What is /dev/root?

[Vincent Farrugia]

Hello,

Today we went to a customer and we noticed that the root file system (/) was mounted on /dev/root instead of /dev/vg00/lvol3. It exhibited weird things, like not being able to go to single user mode from neither init 1 nor hpux -is. When we rebooted, the root filesystem was mounted on /dev/vg00/lvol3 as normal and everything worked normally, including going to single user mode. What is /dev/root? This is just for clarification purposes cuz we are curious about this.

Thanks,
Vince

[James R. Ferguson]

Hi Vincent:

You can correct this without rebooting by doing:

# rm /etc/mnttab
# mount -a

If you want "/" mounted and not /dev/root, make sure that /etc/fstab specifies the mount to "/".

Regards!

...JRF...

[Anthony deRito]

Vincent, this sometimes happens...

Do this...

# mv /etc/mnttab /etc/mnttab.old
# mount ???a
# bdf

Tony

[Vincent Farrugia]

Hello, thanks for the answers so far.

My quesition is: why does it happen in the first time? Why was it mounted on /dev/root instead of /dev/vg00/lvol3?

[Steven Gillard_2 · Accepted solution]

Its been my experience that /dev/root appears in /etc/mnttab after a bootup in maintenance mode (hpux -lm), even following a reboot. It is used as a psuedo pointer to the root file system that will be accessible even if there is a problem with LVM, eg lvol3 cant be mounted due to corruption in the LVM headers.

As others suggest, it can be fixed by removing the mnttab file and running the mount -a.

Regards,
Steve

[Bill Hassell]

/dev/root is used when the kernel cannot find the 'real' device file--it is an emergency bandaid to get the system booted, so something is still not right with your system. Start with commands like:

# lvlnboot -v
# vgdisplay -v vg00

Mistakes in mirroring management or removal and/or replacement of disks can cause this problem.

[James R. Ferguson]

Hi (again) Vincent:

The Knowledge Base indicates that the appearance of /dev/root in /etc/mnttab is triggered by going into LVM maintenance mode and then rebooting. It is noted that "This problem is very well known to the support folks, and to any customer who enters LVM maintenance mode.".

Regards!

...JRF...

[Bernie Vande Griend]

/dev/root is used for root's device when there is an issue with LVM. It will almost always be used after you have booted to maintenance mode. It can also happen during set up mirroring of the boot drive if things are done in the correct manner or if the lvlnboot is messed up.

[Vincent Farrugia]

Hello,

Thanks guys for your help. We are not sure whether the guys at the company entered in maintenance mode. We did an lvlnboot -v at one time and maybe that's what solved the "problem".

Thanks again.