How do I use SFTP without SSH?

Question

I want a fast and flexible file server but I don't need encryption or authentication. How can I use SFTP for this on Linux systems?

Answer 1

SFTP happens to be used by SSH servers but it's a well-developed protocol that works well on its own. The sftp-server developed by OpenSSH has no dependency on an SSH server; sftp-server uses standard input/output. (Other SFTP servers are similar.)

It is trivial to share a filesystem via SFTP, similar to what you might do with NFS but without the need for root access. I'll use socat as the daemon for this ad-hoc example, but xinetd would make a more permanent solution. The location of sftp-server is from my Ubuntu installation of the openssh-sftp-server package.

On the server:

mkdir shared_to_the_world
cd shared_to_the_world
socat tcp-listen:1234,reuseaddr,fork exec:/usr/lib/openssh/sftp-server

On the client:

mkdir /tmp/sftp_test
sshfs -o reconnect,ssh_command="nc my_sftp_server_address 1234 --" : /tmp/sftp_test
cd /tmp/sftp_test

Now your client (and anyone else's!) can seamlessly work with the files in the shared directory on the server. Both read and write are enabled, so be careful.

Consider using socat listen's "bind" and "range" options to limit the access to your server.