Hi Ted, I've checked again, and despite being mounted read-only, the filesystem is definitely changing every time I reboot. The mount options are: ro,relatime,commit=0 I've taken three images of the filesystem (rebooting between each image), and with a bit of research I've managed to discover which fields in the superblock are being changed. They are: s_wtime and s_kbytes_written. Here's how they're being changed: 0x430 (s_wtime): 06C8D94D -> 68D0D94D -> B9D7D94D 0x578 (s_kbytes_written): 42C8000000000000 -> 45C8000000000000 -> 48C8000000000000 These two fields are the only things that are changing in the entire filesystem. Any ideas on what might be causing this and/or how to disable it? Much appreciated, Lee P.S. I just thought to test it after unmounting/re-mounting, and nothing was changed. So it appears to only get changed when I boot the system. It's a fresh Ubuntu Natty installation, with GRUB on the MBR, an ext4 boot partition, and an encrypted ext4 root partition (which I set up through the installer). I can't think what might be writing to the boot partition. ----- Original Message ----- From: Theodore Tso <tytso@xxxxxxx> To: Lee Davis <l.davis37@xxxxxxxxx> Cc: "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx> Sent: Sunday, 22 May 2011 9:47 PM Subject: Re: EXT4 partition changes every time it's mounted. (How to stop this?) On May 21, 2011, at 3:45 PM, Lee Davis wrote: > I'm setting up a Linux system with full disk encryption. I've written a script (to run on every boot) which will verify that neither the MBR or /boot partition (ext4) has been modified. > > Problem is that every time I boot up the system, my /boot partition hashes differently. > > I'm guessing there is something behind the scenes which is changed/updated each time the filesystem is mounted? If so, can it be disabled? Yes, there is a last mounted time in the superblock. If you mount the file system read-only, then not only will that field not be changed, but you can guarantee that nothing else will change... -- Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
