validate tar file on tape

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# 8  
Old 08-03-2011
Another tip from the 1980's ... adjust your file selection list fed to the tar command to include some "First" and "Last" file. You can then write a script to verify the integrity of your tapes (before sending off-site?) by reading back the "First" and "Last" files. If you accidentally overflowed your tape, or the tape is "bad", you'll be missing the "Last" file when your tar -x completes, prompting further investigation.
# 9  
Old 08-04-2011
I think the requirement was to avoid a second full pass on tape.

I figured head would stop tar and the tape when it wrote to EOF or got EPIPE: Not beautiful, but simple.
# 10  
Old 08-04-2011
Sorry, I assumed the original poster wanted, in his own words, to verify that the tape is actually good. IMHO, Reading the first few blocks for the tar header and perhaps a portion of the first file is not sufficient. If the purpose of writing the tape is to have the assurance of a restorable backup, the time spent performing a full read pass over the tape is a small price to pay for the peace of mind that actually knowing a backup is valid provides.

That being said, the quick and dirty kludge would be to use:
$ dd if=/dev/rmt0 bs=20b count=1 2>/dev/null | tar -tvf - 2>/dev/null | head -1 get the first filename off of his tape.
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