TELNET(1)                    BSD Reference Manual                    TELNET(1)

NAME
     telnet - user interface to the TELNET protocol

SYNOPSIS
     telnet [-8EFKLacdfrx] [-S tos] [-X authtype] [-e escapechar] [-k realm]
            [-l user] [-n tracefile] [host [port]]

DESCRIPTION
     The telnet command is used to communicate with another host using the
     TELNET protocol.  If telnet is invoked without the host argument, it en-
     ters 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:

     --88      Specifies an 8-bit data path.  This causes an attempt to negoti-
             ate the TELNET BINARY option on both input and output.

     -E      Stops any character from being recognized as an escape character.

     -F      If Kerberos V5 authentication is being used, the -F option allows
             the local credentials to be forwarded to the remote system, in-
             cluding any credentials that have already been forwarded into the
             local environment.

     -K      Specifies no automatic login to the remote system.

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

     -S tos  Sets the IP type-of-service (TOS) option for the telnet connec-
             tion 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.

     -X atype
             Disables the atype type of authentication.

     -a      Attempt automatic login.  Currently, this sends the user name via
             the USER variable of the ENVIRON option if supported by the re-
             mote system.  The name used is that of the current user as re-
             turned by getlogin(2) if it agrees with the current user ID, oth-
             erwise 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 man page.)

     -d      Sets the initial value of the debug toggle to TRUE

     -e escape char
             Sets the initial telnet telnet escape character to escape char.
             If escape char is omitted, then there will be no escape charac-
             ter.

     -f      If Kerberos V5 authentication is being used, the -f option allows
             the local credentials to be forwarded to the remote system.

     -k realm
             If Kerberos authentication is being used, the -k option requests
             that telnet obtain tickets for the remote host in realm realm in-
             stead of the remote host's realm, as determined by

             krb_realmofhost(3).

     -l user
             When connecting to the remote system, if the remote system under-
             stands the ENVIRON option, then user will be 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 com-
             mand.

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

     -r      Specifies a user interface similar to rlogin(1).  In this mode,
             the escape character is set to the tilde (~) character, unless
             modified by the -e option.

     -x      Turns on encryption of the data stream if possible.  This option
             is not available outside of the United States and Canada.

     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 telnet port is used.

     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, telnet will attempt to enable the
     TELNET LINEMODE option.  If this fails, then telnet will revert 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 sys-
     tem, under the control of the remote system.  When input editing or char-
     acter echoing is to be disabled, the remote system will relay that infor-
     mation.  The remote system will also relay changes to any special charac-
     ters 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 char-
     acter'' (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).

     If 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 se-
     quences to the remote side.  If LINEMODE has ever been enabled, then the
     user's susp and eof 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 flush previous terminal input (in the case of quit
     and intr).

     While connected to a remote host, telnet command mode may be entered by
     typing the telnet ``escape character'' (initially ``^]'').  When in com-
     mand mode, the normal terminal editing conventions are available.

     The following telnet 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).

     auth argument ...
                The auth command manipulates the information sent through the
                TELNET AUTHENTICATE option.  Valid arguments for the auth com-
                mand are as follows:

                disable type  Disables the specified type of authentication.
                              To obtain a list of available types, use the
                              auth disable ?? command.

                enable type   Enables the specified type of authentication.
                              To obtain a list of available types, use the
                              auth enable ?? command.

                status        Lists the current status of the various types of
                              authentication.

     close      Close a TELNET session and return to command mode.

     display argument ...
                Displays all, or some, of the set and toggle values (see be-
                low).

     encrypt argument ...
                The encrypt command manipulates the information sent through
                the TELNET ENCRYPT option.

                Note:  Because of export controls, the TELNET ENCRYPT option
                is not supported outside of the United States and Canada.

                Valid arguments for the encrypt command are as follows:

                disable type [input|output]
                              Disables the specified type of encryption.  If
                              you omit the input and output, both input and
                              output are disabled.  To obtain a list of avail-
                              able types, use the encrypt disable ?? command.

                enable type [input|output]
                              Enables the specified type of encryption.  If
                              you omit input and output, both input and output
                              are enabled.  To obtain a list of available
                              types, use the encrypt enable ?? command.

                input         This is the same as the encrypt start input com-
                              mand.

                -input        This is the same as the encrypt stop input com-
                              mand.

                output        This is the same as the encrypt start output
                              command.

                -output       This is the same as the encrypt stop output com-
                              mand.

                start [input|output]
                              Attempts to start encryption.  If you omit input
                              and output, both input and output are enabled.
                              To obtain a list of available types, use the


                              encrypt enable ?? command.

                status        Lists the current status of encryption.

                stop [input|output]
                              Stops encryption.  If you omit input and output,
                              encryption is on both input and output.

                type type     Sets the default type of encryption to be used
                              with later encrypt start or encrypt stop com-
                              mands.

     environ arguments...
                The environ command is used to manipulate the the variables
                that my be sent through the TELNET ENVIRON option.  The ini-
                tial set of variables is taken from the users 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
                            Define 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
                            Remove variable from the list of environment vari-
                            ables.

                export variable
                            Mark the variable variable to be exported to the
                            remote side.

                unexport variable
                            Mark the variable variable to not be exported un-
                            less explicitly asked for by the remote side.

                list        List the current set of environment variables.
                            Those marked with a ** will be sent automatically,
                            other variables will only be sent if explicitly
                            requested.

                ??           Prints out help information for the environ com-
                            mand.

     logout     Sends the TELNET LOGOUT option to the remote side.  This com-
                mand is similar to a close command; however, if 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 con-
                nection.  If the remote side also supports the concept of sus-
                pending a user's session for later reattachment, the logout
                argument indicates that you should terminate the session imme-
                diately.

     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.  If the remote host is capable of en-
                tering that mode, the requested mode will be entered.

                character     Disable the TELNET LINEMODE option, or, if the
                              remote side does not understand the LINEMODE op-

                              tion, then enter ``character at a time`` mode.

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

                isig (-isig)  Attempt to enable (disable) the TRAPSIG mode of
                              the 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 com-
                              mand.

     open host [-l] user][--port]
                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(5))  or an Internet address specified in the
                ``dot notation'' (see inet(3)).  The [-l] 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 omits any automatic initiation of TELNET options.  When
                the port number is preceded by a minus sign, the initial op-
                tion negotiation is done.  After establishing a connection,
                the file .telnetrc in the users home directory is opened.
                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 the line is the name
                of the machine that is being connected to.  The rest of the
                line, and successive lines that begin with white space are as-
                sumed to be telnet commands and are processed as if they had
                been typed in manually to the telnet command prompt.

     quit       Close any open TELNET session and exit telnet. An end of file
                (in command mode) 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 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 re-


                        spond.

                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 char-
                        acter entered.

                el      Sends the TELNET EL (Erase Line) sequence, which
                        should cause the remote system to erase the line cur-
                        rently 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 likely
                        has no significance to the remote system.

                getstatus
                        If the remote side supports the TELNET STATUS command,
                        getstatus will send 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 cur-
                        rently 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 ur-
                        gent data (and may not work if the remote system is a
                        4.2BSD 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 print out help information, including a
                        list of known symbolic names.

                ??       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 vari-
                ables 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 will
                disable or set to FALSE any of the specified functions.  The
                values of variables may be interrogated with the display com-
                mand.  The variables which may be set or unset, but not tog-
                gled, 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     If TELNET is in localchars mode, or LINEMODE is en-
                        abled, and the status character is typed, a TELNET AYT
                        sequence (see send ayt preceding) is sent to the re-
                        mote host.  The initial value for the "Are You There"
                        character is the terminal's status character.

                echo    This 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 en-
                        tering, say, a password).

                eof     If telnet is operating in LINEMODE or ``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 char-
                        acter.

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

                escape  This is the telnet escape character (initially ``^['')
                        which causes entry into telnet command mode (when con-
                        nected to a remote system).

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

                forw1

                forw2   If TELNET is operating in LINEMODE, these are the
                        characters that, when typed, cause partial lines to be
                        forwarded to the remote system.  The initial value for
                        the forwarding characters are taken from the termi-
                        nal's eol and eol2 characters.

                interrupt
                        If telnet is in localchars mode (see toggle localchars
                        below) and the interrupt character is typed, a TELNET
                        IP sequence (see send ip above) is 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 ``character at a
                        time'' mode, then when this character is typed, a
                        TELNET EL sequence (see send el above) is sent to the
                        remote system.  The initial value for the kill charac-
                        ter is taken to be the terminal's kill character.

                lnext   If telnet 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    If telnet is in localchars mode (see toggle localchars
                        below) and the quit character is typed, a TELNET BRK
                        sequence (see send brk above) is 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 ``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  This is the rlogin escape character.  If set, the nor-
                        mal 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 telnet command.  The initial state is to
                        disable the rlogin escape character.

                start   If the TELNET TOGGLE-FLOW-CONTROL option has been en-
                        abled, then this character is taken to be the termi-
                        nal's start character.  The initial value for the kill
                        character is taken to be the terminal's start charac-
                        ter.

                stop    If the TELNET TOGGLE-FLOW-CONTROL option has been en-
                        abled, then this character is taken to be the termi-
                        nal's stop character.  The initial value for the kill
                        character is taken to be the terminal's stop charac-
                        ter.

                susp    If telnet is in localchars mode, or LINEMODE is en-
                        abled, and the suspend character is typed, a TELNET
                        SUSP sequence (see send susp above) is sent to the re-
                        mote host.  The initial value for the suspend charac-
                        ter is taken to be the terminal's suspend character.

                tracefile
                        This is the file to which the output, caused by
                        netdata or option tracing being TRUE, will be written.
                        If it is set to ``--'', then tracing information will
                        be written to standard output (the default).

                worderase
                        If telnet is operating in LINEMODE or ``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 (unset) commands.

     slc state  The slc command (Set Local Characters) is used to set or
                change the state of the 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       Verify the current settings for the current spe-
                            cial 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 will switch to the remote
                            value.

                export      Switch to the local defaults for the special char-
                            acters.  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.

                ??           Prints out help information for the slc command.

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

     toggle arguments ...
                Toggle (between TRUE and FALSE) various flags 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 display command.
                Valid arguments are:

                authdebug     Turns on debugging information for the authenti-
                              cation 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), telnet 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 se-
                              quences.  The initial value for this toggle is
                              TRUE if the terminal user had not done an "stty
                              noflsh", otherwise FALSE (see stty(1)).

                autodecrypt   When the TELNET ENCRYPT option is negotiated, by
                              default the actual encryption (decryption) of
                              the data stream does not start automatically.
                              The autoencrypt (autodecrypt) command states
                              that encryption of the output (input) stream
                              should be enabled as soon as possible.


                              Note:  Because of export controls, the TELNET
                              ENCRYPT option is not supported outside the
                              United States and Canada.

                autologin     If the remote side supports the TELNET
                              AUTHENTICATION option TELNET attempts to use it
                              to perform automatic authentication.  If the
                              AUTHENTICATION option is not supported, the us-
                              er's login name are propagated through the
                              TELNET ENVIRON option.  This command is the same


                              as specifying _a option on the open command.

                autosynch     If 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        Enable or disable the TELNET BINARY option on
                              both 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 is TRUE, then carriage returns will be
                              sent as <CR><LF>. If this is FALSE, then car-
                              riage returns will be send as <CR><NUL>. The
                              initial value for this toggle is FALSE.

                crmod         Toggle carriage return mode.  When this mode is
                              enabled, most carriage return characters re-
                              ceived from the remote host will be 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 return, but nev-
                              er line feed.  The initial value for this toggle
                              is FALSE.

                debug         Toggles socket level debugging (useful only to
                              the super user). The initial value for this tog-
                              gle is FALSE.

                encdebug      Turns on debugging information for the encryp-
                              tion code.

                localchars    If 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 are sent as eof and
                              susp, see send above).

                netdata       Toggles the display of all network data (in hex-
                              adecimal format).  The initial value for this
                              toggle is FALSE.

                options       Toggles the display of some internal telnet pro-
                              tocol processing (having to do with TELNET op-
                              tions).  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 will be 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 ini-
                              tial 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.

                verbose_encrypt
                              When the verbose_encrypt toggle is TRUE, TELNET
                              prints out a message each time encryption is en-
                              abled or disabled.  The initial value for this
                              toggle is FALSE. Note:  Because of export con-
                              trols, data encryption is not supported outside
                              of the United States and Canada.

                ??             Displays the legal toggle commands.

     zz          Suspend telnet. This command only works when the user is using
                the csh(1).

     !! [command]
                Execute a single command in a subshell on the local system.
                If command is omitted, then an interactive subshell is in-
                voked.

     ?? [command]
                Get help.  With no arguments, telnet prints a help summary.
                If a command is specified, telnet will print the help informa-
                tion for just that command.

ENVIRONMENT
     Telnet uses at least the HOME, SHELL, DISPLAY, and TERM environment vari-
     ables.  Other environment variables may be propagated to the other side
     via the TELNET ENVIRON option.

FILES
     ~/.telnetrc  user customized telnet startup values

HISTORY
     The Telnet command appeared in 4.2BSD.

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.

4.2 Berkeley Distribution        June 1, 1994                               11
