bsdtelnet -- user interface to the TELNET protocol

SYNOPSIS

bsdtelnet [-4] [-6] [-8] [-E] [-L] [-N] [-S tos] [-a] [-c] [-d] [-e escapechar] [-f] [-l user] [-n tracefile] [-r] [host [port]]

DESCRIPTION

The bsdtelnet command is used to communicate with another host using the TELNET protocol. When bsdtelnet is invoked without the host argument, it enters command mode, indicated by its prompt telnet>. In this mode, it accepts and executes the commands listed below. If it is invoked with arguments, it performs an open command with those arguments.

Options

-4

Forces bsdtelnet to use IPv4 addresses only.

-6

Forces bsdtelnet to use IPv6 addresses only.

Note:: The MKS Toolkit telnetd service does not currently support IPv6. Such support is planned for a future release.

-8

Specifies an 8-bit data path. This causes an attempt to negotiate the TELNET BINARY option on both input and output.

-E

Stops any character from being recognized as an escape character.

-L

Specifies an 8-bit data path on output. This causes the BINARY option to be negotiated on output.

-N

Specifies a numeric host address. No attempt is made to look up symbolic names for host addresses.

-S tos

Sets the IP type-of-service (TOS) option for the telnet connection to the value tos, which can be a numeric TOS value or, on systems that support it, a symbolic TOS name found in the /etc/iptos file.

-a

Attempts automatic login. Currently, this sends the user name via the USER variable of the ENVIRON option if supported by the remote system. The name used is that of the current user as returned by ENVIRON if it agrees with the current user ID, otherwise it is the name associated with the user ID.

-c

Disables the reading of the user's .telnetrc file. (See the toggle skiprc command on this reference page.)

-d

Sets the initial value of the debug toggle to TRUE.

-e escape_char

Sets the initial bsdtelnet escape character to escape_char. When escape_char is omitted, there is no escape character.

-f

When Kerberos V5 authentication is being used, allows the local credentials to be forwarded to the remote system.

-l user

When connecting to the remote system, if the remote system understands the ENVIRON option, then user is sent to the remote system as the value for the variable USER. This option implies the -a option. This option may also be used with the open command.

-n tracefile

Opens tracefile for recording trace information. See the set tracefile command below.

-r

Specifies a user interface similar to rlogin. In this mode, the escape character is set to the tilde (~) character, unless modified by the -e option.

host

Indicates the official name, an alias, or the Internet address of a remote host.

port

Indicates a port number (address of an application). If a number is not specified, the default bsdtelnet port is used.

Input Modes

When in rlogin mode, a line of the form ~. disconnects from the remote host; ~ is the telnet escape character. Similarly, the line ~^Z suspends the telnet session. The line ~^] escapes to the normal telnet escape prompt.

Once a connection has been opened, bsdtelnet attempts to enable the TELNET LINEMODE option. If this fails, then bsdtelnet reverts to one of two input modes: either "character at a time" or "old line by line" depending on what the remote system supports.

When LINEMODE is enabled, character processing is done on the local system, under the control of the remote system. When input editing or character echoing is to be disabled, the remote system relays that information. The remote system also relays changes to any special characters that happen on the remote system, so that they can take effect on the local system.

In "character at a time" mode, most text typed is immediately sent to the remote host for processing.

In "old line by line" mode, all text is echoed locally, and (normally) only completed lines are sent to the remote host. The "local echo character" (initially ^E) may be used to turn off and on the local echo (this would mostly be used to enter passwords without the password being echoed).

When the LINEMODE option is enabled, or if the localchars toggle is TRUE (the default for "old line by line"; see below), the user's quit, intr, and flush characters are trapped locally, and sent as TELNET protocol sequences to the remote side. When LINEMODE has ever been enabled, then the user's susp and eof characters are also sent as TELNET protocol sequences, and quit is sent as a TELNET ABORT instead of BREAK. There are options (see toggle autoflush and toggle autosynch below) which cause this action to flush subsequent output to the terminal (until the remote host acknowledges the TELNET sequence) and flushes previous terminal input (in the case of quit and intr).

While connected to a remote host, bsdtelnet command mode may be entered by typing the bsdtelnet "escape character" (initially ^]). When in command mode, the normal terminal editing conventions are available.

Commands

The following bsdtelnet commands are available. Only enough of each command to uniquely identify it need be typed (this is also true for arguments to the mode, set, toggle, unset, slc, environ, and display commands).

close

Closes a TELNET session and returns to command mode.

display argument ...

Displays all, or some, of the set and toggle values (see below).

environ arguments ...

Manipulates the variables that may be sent through the TELNET ENVIRON option. The initial set of variables is taken from the user's environment, with only the DISPLAY and PRINTER variables being exported by default. The USER variable is also exported if the -a or -l options are used.

Valid arguments for the environ command are:

define variable value: Defines the variable variable to have a value of value . Any variables defined by this command are automatically exported. The value may be enclosed in single or double quotes so that tabs and spaces may be included.
undefine variable: Removes variable from the list of environment variables.
export variable: Marks the variable variable to be exported to the remote side.
unexport variable: Marks the variable variable to not be exported unless explicitly asked for by the remote side.
list: Lists the current set of environment variables. Those marked with a * are sent automatically, other variables are only sent if explicitly requested.
?: Displays help information for the environ command.

logout

Sends the TELNET LOGOUT option to the remote side. This command is similar to a close command; however, when the remote side does not support the LOGOUT option, nothing happens. If, however, the remote side does support the LOGOUT option, this command should cause the remote side to close the TELNET connection. When the remote side also supports the concept of suspending a user's session for later reattachment, the logout argument indicates that you should terminate the session immediately.

mode type

type is one of several options, depending on the state of the TELNET session. The remote host is asked for permission to go into the requested mode. When the remote host is capable of entering that mode, the requested mode is entered.

character: Disables the TELNET LINEMODE option, or, if the remote side does not understand the LINEMODE option, then enter "character at a time" mode.
line: Enables the TELNET LINEMODE option, or, if the remote side does not understand the LINEMODE option, then attempt to enter "old-line-by-line" mode.
isig (-isig): Attempts to enable (disable) the TRAPSIG mode of the LINEMODE option. This requires that the LINEMODE option be enabled.
edit (-edit): Attempts to enable (disable) the EDIT mode of the LINEMODE option. This requires that the LINEMODE option be enabled.
softtabs (-softtabs): Attempts to enable (disable) the SOFT_TAB mode of the LINEMODE option. This requires that the LINEMODE option be enabled.
litecho (-litecho): Attempts to enable (disable) the LIT_ECHO mode of the LINEMODE option. This requires that the LINEMODE option be enabled.
?: Displays help information for the mode command.

open host [-l user] [-a] [[-] port]

Opens a connection to the named host. When no port number is specified, bsdtelnet attempts to contact a TELNET server at the default port. The host specification may be either a host name (see hosts) or an Internet address specified in the "dot notation" (see inet()). The -l option may be used to specify the user name to be passed to the remote system via the ENVIRON option. If a port is specified, bsdtelnet omits any automatic initialization of TELNET options. When the port number is preceded by a minus sign, the initial option negotiation is done.

After establishing a connection, the file .telnetrc in the user's home directory is read. Lines beginning with a # are comment lines. Blank lines are ignored. Lines that begin without white space are the start of a machine entry. The first thing on such a line is a string identifying the machine that is being connected to. It may be the hostname or numeric address specified as the argument host, the canonical name of that string as determined by getaddrinfo(), or the string DEFAULT indicating all hosts. The rest of the line, and successive lines that begin with white space are assumed to be bsdtelnet commands and are processed as if they had been typed in manually to the bsdtelnet command prompt.

quit

Closes any open TELNET session and exit bsdtelnet. An end of file (in command mode) also closes a session and exits.

send arguments

Sends one or more special character sequences to the remote host. The following are the arguments which may be specified (more than one argument may be specified at a time):

abort: Sends the TELNET ABORT (Abort processes) sequence.
ao: Sends the TELNET AO (Abort Output) sequence, which should cause the remote system to flush all output from the remote system to the user's terminal.
ayt: Sends the TELNET AYT (Are You There) sequence, to which the remote system may or may not choose to respond.
brk: Sends the TELNET BRK (Break) sequence, which may have significance to the remote system.
ec: Sends the TELNET EC (Erase Character) sequence, which should cause the remote system to erase the last character entered.
el: Sends the TELNET EL (Erase Line) sequence, which should cause the remote system to erase the line currently being entered.
eof: Sends the TELNET EOF (End Of File) sequence.
eor: Sends the TELNET EOR (End of Record) sequence.
escape: Sends the current bsdtelnet escape character (initially ^).
ga: Sends the TELNET GA (Go Ahead) sequence, which likely has no significance to the remote system.
getstatus: When the remote side supports the TELNET STATUS command, sends the subnegotiation to request that the server send its current option status.
ip: Sends the TELNET IP (Interrupt Process) sequence, which should cause the remote system to abort the currently running process.
nop: Sends the TELNET NOP (No OPeration) sequence.
susp: Sends the TELNET SUSP (SUSPend process) sequence.
synch: Sends the TELNET SYNCH sequence. This sequence causes the remote system to discard all previously typed (but not yet read) input. This sequence is sent as TCP urgent data (and may not work if the remote system is a BSD 4.2 system -- if it doesn't work, a lower case r may be echoed on the terminal).
do cmd
dont cmd
will cmd
wont cmd: Sends the TELNET DO cmd sequence. cmd can be either a decimal number between 0 and 255, or a symbolic name for a specific TELNET command. cmd can also be either help or ? to display help information, including a list of known symbolic names.
?: Displays help information for the send command.

set argument value

unset argument value

Sets any one of a number of bsdtelnet variables to a specific value or to TRUE. The special value off turns off the function associated with the variable, this is equivalent to using the unset command. The unset command disables or sets to FALSE any of the specified functions. The values of variables may be interrogated with the display command. The variables which may be set or unset, but not toggled, are listed here. In addition, any of the variables for the toggle command may be explicitly set or unset using the set and unset commands.

ayt: When TELNET is in localchars mode, or LINEMODE is enabled, and the status character is typed, sends a TELNET AYT sequence (see send ayt above) to the remote host. The initial value for the "Are You There" character is the terminal's status character.
echo: Is the value (initially ^E) which, when in "line by line" mode, toggles between doing local echoing of entered characters (for normal processing), and suppressing echoing of entered characters (for entering, say, a password).
eof: When bsdtelnet is operating in LINEMODE or "old line by line" mode, entering this character as the first character on a line causes this character to be sent to the remote system. The initial value of the eof character is taken to be the terminal's eof character.
erase: When bsdtelnet is in localchars mode (see toggle localchars below), and bsdtelnet is operating in "character at a time" mode, this character sends a TELNET EC sequence (see send ec above) to the remote system. The initial value for the erase character is taken to be the terminal's erase character.
escape: Is the bsdtelnet escape character (initially ^[) which causes entry into bsdtelnet command mode (when connected to a remote system).
flushoutput: When bsdtelnet is in localchars mode (see toggle localchars below), this character sends a TELNET AO sequence (see send ao above) to the remote host. The initial value for the flush character is taken to be the terminal's flush character.
forw1
forw2: When TELNET is operating in LINEMODE, these characters, when typed, cause partial lines to be forwarded to the remote system. The initial value for the forwarding characters are taken from the terminal's eol and eol2 characters.
interrupt: When bsdtelnet is in localchars mode (see toggle localchars below), this character sends a TELNET IP sequence (see send ip above) to the remote host. The initial value for the interrupt character is taken to be the terminal's intr character.
kill: When bsdtelnet is in localchars mode (see toggle localchars below), and bsdtelnet is operating in "character at a time" mode, this character, when typed, sends a TELNET EL sequence (see send el above) to the remote system. The initial value for the kill character is taken to be the terminal's kill character.
lnext: When bsdtelnet is operating in LINEMODE or "old line by line" mode, then this character is taken to be the terminal's lnext character. The initial value for the lnext character is taken to be the terminal's lnext character.
quit: When bsdtelnet is in localchars mode (see toggle localchars below), this character sends a TELNET BRK sequence (see send brk above) to the remote host. The initial value for the quit character is taken to be the terminal's quit character.
reprint: When bsdtelnet is operating in LINEMODE or "old line by line" mode, then this character is taken to be the terminal's reprint character. The initial value for the reprint character is taken to be the terminal's reprint character.
rlogin: Is the rlogin escape character. When set, the normal TELNET escape character is ignored unless it is preceded by this character at the beginning of a line. This character, at the beginning of a line followed by a . closes the connection; when followed by a ^Z, it suspends the bsdtelnet command. The initial state is to disable the rlogin escape character.
start: When the TELNET TOGGLE-FLOW-CONTROL option has been enabled, this character is taken to be the terminal's start character. The initial value for the start character is taken to be the terminal's start character.
stop: When the TELNET TOGGLE-FLOW-CONTROL option has been enabled, this character is taken to be the terminal's stop character. The initial value for the stop character is taken to be the terminal's stop character.
susp: When bsdtelnet is in localchars mode, or LINEMODE is enabled, and the suspend character is typed, a TELNET SUSP sequence (see send susp above) is sent to the remote host. The initial value for the suspend character is taken to be the terminal's suspend character.
tracefile: Is the file to which the output, caused by netdata or option tracing being TRUE, is written. When it is set to -, tracing information is written to standard output (the default).
worderase: When bsdtelnet is operating in LINEMODE or "old line by line" mode, this character is taken to be the terminal's worderase character. The initial value for the worderase character is taken to be the terminal's worderase character.
?: Displays the legal set (unset) commands.

slc state

Sets or changes the state of the special characters when the TELNET LINEMODE option has been enabled. Special characters are characters that get mapped to TELNET commands sequences (like ip or quit) or line editing characters (like erase and kill). By default, the local special characters are exported.

check: Verifies the current settings for the current special characters. The remote side is requested to send all the current special character settings, and if there are any discrepancies with the local side, the local side switches to the remote value.
export: Switches to the local defaults for the special characters. The local default characters are those of the local terminal at the time when bsdtelnet was started.
import: Switches to the remote defaults for the special characters. The remote default characters are those of the remote system at the time when the TELNET connection was established.
?: Displays help information for the slc command.

status

Displays the current status of bsdtelnet. This includes the peer one is connected to, as well as the current mode.

toggle arguments ...

Toggles (between TRUE and FALSE) various flags that control how bsdtelnet responds to events. These flags may be set explicitly to TRUE or FALSE using the set and unset commands listed above. More than one argument may be specified. The state of these flags may be interrogated with the display command. Valid arguments are:

authdebug: Turns on debugging information for the authentication code.
autoflush: If autoflush and localchars are both TRUE, then when the ao, or quit characters are recognized (and transformed into TELNET sequences; see set above for details), bsdtelnet refuses to display any data on the user's terminal until the remote system acknowledges (via a TELNET TIMING MARK option) that it has processed those TELNET sequences. The initial value for this toggle is TRUE if the terminal user had not done an stty noflsh; otherwise, FALSE (see stty).
autologin: When the remote side supports the TELNET AUTHENTICATION option, TELNET attempts to use it to perform automatic authentication. When the AUTHENTICATION option is not supported, the user's login name are propagated through the TELNET ENVIRON option. This command is the same as specifying the -a option on the open command.
autosynch: When autosynch and localchars are both TRUE, then when either the intr or quit characters is typed (see set above for descriptions of the intr and quit characters), the resulting TELNET sequence sent is followed by the TELNET SYNCH sequence. This procedure should cause the remote system to begin throwing away all previously typed input until both of the TELNET sequences have been read and acted upon. The initial value of this toggle is FALSE.
binary: Enables or disables the TELNET BINARY option on both input and output.
inbinary: Enables or disables the TELNET BINARY option on input.
outbinary: Enables or disables the TELNET BINARY option on output.
crlf: When this is TRUE, carriage returns are sent as <CR><LF>. When this is FALSE, carriage returns are sent as <CR><NUL>. The initial value for this toggle is FALSE.
crmod: Toggles carriage return mode. When this mode is enabled, most carriage return characters received from the remote host are mapped into a carriage return followed by a line feed. This mode does not affect those characters typed by the user, only those received from the remote host. This mode is not very useful unless the remote host only sends carriage returns, but never line feeds. The initial value for this toggle is FALSE.
debug: Toggles socket level debugging (useful only to the super user). The initial value for this toggle is FALSE.
localchars: When this is TRUE, then the flush, interrupt, quit, erase, and kill characters (see set above) are recognized locally, and transformed into (hopefully) appropriate TELNET control sequences (respectively ao, ip, brk, ec, and el; see send above). The initial value for this toggle is TRUE in "old line by line" mode, and FALSE in "character at a time" mode. When the LINEMODE option is enabled, the value of localchars is ignored, and assumed to always be TRUE. If LINEMODE has ever been enabled, then quit is sent as abort, and eof and suspend are sent as eof and susp (see send above).
netdata: Toggles the display of all network data (in hexadecimal format). The initial value for this toggle is FALSE.
options: Toggles the display of some internal bsdtelnet protocol processing (having to do with TELNET options). The initial value for this toggle is FALSE.
prettydump: When the netdata toggle is enabled, if prettydump is enabled the output from the netdata command is formatted in a more user readable format. Spaces are put between each character in the output, and the beginning of any TELNET escape sequence is preceded by a * to aid in locating them.
skiprc: When the skiprc toggle is TRUE, TELNET skips the reading of the .telnetrc file in the users home directory when connections are opened. The initial value for this toggle is FALSE.
termdata: Toggles the display of all terminal data (in hexadecimal format). The initial value for this toggle is FALSE.
?: Displays the legal toggle commands.

z

Suspends bsdtelnet. This command only works when the user is using csh.

! [command]

Executes a single command in a subshell on the local system. When command is omitted, then an interactive subshell is invoked.

? [command]

Displays help. With no arguments, bsdtelnet displays a help summary. When command is specified, bsdtelnet displays the help information for just that command.

ENVIRONMENT VARIABLES

bsdtelnet uses at least the HOME, SHELL, DISPLAY, and TERM (which should be set to nutc for proper operation) environment variables. Other environment variables may be propagated to the other side via the TELNET ENVIRON option.

FILES

~/.telnetrc: Contains user customized bsdtelnet startup values.

PORTABILITY

Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019. Windows 11. Windows Server 2022.

NOTES

On some remote systems, echo has to be turned off manually when in "old line by line" mode.

In "old line by line" mode or LINEMODE the terminal's eof character is only recognized (and sent to the remote system) when it is the first character on a line.

AVAILABILITY

PTC MKS Toolkit for System Administrators
PTC MKS Toolkit for Developers
PTC MKS Toolkit for Interoperability
PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Professional Developers 64-Bit Edition
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition

bsdtelnet
user interface to the TELNET protocol

Command