Custom initramfs: misc. questions

[sunox]

I think I understand what file, dir, and nod do. 'dir' creates a directory. 'file' copies from the source to a destination, where the destinations path is relative to the root of the initramfs source. 'nod' creates a device node. I'm a bit fuzze on nodes but I think that's good enough for now.

However, I don't really understand what is happening below:

[sunox]

And Mr @pietinger, these come from the example you shared earlier:

file /lib64/libkeyutils.so.1.10 /lib64/libkeykeyutils.so.1.10 755 0 0
slink /lib64/libkeyutils.so.1 /lib64/libkeyutils.so.1.10 777 0 0
file /usr/lib64/libimaevm.so.3.0.0 /usr/libimaevm.so.3.0.0 755 0
slink /usr/lib64/libimaevm.so.3 /usr/libimaevm.so.3.0.0 777 0

These symlinks just look like shortcuts that maybe follow a naming scheme that the initramfs prefers?

I wish I didn't have to pester with so many questions but the documentation on this really seems scarce.

[sunox]

I think I got it to work using the file list, though it was suspiciously trouble-free.

Here is the file list I used, borrowing heavily from pietinger and NeddySeagoon, just in case someone in the same situation stumbles on this thread:

[bad file deleted]

I learned a lot today. Thanks again lads.

[NeddySeagoon]

sunox,

busybox and lvm2 sun whatever command they are called as.

You can write

[pietinger]

[sunox]

[sunox]

[sunox]

For anyone out there who does LUKS encryption I am wondering what kernel parameters should be passed when using a custom initramfs. My understanding is that certain parameters are expected when genkernel generates initramfs, and others for when dracut does it, but I haven't found anything about what is expected when initramfs is custom

I left my parameters the same after switching to custom, and I wondered if it needed anything at all, but when I try to boot with efi stub it doesn't work.

When looking online for examples of working efi stub configs most of the examples seem to use what I believe is a dracut like scheme (e.g. 'rd.luks.name=....).

[Screenager]

Kernel parameters are nothing more than arguments(variables) passed to your init script in this context, you can use whatever you want if you write your own. There seems to be best practices here hence the rd.* naming scheme, but I couldn't find any hard definition for them either. kernel.org lists a bunch of kernel parameters that actually do have a function in the kernel here: https://docs.kernel.org/admin-guide/kernel-parameters.html

[NeddySeagoon]

sunox,

Kernel command line parameters come in two sorts.
Those that are understood by the kernel (and will be used bf the kernel) and everything else. The entire kernel command can be read from /proc/cmdline.
Parsing it is left as an exercise for the reader.

Dracut and genkernel do their own things. So can you.

Picking parameter names that the kernel will use, without being aware of it, is a very bad thing.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[sunox]

Ok, I suspected things went all-too-smoothly with the external file list and indeed it was. All of a sudden grub started to load the initramfs image at abcxyz.old - I think this coincided with me switching to trying to build the initramfs into the kernel - so as soon as I switched to the file list it stopped using my custom initramfs.

I saw today that you can pass the list itself to the kernel and it will build the cpio for you, which I did, and it threw a bunch of errors related to the "file" lines. It turns out I forgot to give the latter 3 arguments for each "file" line. I added them and things went well after that. Sharing my file list again just in case anyone else stumbles on this:

[sunox]

Thanks for the information about kernel parameters: yet more new stuff learned.

It turns out that I don't have to pass any parameters at all when booting using the EFI stub method. I guess this makes sense as I hardcode info related to my partitions etc. right in the init file. I will take a look at the available parameters though to see if anything might be helpful. I might have to tell it to enable TRIM for my SSD for example.

[pietinger]

sunox,

as you have asked for kernel command line parameters:

One parameter is ALWAYS necessary: Where/which is my ROOT partition ?

Now you have two choices WHO needs this information: Kernel OR initramfs ?
(see more here: https://wiki.gentoo.org/wiki/User:Pietinger/Tutorials/Confusion_with_root%3DPARTUUID%3D_and_root%3DUUID%3D )
(yes, there is a rarely used 3. method IF you are using a self made initramfs: You can hardcode the info about root partition INTO the "init" of your initramfs)

You have two choices where you STORE this parameter - depending how you boot:
1. Booting with grub: a) in Kernel: CONFIG_CMDLINE= OR b) grub-mkconfig will find out and do all itself
2. Booting a stub kernel with UEFI: a) in Kernel: CONFIG_CMDLINE= OR b) as additional option when creating the UEFI entry
(see more here: https://wiki.gentoo.org/wiki/User:Pietinger/Tutorials/Kernel_Commandline_Parameter
and here:
https://wiki.gentoo.org/wiki/User:Pietinger/Tutorials/Boot_kernel_via_UEFI )


There is a second famous parameter: initrd=

This parameter tells the efistub where to load an external CPIO - and it is a very special parameter:
1. You will need it ONLY if you are using an external CPIO as initramfs ! (== not necessary if you have an embedded initrams AND not necessary if you have no initramfs)
2. This is one parameter you CANNOT build into the kernel (CONFIG_CMDLINE=) (because it is too late) (*) - it MUST come from a bootmanager (e.g. grub) OR directly from UEFI
(see more: https://forums.gentoo.org/viewtopic-p-8805827.html#8805827 )

*) Look into your dmesg. You will find TWO lines with kernel command line parameter: the first line is what kernel has got from UEFI OR bootmanager. The second line is the complete kernel command line parameter.

I am booting my kernel with UEFI ... and ... I have configured my root= INTO the kernel ... AND there is no parameter coming from UEFI ... and therefore my dmesg looks so:

[pietinger]

[pietinger]

[pietinger]

P.S.: To say it clear:

Yes, it is possible to boot a kernel directly from UEFI (or from grub) without using ANY kernel command line parameter IF:

You are using an embedded initramfs where you have hardcoded the information about the root partition INTO the "init" of your (embedded) initramfs.
_________________
https://wiki.gentoo.org/wiki/User:Pietinger

[sunox]

All very helpful, thank you. When working at this level it gets harder and harder to find answers for whatever questions you have, I suppose because there are so few people who are interested in this sort of thing. It's definitely nice to have this forum to ask quetions. I would feel more guilty about asking so many questions if it wasn't for the fact that anyone else who has the same issue can maybe now find answers. It's remarkable how often the Gentoo wiki and posts from this forum come up, and for this alone it seems like Gentoo contributors like you guys play a really important role imo. Anyway cheers.

[pietinger]

sunox,

You are very Welcome !

... and I agree with everything you said ... but there is never a reason to feel guilty ... or ... as our forums legend always says:

[GDH-gentoo]