udev and UUID

ebal · 2013-10-04 10:34:28

I want to speed up my boot time,
so i've searched our glorious wiki and read these:

1. https://wiki.archlinux.org/index.php/Tw … _boot_time
2. http://blog.falconindy.com/articles/opt … tcpio.html

and make it possible!

I use a LVM2 under LUKS aka lvms2 on luks - but i cant use UUID or any /dev/volume_group/lvm_partiton cause

/dev/disk/by-uuid/xxxx (or any other mapper device)

are being created by rules (/usr/lib/udev/rules.d) of udev.

So ... is it possible to boot up somehow with UUID ?

Thank you in advanced.

bjornoslav · 2013-10-04 13:04:22

Of course. Depending on your boot loader, you may add/replace the root=/dev/sdX option with root=UUID=....

jasonwryan · 2013-10-04 18:02:44

Support thread, moving to Kernel & Hardware...

ebal · 2013-10-04 19:00:23

@bjornoslav this is actually inaccurate !

Of course you can define your root= or your encrypted device via UUID, but how can your kernel (after UEFI/grub2) can find these ??????

As i said, only udev can run rules (via the hook udev) to run shell scripts and create the /dev/disk/* devices.
So with no udev - you have no /dev/disk/by-uuid/xxxx partition.

@jasonwryan sorry for the wrong topic posting

falconindy · 2013-10-04 22:13:19

ebal wrote:

Of course you can define your root= or your encrypted device via UUID, but how can your kernel (after UEFI/grub2) can find these ??????

..And this is why initramfs exists. mkinitcpio understands these tags with or without udev. The difference is that when udev is running, something like UUID=037b9d94-148e-4ee4-8d38-67bfe15bb535 is translated to /dev/disk/by-uuid/037b9d94-148e-4ee4-8d38-67bfe15bb535 in order to be able to wait on it to appear. Without udev, you simply query a tool linked to libblkid (e.g. lsblk or blkid) to probe available block devices.

ebal · 2013-10-05 07:57:37

@falconidny that's what i did to tested it and boot with UUID, Yes lsblk and blkid are working just fine.

So the bottom line: i have to write a custom hook that does exactly that (translate UUID=xxxx to something like /dev/dm-0)
or i can do it another way ?

falconindy · 2013-10-05 16:01:27

ebal wrote:

@falconidny that's what i did to tested it and boot with UUID, Yes lsblk and blkid are working just fine.
So the bottom line: i have to write a custom hook that does exactly that (translate UUID=xxxx to something like /dev/dm-0)
or i can do it another way ?

I have no idea what it is you're doing that you think isn't already supported. Hooks which need to resolve tag names to device nodes use resolve_device.

ebal · 2013-10-06 09:16:27

@falconindy

hmm thanks for the tip - i'll try that and report back my findings

Arch Linux

#1 2013-10-04 10:34:28

udev and UUID

#2 2013-10-04 13:04:22

Re: udev and UUID

#3 2013-10-04 18:02:44

Re: udev and UUID

#4 2013-10-04 19:00:23

Re: udev and UUID

#5 2013-10-04 22:13:19

Re: udev and UUID

#6 2013-10-05 07:57:37

Re: udev and UUID

#7 2013-10-05 16:01:27

Re: udev and UUID

#8 2013-10-06 09:16:27

Re: udev and UUID

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