how universal is tar format? SYSV?

[BostonU SysMgr]

Sorry, but I keep getting these mailings from people that *they* were
able to read/write a cpio tape between UNIXes [usually saying that they
had to use some flag or another to create the tape.]

The *point* is not whether or not one can create a tape, given the
correct parameters (eg. -c) that is portable.  The point was that I was
unable to read the AT&T SYSV VAX source distribution tape on my 3B5 no
matter what switches I fed it. Obviously I had no opportunity to specify
how they wrote the tape.

The only problem I have had with tar is large blocks, hopefully this is
the kind of knowledge that is easier to disseminate (don't write tar
tapes with blocking factors bigger than about 5). The various word/byte
swap problems on the cpio tapes (which the switches that claim to handle
do !not!) are quite obscure to 'users'.

Sum: If a user came to me and said "I need to send a tape of files to a
friend on some UNIX systems what should I use?"  I would recommend:

	cd directory
	tar cbf 5 /dev/rmt0 .	! or whatever tape device

and be about 99% sure my phone wouldn't ring again.  I have no such
confidence in cpio (anymore.)  As a robustness note, even tho UCB puts
directory names on the tape SYSV just grumbles and ignores and finishes
fine.  Conversely, given a tape to read on a new system I would budget
more time if it were a cpio tape.

	-Barry Shein, Boston University