Booting a custom kernel with a new root filesystem

LinuxNewman · 04-15-2009, 03:44 AM

Hi everybody !
I am using OpenSuSE 11.0 . I have built a custom kernel(2.6.25.5-1.1) and I have to boot it with a new root file system.I have created a separate partition (in this case /dev/sda4) and made ext2 filesystem and mounted it on a mount point(/mnt/point1 in this case). I also have populated the new file system with necessary directories like /dev,/bin,/proc etc...

But the major problem is how to boot the custom kernel with newly created file system as root? (i.e. When the kernel boots, "/" should not be root,instead, the root should be located in /mnt/point1/(new root???))

eco · 04-15-2009, 04:06 AM

I can't imagine that would work!

What are you trying to do?

If you want to test a new kernel, you can do that without losing the previous version. Have a look at your grub/lilo man page depending on your boot loader.

If you are trying to test a new environment, you could simply chroot into it.

Code:

# chroot /bin/bash /mnt/point1

We need more info to be able to help you.

colucix · 04-15-2009, 04:10 AM

You can try to add root= to the kernel options in /boot/grub/menu.lst. Opensuse uses the device name as listed in /dev/disk/by-id. You have to identify which id belongs to the new partition and use that in the kernel boot line. Also add the proper line in /etc/fstab to automatically mount the partition at boot.

An example from my system:

Code:

# In /etc/fstab:
/dev/disk/by-id/ata-FUJITSU_MHV2160BT_NU06T6527J10-part8 /                    ext3       acl,user_xattr        1 1

# In /boot/grub/menu.lst:
title openSUSE 11.1 - 2.6.27.21-0.1
    root (hd0,6)
    kernel /vmlinuz-2.6.27.21-0.1-pae root=/dev/disk/by-id/ata-FUJITSU_MHV2160BT_NU06T6527J10-part8 resume=/dev/disk/by-id/ata-FUJITSU_MHV2160BT_NU06T6527J10-part6 splash=silent showopts vga=0x317
    initrd /initrd-2.6.27.21-0.1-pae

Hope this helps!

LinuxNewman · 04-15-2009, 04:46 AM

Quote:

Originally Posted by eco

I can't imagine that would work!

What are you trying to do?

If you want to test a new kernel, you can do that without losing the previous version. Have a look at your grub/lilo man page depending on your boot loader.

If you are trying to test a new environment, you could simply chroot into it.

Code:

# chroot /bin/bash /mnt/point1

We need more info to be able to help you.

Hi ! I have already tested the new kernel and it is working fine. All I need is to boot this kernel with new root file system.
Can I just change the boot flag by using fdisk on /dev/sda4? Or are there some other steps involved?

LinuxNewman · 04-15-2009, 04:56 AM

Quote:

Originally Posted by colucix

You can try to add root= to the kernel options in /boot/grub/menu.lst. Opensuse uses the device name as listed in /dev/disk/by-id. You have to identify which id belongs to the new partition and use that in the kernel boot line. Also add the proper line in /etc/fstab to automatically mount the partition at boot.

An example from my system:

Code:

# In /etc/fstab:
/dev/disk/by-id/ata-FUJITSU_MHV2160BT_NU06T6527J10-part8 /                    ext3       acl,user_xattr        1 1

# In /boot/grub/menu.lst:
title openSUSE 11.1 - 2.6.27.21-0.1
    root (hd0,6)
    kernel /vmlinuz-2.6.27.21-0.1-pae root=/dev/disk/by-id/ata-FUJITSU_MHV2160BT_NU06T6527J10-part8 resume=/dev/disk/by-id/ata-FUJITSU_MHV2160BT_NU06T6527J10-part6 splash=silent showopts vga=0x317
    initrd /initrd-2.6.27.21-0.1-pae

Hope this helps!

Hi ! As suggested by you,I gave root= the device id(too long to write here). I had already modified fstab to mount the new partition. When I rebooted, all I got was a blank screen.No error,no warning,no display...simply nothing.

I had not mentioned anything about initrd because I don't have any initrd image associated with my new kernel.Is there need of initrd image? It should be noted that I booted successfully this new kernel earlier simply by mentioning root (hd0,1) and kernel=/boot/bzImage in grub.

i92guboj · 04-15-2009, 06:30 AM

Quote:

Originally Posted by LinuxNewman

Hi ! I have already tested the new kernel and it is working fine. All I need is to boot this kernel with new root file system.
Can I just change the boot flag by using fdisk on /dev/sda4? Or are there some other steps involved?

The kernel will use as its root whatever you tell it with the root= boot parameter, as has already been said. You usually set these in your bootloader config.

Another different question is whether that fs you created has all the necessary means to boot. Without a proper init system all you are going to get is a nice kernel panic "no init found, try passing init=... to kernel".

PS. Our posts crossed, I was a bit late

i92guboj · 04-15-2009, 06:34 AM

Quote:

Originally Posted by LinuxNewman

Hi ! As suggested by you,I gave root= the device id(too long to write here). I had already modified fstab to mount the new partition. When I rebooted, all I got was a blank screen.No error,no warning,no display...simply nothing.

Fstab? what fstab??' the fstab of your old system? I hope not, since you are not going to be using that file system with your new kernel.

Quote:

I had not mentioned anything about initrd because I don't have any initrd image associated with my new kernel.Is there need of initrd image? It should be noted that I booted successfully this new kernel earlier simply by mentioning root (hd0,1) and kernel=/boot/bzImage in grub.

You don't need an initrd as long as all the modules you need to boot are compiled statically inside your kernel. You will need at least the hd controller driver and the fs driver for whatever fs you used to format your root partition.

If you are really going to do anything serious with this I suggest you to pick either Gentoo or LFS and learn how to install a linux os from scratch. You seem to be lacking the essential knowledge that you will need to do so successfully.

LinuxNewman · 04-16-2009, 12:00 AM

I mentioned root=(the device id of new partition) in grub. then while booting it showed error 15 file not found.

i92guboj · 04-16-2009, 03:02 AM

According to the grub info page:

Code:

15 : File not found
     This error is returned if the specified file name cannot be found,
     but everything else (like the disk/partition info) is OK.

So, check again that the kernel file name is correct and exists inside the partition where /boot resides.

MrUmunhum · 04-18-2009, 02:25 PM

Quote:

Originally Posted by LinuxNewman

Hi everybody !
I am using OpenSuSE 11.0 . I have built a custom kernel(2.6.25.5-1.1) and I have to boot it with a new root file system.I have created a separate partition (in this case /dev/sda4) and made ext2 filesystem and mounted it on a mount point(/mnt/point1 in this case). I also have populated the new file system with necessary directories like /dev,/bin,/proc etc...

But the major problem is how to boot the custom kernel with newly created file system as root? (i.e. When the kernel boots, "/" should not be root,instead, the root should be located in /mnt/point1/(new root???))

I would suggest using the 'root=LABEL=' kernel parm. you will need to change three things:

on the new file system, e2label /dev/xxx New
in grub.conf on the kernel line root=LABEL=New
in /etc/fstab on the new file system, LABEL=New / default blah

In this example I used 'New', you can use whatever you wish, check the e2label man page for limitations.

LinuxNewman · 04-19-2009, 10:53 PM

o.k friends I will try all this and report back here the result.Thanks :-)