Advanced configuration of Telnet connection type
Support for the telnet protocol within Keeper Connection Manager is provided by the
kcm-libguac-client-telnetpackage. Support for telnet is not installed by the
@kcmpackage group, but is installed within the
keeper/guacdDocker 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: WARNING: Support for protocol "telnet" is not installed
If such an error appears within the guacd logs, simply installing
kcm-libguac-client-telnetis 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.
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.
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).
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
USERenvironment variable, sent using telnet's "
NEW-ENVIRON" option. This is the mechanism used by most telnet clients, typically by specifying
-lon the command line.
Passwords cannot typically be sent automatically - at least not as reliably as the username. There is no
PASSWORDenvironment 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.
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.
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:
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: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.
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.
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
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 "
This format is compatible with the format used by the standard UNIX
scriptcommand, and can be replayed using
scriptreplay(if installed). For example, to replay a typescript called "
NAME", you would run:
$ scriptreplay NAME.timing NAME
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).