[TUHS] why does tar have the tape device hard coded into it and why is it mt1 instead of mt0
will.senn at gmail.com
Sat Dec 12 08:27:28 AEST 2015
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
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:
tar c .
list of files
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
More information about the TUHS