I have never used tar before and trying it does not work as I expected. I still have to try it as a normal user but I do not think my problem is due to the fact I do it as root.

First, file "home.tar" does not exist and I execute the following command:
This gives a file "home.tar" of about 1.6G on the usb stick.

then I immediately run the following command:
The same file "home.tar" now takes about 3.3G, it looks like this second command has appended a new archive to the old one when I thought the first command created the archive with "-c" and the second one updated it with "-u" which should have resulted in an unchanged archive since no file has been changed.

I do not understand what is meant by "seekable" in the man page about "-n".

Can someone tell me what I am doing wrong?

Thank you for your help

Couldn't find option -n in the documentation.

1 members found this post helpful.

Well my man page says:
Might help if you tell us which version of tar?

Whilst you are correct that running as root will not alter the outcome (except -p as root can overwrite permissions), I would think you would test a new function that you do not know how to use as
a regular user, just in case something went wrong??

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And for me, "info tar" contains:

`--seek'
`-n'
Assume that the archive media supports seeks to arbitrary locations. Usually `tar' determines automatically whether the archive can be seeked or not. This option is intended for use in cases when such recognition fails.

It's one of those short options that has seen several conflicting uses as tar evolved, and should be avoided.

I can't reproduce the OP's problem. Output from "tar --version" needed.

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Try using a 'date' (-N --newer --after-date) in combination with the -u operator.

http://www.gnu.org/software/tar/manu...ion/after.html

My example (sorry for not using same files was a quick test)

gives:
342M Mar 18 10:26 backup.tar

gives:
342M Mar 18 10:26 backup.tar

Although i also noted while doing this that the excluded file was still included.. but hey..


so it will only update anything modified after 1 day ago.
If you check link above will also give other date formats if checking the link in text.

version used:
tar (GNU tar) 1.23


Edit:
o btw - i did manage to replicate OPs issue with commands given. I think if no date is given it will just reappend all given files again.


Hope this helps.

1 members found this post helpful.

I use tar 1.26
I found tar -u does not replace an old file with a newer one, it keeps both which is not what I wanted.
Thank you all.

The name "tar" comes from "Tape ARchiver". It was designed to work with linear magnetic tapes. There is no practical way to replace a file in the middle of such a tape -- it would require reading and re-writing the whole remainder of the tape.