tar exclude cache

[Patrick Dupre]

Hello,

I am trying to exclude the .cache directories when I tar a home directory
by using:
tar -cjf /mnt/backup/home.tbz2 --exclude-caches-all /home/pdupre
but it does not work.
What am I doing wrong ?

Thank for your help.

===========================================================================
 Patrick DUPRÉ                                 | | email: [e-mail]
 Laboratoire de Physico-Chimie de l'Atmosphère | |
 Université du Littoral-Côte d'Opale           | |
 Tel.  (33)-(0)3 28 23 76 12                   | | Fax: [phone]
 189A, avenue Maurice Schumann                 | | 59140 Dunkerque, France
===========================================================================

[Doug H.]

On Mon, 2015-12-21 at 21:29 +0100, Patrick Dupre wrote:
> Hello,
>
> I am trying to exclude the .cache directories when I tar a home
> directory
> by using:
> tar -cjf /mnt/backup/home.tbz2 --exclude-caches-all /home/pdupre
> but it does not work.
> What am I doing wrong ?

Do the .cache dirs each have a file called CACHEDIR.TAG with just the
below line?

Signature: 8a477f597d28d172789f06886806bc55

I don't remember learning about this tar feature but checking the man
page of tar I found the name of that tag file and a test found the file
to not be enough but a web search came up with the idea that they need
that signature and adding that line to my tag file caused my tar to act
as expected.

[Patrick Dupre]

Thank you

===========================================================================
 Patrick DUPRÉ                                 | | email: [e-mail]
 Laboratoire de Physico-Chimie de l'Atmosphère | |
 Université du Littoral-Côte d'Opale           | |
 Tel.  (33)-(0)3 28 23 76 12                   | | Fax: [phone]
 189A, avenue Maurice Schumann                 | | 59140 Dunkerque, France
===========================================================================
> Sent: Monday, December 21, 2015 at 9:50 PM
> From: "Doug H." 
> To: [e-mail]
> Subject: Re: tar exclude cache
>
> On Mon, 2015-12-21 at 21:29 +0100, Patrick Dupre wrote:
> > Hello,
> >
> > I am trying to exclude the .cache directories when I tar a home
> > directory
> > by using:
> > tar -cjf /mnt/backup/home.tbz2 --exclude-caches-all /home/pdupre
> > but it does not work.
> > What am I doing wrong ?
>
> Do the .cache dirs each have a file called CACHEDIR.TAG with just the
> below line?
>
> Signature: 8a477f597d28d172789f06886806bc55
>
> I don't remember learning about this tar feature but checking the man
> page of tar I found the name of that tag file and a test found the file
> to not be enough but a web search came up with the idea that they need
> that signature and adding that line to my tag file caused my tar to act
> as expected.
>
> -- 
> Doug H.
> -- 
> users mailing list
> [e-mail]
> To unsubscribe or change subscription options:
> https://admin.fedoraproject.org/mailman/listinfo/users
> Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct
> Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
> Have a question? Ask away: http://ask.fedoraproject.org

[Rick Stevens]

On 12/21/2015 02:41 PM, Patrick Dupre wrote:
> Thank you

By the way, the signature is the MD5 hash of the string
".IsCacheDirectory" and it's SPECIFICALLY looked for by tar:

[root@prophead tmp]# strings /bin/tar | grep 
8a477f597d28d172789f06886806bc55
    Signature: 8a477f597d28d172789f06886806bc55

They don't mention the need for the signature in the man page, but it IS
buried in the "info" pages (under section 6.4):

<quote>
    When creating an archive, the '--exclude-caches' option family causes
'tar' to exclude all directories that contain a "cache directory tag".
A cache directory tag is a short file with the well-known name
'CACHEDIR.TAG' and having a standard header specified in
http://www.brynosaurus.com/cachedir/spec.html.  Various applications
write cache directory tags into directories they use to hold
regenerable, non-precious data, so that such data can be more easily
excluded from backups.

There are three 'exclude-caches' options, each providing a different
exclusion semantics:

'--exclude-caches'
      Do not archive the contents of the directory, but archive the
      directory itself and the 'CACHEDIR.TAG' file.

'--exclude-caches-under'
      Do not archive the contents of the directory, nor the
      'CACHEDIR.TAG' file, archive only the directory itself.

'--exclude-caches-all'
      Omit directories containing 'CACHEDIR.TAG' file entirely.
</quote>

And the spec mentioned was written in...2004! Jeeze! I don't think they
could have buried this information deeper if they tried. I knew about
it, but it's pretty damned silly to not put it in the man page since not
everyone installs info and its database. And even with info, the
signature itself is NOT defined except in the webpage cited. What if
they decide to take that site offline because the author doesn't wish
to keep it up?

I'm sending a copy of this note to [e-mail]. Perhaps they'll 
update their docs.
> > Sent: Monday, December 21, 2015 at 9:50 PM
> > From: "Doug H." 
> > To: [e-mail]
> > Subject: Re: tar exclude cache
> >
> > On Mon, 2015-12-21 at 21:29 +0100, Patrick Dupre wrote:
> > > Hello,
> > >
> > > I am trying to exclude the .cache directories when I tar a home
> > > directory
> > > by using:
> > > tar -cjf /mnt/backup/home.tbz2 --exclude-caches-all /home/pdupre
> > > but it does not work.
> > > What am I doing wrong ?
> >
> > Do the .cache dirs each have a file called CACHEDIR.TAG with just the
> > below line?
> >
> > Signature: 8a477f597d28d172789f06886806bc55
> >
> > I don't remember learning about this tar feature but checking the man
> > page of tar I found the name of that tag file and a test found the file
> > to not be enough but a web search came up with the idea that they need
> > that signature and adding that line to my tag file caused my tar to act
> > as expected.
> >
> > --
> > Doug H.
> > --
> > users mailing list
> > [e-mail]
> > To unsubscribe or change subscription options:
> > https://admin.fedoraproject.org/mailman/listinfo/users
> > Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct
> > Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
> > Have a question? Ask away: http://ask.fedoraproject.org

[Doug H.]

On Mon, 2015-12-21 at 16:19 -0800, Rick Stevens wrote:
> On 12/21/2015 02:41 PM, Patrick Dupre wrote:
> > Thank you
>
> By the way, the signature is the MD5 hash of the string
> ".IsCacheDirectory" and it's SPECIFICALLY looked for by tar:

[snip of great info]

As a bonus question; do you know why md5sum is showing a different
value, as in...
> echo ".IsCacheDirectory" | md5sum -

6929f806dd11bc634be8205d11af24d6  -

I used "John the Ripper" to prove that 8a477f597d28d172789f06886806bc55
really *is* the hash of .IsCacheDirectory but I am not clear on what
md5sum is giving me.

[Rick Stevens]

On 12/21/2015 05:37 PM, Doug H. wrote:
> On Mon, 2015-12-21 at 16:19 -0800, Rick Stevens wrote:
> > On 12/21/2015 02:41 PM, Patrick Dupre wrote:
> > > Thank you
> >
> > By the way, the signature is the MD5 hash of the string
> > ".IsCacheDirectory" and it's SPECIFICALLY looked for by tar:
>
> [snip of great info]
>
> As a bonus question; do you know why md5sum is showing a different
> value, as in...
> > echo ".IsCacheDirectory" | md5sum -
>
> 6929f806dd11bc634be8205d11af24d6  -
>
> I used "John the Ripper" to prove that 8a477f597d28d172789f06886806bc55
> really *is* the hash of .IsCacheDirectory but I am not clear on what
> md5sum is giving me.

Has to do with end-of-line stuff. Try:

[root@prophead tmp]# printf "%s" ".IsCacheDirectory" | md5sum
    8a477f597d28d172789f06886806bc55  -

(the "-" at the end is md5sum telling me that it was looking at stdin).
----------------------------------------------------------------------
- Rick Stevens, Systems Engineer, AllDigital    [e-mail] -
- AIM/Skype: therps2        ICQ: 226437340           Yahoo: origrps2 -
-                                                                    -
-     Make it idiot proof and someone will make a better idiot.      -
----------------------------------------------------------------------

[Rick Stevens]

On 12/21/2015 06:11 PM, Rick Stevens wrote:
> On 12/21/2015 05:37 PM, Doug H. wrote:
> > On Mon, 2015-12-21 at 16:19 -0800, Rick Stevens wrote:
> > > On 12/21/2015 02:41 PM, Patrick Dupre wrote:
> > > > Thank you
> > >
> > > By the way, the signature is the MD5 hash of the string
> > > ".IsCacheDirectory" and it's SPECIFICALLY looked for by tar:
> >
> > [snip of great info]
> >
> > As a bonus question; do you know why md5sum is showing a different
> > value, as in...
> > > echo ".IsCacheDirectory" | md5sum -
> >
> > 6929f806dd11bc634be8205d11af24d6  -
> >
> > I used "John the Ripper" to prove that 8a477f597d28d172789f06886806bc55
> > really *is* the hash of .IsCacheDirectory but I am not clear on what
> > md5sum is giving me.
>
> Has to do with end-of-line stuff. Try:
>  [root@prophead tmp]# printf "%s" ".IsCacheDirectory" | md5sum
>  8a477f597d28d172789f06886806bc55  -
>
> (the "-" at the end is md5sum telling me that it was looking at stdin).

Additional:
    [root@prophead tmp]# echo -n ".IsCacheDirectory" | md5sum
    8a477f597d28d172789f06886806bc55  -

("echo -n" means "don't include the newline")

----------------------------------------------------------------------
- Rick Stevens, Systems Engineer, AllDigital    [e-mail] -
- AIM/Skype: therps2        ICQ: 226437340           Yahoo: origrps2 -
-                                                                    -
-   I haven't lost my mind.  It's backed up on tape somewhere, but   -
-                       probably not recoverable.                    -
----------------------------------------------------------------------