Vaughan Harper's blog MythTV “Gave up waiting for root device” error on Ubuntu 14.04 system
“Gave up waiting for root device” error on Ubuntu 14.04 system

MythTV

“Gave up waiting for root device” error on Ubuntu 14.04 system

My Mythbuntu system recently failed to boot up, and instead displayed this error message:

Gave up waiting for root device. Common problems:
   Boot args (cat /proc/cmdline)
   - Check rootdelay= (did the system wait long enough?)
   - Check root= (did the system wait for right device?)
   Missing modules (cat /proc/modules; ls /dev)
ALERT! /dev/mapper/vgmain-lvroot does not exist.  Dropping to a shell!

BusyBox v1.21.1 (Ubuntu 1:1.21.0-1ubuntu1) built-in shell (ash)
Enter 'help' for a list of built-in commands.

So the problem was that it couldn’t find /dev/mapper/vgmain-lvroot. But why?

Most of the online solutions for similar errors talked about running running fdisk and checking the partition table, etc, so I booted off a Ubuntu Live CD and poked around, but everything seemed fine. So I then rebooted and let it boot into BusyBox and did some experimenting. I found that when I ran ‘blkid’ initially it just listed sda1, sda2 and vgmain-lvsnap-cow – no reference to /dev/mapper/vgmain-lvroot so it wouldn’t boot. But if I waited about five minutes and ran ‘blkid’ again, it then listed the other logical volumes including vgmain-lvroot. After that I could ‘exit’ and boot into Ubuntu/MythTV OK.

Why was it taking so long for vgmain-lvroot to come on line? I had had a LVM snapshot running on vgmain-lvroot, so I tried running ‘lvremove’ to stop the snapshot – and after that it booted up OK. So presumably there was some problem related to LVM and/or the snapshots.

Vaughan

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Written by Vaughan

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