I'm running the lastest Ubuntu 12.04 AMI (ami-a29943cb) from Canonical on Amazon EC2 and quite often when I log in I get the message:

*** /dev/xvda1 will be checked for errors at next reboot ***

I have read a bunch of documentation on this and seem to understand that every so many reboots (around 37 see Mount count / Maximum mount count below) Ubuntu wants to check a disk for errors. I can see that by using dumpe2fs -h /dev/xvda1 (reference) to get information such as:

Last mounted on:          /
Filesystem UUID:          1ad27d06-4ecf-493d-bb19-4710c3caf924
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
Filesystem flags:         signed_directory_hash 
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              524288
Block count:              2097152
Reserved block count:     104857
Free blocks:              1778055
Free inodes:              482659
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      511
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512
Flex block group size:    16
Filesystem created:       Tue Apr 24 03:07:48 2012
Last mount time:          Thu Nov  8 03:17:58 2012
Last write time:          Tue Apr 24 03:08:52 2012
Mount count:              3
Maximum mount count:      37
Last checked:             Tue Apr 24 03:07:48 2012
Check interval:           15552000 (6 months)
Next check after:         Sun Oct 21 03:07:48 2012
Lifetime writes:          2454 MB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:           256
Required extra isize:     28
Desired extra isize:      28
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      0a25e04c-6169-4d68-bfa6-a1acd8e39632
Journal backup:           inode blocks
Journal features:         journal_incompat_revoke
Journal size:             128M
Journal length:           32768
Journal sequence:         0x0000158b
Journal start:            1

I've tried these things to get rid of the message and usually the badblocks is what does it for me:

Run this command and reboot:

sudo touch /forcefsck

Run badblocks to check the disk:

badblocks /dev/sda1

Edit /etc/fstab and change the last "0" which is the fs_passno column accordingly and then reboot:

The root filesystem should be specified with a fs_passno of 1, and other filesystems should have a fs_passno of 2.

I don't understand:

1. If this is a virtual drive shouldn't it be less prone to errors?
2. Was the image created with one of the flags set? If not what is triggering it?
3. Why is fs_passno set to 0 on Amazon EC2 Ubuntu images? This is not the first one that is like this.