Telnet

Advanced configuration of Telnet connection type
Support for the telnet protocol within Keeper Connection Manager is provided by the kcm-libguac-client-telnet package. Support for telnet is not installed by the @kcm package group, but is installed within the keeper/guacd Docker image. If this package has not yet been installed, telnet connections will not be functional, with guacd logging a warning noting the absence of needed protocol support:
guacd[8]: WARNING: Support for protocol "telnet" is not installed
If such an error appears within the guacd logs, simply installing kcm-libguac-client-telnet is sufficient to resolve the issue:
$ sudo yum install kcm-libguac-client-telnet
The guacd service does not need to be restarted for installation of telnet support to take effect.

Overview

Telnet is a text protocol and provides similar functionality to SSH. By nature, it is not encrypted, and does not provide support for file transfer. As far as graphics are concerned, Guacamole's telnet support works in the same manner as SSH: it emulates a terminal on the server side which renders to the Guacamole client's display.
Keeper's support for the telnet protocol is controlled through the use of several parameters. When a database like MySQL or PostgreSQL is used, these parameters are presented in a convenient web interface. If defining connections through another mechanism, such as through encrypted JSON or LDAP schema modifications, parameters are specified using their internal parameter names.
This document is intended to cover all supported parameters, grouped in the same way they are grouped within the web interface. The field headings which would appear in the web interface are provided for each parameter, along with each parameter's internal name and a thorough description of the behavior and legal values for that parameter.

Network parameters

Telnet connections are established over TCP to a specific port and a specific hostname or IP address. The hostname/address must be specified for all telnet connections, but you only need to specify a port if you are not using the standard telnet port (23).
Field header (web interface)
Parameter name
Description
Hostname:
hostname
REQUIRED: The hostname or IP address of the telnet server Guacamole should connect to.
Port:
port
The port the telnet server is listening on. By default, the standard telnet port of 23 will be used.

Authentication parameters

Telnet does not actually provide any standard means of authentication. Authentication over telnet depends entirely on the login process running on the server and is interactive. To cope with this, Guacamole provides non-standard mechanisms for automatically passing the username and entering password. Whether these mechanisms work depends on specific login process used by your telnet server.
The de-facto method for passing the username automatically via telnet is to submit it via the USER environment variable, sent using telnet's "NEW-ENVIRON" option. This is the mechanism used by most telnet clients, typically by specifying -l on the command line.
Passwords cannot typically be sent automatically - at least not as reliably as the username. There is no PASSWORD environment variable, nor any similar mechanism for passing the password to the telnet login process, and most telnet clients provide no built-in support for automatically entering the password. The best that can be done is to heuristically detect the password prompt and type the password on behalf of the user if/when the prompt appears. The prescribed method for doing this with a traditional command-line telnet is to use a utility like expect. Guacamole provides similar functionality by searching for the password prompt with a regular expression. This same regular expression mechanism is also implemented as an option for handling the username prompt (if "NEW-ENVIRON" is unavailable), as well as for detecting login success/failure.
Field header (web interface)
Parameter name
Description
Username:
username
The username to use to authenticate, if any. If not specified, or not supported by the telnet server, the login process on the telnet server will prompt you for your credentials. For this to work, your telnet server must either support the "NEW-ENVIRON" option (and pay attention to the USER environment variable) or provide a prompt which can be matched against a regular expression. Most telnet servers satisfy this criteria.
Password:
password
The password to use when attempting authentication, if any. If specified, your password will be typed on your behalf when the password prompt is detected.
Username regular expression:
username-regex
The regular expression to use to detect the username prompt when the username cannot be provided using "NEW-ENVIRON". If not specified, a reasonable default built into Guacamole will be used. Any regular expression provided must be written in the standard POSIX ERE dialect (the dialect used by egrep).
Password regular expression:
password-regex
The regular expression to use to detect the password prompt. If not specified, a reasonable default built into Guacamole will be used. Any regular expression provided must be written in the standard POSIX ERE dialect (the dialect used by egrep).
Login success regular expression:
login-success-regex
The regular expression to use when detecting that the login attempt has succeeded. If specified, the terminal display will not be shown to the user until text matching this regular expression has been received from the telnet server. Any regular expression provided must be written in the standard POSIX ERE dialect (the dialect used by egrep).
Login failure regular expression:
login-failure-regex
The regular expression to use when detecting that the login attempt has failed. If specified, the connection will be closed with an explicit login failure error if text matching this regular expression has been received from the telnet server. Any regular expression provided must be written in the standard POSIX ERE dialect (the dialect used by egrep).

Display settings

Guacamole's telnet support provides a display, but not in the same sense as a remote desktop protocol like VNC or RDP. The display is a terminal emulator, and thus provides options for configuring the font used and its size.
If selecting a different font for a telnet connection, the chosen font must be installed on the server running guacd. It is the server that will handle rendering of characters to the terminal display, not the client.
Field header (web interface)
Parameter name
Description
Color scheme:
color-scheme
The color scheme to use for the terminal emulator used by telnet connections. Each color scheme dictates the default foreground and background color for the terminal. Programs which specify colors when printing text will override these defaults. Legal values are:
  • "black-white" - Black text over a white background
  • "gray-black" - Gray text over a black background (the default)
  • "green-black" - Green text over a black background
  • "white-black" - White text over a black background
  • A custom color scheme (as described below)
By default, Guacamole will render text as gray over a black background.
Font name:
font-name
The name of the font to use. If not specified, the default of "monospace" will be used instead. This must be the name of a font installed on the server running guacd, and should be a monospaced font. If a non-monospaced font is used, individual glyphs may render incorrectly.
Font size:
font-size
The size of the font to use, in points. By default, the size of rendered text will be 12 point.
Maximum scrollback size:
scrollback
The maximum number of rows to allow within the terminal scrollback buffer. By default, the scrollback buffer will be limited to a maximum of 1000 rows.
Read-only:
read-only
Whether this connection should be read-only. If set to "true", no input will be accepted on the connection at all. Users will be able to see the terminal (or the application running within the terminal) but will be unable to interact.

Custom color schemes

Custom color schemes may be provided for the terminal emulator used by telnet connections. Custom schemes mimic the format used by Xterm and consist of a semicolon-separated series of name-value pairs. Each name-value pair is separated by a colon and assigns a value to a color in the terminal emulator palette.
For example, to use blue text on white background by default, and change the red color to a purple shade, you would specify:
foreground: rgb:00/00/ff;
background: rgb:ff/ff/ff;
color9: rgb:80/00/80
Legal color names are:
  • "foreground" - the default foreground color.
  • "background" - the default background color.
  • "colorN" - the color at index N within the Xterm 256-color palette. For example, "color9" refers to the color at palette index 9, normally red.
Legal color values are:
  • "rgb:RR/GG/BB" - a color in RGB format, with each component in hexadecimal. For example, "rgb:ff/00/00" specifies the color red. Each hexadecimal component may be one to four digits, but the effective values are always zero-extended or truncated to two digits; for example, "rgb:f/8/0", "rgb:f0/80/00", and "rgb:f0f/808/00f" all refer to the same effective color.
  • "colorN" - the color currently assigned to index N within the Xterm 256-color palette. For example, "color9" specifies the color currently assigned to palette index 9. Note that the current color value is used rather than a reference to that color. If the referenced color is changed later in the color scheme configuration, that new color value will not be reflected in this assignment.
  • "NAME" - the color with human-readable name "NAME", where "NAME" is one of the standard color names supported by X11. These names generally correspond to the names standardized by the W3C for CSS.

Clipboard parameters

Guacamole provides bidirectional access to the clipboard by default for telnet connections. This behavior can be overridden on a per-connection basis, restricting access to the clipboard.
Field header (web interface)
Parameter name
Description
Disable copying from terminal:
disable-copy
If set to "true", text copied within the telnet session will not be accessible by the user at the browser side of the Guacamole session, and will be usable only within the remote desktop. By default, the user will be given access to the copied text.
Disable pasting from client:
disable-paste
If set to "true", text copied at the browser side of the Guacamole session will not be accessible within the telnet session. By default, the user will be able to paste data from outside the browser within the telnet session.

Terminal behavior parameters

In most cases, the default behavior of the Guacamole terminal emulator works without modification. However, when connecting to certain systems (particularly operating systems other than Linux), the terminal behavior may need to be tweaked to allow it to operate properly. Guacamole's telnet support provides parameters for controlling the control code sent for backspace, as well as the terminal type claimed via the TERM environment variable.
Field header (web interface)
Parameter name
Description
Backspace key sends:
backspace
The integer value of the terminal control code that should be sent when backspace is pressed. Under most circumstances this should not need to be adjusted; however, if, when pressing the backspace key, you see control characters (often either ^? or ^H) instead of seeing the text erased, you may need to adjust this parameter. By default, the control code 127 (Delete) is sent.
Terminal type:
terminal-type
The terminal type string that should be passed to the telnet server. This value will typically be exposed within the telnet session as the TERM environment variable and will affect the control characters sent by applications. By default, the terminal type string "linux" is used.

Text session recording (typescripts)

The full, raw text content of telnet sessions, including timing information, can be recorded automatically to a specified directory. This recording, also known as a "typescript", will be written to two files within the directory specified: one file contains the raw text data, and the other contains timing information. Where "NAME" is the value provided for the typescript name, these files will be named "NAME" and "NAME.timing" respectively.
This format is compatible with the format used by the standard UNIX script command, and can be replayed using scriptreplay (if installed). For example, to replay a typescript called "NAME", you would run:
$ scriptreplay NAME.timing NAME
Field header (web interface)
Parameter name
Description
Typescript path:
typescript-path
The directory in which typescript files should be created. If a typescript needs to be recorded, then this parameter is required. Specifying this parameter enables typescript recording. If this parameter is omitted, no typescript will be recorded.
Typescript name:
typescript-name
The base filename to use for any created recordings. If omitted, the base filename "typescript" will be used.
Guacamole will never overwrite an existing typescript. If necessary, a numeric suffix like ".1", ".2", ".3", etc. will be appended to the base filename to avoid overwriting an existing recording. If even appending a numeric suffix does not help, the typescript will not be recorded, and an error will be logged.
This parameter only has an effect if typescript recording is enabled, which is controlled by specifying a typescript path. If the typescript path is not specified, recording of typescripts will not be enabled, and this parameter will be ignored.
Automatically create typescript path:
create-typescript-path
If set to "true", the final directory within the specified typescript path will automatically be created if it does not yet exist. By default, no part of the typescript path will be automatically created, and any attempt to use a non-existent directory will result in the typescript not being recorded and an error being logged.
Only the final directory in the path will be automatically created. If other directories earlier in the path do not exist, the typescript will not be recorded, and an error will be logged.
This parameter only has an effect if typescript recording is enabled, which is controlled by specifying a typescript path. If the typescript path is not specified, recording of typescripts will not be enabled, and this parameter will be ignored.

Screen recording parameters

Telnet sessions can be recorded graphically. These recordings take the form of Guacamole protocol dumps and are recorded automatically to a specified directory. Recordings can be subsequently played back using the Keeper Connection Manager Session Recording Player application hosted at player.glyptodon.com (or using a local deployment of this application).
The player is a static web application, using only JavaScript to play back provided recordings. This functionality is implemented strictly locally; the recordings are not uploaded to a remote service for processing. If you would prefer to use your own deployment of this application, or would like to investigate the source, the full source of the Keeper Connection Manager Session Recording Player can be found on GitHub, along with instructions for local deployment: https://github.com/glyptodon/glyptodon-enterprise-player
The latest version of Keeper Connection Manager supports on-screen playback of recorded sessions. See the Session Recording documentation page.
Field header (web interface)
Parameter name
Description
Recording path:
recording-path
The directory in which screen recording files should be created. If a graphical recording needs to be created, then this parameter is required. Specifying this parameter enables graphical screen recording. If this parameter is omitted, no graphical recording will be created.
Recording name:
recording-name
The filename to use for any created recordings. If omitted, the filename of each recording will simply be "recording".
Guacamole will never overwrite an existing recording. If necessary, a numeric suffix like ".1", ".2", ".3", etc. will be appended to the filename to avoid overwriting an existing recording. If even appending a numeric suffix does not help, the session will not be recorded, and an error will be logged.
This parameter only has an effect if graphical recording is enabled, which is controlled by specifying a recording path. If the recording path is not specified, graphical session recording will not be enabled, and this parameter will be ignored.
Exclude graphics/streams:
recording-exclude-output
If set to "true", graphical output and other data normally streamed from server to client will be excluded from the recording, producing a recording which contains only user input events. By default, graphical output will be included in the recording.
This parameter only has an effect if graphical recording is enabled, which is controlled by specifying a recording path. If the recording path is not specified, graphical session recording will not be enabled, and this parameter will be ignored.
Exclude mouse:
recording-exclude-mouse
If set to "true", user mouse events will be excluded from the recording, producing a recording which lacks a visible mouse cursor. By default, mouse events will be included in the recording.
This parameter only has an effect if graphical recording is enabled, which is controlled by specifying a recording path. If the recording path is not specified, graphical session recording will not be enabled, and this parameter will be ignored.
Include key events:
recording-include-keys
If set to "true", user key events will be included in the recording. The recording can subsequently be passed through the guaclog utility to produce a human-readable interpretation of the keys pressed during the session. By default, for privacy's sake, key events will be NOT included in the recording.
This parameter only has an effect if graphical recording is enabled, which is controlled by specifying a recording path. If the recording path is not specified, graphical session recording will not be enabled, and this parameter will be ignored.
Automatically create recording path:
create-recording-path
If set to "true", the final directory within the specified recording path will automatically be created if it does not yet exist. By default, no part of the recording path will be automatically created, and any attempt to use a non-existent directory will result in the session not being recorded and an error being logged.
Only the final directory in the path will be automatically created. If other directories earlier in the path do not exist, the session will not be recorded, and an error will be logged.
This parameter only has an effect if graphical recording is enabled, which is controlled by specifying a recording path. If the recording path is not specified, graphical session recording will not be enabled, and this parameter will be ignored.