Keith Winstein
151 lines
4.8 KiB
Markdown
151 lines
4.8 KiB
Markdown
Mosh: the mobile shell
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======================
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Mosh is a remote terminal application that supports intermittent
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connectivity, allows roaming, and provides speculative local echo
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and line editing of user keystrokes.
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It aims to support the typical interactive uses of SSH, plus:
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* Mosh keeps the session alive if the client goes to sleep and
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wakes up later, or temporarily loses its Internet connection.
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* Mosh allows the client and server to "roam" and change IP
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addresses, while keeping the connection alive. Unlike SSH, Mosh
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can be used while switching between Wi-Fi networks or from Wi-Fi
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to cellular data to wired Ethernet.
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* The Mosh client runs a predictive model of the server's behavior
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in the background and tries to guess intelligently how each
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keystroke will affect the screen state. When it is confident in
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its predictions, it will show them to the user while waiting for
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confirmation from the server. Most typing and uses of the left-
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and right-arrow keys can be echoed immediately.
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As a result, Mosh is usable on high-latency links, e.g. on a
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cellular data connection or spotty Wi-Fi. In distinction from
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previous attempts at local echo modes in other protocols, Mosh
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works properly with full-screen applications such as emacs, vi,
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alpine, and irssi, and automatically recovers from occasional
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prediction errors within an RTT. On high-latency links, Mosh
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underlines its predictions while they are outstanding and removes
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the underline when they are confirmed by the server.
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Mosh does not support X forwarding or the non-interactive uses of SSH,
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including port forwarding.
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Other features
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--------------
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* Mosh adjusts its frame rate so as not to fill up network queues
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on slow links, so "Control-C" always works within an RTT to halt
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a runaway process.
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* Mosh warns the user when it has not heard from the server
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in a while.
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* Mosh supports lossy links that lose a significant fraction
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of their packets.
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* Mosh handles some Unicode edge cases better than SSH and existing
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terminal emulators by themselves, but requires a UTF-8
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environment to run.
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* Mosh leverages SSH to set up the connection and authenticate
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users. Mosh does not contain any privileged (root) code.
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Getting Mosh
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------------
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Mosh is available from an [Ubuntu PPA][] and has a [package in
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Debian unstable][Debian]. Packages for other operating systems are
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planned.
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[Ubuntu PPA]: https://launchpad.net/~keithw/+archive/mosh
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[Debian]: http://packages.debian.org/sid/mosh
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Ubuntu installation instructions:
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sudo add-apt-repository ppa:keithw/mosh
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sudo apt-get update
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sudo apt-get install mosh
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On a Unix-like system you can build Mosh from source using the following
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commands:
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./autogen.sh
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./configure
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make
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make install # as root
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`configure` accepts standard options, like `--prefix` to set the installation
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prefix. Pass `--help` for a full listing.
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To build and use Mosh you will need
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* [GNU Autotools][]
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* the [Protocol Buffers][] library and compiler
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* [Boost][]
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* `libutempter`
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* `zlib`
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* the Perl module [IO::Pty][]
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including development packages where applicable.
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The file `debian/control` contains a list of the relevant Debian packages.
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[GNU Autotools]: http://www.gnu.org/software/autoconf/
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[Protocol Buffers]: http://code.google.com/p/protobuf/
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[Boost]: http://www.boost.org/
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[IO::Pty]: http://search.cpan.org/~toddr/IO-Tty/Pty.pm
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Usage
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-----
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The `mosh-client` binary must be installed on the user's machine, and
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the `mosh-server` binary on the remote host.
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The user runs:
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$ mosh [user@]host
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If the `mosh-client` or `mosh-server` binaries are installed outside the
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user's PATH, `mosh` accepts the arguments `--client=PATH` and
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`--server=PATH` to select alternate locations.
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How it works
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------------
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The `mosh` program will SSH to `user@host` to establish the connection.
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SSH may prompt the user for a password or use public-key
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authentication to log in.
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From this point, `mosh` runs the `mosh-server` process (as the user)
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on the server machine. The server process listens on a high UDP port
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and sends its port number and an AES-128 secret key back to the
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client over SSH. The SSH connection is then shut down and the
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terminal session begins over UDP.
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If the client changes IP addresses, the server will begin sending
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to the client on the new IP address within a few seconds.
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To function, Mosh requires high-port UDP datagrams to be passed
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between client and server. Sites that have these ports firewalled
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would not be able to use Mosh.
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More info
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---------
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* Mosh Web site:
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<http://mosh.mit.edu>
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* `mosh-users@mit.edu` mailing list:
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<http://mailman.mit.edu/mailman/listinfo/mosh-users>
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