|
1 | | -Mosh: the mobile shell |
2 | | -====================== |
3 | | - |
4 | | -Mosh is a remote terminal application that supports intermittent |
5 | | -connectivity, allows roaming, and provides speculative local echo |
6 | | -and line editing of user keystrokes. |
7 | | - |
8 | | -It aims to support the typical interactive uses of SSH, plus: |
9 | | - |
10 | | - * Mosh keeps the session alive if the client goes to sleep and |
11 | | - wakes up later, or temporarily loses its Internet connection. |
12 | | - |
13 | | - * Mosh allows the client and server to "roam" and change IP |
14 | | - addresses, while keeping the connection alive. Unlike SSH, Mosh |
15 | | - can be used while switching between Wi-Fi networks or from Wi-Fi |
16 | | - to cellular data to wired Ethernet. |
17 | | - |
18 | | - * The Mosh client runs a predictive model of the server's behavior |
19 | | - in the background and tries to guess intelligently how each |
20 | | - keystroke will affect the screen state. When it is confident in |
21 | | - its predictions, it will show them to the user while waiting for |
22 | | - confirmation from the server. Most typing and uses of the left- |
23 | | - and right-arrow keys can be echoed immediately. |
24 | | - |
25 | | - As a result, Mosh is usable on high-latency links, e.g. on a |
26 | | - cellular data connection or spotty Wi-Fi. In distinction from |
27 | | - previous attempts at local echo modes in other protocols, Mosh |
28 | | - works properly with full-screen applications such as emacs, vi, |
29 | | - alpine, and irssi, and automatically recovers from occasional |
30 | | - prediction errors within an RTT. On high-latency links, Mosh |
31 | | - underlines its predictions while they are outstanding and removes |
32 | | - the underline when they are confirmed by the server. |
33 | | - |
34 | | -Mosh does not support X forwarding or the non-interactive uses of SSH, |
35 | | -including port forwarding. |
36 | | - |
37 | | -Other features |
38 | | --------------- |
39 | | - |
40 | | - * Mosh adjusts its frame rate so as not to fill up network queues |
41 | | - on slow links, so "Control-C" always works within an RTT to halt |
42 | | - a runaway process. |
43 | | - |
44 | | - * Mosh warns the user when it has not heard from the server |
45 | | - in a while. |
46 | | - |
47 | | - * Mosh supports lossy links that lose a significant fraction |
48 | | - of their packets. |
49 | | - |
50 | | - * Mosh handles some Unicode edge cases better than SSH and existing |
51 | | - terminal emulators by themselves, but requires a UTF-8 |
52 | | - environment to run. |
53 | | - |
54 | | - * Mosh leverages SSH to set up the connection and authenticate |
55 | | - users. Mosh does not contain any privileged (root) code. |
56 | | - |
57 | | -Getting Mosh |
58 | | ------------- |
59 | | - |
60 | | - [The Mosh web site](http://mosh.mit.edu/#getting) has information about |
61 | | - packages for many operating systems, as well as instructions for building |
62 | | - from source. |
63 | | - |
64 | | - Note that `mosh-client` receives an AES session key as an environment |
65 | | - variable. If you are porting Mosh to a new operating system, please make |
66 | | - sure that a running process's environment variables are not readable by other |
67 | | - users. We have confirmed that this is the case on GNU/Linux, OS X, and |
68 | | - FreeBSD. |
69 | | - |
70 | | -Usage |
71 | | ------ |
72 | | - |
73 | | - The `mosh-client` binary must exist on the user's machine, and the |
74 | | - `mosh-server` binary on the remote host. |
75 | | - |
76 | | - The user runs: |
77 | | - |
78 | | - $ mosh [user@]host |
79 | | - |
80 | | - If the `mosh-client` or `mosh-server` binaries live outside the user's |
81 | | - `$PATH`, `mosh` accepts the arguments `--client=PATH` and `--server=PATH` to |
82 | | - select alternate locations. More options are documented in the mosh(1) manual |
83 | | - page. |
84 | | - |
85 | | - There are [more examples](http://mosh.mit.edu/#usage) and a |
86 | | - [FAQ](http://mosh.mit.edu/#faq) on the Mosh web site. |
87 | | - |
88 | | -How it works |
89 | | ------------- |
90 | | - |
91 | | - The `mosh` program will SSH to `user@host` to establish the connection. |
92 | | - SSH may prompt the user for a password or use public-key |
93 | | - authentication to log in. |
94 | | - |
95 | | - From this point, `mosh` runs the `mosh-server` process (as the user) |
96 | | - on the server machine. The server process listens on a high UDP port |
97 | | - and sends its port number and an AES-128 secret key back to the |
98 | | - client over SSH. The SSH connection is then shut down and the |
99 | | - terminal session begins over UDP. |
100 | | - |
101 | | - If the client changes IP addresses, the server will begin sending |
102 | | - to the client on the new IP address within a few seconds. |
103 | | - |
104 | | - To function, Mosh requires UDP datagrams to be passed between client |
105 | | - and server. By default, `mosh` uses a port number between 60000 and |
106 | | - 61000, but the user can select a particular port with the -p option. |
107 | | - |
108 | | -Advice to distributors |
109 | | ----------------------- |
110 | | - |
111 | | -A note on compiler flags: Mosh is security-sensitive code. When making |
112 | | -automated builds for a binary package, we recommend passing the option |
113 | | -`--enable-compile-warnings=error` to `./configure`. On GNU/Linux with |
114 | | -`g++` or `clang++`, the package should compile cleanly with |
115 | | -`-Werror`. Please report a bug if it doesn't. |
116 | | - |
117 | | -Where available, Mosh builds with a variety of binary hardening flags |
118 | | -such as `-fstack-protector-all`, `-D_FORTIFY_SOURCE=2`, etc. These |
119 | | -provide proactive security against the possibility of a memory |
120 | | -corruption bug in Mosh or one of the libraries it uses. For a full |
121 | | -list of flags, search for `HARDEN` in `configure.ac`. The `configure` |
122 | | -script detects which flags are supported by your compiler, and enables |
123 | | -them automatically. To disable this detection, pass |
124 | | -`--disable-hardening` to `./configure`. Please report a bug if you |
125 | | -have trouble with the default settings; we would like as many users as |
126 | | -possible to be running a configuration as secure as possible. |
127 | | - |
128 | | -Mosh ships with a default optimization setting of `-O2`. Some |
129 | | -distributors have asked about changing this to `-Os` (which causes a |
130 | | -compiler to prefer space optimizations to time optimizations). We have |
131 | | -benchmarked with the included `src/examples/benchmark` program to test |
132 | | -this. The results are that `-O2` is 40% faster than `-Os` with g++ 4.6 |
133 | | -on GNU/Linux, and 16% faster than `-Os` with clang++ 3.1 on Mac OS |
134 | | -X. In both cases, `-Os` did produce a smaller binary (by up to 40%, |
135 | | -saving almost 200 kilobytes on disk). While Mosh is not especially CPU |
136 | | -intensive and mostly sits idle when the user is not typing, we think |
137 | | -the results suggest that `-O2` (the default) is preferable. |
138 | | - |
139 | | -More info |
140 | | ---------- |
141 | | - |
142 | | - * Mosh Web site: |
143 | | - |
144 | | - <http://mosh.mit.edu> |
145 | | - |
146 | | - * `[email protected]` mailing list: |
147 | | - |
148 | | - <http://mailman.mit.edu/mailman/listinfo/mosh-devel> |
149 | | - |
150 | | - * `[email protected]` mailing list: |
151 | | - |
152 | | - <http://mailman.mit.edu/mailman/listinfo/mosh-users> |
153 | | - |
154 | | - * `#mosh` channel on [Freenode IRC](http://freenode.net/) |
155 | | - |
156 | | - http://webchat.freenode.net/?channels=mosh |
| 1 | +Alfalfa is a research project to build a videoconferencing system |
| 2 | +that works well over cellular wireless networks. It uses the same |
| 3 | +SSP protocol as Mosh, the mobile shell. |
0 commit comments