SSH forward tunnel with tsocks

It is sometimes useful to open a tunnel to a given server, and make sure some programs access the network through that tunnel. For example, this could be used to avoid sniffing while browsing. Another example: only after connecting to the EPFL "tremplin" server can we access the school's private network.

The with-tsocks script is used to establish such SSH tunnel with SOCKS, and route a given command through it.

Download

with-tsocks is available both as a Pacman package (x86_64 only), or in source form. For source or Pacman installation, please refer to the Generic download and install instructions.

Usage

First of all, you should edit /etc/tsocks.conf and set a forwarding port there (using the server_port variable). Pick a value larger than 10000. I use port 19999. The file should look like this:

server = 127.0.0.1
server_port = 19999
server_type = 5

with-tsocks can be configured either through command line options or environment variables. Command line options take precedence over environment variable. The environment variables, and their respective command line options, are:

WITH_TSOCKS_SERVER: contains the server argument given to ssh, with the username. It is of the form username@example.com. The equivalent command line option is --server=SERVER. This parameter is required.
WITH_TSOCKS_SSHOPTS: space-separated additionnal options to pass to ssh. The equivalent command line option is --sshopts=OPTS
WITH_TSOCKS_NOPASS: whether with-tsocks should ask for a password when connecting to the SSH server. If 1, do not ask, otherwise ask. The equivalent command line option is --nopass
WITH_TSOCKS_FORWARD_PORT: the port number to use for local forwarding. The equivalent command line option is --forward-port=PORT. This parameter is required.

with-tsocks takes as argument the program to run through the tunnel. For example, to run mutt through an ssh tunnel at example.com, you would do something like:

$ with-tsocks --server=luser@example.com --forward-port=19999 mutt