Mobile Terminal Application for Intermittent Connectivity - Mosh

Remote terminal application that allows roaming, supports intermittent connectivity, and provides intelligent local echo and line editing of user keystrokes. This is a replacement for SSH. It’s more robust and responsive, especially over Wi-Fi, cellular, and long-distance inks. Mosh is free software, available for GNU/Linux, FreeBSD, and Mac OS X.

Mosh is a remote terminal application that supports intermittent connectivity, allows roaming, and provides speculative local echo and line editing of user keystrokes.

Mobile Terminal Application: Mosh

It aims to support the typical interactive uses of SSH, plus: Mobile Terminal Application for 

ºMosh keeps the session alive if the client goes to sleep and wakes up later, or temporarily loses its Internet connection.
ºMosh allows the client and server to “roam” and change IP addresses, while keeping the connection alive. Unlike SSH, Mosh can be used while switching between Wi-Fi networks or from Wi-Fi to cellular data to wired Ethernet.
ºThe Mosh client runs a predictive model of the server’s behavior in the background and tries to guess intelligently how each keystroke will affect the screen state. When it is confident in its predictions, it will show them to the user while waiting for confirmation from the server. Most typing and uses of the left- and right-arrow keys can be echoed immediately.As a result, Mosh is usable on high-latency links, e.g. on a cellular data connection or spotty Wi-Fi. In distinction from previous attempts at local echo modes in other protocols, Mosh works properly with full-screen applications such as emacs, vi, alpine, and irssi, and automatically recovers from occasional prediction errors within an RTT. On high-latency links, Mosh underlines its predictions while they are outstanding and removes the underline when they are confirmed by the server.


Mosh does not support X forwarding or the non-interactive uses of SSH, including port forwarding.

Other features

ºadjusts its frame rate so as not to fill up network queues on slow links, so “Control-C” always works within an RTT to halt a runaway process.
ºwarns the user when it has not heard from the server in a while.
ºsupports lossy links that lose a significant fraction of their packets.
ºhandles some Unicode edge cases better than SSH and existing terminal emulators by themselves, but requires a UTF-8 environment to run.
ºleverages SSH to set up the connection and authenticate users. Mosh does not contain any privileged (root) code.

Usage

The mosh-client binary must exist on the user’s machine, and the mosh-server binary on the remote host.

The user runs:

$ mosh [user@]host

If the mosh-client or mosh-server binaries live outside the user’s $PATH, mosh accepts the arguments --client=PATH and --server=PATH to select alternate locations. More options are documented in the mosh(1) manual page.

There are more examples and a FAQ on the Mosh web site.

How it works

The mosh program will SSH to user@host to establish the connection. SSH may prompt the user for a password or use public-key authentication to log in.

From this point, mosh runs the mosh-server process (as the user) on the server machine. The server process listens on a high UDP port and sends its port number and an AES-128 secret key back to the client over SSH. The SSH connection is then shut down and the terminal session begins over UDP.

If the client changes IP addresses, the server will begin sending to the client on the new IP address within a few seconds.


To function, Mosh requires UDP datagrams to be passed between client and server. By default, moshuses a port number between 60000 and 61000, but the user can select a particular port with the -p option.

Download Mosh