[rb-general] How to modify mount-time and write when you write in a file system

Andres Pavez apavez.zavala at gmail.com
Wed Jul 12 19:16:59 CEST 2017

Andrés Pavez

On Wed, Jul 12, 2017 at 3:39 AM, Ximin Luo <infinity0 at debian.org> wrote:
> Daniel Shahaf:
>> Andres Pavez wrote on Tue, 11 Jul 2017 16:36 -0700:
>>> Problem: during the creation/reproduction of the custom live cd, when
>>> i use "mount' to mount the filesystem to copy my sw inside of the
>>> rootfs (after unsquashfs) i noted usign tune2fs every time i mont the
>>> file system the values "last mount time", "last write time" and
>>> "Lifetime writes" changes and i don't know how to fix it.
>>> With tune2fs i can only  fix the "Mount Count", but no the mount time
>>> and writes.
>> Perhaps, instead of backdating the metadata, teach diffoscope to parse
>> the metadata, so diffoscope's output would pretty-print the metadata
>> diff?  If it's just those three values that differ, presumably that wouldn't
>> make the output much harder to audit for your downstream users.
> This approach, of adding exceptions to diffoscope and still calling the result "reproducible", isn't scalable (what if you need to put the result inside more containers?) So I wouldn't recommend this.
> @Andres: Have you tried `mount -o ro` to mount read-only? `man mount` also suggests some other options, in case that doesn't work:
> -r, --read-only
> Mount the filesystem read-only.  A synonym is -o ro.
> Note that, depending on the filesystem type, state and kernel behavior, the
> system may still write to the device.  For example, ext3 and ext4 will replay
> the journal if the filesystem is dirty.  To prevent this kind of write access,
> you may want to mount an ext3 or ext4 filesystem with the ro,noload mount
> options or set the block device itself to read-only mode, see the blockdev(8)
> command.

Hi Ximin,
Thanks for your comment. But i need to copy my sw inside of the ext4
file system, so read only doesn't work.

Best regards,

> X
> --
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> https://github.com/infinity0/pubkeys.git

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