mosh - Online in the Cloud

PROGRAM:

NAME

mosh - mobile shell with roaming and intelligent local echo

SYNOPSIS

mosh [options] [--] [user@]host [command...]

DESCRIPTION

mosh (mobile shell) is a remote terminal application that supports intermittent
connectivity, allows roaming, and provides speculative local echo and line editing of user
keystrokes.

Compared with ssh, mosh is more robust — its connections stay up across sleeps and changes
in the client's IP address — and more responsive, because the protocol is tolerant of
packet loss and the client can echo most keystrokes immediately, without waiting for a
network round-trip.

mosh uses ssh to establish a connection to the remote host and authenticate with existing
means (e.g., public-key authentication or a password). mosh executes the unprivileged
mosh-server helper program on the server, then closes the SSH connection and starts the
mosh-client, which establishes a long-lived datagram connection over UDP.

To improve responsiveness, mosh runs a predictive model of the server's behavior in the
background, trying to guess the effect of each keystroke on the screen. It makes
predictions for normal typing, backspace, and the left- and right-arrow keys. When it is
confident, mosh displays the predictions without waiting for the server. The predictive
model must prove itself anew on each row of the terminal and after each control character,
so mosh avoids echoing passwords or non-echoing editor commands.

By default, mosh shows its predictions only on high-latency connections and to smooth out
network glitches. (On longer-latency links, the predicted cells are underlined until
confirmed by the server.) Occasional echo mistakes are corrected within a network round-
trip and do not cause lasting effect.

mosh does not support X forwarding or the non-interactive uses of SSH, including port
forwarding or sshfs. mosh works through typical client-side network address translators
but requires UDP to pass between client and server. By default, mosh uses the ports
between 60000 and 61000, but allows the user to request a particular UDP port instead.

mosh will do its best to arrange a UTF-8 character set locale on the client and server.
The client must have locale-related environment variables that specify UTF-8. mosh will
pass these client variables to the mosh-server on its command line, but in most cases they
will not need to be used. mosh-server first attempts to use its own locale-related
environment variables, which come from the system default configuration (sometimes
/etc/default/locale) or from having been passed over the SSH connection. But if these
variables don't call for the use of UTF-8, mosh-server will apply the locale-related
environment variables from the client and try again.

OPTIONS

command
Command to run on remote host. By default, mosh executes a login shell.

--client=PATH
path to client helper on local machine (default: "mosh-client")

--server=COMMAND
command to run server helper on remote machine (default: "mosh-server")

The server helper is unprivileged and can be installed in the user's home
directory.

--ssh=COMMAND
OpenSSH command to remotely execute mosh-server on remote machine (default: "ssh")

An alternate ssh port can be specified with, e.g., --ssh="ssh -p 2222".

--predict=WHEN
Controls use of speculative local echo. WHEN defaults to `adaptive' (show
predictions on slower links and to smooth out network glitches) and can also be
`always` or `never'.

The MOSH_PREDICTION_DISPLAY environment variable controls this setting permanently
and can adopt the same three values.

Even on `always', mosh will only show predictions when it is confident. This
generally means a previous prediction on the same row of the terminal has been
confirmed by the server, without any intervening control character keystrokes.

-a Synonym for --predict=always

-n Synonym for --predict=never

--family=FAMILY
Force the use of a particular address family, which defaults to `inet' (IPv4), and
can also be `inet6' (IPv6; requires IO::Socket::IP or IO::Socket::INET6).

-4 Synonym for --family=inet

-6 Synonym for --family=inet6

-p PORT[:PORT2], --port=PORT[:PORT2]
Use a particular server-side UDP port or port range, for example, if this is the
only port that is forwarded through a firewall to the server. Otherwise, mosh will
choose a port between 60000 and 61000.

--bind-server={ssh|any|IP}
Control the IP address that the mosh-server binds to.

The default is `ssh', in which case the server will reply from the IP address that
the SSH connection came from (as found in the SSH_CONNECTION environment variable).
This is useful for multihomed servers.

With --bind-server=any, the server will reply on the default interface and will not
bind to a particular IP address. This can be useful if the connection is made
through sslh or another tool that makes the SSH connection appear to come from
localhost.

With --bind-server=IP, the server will attempt to bind to the specified IP address.

--no-init
Do not send the smcup initialization string and rmcup deinitialization string to
the client's terminal. On many terminals this disables alternate screen mode.

ESCAPE SEQUENCES

The default escape character used by Mosh is ASCII RS (decimal 30). This is typically
typed as Ctrl-^ or Ctrl-Shift-6, on US English keyboards. Users of non-English keyboards
may find it difficult or impossible to type the default escape character, and may need to
change the escape character. See the description of MOSH_ESCAPE_KEY, below. In this
description, the configured escape character is represented as Esc.

There are two slightly different modes for escape sequences, depending whether the escape
character is printable or not.

If the escape character is a printable character, it must be prefixed with a newline,
similar to OpenSSH. To send the escape character itself, type it twice. If the escape
character is set to ~, mosh will behave much like OpenSSH.

If the escape character is a non-printable control character, no prefix is used and the
escape character is recognized at any time. To send the escape character itself, type the
escape character, then its corresponding ASCII character (for Ctrl-^ you would type ^, for
Ctrl-B you would type B).

The escape sequence to shut down the connection is Esc .. The sequence Esc Ctrl-Z suspends
the client. Any other sequence passes both characters through to the server.

ENVIRONMENT VARIABLES

These variables are not actually interpreted by mosh(1) itself, but are passed through to
mosh-server(1). They are described here for ease of use.

MOSH_ESCAPE_KEY
When set, this configures the escape character used for local commands. The escape
character may be set to any ASCII character in the range 1-127. The variable must
be set with a single literal ASCII character. Control characters are set with the
actual ASCII control character, not with a printable representation such as "^B".

MOSH_PREDICTION_DISPLAY
Controls local echo as described above. The command-line flag overrides this
variable.

MOSH_TITLE_NOPREFIX
When set, inhibits prepending "[mosh]" to window title.

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