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/usr on separate partition and no initramfs, whats the risk?
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hefe
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PostPosted: Sun Feb 03, 2013 12:07 pm    Post subject: /usr on separate partition and no initramfs, whats the risk? Reply with quote

Hi,

i have a few questions about the requirement of an initramfs when /usr is on a separate partition. I dont have initramfs yet and there are no (aparent) problems.
1) Is there a way to avoid initramfs when /usr is on a separate partition?
2) Where can i find more information about the internals of the early boot phase, where initramfs comes into play?
3) I know initramfs as a way to provide modules that are needed to access the block device where the root partition is, but i have these built in. What else would i use it for?
4) I could just follow http://wiki.gentoo.org/wiki/Dracut but how can i know if initramfs works, because my system seems okay even without initramfs.

Every hint is welcome,
hefe
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frostschutz
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PostPosted: Sun Feb 03, 2013 3:17 pm    Post subject: Reply with quote

It just won't work or stop working when you get an update that expects /usr to be present.

Even with Initramfs, I just got rid of the / /usr separation. It's simply not worth the potential trouble.
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hefe
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PostPosted: Mon Feb 04, 2013 9:20 pm    Post subject: Reply with quote

Thank you for your info.

I found that genkernel is able to create an initrd image and will early-mount all filesystems given in /etc/initramfs.mounts.
However it seems that the init-script from initramfs is unable to cope with hexadecimal device numbers in the kernel commad line, see /usr/src/linux/Documentation/kernel-parameters.txt (root= entry). Because root=/dev/sda5 works but root=805 does not but is a valid way to provide the root device. This is a problem whe you use lilo, becaus lilo will translate your root=/dev/sdXY into the correct hex number.
Links i used:


cheers
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ulenrich
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PostPosted: Mon Feb 04, 2013 9:44 pm    Post subject: Reply with quote

Upstream dracut is the real thing to produce a viable initramfs. It is easy to configure and has a big crowd of developers for all that special cases. Keep away from genkernel hacks!

And it is not that hard to submit make command yourself. For the benefit you keep yourself clean of genkernel bugs!
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NeddySeagoon
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PostPosted: Mon Feb 04, 2013 10:14 pm    Post subject: Reply with quote

hefe,

Its not hard to roll your own initramfs. Then you can stay away from all the auto black magic.
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Etal
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PostPosted: Mon Feb 04, 2013 10:48 pm    Post subject: Reply with quote

You can also use busybox with sep-usr USE-flag if you don't have a very complicated setup.

See here: http://thread.gmane.org/gmane.linux.gentoo.devel/76653
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The Doctor
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PostPosted: Tue Feb 05, 2013 12:49 am    Post subject: Reply with quote

I keep an initramfs that mounts user handy in case anything breaks. So far, everything works. A failed boot just splashes a lot of failure messages at you. The solution is simple: log in, reboot, change boot option, reboot. losing /usr will cripple the system, not kill it.
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hefe
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PostPosted: Wed Feb 06, 2013 5:56 am    Post subject: Reply with quote

Thank you for your answers!

ulenrich, do you think genkernel will be dropped in future? I use genkernel only to create the ramdisk, because i tend to manually install the kernel.
The bug [1] i filed is still unconfirmed. I will take a closer look at Dracut.

Etal, separate /usr without initrd using busybox is quite neat, i will try that too.

hefe

[1] https://bugs.gentoo.org/show_bug.cgi?id=455518
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ulenrich
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PostPosted: Wed Feb 06, 2013 5:39 pm    Post subject: Reply with quote

On then contrary genkernel is worked on very hard recently. As some stated it is not hard to build your own initramfs - this is true for the most simple case. Dracut has a very fine infrastructure which will fit for all cases.

But Dracut was initiated by some Fedora guys. Redhat is hated by most Gentoo developers. I don't know why.
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Bitspyer
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PostPosted: Fri Feb 08, 2013 9:34 am    Post subject: Reply with quote

As you write in No. 3.) you have built in the needed Drivers, so you don't need initramfs.

I do this for many years.

Greetz

bitspyer
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hcaulfield57
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PostPosted: Fri Feb 15, 2013 6:38 am    Post subject: Reply with quote

I have separate /usr and no initramfs (with eudev), everything works properly without any additional configuration. The separate /usr is broken thing is basically a myth, although it does break some rare use cases.
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DaggyStyle
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PostPosted: Fri Feb 15, 2013 9:42 am    Post subject: Reply with quote

hcaulfield57 wrote:
I have separate /usr and no initramfs (with eudev), everything works properly without any additional configuration. The separate /usr is broken thing is basically a myth, although it does break some rare use cases.


same with latest udev.
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