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If I have my root device is a LVM logical volume, how can I figure out the path via the Grub CLI without access to the original grub.conf file?

This is for use in the kernel command's root and rd_LVM_LV parameters. E.g.:

kernel /vmlinuz-2.6.34.8-68.fc13.i686.PAE ro root=/dev/mapper/vg_sever1-root rd_LVM_LV=vg_server1/root

Normally, you could tab in the CLI to get hints as far as file location, available HDs, etc.. However, I am not sure how to obtain the volume group's name or the root logical volume.

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If it is an option, boot from a decent Live CD like grml to find out details about the LVM configuration. Then adjust the Grub configuration on the fly or maybe fix it from within the Live CD. –  daff Jul 24 '11 at 23:13
    
Thanks daff. Was hoping to find a solution that did not involve a Live CD. However, it could very well be the only way. –  Belmin Fernandez Jul 24 '11 at 23:18

1 Answer 1

up vote 2 down vote accepted

grub has a cat command, so you can look at grub.conf from the prompt:

grub> root (hd0,0)
 Filesystem type is ext2fs, partition type 0x83

grub> cat /grub/grub.conf
#splashimage=(hd0,0)/grub/splashimage.xpm.gz
timeout 30
[...]

This may not help if the drive you're working on no longer has the grub.conf file, but even if it's not bootable the file is still accessible.

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I was hoping to find a solution when you no longer have access to the grub.conf file for whatever reason. Based on my research, seems that there is no way to figure out if partition is a PV for an LVM just from the grub shell. I was hoping someone could enlighten me :-) –  Belmin Fernandez Jul 25 '11 at 12:01
    
Well, if you try to run root (hdX,X) within grub, it should tell you the filesystem type, which will be different for LVM than it is for standard partitions, so you can detect an LVM physical volume that way. However, that doesn't help with any of the rest of the LVM layers. –  Handyman5 Jul 25 '11 at 13:08
    
Noticed that during the boot process, right before it attempts to mount the root volume, there's a printed list of the LVM LV's that were auto-detected. This might be sufficient information for a trial-and-error process. Not the preferable way to go about it but could be effective nonetheless. –  Belmin Fernandez Jul 25 '11 at 14:08

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