turn off a menu, the options on that menu assume sensible default values, usually off.
The example here is if you don't have a TV Tuner, turn the menu off. Don't read all the options and turn them off one by one.
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Cuong Nguyen
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PostPosted: Tue Nov 13, 2018 3:06 am    Post subject: Reply with quote

NeddySeagoon wrote:

My rules of thumb are to build everything needed to boot, into the kernel.
That way, either no initrd is required, or if you need user space tools to a assemble raid and start LVM, like I do, the initrd does not contain any kernel modules.
That means that the initrd need not be rebuilt for kernel updates. Its just like firmware.


Thank you, more than a year with Gentoo and I am still on the way to maximize its customization capability which helps me a lot in learning the OS. Being scared of not booting I turn on all modules as loadable and include all + firmwares in initrd Kernel is small but initramfs is quite big up to 200MB xz compressed.

Maybe I will start soon next round of gentoo experiment starting from "make tinyconfig" and topup necessary modules into kernel and initrd.
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NeddySeagoon
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PostPosted: Tue Nov 13, 2018 10:56 am    Post subject: Reply with quote

Cuong Nguyen,

See kernel seeds for the method and Pappy's preconfigs! for more up to date 'seed' .config files.
The first link is unmaintained but the method is still good.

Keep several kernels, everyone make one that won't boot sometime and its easier go use the grub menu to fix things than find your boot media and do the mounts and chroot.
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majoron
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PostPosted: Wed Nov 14, 2018 11:55 am    Post subject: Reply with quote

NeddySeagoon wrote:
majoron,

Please start with SystemRescueCD. Its Gentoo based.
Either on a CD or a USB stick.

Is this a computer you assembled yourself?
Has it ever done anything except power off ?


Hello,
sorry for the sloppy description.
I had follwed the Gentoo Handbook and compiled a kernel, so yes, the system can boot with a pendrive containing the minimal installation image.

When the system was required to boot without the pendrive, from the newly installed kernel, it only halted the system.

I solved it.
I had made a mistake in the "Built-in kernel command line" option (CONFIG_CMDLINE): I'm using UEFI and I need this, but I wrote a wrong PARTUUID there :oops:

Thank you anyway.
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