cp -r -u ?

[dieterhansbritz]

I use the command
cp -u ...
to copy from one place to another (e.g. to a backup device), but only
files that are new to the target directory. For large directories with large
files, this avoids long transfers. However, when I copy not only files but
directories with files, as in
cp -r -u ...
this seems not to work; it then takes the time it takes to copy everything,
new and old. Does the -r override the -u, and if so, why?

[Mudgen]

Seems that it does, you'd have to read the source code to see why.

Consider using rsync instead. It using a "sliding window checksum" algorithm, and not only transfers only the files that have changed, it transfers only the changed blocks of those.

[dieterhansbritz]

Thanks! I was not aware of that command. Makes me wonder how many
other commands there might be that I could use...

[lindylex]

dieterhansbritz, try these rysnc commands.

Rysnc with resume:
rsync -r --partial --progress --append --rsh=ssh /media/mounteddrive /media/mounteddrivebackup

Rysnc with resume, delete empty directories and extra files and directories that no longer exist from the source that currently exists on the destination.
rsync -r --partial --progress --append --prune-empty-dirs --delete

[donskn]

I have this in my backup script:

cp -v --update -p -r $1/* $2

and it does exactly what you (and I) want. I would suggest you look for some other reason why it isn't working.

Don

[unlimitedscolobb]

cp -r -u ...
this seems not to work; it then takes the time it takes to copy everything,
new and old. Does the -r override the -u, and if so, why?

Just throwing in a wild guess. Sorry, no time to look through the source now

May it be so that cp checks not only files, but also directories when run with -u? In that case, if you create a new file in a directory, it will copy the entire directory, because the modification time of the entire directory has changed.

rsync should cope better with the problem, though

[Mudgen]

dieterhansbritz, try these rysnc commands.

Rysnc with resume:
rsync -r --partial --progress --append --rsh=ssh /media/mounteddrive /media/mounteddrivebackup

Why specify a remote shell on a local-to-local copy?

[Mudgen]

Just throwing in a wild guess. Sorry, no time to look through the source now

May it be so that cp checks not only files, but also directories when run with -u? In that case, if you create a new file in a directory, it will copy the entire directory, because the modification time of the entire directory has changed.

rsync should cope better with the problem, though

Intuitively that sounds exactly right. I have time to look through the source, I'm just too lazy.