Ubuntu – Weird problem with connection from putty to ubuntu server via SSH

To use your EC2-priv.ppk key from your Ubuntu desktop you will have to convert it into a format that OpenSSH will understand. You can go this with the PutTTYgen program.

Run PuTTYgen and click on Conversions->Import key. Import your EC2-priv.ppk private key. Then click Conversions->Export OpenSSH key. Save the converted key.

PuTTYgen will also show the public key associated with the private key. This should be added to the $HOME/.ssh/authorized_keys file on your ec2 instance.

Now you have a key in a format that ssh on your Ubuntu system will understand. copy this key to $HOME/.ssh/identity. Ensure that the permissions are 600 on the identity file.

You should now be good to go.

Regarding the use of public key authentication. This really is the way that you should authenticate to your system. It is extremely unlikely that any brute force attack will succeed and is far more secure than simple passwords.

I think you can skip rsyncd and plink entirely, by rearranging your architecture a bit (which will have other benefits).

I believe that rsyncd daemon doesn't actually need to be running to do a basic rsync for backup purposes. rsync normally just connects to the other box over SSH, fires up an instance of rsync on the far side, and the two rsyncs talk to each other over ssh -- the rsyncd daemon isn't really involved. rsyncd is normally used to serve content for download by multiple clients (like a mirror server).

In this setup, I assume that the box receiving the backup (the Ubuntu box) is the more "trusted" system (from a security perspective) --- not because it's Ubuntu, but because backup servers naturally have to hold data for multiple sensitive hosts. As such, I would recommend initiating the rsync from the Ubuntu box, and setting the key trust relationship so that it's the Windows box that trusts the Ubuntu box, and not the other way around. This would mean setting up sshd under Cygwin, and locking it down (with a host-based firewall) so that only connections from your backup server are permitted.

You could then simply execute:

rsync -qrtz windowsbox:/path/to/files /path/to/ubuntu/backups

... which also demonstrates how to specify the directory on the serving side.

As the next troubleshooting step, I would drop trying to use rsyncd, temporarily leaving out key-based authentication just as you did in your earlier troubleshooting, and just try a simple rsync (of a couple of test files) using password-based authentication.

Once you get the basic sync working, you'll also want to look at rsync's --modify-window option, which will ignore the small drift in timestamps that can result from the differences in how Windows and Unix-likes handle seconds in timestamps. Otherwise, files that could otherwise be skipped will get copied over and over again.

I also strongly recommend leaving off the --delete option until after you have finished debugging and testing your solution. One typo and you can delete far more than you intended.