Re: [Help-tar] Merge incremental backups created by tar -g

[CUI Hao]

Thank you for answering.

> And that's not. You use old snapshot file here (testbk) and that
> instructs tar to archive only those files that have changed since this
> file was created. For example, if nothing has changed, the test01.tar
> will be effectively empty (it will contain only the directory structure,
> not files). This is hardly what you need.
Sorry I didn't make it clear that test0.tar is the first full dump. So
test01.tar shouldn't be empty.
I want it to be the new full dump in place of test0.tar.

> When listing or extracting, snapshot file is not used, but it is
> required syntactically (because the -g option requires an argument).
I don't think so. It's because snapshot file is provided that tar will
delete files that should be deleted correctly, instead of extracting
every file directly.


2012/5/26 Sergey Poznyakoff <address@hidden>:
> CUI Hao <address@hidden> ha escrit:
>
>> As time goes by, a lot of archives is made. I want to merge some old
>> backups to one archive.
>> I simply tried to restore old ones and re-archive them:
>>    tar -g testbk -xvpf test0.tar test
>>    tar -g testbk -xvpf test1.tar test
>
> Yes, that's right.
>
>>    tar -g testbk -cvpf test01.tar test
>
> And that's not. You use old snapshot file here (testbk) and that
> instructs tar to archive only those files that have changed since this
> file was created. For example, if nothing has changed, the test01.tar
> will be effectively empty (it will contain only the directory structure,
> not files). This is hardly what you need.
>
> To create a full backup you should start with a clean snapshot file, i.e.:
>
>    > testbk
>     tar -g testbk -cvpf test01.tar test
>
> If you use tar version 1.23 or later, you can use the --level=0 option
> for that, e.g.:
>
>     tar -g testbk --level=0 -cvpf test01.tar test
>
> It will clear the contents of testbk prior to archiving, just as the
> shell command "> testbk" does.
>
>> As I am not sure about the content of data file (testbk in above
>> example),
>
> A snapshot file preserves the state of the file system at the moment when
> the archive was created.  In general, wherever you start a full dump you
> should clear it, using one of the methods above.  In contrast, if you do
> an incremental dump, use the snapshot file created previously.
>
> When listing or extracting, snapshot file is not used, but it is
> required syntactically (because the -g option requires an argument).  It
> is a common practice to use /dev/null in these cases, e.g.:
>
>     tar -g /dev/null -xvpf test0.tar test
>
> Regards,
> Sergey
>