Backing up the same unchanged SD card in two distributions processes all files as changed

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Backing up the same unchanged SD card in two distributions processes all files as changed

白い熊@相撲道
User case:

I have an SD card that I back up to an external harddisk. On the same
machine, however use a number of GNU/Linux distributions.

If I back it up from the same distribution repeatedly, without any
change to the SD file system, no file is processed as changed - that's
the way it should be.

If I reboot into another distribution, and run the back up there, it
will mark all the files as changed, and copy all the data to the backup
directory - clearly wrong.

Why is this? I'm not sure what's causing this - seems to be distribution
independent, simply boot into some other distribution and its
rdiff-backup thinks all the files have been modified. Why?

How can I have it not do this and process the files as unchanged?
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白い熊@相撲道

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Re: Backing up the same unchanged SD card in two distributions processes all files as changed

白い熊@相撲道
On 2015-08-31 15:31, Andrew Engelbrecht wrote:
> Is it a FAT filesystem? Some distros mount it with UTC, others use the
> local time. The latter is correct.

It's an exfat system, so FUSE mount it - this could be the case though.

I mount it with 'mount.exfat -o iocharset=utf8,umask=000' in both
distros. On one this results in a mount of 'type fuseblk
(rw,nosuid,nodev,relatime,user_id=0,group_id=0,allow_other,blksize=4096'

Can't check the other distro now as running a backup which has been
taking ages exactly due to this problem.

What should I add to mount options to ensure identical mounts in both
distros, so the system will look identical?
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白い熊@相撲道

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Re: Backing up the same unchanged SD card in two distributions processes all files as changed

白い熊@相撲道
On 2015-08-31 15:57, 白い熊@相撲道 wrote:
> On 2015-08-31 15:31, Andrew Engelbrecht wrote:
>> Is it a FAT filesystem? Some distros mount it with UTC, others use the
>> local time. The latter is correct.

> It's an exfat system, so FUSE mount it - this could be the case though.

Alas, it is indeed so, in fact the system is mounted local time in both
cases, however with different TZ setting, resulting in the file
timestamp differences.

Interestingly now, this is easily manipulated in GuixSD - my main
distro, via just prepending the correct TZ= value. Changing the TZ
results in changing the timestamps with which the card is mounted - as
should. However, the culprit now is Trisquel, which for some reason
mounts it in an arbitrary timezone and the TZ variable has no effect on
the timestamps with which the card is mounted - making backups
problematic in Trisquel.
--
白い熊@相撲道

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