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.
