What's the best way to set up a backup transfer?

Question

Machine A holds important source data that needs to be backed up. Machine B is where the data will be backed up to. They're both Ubuntu. I want to have an automated process that allows machine A to create an encrypted tarball and copy it to machine B, without human intervention, but doesn't allow anything except copying the file over to a target directory.

I thought about using a chroot jailed account, but this seems to be a pain to set up and overly complex. I really just want to be able to have machine A to copy files to machine B, via automatic cron, but I also want to prevent the mechanism that allows the copy from allowing any other actions (copying to any other directory, logging in, executing any other commands noninteractively, etc.). Also, the transfer must be encrypted (e.g. using ssh somehow).

Answer 1

You may want to consider letting B pull tarballs from A rather than have A push them onto B.

Basically a cron job on A would create a tarball, name it uniquely (add a timestamp for example), place it into a directory that B can access (through a restricted account on A) and then have B periodically check that directory and move any files it finds there over to itself.

This setup has an added benefit of not requiring A to have an account on B, meaning that should A get compromised, the attacker would not get a access to B as a freebie.

(edit) For copying over SSH have a look at 'scp' command.