Re: --sequential-read not sequential???

Denis Corbin <[email protected]> Tue, 25 Feb 2020 22:22:42 +0100
Newsgroups	gmane.comp.sysutils.backup.dar.support
Message-ID	<[email protected]>
On 25/02/2020 17:16, Graham Cobb wrote:
>>>>> 1) Using dar_xform and an actual pipe to feed "dar -t". That caused
>>>>> dar to emit a hard error because it cannot go backwards on a pipe.
>>>>> So the "dar -t" failed. It didn't emit any message explaining why
>>>>> it wanted to go backwards.
>>>>
>>>> strange, which version of dar are you using by the way?
>>>
>>> 2.6.6
>>
>> OK so this explains one point, as described on the Changelog:
>>
>> from 2.6.6 to 2.6.7
>> [...]
>> - fixed bug: dar failed creating an archive on its standard output
>>   reporting the error message "Skipping backward is not possible on a pipe"
>>
> 
> I have now upgraded to 2.6.8 but it hasn't changed the results in my
> cases. Maybe because I am not doing archive creation?

correct, I should have read with more attention :^)

[...]
> 
> I saw:
> 
> [--- REMOVED ENTRY ----] (Tue Jan 21 03:49:58 2020) [s]
> var/lib/samba/private/msg.sock/3238
> [--- REMOVED ENTRY ----] (Tue Jan 21 03:49:58 2020) [s]
> var/lib/samba/private/msg.sock/3331
> 
> No other REMOVED ENTRY, and no other mentions of those files. So, I
> think that is consistent with your hypothesis.

great! So I can look forward on how to solve this

> 
>> So to summarize:
>>
>> - you have been hitting a bug fixed in 2.6.7 that avoid you outputing
>> archive on stdout, thus the dar_xform hint should workaround the issue
>> using 2.6.7 or 2.6.8.

in fact no, because the problem is the same with the dar_xform + dar
proposal I did. Dar will try to skip backward and will fail as it is not
possible to skip on a pipe, so the message "Skipping backward is not
posible on a pipe" is normal here (unlike for the archive creation which
is not used here).

> 
> Unfortunately, no. Even with 2.6.8 it seems that the bug you outline
> below means "dar -t" still tries (and fails) to go backwards on the
> pipe, even when dar_xform is being used. 

Yes, that's exactly that.

> In particular, using dar_xform
> with the archive mentioned above (DARsystemDiff06.1.dar) to pipe into
> "dar -t - --sequential-read" still gets these errors:
> 
> ERR <ROOT>/var/indexes/cobb : Skipping backward is not possible on a pipe
> ERR <ROOT>/var/indexes/cobb/.Trash : Skipping backward is not possible
> on a pipe
> ERR <ROOT>/home/cobb : Skipping backward is not possible on a pipe
> ERR <ROOT>/home/cobb/dovecot : Skipping backward is not possible on a pipe
> ERR <ROOT>/home/cobb/dovecot/cur : Skipping backward is not possible on
> a pipe
> 
>> - there is probably an inconsistency between the testing routing and
>> the escape_catalogue object that reads archive content sequentially from
>> the archive... I let you confirm that or not.
> 
> Your hypothesis seems likely given the results on the msg.sock directory
> I include above.

I must take some time to fix that properly, keep you informed.

In the meanwhile, a workaround would be to not use --sequential-read
and, in order to avoid twice the download of the last slice, you could
use an isolated catalogue to read the archive contents:

dar -t "/var/tmp/$archive" \
	-E 'rm "%p/%b."*".%e"' \
	-E "echo Fetching $dir/%b.%n.%e.gpg..." \
	-E "gpg -d -q -o '%p/%b.%n.%e' --batch  '$dir/%b.%n.%e.gpg'" \
	-A <isolated catalogue of this archive>

it should work... let me know if you try it

> 
> Graham
> 
> 

Denis

_______________________________________________
Dar-support mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/dar-support
signature.asc (application/pgp-signature, 833 B)