First, the device # should be usable from the command line, i.e. tar cv0
foo
As for mt, it was written for the tape device and in those days most of us
had at least one 9-track device. I have no memory of why Ken used mt1
not mt0. Doug may know.
On Fri, Dec 11, 2015 at 5:27 PM, Will Senn <will.senn(a)gmail.com> wrote:
All,
In my exploration of v6, I followed the advice in "Setting up Unix -
Seventh Edition" and copied v6tar from v7 to v6. Life is good. However, tar
is using mt1 and it is hard coded into the source, tar.c:
char magtape[] = "/dev/mt1";
As the subject line suggested, I have two questions for those of you who
might know:
1. Why is it hard coded?
2. Why is it the second device and not the first?
Interestingly, it took me a little while to figure out it was doing this
because I didn't actually move files between v6 and v7 until today. Before
this my tests had been limited to separate tests on v6 and v7 along the
lines of:
cd /wherever
tar c .
followed by
tar t
list of files
cd /elsewhere
tar x
files extracted and matching
What it was doing was writing to the non-existant /dev/mt1, which it then
created, tarring up stuff, and exiting. Then when I listed the contents of
the tarfile, or extracted the contents, it was successful. But, when I went
to move the tape between v6 and v7, the tape (mt0) was blank, of course. It
was at this point that I followed Noel's advice and "Used the source",
and
figured out that it was hard-coded as you see above.
Thanks,
Will
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