Fallback kernel

dejavu · 2011-05-05 11:12:15

Hey,

I just want to know if anyone of you uses sometimes or needs the fallback kernel image?!
If I really need to repair my system then I repair it with a live CD or usb stick...

It would be nice if we could disable generating this in the /etc/mkinitcpio.conf file.

What do you think?

jeslinmx · 2011-05-05 11:27:55

It's probably compiled a little differently and acts as a spare for when you are compiling your own kernel. If you are not trying stuff like that it's probably okay to disable it. Don't expect it as default though; it's not a smart default for Arch users.

falconindy · 2011-05-05 12:31:34

If you want to disable it, you'll need to alter the preset file that comes packed with the kernel26 package (/etc/mkinitcpio.d/kernel26.preset). Of course, altering that file means installing the package first, which means generating both images... I don't see what harm it causes -- 5mb on your /boot partition for something that might save you from having to chroot seems like a win to me.

@jeslinmx: I think you're misunderstanding what the fallback image is... its not a kernel at all.

karol · 2011-05-05 12:47:59

falconindy wrote:

@jeslinmx: I think you're misunderstanding what the fallback image is... its not a kernel at all.

[OT]
This name leads to many misunderstandings, can we call it another way or is it customary to say 'kernel image'?
[/OT]

Another Archer wanted to boot faster, so he wished to disable the fallback image. It's your system, do what you want.

jeslinmx · 2011-05-05 13:26:08

It's a compressed ramdisk thing to bootstrap the system enough to go into kernel spaceish right?

pointone · 2011-05-05 13:27:32

Compared to the default, the fallback initramfs image contains additional modules/drivers because the autodetect hook is not run during its creation. This means it is a generic image -- it can be used to boot your system after hardware changes, or if you transfer your hard drive to another computer. In contrast, the default image is tailored to your specific machine at the time of creation.

See the mkinitcpio ArchWiki page for more information.

falconindy · 2011-05-05 13:28:44

To be precise, it's a (compressed) cpio archive, the contents of which become your initramfs. It's only tied to a specific kernel if modules are involved, and it's extremely unfortunate that the word 'kernel' ended up in the name. Other than any "shock" factor involved, it wouldn't be hard to change the name of this file given that its completely controllable within the kernel26 package.

karol · 2011-05-05 13:41:20

falconindy wrote:

To be precise, it's a (compressed) cpio archive, the contents of which become your initramfs. It's only tied to a specific kernel if modules are involved, and it's extremely unfortunate that the word 'kernel' ended up in the name. Other than any "shock" factor involved, it wouldn't be hard to change the name of this file given that its completely controllable within the kernel26 package.

linux-api-headers package underwent a similar namechnage:
https://bbs.archlinux.org/viewtopic.php … 90#p697190
https://bbs.archlinux.org/viewtopic.php … 34#p697434

I will file a feature request in the weekend. Unless somebody beats me to it ;P

Last edited by karol (2011-05-05 13:44:54)

falconindy · 2011-05-05 13:44:47

Truth, although changing the name of the boot image would require user intervention to change their bootloaders... perhaps not zero impact, but I think it's a worthy change. I might be doing something about that myself...

PReP · 2011-05-07 20:58:08

I most often just comment it out in grubs menu.lst, though i might be sorry about that someday.
But then i guess i could try to remeber the grub-lines that booted into it.

Leraning about it's intended use as a fallback if hardware changes, might make it a neat thing to just comment it back before a swtich then

Ramses de Norre · 2011-05-07 21:39:07

It's saved me already when for some reason my normal image would not boot. There are no guarantees but I've been in the situation before where my normal image wouldn't boot but I could continue working with the fallback image until I found the time to fix the problem. You're really glad the fallback image exists then

ljshap · 2011-05-08 02:36:46

Ramses de Norre wrote:

It's saved me already when for some reason my normal image would not boot. There are no guarantees but I've been in the situation before where my normal image wouldn't boot but I could continue working with the fallback image until I found the time to fix the problem. You're really glad the fallback image exists then

I had the same problem after installing Ubuntu as a second linux partion on my netbook. After installing Ubuntu (which installed grub2 without "asking") I was not able to boot into Arch using the regular image file. Fortunately, the fallback image did boot into Arch after which I able to reinstall grub to point to my Arch boot partitiion. I still could not boot into Arch with the regular image file until I ran mkinitcpio to create a new image file.

You may not need the fallback image that often (if ever), but it does come in handy when you need it. Considering how much wasted storage bloat we have these days, not having a fallback image is not a prudent way to save a few bytes.

dejavu · 2011-05-09 08:27:59

Thanks for your answer...
I just thought of it, because lastly I have played a lot with the hooks and have every time seen the fallback stuff "compiling / generating". ;-)

Fortunately this thread became the placeholder for a different discussion and so it wasn't senseless. ;-)

So I will simply leave the fallback thing as it is.

Best Regards

karol · 2011-05-09 20:41:39

Just FYI there already is a bug report [kernel26] "kernel26.img" is a silly name for an initramfs image. It's still open but not much going on.

Note to self: always search first

skodabenz · 2011-05-10 07:16:36

I would suggest something like initramfs26 and initramfs26-fallback (or initramfs26-mainline-fallback for kernel26-mainline for example). But how will this work out in case http://bugs.archlinux.org/task/16702 (Versioned kernel installs) is accepted.

PS: Posted the same in the bug report karol linked above.

karol · 2011-05-10 14:09:03

skodabenz wrote:

I would suggest something like initramfs26 and initramfs26-fallback (or initramfs26-mainline-fallback for kernel26-mainline for example). But how will this work out in case http://bugs.archlinux.org/task/16702 (Versioned kernel installs) is accepted.

The versioned kernel task doesn't get much attention so I wouldn't hold my breath ...

brando56894 · 2011-05-10 20:30:46

I've been using arch for about 2 years, and linux in general for about 7 years. I've never had to use the fallback image, if something screws up I always go straight to a live cd since most of the time its not a module problem.

Arch Linux

#1 2011-05-05 11:12:15

Fallback kernel

#2 2011-05-05 11:27:55

Re: Fallback kernel

#3 2011-05-05 12:31:34

Re: Fallback kernel

#4 2011-05-05 12:47:59

Re: Fallback kernel

#5 2011-05-05 13:26:08

Re: Fallback kernel

#6 2011-05-05 13:27:32

Re: Fallback kernel

#7 2011-05-05 13:28:44

Re: Fallback kernel

#8 2011-05-05 13:41:20

Re: Fallback kernel

#9 2011-05-05 13:44:47

Re: Fallback kernel

#10 2011-05-07 20:58:08

Re: Fallback kernel

#11 2011-05-07 21:39:07

Re: Fallback kernel

#12 2011-05-08 02:36:46

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#13 2011-05-09 08:27:59

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#14 2011-05-09 20:41:39

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#15 2011-05-10 07:16:36

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#16 2011-05-10 14:09:03

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#17 2011-05-10 20:30:46

Re: Fallback kernel

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