Worried: An error occurred while mounting /

[joneall]

During boot, it says:

EXT4-fs: error (device sdb6):
ext4-remount: 4845
Abort forced by user
An error occurred while mounting /

When I rebooted, the system seemed ok, but rebooted itself again before the logon screen. (Is that normal in such a case?)

Not clear if this is related, but when it came up, Psensor only displayed one cpu. I restarted and after the next boot, Psensor found both CPUs. What gives here?

That makes two questions, but my main one is: What to do with this / error? It's not the first time I have seen this (tho the system runs well after another boot). There must be procedures to follow, but I do not know what they are.

E.g., can I use dd to copy the apparently defective partition sdb6 to another, then re-run update-grub? Will update-grub find the "new": partition? Or will dd just copy the error?

Where are the logs for this? /var/log/boot.log seems to only contain stuff for the last boot and nothing that early in the process.

I am running Trusty with kernel 3.15.0-031500rc5
.

[oshunluvr]

Backup your important files.

The auto reboot would be normal I think, if it didn't get far enough in the process to dump you to the console.

Unusual that a partition would fail individually. Usually a sign the disk is dying or some other problem is causing the issue. Point being, without more data about what's actually going on, it's probable that using a new partition won't make a difference. A file corruption wouldn't be a reoccurring problem unless some program has gone haywire.

I would:

Check the S.M.A.R.T. data on the drive.
Swap or change the cable (early and/or cheap sata cables are notoriously poor in quality).
Check RAM (reset sticks, then run a few memory tests)
Review boot and system logs (seems you did this?)

If nothing is logged, usually it's hardware. You can look at past logs to see if something is happening while you're running. As far as dd is concerned, it won't copy bad sectors but will copy corrupted data. In other words, if sdb6 sector X is bad, dd won't make sdb7 sector X bad. It will put bad data on it.

You might consider a new install to a new partition on the same disk to see if the error goes away.

[ronw]

Check /var/log/kern.log, /var/log/fsck, and consider booting from a CD/USB and running fsck.