4.4 Connecting to a remote host using multiple hops

Sometimes, the methods described before are not sufficient. Sometimes, it is not possible to connect to a remote host using a simple command. For example, if you are in a secured network, you might have to log in to a `bastion host' first before you can connect to the outside world. Of course, the target host may also require a bastion host. The format of multi-hop filenames is slightly different than the format of normal tramp methods.

A multi-hop file name specifies a method, a number of hops, and a localname (path name on the remote system). The method name is always multi.

Each hop consists of a hop method specification, a user name and a host name. The hop method can be an inline method only. The following hop methods are (currently) available:

telnet

Uses the well-known telnet program to connect to the host. Whereas user name and host name are supplied in the file name, the user is queried for the password.

rsh

This uses rsh to connect to the host. You do not need to enter a password unless rsh explicitly asks for it.

The variant remsh uses the remsh command. It should be applied on machines where remsh is used instead of rsh.

ssh

This uses ssh to connect to the host. You might have to enter a password or a pass phrase.

su

This method does not actually contact a different host, but it allows you to become a different user on the host you're currently on. This might be useful if you want to edit files as root, but the remote host does not allow remote root logins. In this case you can use telnet, rsh or ssh to connect to the remote host as a non-root user, then use an su hop to become root. But su need not be the last hop in a sequence, you could also use it somewhere in the middle, if the need arises.

Even though you must specify both user and host with an su hop, the host name is ignored and only the user name is used.

sudo

This is similar to the su hop, except that it uses sudo rather than su to become a different user.

Some people might wish to use port forwarding with ssh or maybe they have to use a nonstandard port. This can be accomplished by putting a stanza in ~/.ssh/config for the account which specifies a different port number for a certain host name. But it can also be accomplished within tramp, by adding a multi-hop method. For example:

     (add-to-list
      'tramp-multi-connection-function-alist
      '("sshf" tramp-multi-connect-rlogin "ssh %h -l %u -p 4400%n"))

Now you can use an sshf hop which connects to port 4400 instead of the standard port.