* EXT4 partition changes every time it's mounted. (How to stop this?) @ 2011-05-21 19:45 Lee Davis 2011-05-22 11:47 ` Theodore Tso 0 siblings, 1 reply; 4+ messages in thread From: Lee Davis @ 2011-05-21 19:45 UTC (permalink / raw) To: linux-ext4 Hi folks, 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. Trying to solve this, I set the /boot partition to mount as read only in fstab. I then took individual hashes of every file on /boot. After I rebooted none of the files had changed (and there were no new files), yet the filesystem hashed as a whole had changed. 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? Any advice would be greatly appreciated! Cheers, Lee ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: EXT4 partition changes every time it's mounted. (How to stop this?) 2011-05-21 19:45 EXT4 partition changes every time it's mounted. (How to stop this?) Lee Davis @ 2011-05-22 11:47 ` Theodore Tso 2011-05-23 4:39 ` Lee Davis 0 siblings, 1 reply; 4+ messages in thread From: Theodore Tso @ 2011-05-22 11:47 UTC (permalink / raw) To: Lee Davis; +Cc: linux-ext4 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: EXT4 partition changes every time it's mounted. (How to stop this?) 2011-05-22 11:47 ` Theodore Tso @ 2011-05-23 4:39 ` Lee Davis 2011-05-26 6:15 ` Lee Davis 0 siblings, 1 reply; 4+ messages in thread From: Lee Davis @ 2011-05-23 4:39 UTC (permalink / raw) To: Theodore Tso; +Cc: linux-ext4 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@MIT.EDU> To: Lee Davis <l.davis37@ymail.com> Cc: "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org> 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: EXT4 partition changes every time it's mounted. (How to stop this?) 2011-05-23 4:39 ` Lee Davis @ 2011-05-26 6:15 ` Lee Davis 0 siblings, 0 replies; 4+ messages in thread From: Lee Davis @ 2011-05-26 6:15 UTC (permalink / raw) To: Lee Davis, Theodore Tso; +Cc: linux-ext4 I've just tested this on a clean Ubuntu installation without any crypto -- exact same thing happens. Should I log this as an ext4 bug? Regards, Lee ----- Original Message ----- From: Lee Davis <l.davis37@ymail.com> To: Theodore Tso <tytso@MIT.EDU> Cc: "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org> Sent: Monday, 23 May 2011 2:39 PM Subject: Re: EXT4 partition changes every time it's mounted. (How to stop this?) 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@MIT.EDU> To: Lee Davis <l.davis37@ymail.com> Cc: "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org> 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2011-05-26 6:15 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2011-05-21 19:45 EXT4 partition changes every time it's mounted. (How to stop this?) Lee Davis 2011-05-22 11:47 ` Theodore Tso 2011-05-23 4:39 ` Lee Davis 2011-05-26 6:15 ` Lee Davis
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