Difference between two tar commands -cf and -Jchf

Question

I have a python script that is running in two places, two different, but similar commands:

os.system("tar cf - -C %s . 2>/dev/null 3>/dev/null | 7za a -p%s -si %s 1>/dev/null 2>/dev/null 3>/dev/null" % (cf, self.config.get(jn, "archpass"), filename))


os.system("tar -Jchf - -C %s . 2>/dev/null 3>/dev/null | 7za a -p%s -si %s 1>/dev/null 2>/dev/null 3>/dev/null" % (cf, self.config.get(jn, "archpass"), filename))

This script is used to backup websited on a Ubuntu server. So most of files are html/php/js/jpg. I need to understand this command more in order to have an idea if there is place for improvement.

Question 1) What's the difference between: tar cf and tar -Jchf. Unfortunately tar --help didn't help me understand the additional -Jf parameters.

Question 2) Is tar also archiving? What could be the purpose of sending everything to 7za? Is it doing a double archivisation?

Some bad practice (passwords in arguments) and command injection vulnerabilities in there. I wouldn't trust a software with that code. — Stéphane Chazelas, Feb 05 '22 at 18:43

score 2 · Accepted Answer · answered Feb 05 '22 at 17:05

2

The actual difference in the commands are the Jh switches, which are described here (from man tar):

-h, --dereference
              Follow symlinks; archive and dump the files they point to.
-J, --xz
              Filter the archive through xz(1).

So you're forcing the archive to be compressed with xz and following symlinks instead of archiving the links themselves.

answered Feb 05 '22 at 17:05

ajgringo619

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thank you, what about the question 2? – Pikk Feb 05 '22 at 17:22
I'm not familiar with 7za so I can't comment. If it is a compression utility, then the -J switch seems redundant. – ajgringo619 Feb 05 '22 at 17:51
Yes, using -J and 7za together is redundant and unproductive. It is trying to compress a compressed stream, which isn't going to help. – user10489 Feb 05 '22 at 18:22
thank you both. – Pikk Feb 05 '22 at 18:36

Difference between two tar commands -cf and -Jchf

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