I upgraded from Win 7 to Win 10 and I am not able to run a tar command on files that previously worked with Cygwin. All the files are currently showing as Unknown+User and Unknown+Group. As far as I was reading the new Windows created a brand new user and the previous one no longer exists. I am looking for the best and the safest way of getting out of this. I will add that this is a backup and if something does not go as expected, I can lose a year and a half of all day / week work.

I want to make .tar.gz files of two websites that I have on my drive. I could use .zip or .rar on Windows, but I guess it would be better to do it from within Cygwin and use the tar.

you may try to change the owner (as admin) recursively of all those files/dirs - just to make them accessible, but probably better to reinstall cygwin again.

Just curious: Why do you think tar would be better than zip or rar? The files are on your windows PC, yes? Wouldn't the best way to back them up be with a windows utility? I back up source files built and maintained in windows with zip.

As I say, just curious.