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 bug-tar@xxxxxxx. Perhaps they'll
update their docs.
Sent: Monday, December 21, 2015 at 9:50 PM
From: "Doug H." <fedoraproject.org@xxxxxxxxxxx>
To: users@xxxxxxxxxxxxxxxxxxxxxxx
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.
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