telnet(TC)

Syntax

Description

The following options are available:

-8

Use an eight bit data path. This will cause an attempt to negotiate the BINARY option on both input and output.

-E

Option stops any character from being recognized as an escape character.

-K

Disable automatic login.

-L

Use an eight bit data path on output. This causes the BINARY option to be negotiated on output.

-X atype

Disable authentication type atype. Currently, the only type supported is KERBEROS_V5.

-a

Automatic login into the remote system. If the remote system understands the ENVIRON option, then the variable USER will be exported to the remote system. This option may also be used with the open command.

-d

Toggles socket level debugging (useful only to root). Sets the initial value of the debug toggle to ``TRUE''.

-e [ escape_char ]

Sets the initial TELNET escape character to escape_char. If escape_char is omitted, then there will be no pre-defined escape character.

-k realm

Used to connect to a Kerberos Version 4 realm. This is not currently supported.

-l user

When connecting to the remote system and if the remote system understands the ENVIRON option, then user will be exported to the remote system as the value for the variable USER. This option may also be used with the open command.

-n tracefile

Opens tracefile for recording the trace information. (See the settracefile command below.)

-r

Use a user interface similar to rlogin(TC). In this mode, the escape character is set to the tilde (∼) character, unless modified by the -e flag.

host

Indicates the host's official name: an alias or the Internet address of a remote host.

host may be specified as an IP source-route. This takes the form of [!]@addr@addr@addr:dest. If the source-route is prefixed with the ``!'' character, it is interpreted as a strict source route. Otherwise, it is interpreted as a loose source route. See the IP specification for more information about source routing. Note: This exists primarily for debugging or for use when network connectivity is problematic. Use of source-routing is not normally recommended.

port

Indicates a port number (that is, the address of an application). If a number is not specified, the default TELNET port will be used.

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

In the character at a time mode, most entered text will be sent immediately to the remote host for processing.

In the old line by line mode, all text will be echoed locally, but (normally) only completed lines will be sent to the remote host. The ``local echo character'' (initially ``^E'') may be used to enable and disable the local echo mode; normally, this would be used only for entering passwords so that the password will not be echoed.

If the LINEMODE option is enabled or if the localchars toggle is ``TRUE'' (the default value for the old line by line mode; see below), the user's quit, intr, and flush characters will be trapped locally and sent as TELNET protocol sequences to the remote machine. If LINEMODE had been enabled at any earlier time, then the user's susp and eof characters will also be sent as TELNET protocol sequences; quit will be sent as a TELNET ABORT instead of <Break>. There are options (see toggle autoflush and toggle autosynch below) which cause this action to flush any subsequent output to the terminal (until the remote host acknowledges the TELNET sequence) and to flush previous terminal input (in the case of quit and intr).

While connected to a remote host, the telnet command mode may be entered by typing the TELNET <Esc> (initially ``^]'').

When in command mode, the normal terminal editing conventions will be available.

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

auth argument

This command controls authentication according to the value of argument:

enable type

Enable authentication type type. Currently, the only type supported is KERBEROS_V5.

disable type

Disable authentication type type. Currently, the only type supported is KERBEROS_V5.

help

Display help information about the auth command.

status

Display the current types of authentication, and whether they are enabled or disabled.

?

Same as help

close

Close a TELNET session and return to command mode.

display argument ...

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

mode [ type ]

Depending on the state of the TELNET session, the type argument is one of several available options. The remote host will be asked for permission to go into the requested mode. If the remote host is capable of entering that mode, the requested mode will be entered.

character

Disable the TELNET LINEMODE option; or, if the remote side does not understand the TELNET LINEMODE option, then enter the character at a time mode.

line

Enable the TELNET LINEMODE option; or, if the remote side does not understand the TELNET LINEMODE option, then attempt to enter the old line by line mode.

isig
-isig

Attempt to enable (disable) the TRAPSIG mode of the TELNET LINEMODE option. This requires that the LINEMODE option be enabled.

edit
-edit

Attempt to enable (disable) the EDIT mode of the LINEMODE option. This requires that the LINEMODE option be enabled.

softtabs
-softtabs

Attempt to enable (disable) the SOFT_TAB mode of the LINEMODE option. This requires that the LINEMODE option be enabled.

litecho
-litecho

Attempt to enable (disable) the LIT_ECHO mode of the LINEMODE option. This requires that the LINEMODE option be enabled.

?

Prints out help information for the mode command.

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

Open a connection to the named host. If no port number is specified, telnet will attempt to contact a TELNET server at the default port. The host specification may be either a host name (see hosts(SFF)) or an Internet address specified in the ``dot notation'' (see inet(SLIB)).

The -l or the -a option may be used to specify the user name to be passed to the remote system via the ENVIRON option.

When connecting to a non-standard port, telnet will omit the automatic initiation of any TELNET options. When the port number is preceded by a minus sign, the initial option negotiation will be done as follows: After establishing a connection, the file .telnetrc in the user's home directory will be opened. Lines beginning with a ``#'' will be treated as comment lines; blank lines will be ignored. Lines that begin without whitespace will be the start of a machine entry. The first thing on the line will be the name of the machine to which this host is being connected. The rest of the line -- and successive lines which begin with whitespace -- will be assumed to be telnet commands and will be processed as if they had been entered manually in response to the telnet command prompt.

quit

Close any open TELNET session and exit telnet. When in command mode, an End-of-File (EOF) will also close a session and exit.

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 given 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; the remote system may or may not choose to respond to this transmission.

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 TELNET escape character (initially ``^]'').

ga

Sends the TELNET GA (Go Ahead) sequence, which probably has no significance to the remote system.

getstatus

If the remote side supports the TELNET STATUS command, getstatus will send the subnegotiation 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 will be sent as TCP urgent data (and may not work if the remote system is a 4.2 BSD system; if it does not work, a lowercase ``|'' may be echoed on the terminal).

?

Prints out help information for the send command.

set argument value
unset argument value

The set command will set any one of a number of TELNET variables to a specific value or to ``TRUE''. The special value off will turn off the function associated with this variable; this is equivalent to using the unset command. The unset command will disable (or set to ``FALSE'') any of the specified functions. The values of variables may be interrogated with the aid of 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 enabled or disabled using the set and unset commands.

echo

This is the value (initially ``^['') which, when in the line by line mode, will toggle between doing local echoing of entered characters (for normal processing) and suppressing echoing of entered characters (for example, for entering a password).

eof

If telnet is operating in LINEMODE or in the old line by line mode, entering this character as the first character on a line will cause 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

If telnet is in localchars mode (see ``toggle'' localchars below), and if telnet is operating in the character at a time mode, then when this character is entered, a TELNET EC sequence (see send ec above) will be sent to the remote system. The initial value for the erase character is taken to be the terminal's erase character.

escape

This is the TELNET escape character (initially ``^]'') which causes entry into the TELNET command mode when connected to a remote system.

flushoutput

If telnet is in localchars mode (see toggle localchars below) and the flushoutput character is entered, a TELNET AO sequence (see send ao above) will be sent to the remote host. The initial value for the flush character is taken to be the terminal's flush character.

interrupt

If TELNET is in localchars mode (see toggle localchars below) and the interrupt character is entered, a TELNET IP sequence (see send ip above) will be sent to the remote host. The initial value for the interrupt character is taken to be the terminal's intr character.

kill

If TELNET is in localchars mode (see toggle localchars below), and if TELNET is operating in the character at a time mode, then when this character is entered, a TELNET EL sequence (see send el above) will be sent to the remote system. The initial value for the kill character is taken to be the terminal's kill character.

lnext

If TELNET is operating in LINEMODE or in the 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

If TELNET is in localchars mode (see toggle localchars below) and the quit character is entered, a TELNET BRK sequence (see send brk above) will be sent to the remote host. The initial value for the quit character is taken to be the terminal's quit character.

reprint

If TELNET is operating in LINEMODE or in the 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.

start

If the TELNET TOGGLE-FLOW-CONTROL option has been enabled, then 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

If the TELNET TOGGLE-FLOW-CONTROL option has been enabled, then 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.

forw1

If TELNET is in the localchars mode, then this character is taken to be an alternate end of line character.

forw2

If TELNET is in the localchars mode, then this character is taken to be an alternate end of line character.

ayt

If TELNET is in the localchars mode, then this character is taken to be the alternate AYT character.

susp

If TELNET is in the localchars mode or if the LINEMODE is enabled and the suspend character is entered, a TELNET SUSP sequence (see send susp above) will be sent to the remote host. The initial value for the suspend character is taken to be the terminal's suspend character.

tracefile

This is the file to which the output generated by the netdata command will be written.

worderase

If TELNET is operating in LINEMODE or in the old line by line mode, then 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 and unset commands.

slc [ state ]

The slc command (Set Local Characters) sets (or changes) the state of the special characters when the TELNET LINEMODE option has been enabled. The ``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.

export

Switch to the local defaults for the ``special characters''. The local default characters are those of the local terminal at the time when telnet was started.

import

Switch 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.

check

Verify the current settings for the current ``special characters''. The remote side is requested to send all the current special character settings; if there are any discrepancies with the local side, the local side will switch to the set of remote values.

?

Prints out help information for the slc command.

environ [ argument [ ... ] ]

The environ command manipulates the variables that may be sent through the TELNET ENVIRON option. The initial set of variables is taken from the user's environment; only the DISPLAY, LANG, and PRINTER variables are automatically exported although USER may also be exported in some circumstances.

The valid arguments for the environ command are:

define variable value

Define the 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 embedded spaces may be included.

undefine variable

Remove variable from the list of environment variables.

export variable

Mark the variable to be exported to the remote side.

unexport variable

Mark the variable to not be exported unless explicitly requested by the remote side.

list

List the current set of environment variables. Those marked with a ``*'' will be sent automatically; any other variables will be sent only if requested explicitly.

send variable

Send environment variable.

?

Prints out help information for the environ command.

toggle arguments [ ... ]

Toggle various flags (between ``TRUE'' and ``FALSE'') that control how TELNET 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 aid of the display command.

The valid arguments are:

autoflush

If autoflush and localchars are both ``TRUE'', then when the ao or the quit characters are recognized (and transformed into TELNET sequences; see set above for details), TELNET will refuse 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 executed an stty noflsh; otherwise ``FALSE'' (see stty(C)).

autologin

Same as the -a option on the command line.

toggle authdebug

authdebug

Display verbose debugging information about authentication.

autosynch

If autosynch and localchars are both ``TRUE'', then when either the intr or quit character is entered (see set above for descriptions of the intr and quit characters), the resulting TELNET sequence sent will be followed by the TELNET SYNCH sequence. This procedure should cause the remote system to begin throwing away all previously entered input until both of the TELNET sequences have been read and acted upon. The initial value of this toggle is ``FALSE''.

binary

Enable or disable the TELNET BINARY option on both the input and output.

inbinary

Enable or disable the TELNET BINARY option on input.

outbinary

Enable or disable the TELNET BINARY option on output.

crlf

If this toggle value is ``TRUE'', then Carriage Returns will be sent as ``<CR><LF>''. If this is ``FALSE'', then Carriage Returns will be sent as ``<CR><NUL>''. The initial value for this toggle is ``FALSE''.

crmod

Toggle the Carriage Return mode. When this mode is enabled, most Carriage Return characters received from the remote host will be mapped into a Carriage Return followed by a Line Feed. This mode does not affect those characters entered by the user, but only those received from the remote host. This mode is not very useful unless the remote host only sends Carriage Return, but never any Line Feeds. The initial value for this toggle is ``FALSE''.

debug

Toggles the socket level debugging mode (useful only to root). The initial value for this toggle is ``FALSE''.

localchars

If this is ``TRUE'', then the flush, interrupt, quit, erase, and kill characters (see set above) are recognized locally and then transformed into 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 will be sent as abort; eof and suspend will be 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 telnet protocol processing which pertain to TELNET options. The initial value for this toggle is ``FALSE''.

prettydump

When the netdata toggle is enabled and if prettydump is enabled, the output from the netdata command will be reorganized into a more user-friendly format. Spaces will be put between each character in the output and the beginning of any TELNET escape sequence will be preceded by a ``*'' to aid in locating them.

skiprc

Toggle does not process ∼/.telnetrc file. The initial value for this toggle is ``FALSE''.

termdata

Toggles printing of hexadecimal terminal data. The initial value for this toggle is ``FALSE''.

?

Displays the legal toggle commands.

<Ctrl>Z

Suspend telnet. This command will work only when the user is using csh(C) or ksh(C).

! [ command ]

Execute a single command in a subshell on the local system. If command is omitted, then an interactive subshell will be invoked.

status

Show the current status of telnet. This includes the peer to which one is connected, as well as the current mode.

? [ command ]

Get help. When no command is specified, telnet will print a summary for the help command. If a command is specified, telnet will print the help information for just that command.

Environment variables

Other environment variables may be propagated to the remote side via the TELNET ENVIRON option.

USER is set to LOGNAME if LOGNAME is set locally but USER is not. By default, USER is not set.

Authenticated telnet using Kerberos

The user executing telnet is logged in on the remote host without entering a password, provided the -a or -l user options are used (these send a user name to the telnetd service daemon), the user has network credentials, and the user's principal name appears in the $HOME/.k5login file on the remote host.

Limitations

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

Authentication is based on Version 5 of the Kerberos Network Authentication Service protocol. Only this version of the protocol is supported.

Data encryption is not supported.

Using telnet(TC) to log into a machine running SCO UNIX System V/386 Release 3.2 Operating System Version 4.2 can give the error message bad login user id.

This message appears when a user, already logged in as a non-root user, recursively logs in as root and runs tcp stop followed by tcp start -- see the tcp(ADMN) manual page.

To avoid this error, start TCP/IP using the sd(ADM) command while logged in as root. To do so, enter the following command:

sd tcp start

Only root and other users with the sysadmin authorization are permitted to run sd.

Files

$HOME/.telnetrc

user-customized telnet startup values

$HOME/.k5login

equivalent users for authenticated rcmd

/krb5/v5srvtab

local default service key table

See also

Standards conformance

telnet is conformant with:
RFC 727, RFC 854, RFC 856 (STD 27), RFC 857 (STD 28), RFC 858 (STD 29), RFC 859 (STD 30), RFC 860 (STD 31), RFC 1073, RFC 1079, RFC 1080, RFC 1091, RFC 1096, RFC 1123, RFC 1184

SCO OpenServer Release 5.0.6 -- 1 August 2000