Oops...I broke fstab on Centos 5.3

jedispy · 11-11-2009, 12:35 PM

I was dabbling with some CIS 6.1.1 guidelines and I misread the part about adding "nodev" to the "/dev/VolGroup00/LogVol00 / ext3 defaults 1 1" line. I accidentally entered it as

Code:

nodev,/dev/VolGroup00/LogVol00 / ext3 defaults 1 1

After a reboot my system won't mount. It trips during bootup at the line that reads

Code:

fsck.ext3: No such file of directory while trying to open nodev,/dev/VolGroup00/LogVol00
nodev,/dev/VolGroup00/LogVol00:
The superblock could not be read or does not describe a correct ext2 filesystem.  
If the device is valid and it really contains an ext2 filesystem (and no swap or
ufs or something else), then the superblock is corrupt, and you might try running
e2fsck with an alternate superblock:
   e2fsck -b 8193 <device>

Here's what I've tried

When this error comes up it dumps me out to emergency mode, which is of course read-only. I can't really do anything useful here from what I can tell. I certainly can't edit fstab, which is the source of the error
I tried going into rescue mode with my centos installation media, but the rescue operation can't properly mount the volume (I assume since fstab is borkificated).
Single user mode fails for the same reason a straight boot up fails.
Interrupting GRUB loader by entering cmd prompt and manually running "mount -t ext3 /dev/VolGroup00/LogVol00".

So far none of these have worked at all. Is there any way for me to edit fstab and allow for a successful mount of /dev?

Thankfully this is just a test machine, and not used in production at all.

acid_kewpie · 11-11-2009, 12:40 PM

use a rescue cd, and just don't search for existing systems, then mount / yourself manually and edit away.

jedispy · 11-11-2009, 01:02 PM

Alas, my problem. I just gave your recommendation a shot. When I go into rescue mode and skip the autodiscover, I run the cmd "mount -t ext3 /". I get the error

Code:

mount: Cannot read /etc/fstab: No such file or directory

I really did a number on this one. Ha ha.

Someone else mentioned using a liveCD. I haven't used liveCD much, so a little clarification is needed. How could I edit the /etc/fstab on my filesystem via liveCD? Won't it only show the relative fstab for the liveCD mount?

anomie · 11-11-2009, 01:12 PM

From within the live cd environment, mount your host's / filesystem somewhere (e.g. /mnt/foo). Then edit /mnt/foo/etc/fstab as needed.

jedispy · 11-11-2009, 02:51 PM

When I attempt that i get

Code:

mount: /dev/VolGroup00/LogVol00 already mounted or /mnt busy

Strangely I can't seem to use "unmount" here. Is there an alternative to unmount in Centos?

syg00 · 11-11-2009, 05:31 PM

The command is "umount" - odd but true. But if you are using a Redhat derivative like Centos that probably won't work as that will be a filesystem for the CD itself. Use another liveCD that has LVM support - Knoppix used to.

prik420 · 11-12-2009, 12:30 AM

Here's what I've tried

When this error comes up it dumps me out to emergency mode, which is of course read-only. I can't really do anything useful here from what I can tell. I certainly can't edit fstab, which is the source of the error
I tried going into rescue mode with my centos installation media, but the rescue operation can't properly mount the volume (I assume since fstab is borkificated).
Single user mode fails for the same reason a straight boot up fails.
Interrupting GRUB loader by entering cmd prompt and manually running "mount -t ext3 /dev/VolGroup00/LogVol00".

So far none of these have worked at all. Is there any way for me to edit fstab and allow for a successful mount of /dev?

[/QUOTE]

In rescue mode, the LVM system isn't activated by default. Run these commands at the command prompt upon booting to rescue mode:

#lvm vgscan
#lvm vgchange -ay

To display your lvm partitions, run:

#lvm lvs

By then, you should be able to mount the / LVM partition.

I hope this helps. cheers!