Re: tar and the braindead man

[servis@purdue.edu]

*- Nikolai Andreyevich Luzan wrote about "Re: tar and the braindead man"
| On Sun, 25 Oct 1998 servis@purdue.edu wrote:
| 
| > You can't mount a tape. You need to write directly to the tape.
| > Otherwise how could you do a full backup of your largest partition if
| > it was over 50% full?
| > 
| > Do this instead:
| > 
| > tar -cvf /dev/st0 /usr/thedirectory  
| > 
| > where /dev/st0 is the device file for your tape.  Assuming your tape is
| > a scsi one(since it is a dat this is most likely true), you have scsi
| > tape support for the kernel and it is your only or first one found by
| > the kernel then the above device is correct.
| 
| To the best of my knowledge  the f option is not needed unless you
| want to create, test or extract from a file. the actual command would
| be 
| 	tar -cv /path/to/tar/up   
| 
| tar automagically looks for the first tape device and writes it's
| archive there. if you doubt me then read the tar man page or the
| appropriate HOWTO.
| 
| 
| Nikolai
| 
| 

I am doubting you.

>From tar's info page Node:Device

========================================
   Starting with version 1.11.5, GNU `tar' uses standard input and
standard output as the default device, and I will not try anymore
supporting automatic device detection at installation time.  This was
failing really in too many cases, it was hopeless.  This is now
completely left to the installer to override standard input and standard
output for default device, if this seems preferrable to him/her.
Further, I think *most* actual usages of `tar' are done with pipes or
disks, not really tapes, cartridges or diskettes.

   Some users think that using standard input and output is running
after trouble.  This could lead to a nasty surprise on your screen if
you forget to specify an output file name--especially if you are going
through a network or terminal server capable of buffering large amounts
of output.  We had so many bug reports in that area of configuring
default tapes automatically, and so many contradicting requests, that
we finally consider the problem to be portably intractable.  We could
of course use something like `/dev/tape' as a default, but this is
*also* running after various kind of trouble, going from hung processes
to accidental destruction of real tapes.  After having seen all this
mess, using standard input and output as a default really sounds like
the only clean choice left, and a very useful one too.

========================================

And a simple test confirms this:

{root@brian}{/tmp}[300]>touch test.txt
{root@brian}{/tmp}[301]>echo hello >> test.txt
{root@brian}{/tmp}[302]>tar cv test.txt
test.txt
test.txt100644      0      0           6  6614732352  10601 0ustar  rootroothello
{root@brian}{/tmp}[303]>

So you DO need the -f or --file option.

Brian 
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Mechanical Engineering                              servis@purdue.edu
Purdue University                   http://www.ecn.purdue.edu/~servis
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