this post was submitted on 07 Dec 2023
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Does cp -v print out the file name when it starts copying it or when it's done? (lemmy.ml)
submitted 11 months ago* (last edited 11 months ago) by HiddenLayer5@lemmy.ml to c/linux@lemmy.ml
12 comments fedilink hide all child comments
 

So if I had a cp -v operation fail, is the last file name it printed out the last successful file copy, or is it the failed partially copied file? If you had to ensure all files are copied correctly without overwriting anything, would deleting the last filename that was printed from the destination folder delete the partially copied file that the operation failed on?

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[–] taladar@sh.itjust.works 28 points 11 months ago* (last edited 11 months ago) (4 children)

Just use rsync -va (possibly with --chown if you want user/group to be different at the destination and with --delete if you want removed files to be deleted) to continue the copy operation, it automatically takes care of figuring out which files still need to be copied and which are already there.

[–] SpaceCadet@feddit.nl 31 points 11 months ago* (last edited 11 months ago) (2 children)

Just use rsync -va

NO STOP!

The default quick check algorithm of rsync is not safe for this. It only checks filesize and modification time to determine if files are equal. After a b0rked copy, these are not to be trusted.

You should add the -c flag so that files are properly checksummed, unfortunately if you have slow storage on either end, this often negates the speed advantage of rsync.

For example, consider this example:

mkdir source
mkdir destination
echo "hello" > source/file.txt
echo "world" > destination/file.txt
touch -r source/file.txt destination/file.txt
rsync -avh source/ destination/
cat source/file.txt
cat destination/file.txt

Contrary to what you might expect, the rsync command copies nothing and the output at the end will show:

hello
world

If you change the rsync command in the example above to rsync -c -avh source/ destination/, it will work as expected.

[–] taladar@sh.itjust.works 1 points 11 months ago

True if the initial state is unknown but if you do your initial copy and all the later syncs with rsync it is not really necessary since rsync puts the partial files in a temporary location (there are same parameters to control the details of that too).

[–] damium@programming.dev 1 points 11 months ago

My memory of the cp command is that attributes such as file times were transferred at the last step. I think this would make rsync safe in most situations where a system crash wasn't involved.

[–] tetris11@lemmy.ml 16 points 11 months ago (1 children)

rsync -avP

[–] s38b35M5@lemmy.world 23 points 11 months ago (1 children)

rsync even supports Alien vs Predator? What doesn't rsync do???

[–] mariah@feddit.rocks 8 points 11 months ago

Bring my dad back

[–] luthis 10 points 11 months ago

All hail the rsync!

We thank the rsync for it's unwavering reliability.

Amen.

[–] HiddenLayer5@lemmy.ml 4 points 11 months ago

Thank you!