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SSH and Mosh on Debian

Ronald MacDonald <ronald@rmacd.com> v1.0, Sat Apr 14 15:22:16 EDT 2012

Ever been stuck on a train, with a half-assed connection, trying to access your SSH server, only for the connection to drop every time you hit a tunnel? Ever sat in Starbucks for way too long, only for your VPN to die as the Powers That Be™ decide you should reauthenticate to the AP? Dropping all 10 of your sessions? Mosh is your answer (and mine).

Introduction

I run Debian Squeeze with OpenSSH, sitting behind Shorewall. I access my systems using OS X’s SSH client. I also use MacPorts.

This simple guide will show you how to quickly get up and running with Mosh.

Installation

Mosh sits between your usual SSH session, setting up a session across UDP. Obviously, we’ll need to set up both the server and the client. Note we don’t actually need to run as a privileged user (though piercing holes through Shorewall, to get it to actually work, is another matter).

Client-side

If you’re using OS X, things are easy. With MacPorts:

sudo port install mosh

Or you may head on over to downloads, to grab a binary (OS X 10.5 or later). Once it’s installed, you’re good to go, unless you’re setting up the server-side as well, below.

Server-side

apt-gpt install libboost-dev libncurses5-dev libprotobuf-dev libutempter-dev protobuf-compiler

This’ll install libboost1.42 development libraries and libicu44, which is a set of libraries to support unicode. As we also need ncurses headers, we’ve added that as well. Finally, apt should correct dependencies so as to also add libprotobuf-lite6 and libprotobuf6 to the list.

If you also wish to allow dpkg to manage your packages (which is what I do), consider also doing the following:

apt-get install dpkg-dev checkinstall

Once that’s done, download and untar, then make sure you’re a normal user (not root), cd into the directory, and do the usual:

wget https://github.com/downloads/keithw/mosh/mosh-1.1.3.tar.gz
tar -zxvf mosh-1.1.3.tar.gz
cd mosh-1.1.3
./autogen.sh
./configure

Good stuff. Now:

make
checkinstall make install

I tend to carry out the checkinstall as a normal user, just so I can review everything before:

dpkg -i mosh_1.1.3-1_amd64.deb

Done! Now, you should be ready to go, unless you’re also using Shorewall, which we’ll have a look at in a second. To SSH using Mosh:

mosh user@example.com

Easy!

Shorewall config

Macros are already defined under /usr/share/shorewall, so let’s just use the SSH macro. In /usr/share/shorewall/macro.SSH add the bottom line to make it look like follows

PARAM  -       -       tcp     22
PARAM  -       -       udp     60000:61000

Restart, and you’re done. Happy days.