How can I use Emacs Tramp to double hop ssh?

Question

My campus only lets ssh access through a gateway server. So to access the cluster I am coding on I have to ssh to the gateway and then ssh to the machine I am working on. The connection is very slow at times and is frustrating to work on.

I would love to use something like tramp which I understand would have the buffer open on my local machine and only talk through the network when I save to disk. I am not very familiar with tramp at all and struggling to get it to work, especially through the double hop. The documentation says this is accomplished through defining proxies in tramp, but I am unable to understand the syntax.

Does anyone know how to use emacs to code through a double hop or have an alternate workaround for editing code through two ssh hops?

Answer 1

If you have Emacs 24.3 or later, see Joe's answer for an alternative to the configuration described below. If you'll be using this double hop more than once, it may be worth either modifying tramp-default-proxies-alist as described below, or setting tramp-save-ad-hoc-proxies to t.

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If you have Emacs 23.1 or later, then the multi method is no longer supported. You can achieve the same result by configuring "proxies".

In your .emacs config file add the following:

(add-to-list 'tramp-default-proxies-alist
                 '("HOSTB" nil "/ssh:USERA@HOSTA:"))

Where HOSTB is the destination host behind HOSTA.

Then type /ssh:USERB@HOSTB: and emacs will prompt for the HOSTA password then the HOSTB password.

Answer 2

At least as of Emacs 24 they have a new version of multi you can open paths like this:

   /ssh:bird@bastion|ssh:you@remotehost:/path

I can confirm that this works on my version of Emacs 24.3.1. The docs describe it here.

Answer 3

You should use ssh to do the double hop. In your .ssh/config:

Host <host that must be proxied too>
ProxyCommand ssh -qxT <gateway host> nc %h %p

Answer 4

In earlier Emacs versions, Tramp had a multi method. On GNU Emacs 22 and below, you could use it like this:

/multi:ssh:user1@host1:ssh:user2@host2:/foo/bar/baz

to open /foo/bar/baz on host2. The same thing is possible on XEmacs, but with a somewhat different syntax. You can use different access methods, too.