dumpe2fs/tune2fs: Manipulating the ext fs auto-check parameters

File-system checks are a good and necessary thing.  So I don’t wish to debate their appropriateness.  I just want to show you how to avoid them by manipulating the counters stored in the superblock of your ext3 and ext4 file-systems.   There are many setttings stored in your file-system’s superblock.  The ones that I a’m concerned with today are:

  • Mount count – Number of times the file system has been mounted
  • Maximum mount count – When this value is reached force a file-system check at boot
  • Last checked – Date of the last file-system check
  • Check interval – How often should file-system checks be done
  • Next check after – Based on the current Check interval when will the next forced file-system check occur.

You can display these values using dumpe2fs.  I have an ext4 file-system on a device named /dev/md0.

$sudo dumpe2fs -h /dev/md0 | egrep -i 'mount count|check'
dumpe2fs 1.41.9 (22-Aug-2009)
Mount count:              7
Maximum mount count:      29
Last checked:             Sat May  8 17:58:12 2010
Check interval:           15552000 (6 months)
Next check after:         Thu Nov  4 17:58:12 2010

I have used dumpe2fs a few times to check whether or not I can expect a lengthy file-system check pending on my next reboot.

Lets set the “Last checked” date to now.  In other words lets make it appear as though we have already completed a successful file-system check.

$sudo tune2fs -T now /dev/md0

Lets verify the results.  The “Next check” has now been pushed out to April.

$ sudo dumpe2fs -h /dev/md0 | egrep -i 'check'
dumpe2fs 1.41.9 (22-Aug-2009)
Last checked:             Sun Oct 24 12:20:43 2010
Check interval:           15552000 (6 months)
Next check after:         Fri Apr 22 12:20:43 2011

Similarly if you want to set the “Mount count” to a particular value (such as 6)

$sudo tune2fs -C 6 /dev/md0

To change the time based check interval to 3 months (90 days), use the -i option.

$sudo tune2fs -i 90d /dev/md0

If you have used tune2fs in an interesting way, post a comment and let me know.