Key based authenication with net-sftp in Ruby

Question

I want to be able to use SFTP to login into a number of servers and download certain files to help debug issues as and when they arise. While we could use a client, we wanted to start automating the process to streamline everything.

My first attempt looks something like this:

def download(files_to_download, destination_directory)
    Net::SFTP.start(@server, @username, :password => @password) do |sftp|
        files_to_download.each do |f|
            local_path = File.join(destination_directory, File.basename(f))
            sftp.download!(f, local_path)
        end
    end
end

While this works, it means we need the password. Ideally, I want to be using public key authentication however I can't see any reference to this in the documentation or online - is this possible?

I would prefer not to use chilkat.

Thanks

Answer 1

It's automatically done, just upload your public key and should work out of the box.

Connecting using public/private keys

Public/private keys are always tried before the explicit password authentication, even if you provide a password. Thus, if you only want to use public/private key authentication, simply remove the password from the argument list. If you can successfully obtain a session handle, then your keys are set up correctly!

• http://net-ssh.rubyforge.org/ssh/v1/chapter-2.html#s2

Answer 2

If you want to directly specify the key (or other SSH options) you can first open a Net::SSH connection, and then do SFTP operations from there.

Net::SSH.start("localhost", "user", keys: ['keys/my_key']) do |ssh|
  ssh.sftp.upload!("/local/file.tgz", "/remote/file.tgz")
  ssh.exec! "cd /some/path && tar xf /remote/file.tgz && rm /remote/file.tgz"
end

This also works for Net::SCP

Net::SSH.start('localhost', 'user', keys: ['keys/my_key'] ) do |ssh|
  ssh.scp.download("/local/file.txt", "/remote/file.txt")
end