chromeapps/nassh/doc/faq.txt

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                            hterm and  Secure Shell
                          Frequently  Asked Questions

                                 Version 0.8.2
                                August 27, 2012


Hello World.  This is the hterm/Secure Shell FAQ.  If you have a question that
is not answered here, please ask it on the chromium-hterm mailing list located
at <http://goo.gl/RYHiK>.


> What is "Secure Shell"?

  Secure Shell is a Chrome Application that combines the "ssh" command (see
  http://openssh.org/ for details) ported to NativeClient with the "hterm"
  terminal emulator to provide a secure shell client for the Chrome browser.

  Secure Shell provides similar functionality to PuTTY on Microsoft Windows(c)
  systems, and the ssh command-line application on Mac OS X and Linux systems.


> What is "hterm"?

  "HTML Terminal", or hterm, is an xterm-compatible terminal emulator written
  entirely in JavaScript.

  It is intended to be fast enough and correct enough to compete with native
  terminals such as xterm, gnome-terminal, konsole and Terminal.app.

  hterm is only a terminal emulator.  It does not provide SSH access (or any
  other text-based command) on its own.


> How do Secure Shell and hterm relate to the "crosh" (Ctrl-Alt-T) command in
  Chrome OS?

  See chromeos-crosh.txt in this directory for the details.

  TL;DR - Don't use crosh for ssh any more, use the Secure Shell app instead.
  The crosh shell will use the newer terminal emulator from Secure Shell when
  possible.


> How do hterm and Secure Shell differ from existing web terminals?

  hterm stands out from many existing web terminals in that it was built from
  the start to match the performance and correctness of "native" terminals such
  as xterm and Terminal.app.

  It can handle large bursts of text quickly, support very large scrollback
  buffers, and it closely matches xterm's behavior.  The keyboard even mostly
  works.  (ha!  See the note about how to get Ctrl-W below.)

  The Secure Shell app is different because it does not require a proxy or
  relay server to function.  Secure Shell can make a direct connection to
  a standard sshd server on any port of the destination machine.  Other
  web terminals require a proxy server in the middle.  In some cases you
  are even required to hand the proxy your credentials in plain text.


> Is my connection proxied in any way?

  No.  By default all connections are made directly to the sshd server on the
  destination machine.


> But, what if I *want* to ssh over HTTP?

  Secure Shell also knows how to connect to an HTTP-to-ssh relay that was
  built inside Google.  Unfortunately that relay isn't open source, and Google
  doesn't maintain a public pool of relays.

  However, you're free to build one that works the same way.  There should be
  enough documentation in nassh_google_relay.js to reverse engineer a
  compatible relay.

  If you're interested in writing an alternative relay library, please mention
  it on the mailing list.


> Is my connection really secure?

  The Secure Shell app uses ssh to manage the encrypted communication channels.
  This makes it about as secure as any other connection based on the ssh
  command.

  It does have the added advantage of running ssh as a sandboxed
  Native Client plugin, which in theory makes it more secure than an
  unsandboxed ssh connection.

  Additionally, the Secure Shell application follows a strict Content Security
  Policy that does not allow access to the JavaScript 'eval' function.  This
  helps lower the risk that a terminal exploit could run arbitrary JavaScript.


> What should I do if I notice a bug?

  First, please continue reading this FAQ to make sure your issue isn't
  mentioned.  Then check the bug list at <http://goo.gl/hpqWk>.

  If you don't see the issue there, you can search the archives of the
  chromium-hterm mailing list here: <http://goo.gl/RYHiK>.

  If all else fails then join the chromium-hterm mailing list and post
  about what you've found.

  If your bug involves some mis-interpreted escape sequence and you want
  to file a really useful bug report, then add in a recording of the
  session.  For bonus points, track down the troublesome sequence and
  include the offset into the log file.  For more information about how to
  do this, see the "Debugging escape sequences" section in the hack.txt file
  in this directory.


> Is there a mailing list to discuss hterm or Secure Shell?

  Yes, the public chromium-hterm mailing list is here: <http://goo.gl/RYHiK>.


> Can I connect using a public key pair or certificate?

  You can import identity files from the connection dialog.  Select the
  "Import..." link to bring up a file picker.

  You must import two files for each identity.  One should be the private key
  and should not have a file extension.  The other should be the public key,
  and must end in ".pub".  For example, "id_rsa" and "id_rsa.pub".

  If you have a key stored in a single ".pem" file, you must split it into two
  files before importing.

  This will import your public/private key files into the HTML5 filesystem
  associated with Secure Shell.  There should be no way for another extension,
  app, or web page to access this sandboxed filesystem.

  +-------------------------------------------------------------------------+
  | Keep in mind that HTML5 filesystems are relatively new.  As always,     |
  | it's possible that there are still exploits to be found or disclosed.   |
  |                                                                         |
  | Additionaly, Chrome stores HTML5 filesystems as normal files (with mode |
  | 600, "-rw-------") under your profile directory.  Non-Chrome            |
  | applications on your system may be able to access these files.          |
  |                                                                         |
  | For your own good, protect your important private keys with a strong    |
  | passphrase.                                                             |
  +-------------------------------------------------------------------------+

  You can also import a traditional ssh 'config' file using this dialog.
  Nearly anything that ssh might care about from your ~/.ssh directory can go
  here.

  See <http://www.openbsd.org/cgi-bin/man.cgi?query=ssh_config> for more
  information about the ssh configuration syntax.  Keep in mind that any
  directives that would require access outside of the NaCl sandbox will not
  function properly.  This includes (but is not limited to) X11 forwarding,
  syslog functionality, and anything that requires a domain socket.


> Can Secure Shell use my ~/.ssh/config file?

  Probably.  It depends on what it does.  See the answer to the previous
  question for more details.


> How do I remove a key?

  From the connection dialog, select an identity from the dropdown and press
  the DELETE key.  This will remove both the private and public key files from
  the HTML5 filesystem.


> How do I remove ALL keys?

  Open the JavaScript console and type...

    term_.command.removeDirectory('/.ssh/')

  This will remove any non-key files you may have uploaded as well.  It will
  *not* affect your preferences.


> Does Secure Shell support a keychain of some sort?

  Sorry, not yet.  This is a bit of a technical challenge given the nature
  of the NaCl sandbox.  We have a few options that we're exploring.  Feel
  free to post your ideas to the mailing list.

  (And yes, we're already considering integrating with the Chrome NSS
  certificate store.)


> Can I use Secure Shell for port forwarding?

  Yes.  Enter your port forwarding options in the "SSH Arguments" field of
  the connect dialog.  The port forward will be active for the duration of
  the Secure Shell session.


> What is the "Terminal Profile" field for?

  This is the last field in the connect dialog.  It allows you to select
  which set of terminal preferences to use for the connection.

  If you name a terminal profile that doesn't yet exist, it will be created
  and all preferences will be set to their default value.  Any preference
  changes will affect the active terminal profile only.

  For example, enter "light" as the name of a terminal profile for a new
  connection.  Once you've connected, change the color scheme to
  black-on-white (as described in the FAQ entried below).  That change will
  be associated with the "light" profile, and you'll be able to re-use it for
  other saved connections.


> How do I set terminal preferences?

  The Secure Shell application does not currently have a preferences page.
  It's in the works, and will be available before Secure Shell leaves
  "beta" status.  For now, you need to open the JavaScript console to
  change the user preferences.  Sorry about that.

  In general, you open the JavaScript console and type something like...

     term_.prefs_.set('pref-name', 'pref-value')

  Preferences are saved in your local storage, so they're remembered the
  next time you launch Secure Shell.

  If you want to check the current value of a preference, type this...

     term_.prefs_.get('pref-name')

  To reset a single preference to its default state, type this...

     term_.prefs_.reset('pref-name')

  To reset all preferences to their default state, type this...

     localStorage.clear()

  Most preference changes take effect immediately, in all open instances of
  Secure Shell.  The exception is the 'environment' setting, which won't
  take effect until the next time you reconnect.

  Some common preferences are listed in questions that follow.  For the full
  list, you'll have to read through the "setProfile" function in terminal.js.
  It's here: <http://goo.gl/FDEXb>, around line 130.


> How do I change the audible bell sound?

  Open the JavaScript console and type...

     term_.prefs_.set('audible-bell-sound', 'http://example.com/bell.ogg')

  Change the example url to point to the sound file you want to use.
  Unfortunately, local file: urls are not supported at this time.  If you
  want to get fancy you could construct a data: url, but the details of
  that are beyond the scope of this FAQ.


> How do I disable the audible bell?

  Open the JavaScript console and type...

     term_.prefs_.set('audible-bell-sound', '')


> How do I change the color scheme?

  You can change the foreground, background or cursor color preferences from
  the JavaScript console like this...

     term_.prefs_.set('background-color', 'wheat')
     term_.prefs_.set('foreground-color', '#533300')
     term_.prefs_.set('cursor-color', 'rgba(100, 100, 10, 0.5)')

  You can use any valid CSS color value for any of these colors.  You need
  to use a semi-transparent color (the fourth parameter in the rgba value)
  for the cursor if you want to be able to see the character behind it.


> How do I change the font face?

  Open the JavaScript console and type...

     term_.prefs_.set('font-family', 'Lucida Console')

  Replace 'Lucida Console' with your favorite monospace font.

  Keep in mind that some fonts, especially on Mac OS X systems, have bold
  characters that are larger than the non-bold version.  hterm will print a
  warning to the JS console if it detects that you've selected a font like
  this.  It will also disable "real" bold characters, using only bright
  colors to indicate bold.


> How do I change the default font size?

  Open the JavaScript console and type...

     term_.prefs_.set('font-size', 15)

  Replace 15 with your desired font size in pixels.  15 is the default, so
  you'll have to pick a different number to have any effect at all.


> Can I quickly make temporarily changes to the font size?

  Yes.  The Ctrl-Plus, Ctrl-Minus and Ctrl-Zero keys can increase, decrease,
  or reset the current font size.  This zoomed size is not remembered the
  next time you start hterm.  See the previous question if you want something
  that will stick.

  It's useful to know that hterm has to handle font zooming on its own.
  Without interference from the browser's built-in zoom function.

  The browser zoom introduces rounding errors in pixel measurements that
  make it difficult (maybe impossible) for hterm to accurately position the
  cursor on the screen.  (It could do a little better than it does but
  probably not enough to be worth the effort.)

  To mitigate this, hterm will display a warning message when your browser
  zoom is not 100%.  In this mode the Ctrl-Plus, Ctrl-Minus and Ctrl-Zero
  keys are passed directly to the browser.  Just press Ctrl-Zero to reset your
  zoom and dismiss the warning.

  hterm should start handling Ctrl-Plus, Ctrl-Minus and Ctrl-Zero on its
  own once your zoom setting is fixed.


> Why do I get a warning about my browser zoom?

  Because hterm requires you to set your browser to 100%, or 1:1 zoom.
  Try Ctrl-Zero or the Wrench->Zoom menu to reset your browser zoom.  The
  warning should go away after you correct the zoom level.

  See the previous question for more information.


> How do I disable anti-aliasing?

  Open the JavaScript console and type...

     term_.prefs_.set('font-smoothing', 'none')

  This directly modifies the '-webkit-font-smoothing' CSS property for the
  terminal.  As such, 'none', 'antialiased', and 'subpixel-antialiased' are
  all valid values.

  The default setting is 'antialiased'.


> How do I make the cursor blink?

  Open the JavaScript console and type...

     term_.prefs_.set('cursor-blink', true)

  Notice that true is NOT in quotes.  This is especially important if you try
  to turn blinking back off, with...

     term_.prefs_.set('cursor-blink', false)

  or you could just revert to the default value of false with...

     term_.prefs_.reset('cursor-blink')


> Why does hterm ignore the cursor blink escape sequence?

  Most terminals ignore attempts by the host to change the blink-state of the
  cursor.  This lets you choose between a blink/steady cursor via the
  cursor-blink preference, without having the host change your setting.

  By default, hterm also ignores this escape sequence.  To enable it, set the
  'enable-dec12' preference to true.

     term_.prefs_.set('enable-dec12', true)

> How do I change the TERM environment variable?

  Open the JavaScript console and type...

     term_.prefs_.set('environment', {TERM: 'hterm'})

  Notice that only 'hterm' is quoted, not the entire value.  You can replace
  'hterm' with whichever value you prefer.

  The default TERM value is 'xterm-256color'.  If you prefer to simulate a
  16 color xterm, try setting TERM to 'xterm'.

  You will have to reconnect for this setting to take effect.


> How do I enter accented characters?

  That depends on your platform and which accented characters you want to
  enter.

  In xterm, you could use Alt-plus-a-letter-or-number to select from the
  upper 128 characters.  The palette of 128 characters was "hardcoded" and
  not dependent on your keyboard locale.  You can set hterm to do the same
  thing by opening the JavaScript console and typing...

     term_.prefs_.set('alt-sends-what', '8-bit')

  However, if you are on Mac OS X and you prefer that Alt sends a character
  based on your keyboard locale, try this instead...

     term_.prefs_.set('alt-sends-what', 'browser-key')

  Note that composed characters (those that require multiple keystrokes) are
  not currently supported by this mode.

  If you are running Chrome OS on a Chromebook you can select your keyboard
  locale from the system settings and just use the Right-Alt (the small one,
  on the right) to enter accented characters.  No need to change the
  'alt-sends-what' preference at all.

  The default value for 'alt-sends-what' is 'escape'.  This makes Alt work
  mostly like a traditional Meta key.

  If you really, really want Alt to be an alias for the Meta key in every
  sense, use...

     term_.prefs_.set('alt-is-meta', true)


> How do I make backspace send ^H?

  By default, hterm sends a delete (DEL, '\x7f') character for the
  backspace key.  Sounds crazy, but it tends to be the right thing for
  most people.  If you'd prefer it send the backspace (BS, '\x08', aka ^H)
  character, then open the JavaScript console and type...

     term_.prefs_.set('backspace-sends-backspace', true)


> How do I remove a known host fingerprint (aka known_hosts) entry?

  If you know the index of the offending host entry (it's usually reported
  by ssh if the connection fails) you can open the JavaScript console and
  type...

     term_.command.removeKnownHostByIndex(index)

  Replace index with the numeric, one-based host index.

  If you don't know the index, or you'd like to clear all known hosts,
  type...

     term_.command.removeAllKnownHosts()


> How do I send Ctrl-W, Ctrl-N or Ctrl-T to the terminal?

  Chrome blocks tab contents from getting access to these (and a few other)
  keys.  You can open Secure Shell in a dedicated window to get around
  this limitation.  Just right-click on the Secure Shell icon and enable
  "Open as Window".

  After that, any time you launch Secure Shell it will open in a new window
  and respond properly to these accelerator keys.

  Note that the "Open as Window" option is not available on the Mac.  However,
  Mac keyboards typically have distinct Control, Alt, and Command keys, so it's
  less of an issue on that platform.  Secure Shell cannot treat Command as
  Control or Meta, but there are some third party keyboard utilities that may
  provide a solution.


> How do I copy text from the terminal?

  By default, Secure Shell automatically copies your active selection to the
  clipboard.

  You can disable this by setting the 'copy-on-select' preference to false.
  If you disable it you'll need to use one of the following key sequences
  to copy to the clipboard...

  * Under Mac OS X the normal Command-C sequence works.

  * On other platforms Ctrl-C will perform a Copy only when text is selected.
    When there is no current selection Ctrl-C will send a "^C" to the host.

    Note that after copying text to the clipboard the active selection will be
    cleared.  If you happen to have text selected but want to send "^C",
    just hit Ctrl-C twice.

  * Under all platforms you can also use the "Copy" command from the Wrench
    menu, when running Secure Shell in a browser tab.


> How do I paste text to the terminal?

  By default, Shift-Insert pastes the clipboard on all platforms.  If you'd
  prefer to be able to send Shift-Insert to the host, set the
  'shift-insert-paste' preference to false.

  Also...

  * Under Mac OS X the normal Command-V sequence can be used to paste from
    the clipboard.

  * On other platforms use Ctrl-Shift-V to paste from the clipboard.

  * Under X11, you can use middle-mouse-click to paste from the X clipboard.

  * Under all platforms you can also use the "Paste" command from the Wrench
    menu.


> Why does the cursor blink in emacs?

  This answer only applies if you've set the 'enable-dec12' preference to true.

  Do you normally use Terminal.app or xterm?  Those terminals (and many others)
  ignore the "ESC [ ? 12 h" and "ESC [ ? 12 l" sequences (DEC Private Mode 12).
  Emacs uses these sequences (on purpose) to enable and disable cursor blink.

  If you prefer a steady cursor in emacs, set visible-cursor to nil as
  described in <http://goo.gl/i9THb>.


> Why does the color scheme look funny in emacs/vi/vim?

  hterm's default value for the TERM environment variable is
  'xterm-256color'.  This causes emacs, vi, and some other programs to
  use a different color palette than when TERM='xterm'.

  You may notice these programs use a font color that is difficult to read
  over a dark background (such as dark blue).

  You can fix vi with ':set bg=dark'.  Emacs can be started in "reverse
  video" mode with 'emacs -rv'.

  If you just want your old 16 color palette back, open the JavaScript
  console and type...

     term_.prefs_.set('environment', {TERM: 'xterm'})

  Then restart Secure Shell.


> Can I use my mouse with Secure Shell?

  Sort of.  Both emacs and vi have mouse modes that are compatible with Secure
  Shell.

  In emacs, use `M-x xterm-mouse-mode` and `M-x mouse-wheel-mode`.  This will
  allow you to position the cursor with a mouse click, and use the wheel
  (or two-finger scroll) to scroll the buffer.

  In vi, use ":set mouse=a" to enable mouse mode.  Vi's mouse mode is slightly
  different from emacs in that it manages your text selection.  Some people
  prefer this, others may go crazy.

  A quick way to get your native selection back is to set the
  'mouse-cell-motion-trick' to true.  This will make vi's mouse support
  essentially the same as emacs.

  With the cell motion trick enabled, you lose the ability to select more
  than one screenful of text with the mouse.  Instead of using this trick,
  you may want to script vi so that it sends the current selection to
  Secure Shell to be copied to the system clipboard.  See the next question
  for some more information on this.


> Does hterm support the "OSC 52", aka "clipboard operations" sequence?

  Clipboard writing is allowed by default, but you can disable it if you're
  paranoid.  Set the 'enable-clipboard-write' preference to false to disable
  the control sequence.

  Clipboard read is not implemented.  Reading is a security hole you probably
  didn't want anyway.

  Clipboard writes are triggered by an escape sequence from the host.  Here's
  an example...

    $ echo -e "\x1b]52;c;Y29weXBhc3RhIQ==\x07"

  The sequence "\x1b]52;" identifies this as a clipboard operation.  The "c;"
  option selects the system clipboard.  "Y29weXBhc3RhIQ==" is the base64 encoded
  value to place on the clipboard, in this case it's the string "copypasta!".
  Finally, "\x07" terminates the sequence.

  If you execute this command when 'enable-clipboard-write' on you should see
  the "Selection Copied" message appear in the terminal, and your system
  clipboard should contain the text, "copypasta!".

  Note that the specification for OSC 52 mentions destinations other than
  the "c;" system clipboard.  Hterm treats them all as the system clipboard.


> Can I synchronize my emacs selection with the system clipboard?

  Yes, as long as you're not using tmux.  See ../etc/osc52.el (also,
  <http://goo.gl/5vWiS>) for the details.


> Is there a way to try early releases of Secure Shell?

  Yes.  First, you need to subscribe to the mailing list mentioned above.
  Subscribers have access to the "Dev" version in the Chrome Web Store, which
  is located here: <http://goo.gl/cFZlv>.

  Please keep in mind that the Dev version has gone through significantly less
  testing than the Beta.  Fortunately, you can install both and switch back
  to Beta if you have trouble with Dev.


> Where is the source code?

  The hterm source is here: <http://goo.gl/EqrV0>.  This includes the
  front-end code for Secure Shell.

  The Native Client wrapper around ssh is here: <http://goo.gl/760JC>.


> Is there a change log?

  Yes.  Look under the doc/ directory of the hterm source.

  There are two change logs.  One shows changes to the development version
  of Secure Shell.  The other shows stable releases.

  In general, the dev series of the form 0.X.Y.Z becomes the stable
  version 0.X.Y.  So SecureShell-dev-0.7.2.0, 0.7.2.1 and 0.7.2.2 all lead up
  to SecureShell-0.7.2.


> What if I want to make changes to the source?

  Read the hack.txt file in this directory.