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TELNET(1)                 BSD General Commands Manual                TELNET(1)

NAME
     telnet -- user interface to the TELNET protocol

SYNOPSIS
     telnet [-468EFKLNacdfruxy] [-S tos] [-X authtype] [-e escapechar] [-k realm] [-l user] [-n tracefile]
            [-s src_addr] [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 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 per-forms performs
     forms an open command with those arguments.

     Options:

     -4      Forces telnet to use IPv4 addresses only.

     -6      Forces telnet to use IPv6 addresses only.

     -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.

     -F      If Kerberos V5 authentication is being used, the -F option allows the local credentials to be
             forwarded to the remote system, including 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 out-put. output.
             put.

     -N      Prevents IP address to name lookup when destination host is given as an IP address.

     -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.

     -X atype
             Disables the atype type of authentication.

     -a      Attempt automatic login.  This is now the default, so this option is ignored.  Currently, this
             sends the user name via the USER variable of the ENVIRON option if supported by the remote sys-tem. system.
             tem.  The name used is that of the current user as returned by getlogin(2) 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 man
             page.)

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

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

     -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 instead of the remote host's realm, as determined by
             krb_realmofhost(3).

     -l user
             When connecting to the remote system, if the remote system understands 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 command.

     -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.

     -s src_addr
             Set the source IP address for the telnet connection to src_addr, which can be an IP address or
             a host name.

     -u      Forces telnet to use AF_UNIX addresses only (e.g., UNIX domain sockets, accessed with a file
             path).

     -x      Turns on encryption of the data stream if possible.  This is now the default, so this option is
             ignored.

     -y      Suppresses encryption of the data stream.

     host    Indicates the official name, an alias, or the Internet address of a remote host.  If host
             starts with a `/', telnet establishes a connection to the corresponding named socket.

     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 system, 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 ``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).

     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 sequences 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 subse-quent subsequent
     quent output to the terminal (until the remote host acknowledges the TELNET sequence) and flush previ-ous previous
     ous 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 command 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 command are:

                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 below).

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

                Valid arguments for the encrypt command are:

                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 available 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 command.

                -input        This is the same as the encrypt stop input command.

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

                -output       This is the same as the encrypt stop output command.

                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 commands.

     environ arguments ...
                The environ command is used to manipulate the variables that may be sent through the TELNET
                ENVIRON option.  The initial set of variables is populated with the contents of the follow-ing following
                ing environment variables, if present: USER, PRINTER, DISPLAY, TERM, COLUMNS, LINES. Only
                the first three are exported, by default.

                Valid arguments for the environ command are:

                define variable [value]
                            Define the variable variable to have a value of value.  If value is empty, the
                            value is taken from the environment variable.  Any variables defined by this
                            command are automatically exported.  The value may be enclosed in single or dou-ble double
                            ble quotes so that tabs and spaces may be included.

                undefine variable
                            Remove variable from the list of environment variables.

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

                unexport variable
                            Mark the variable variable to not be exported unless 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 command.

     logout     Sends the TELNET LOGOUT option to the remote side.  This command is similar to a close com-mand; command;
                mand; 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 connection.  If 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.  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 LINEMODE option, then enter ``character at a time'' mode.

                line          Enable 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)  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 command.

     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)), an Internet address specified in the ``dot notation'' (see inet(3)), or
                IPv6 host name or IPv6 coloned-hexadecimal addreess.  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 option negotiation is done.  After estab-lishing establishing
                lishing 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 assumed 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 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 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 sub-negotiation subnegotiation
                        negotiation to request that the server send its current option status.

                ip      Sends the TELNET IP (Interrupt Process) sequence, which should cause the remote sys-tem system
                        tem 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 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 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 will disable or set 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     If TELNET is in localchars mode, or LINEMODE is enabled, and the status character is
                        typed, a TELNET AYT sequence (see send ayt preceding) is sent to the remote host.
                        The initial value for the ``Are You There'' character is the terminal's status char-acter. character.
                        acter.

                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 sup-pressing suppressing
                        pressing echoing of entered characters (for entering, say, a password).

                eof     If telnet is operating in LINEMODE or ``old line by line'' mode, entering this char-acter character
                        acter 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 ``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 character 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 connected 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 character 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 for-warding forwarding
                        warding characters are taken from the terminal'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 character 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 charac-ter. character.
                        ter.

                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 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 telnet command.  The initial state is to disable
                        the rlogin escape 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 charac-ter character
                        ter 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.

                susp    If telnet 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
                        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.

     opie sequence challenge
                The opie command computes a response to the OPIE challenge.

     slc state  The slc command (Set Local Characters) is used to set or change the state of the special
                characters when the TELNET LINEMODE option has been enabled.  Special characters are charac-ters characters
                ters that get mapped to TELNET commands sequences (like ip or quit) or line editing charac-ters characters
                ters (like erase and kill).  By default, the local special characters are exported.

                check       Verify 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 will switch to the
                            remote value.

                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.

                ?           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 interro-gated interrogated
                gated 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 charac-ters characters
                              ters 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 pro-cessed processed
                              cessed 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(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.

                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 user'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 char-acters), characters),
                              acters), 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 carriage 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 received 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 never 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 toggle is FALSE.

                encdebug      Turns on debugging information for the encryption 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 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 telnet 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 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 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.

                verbose_encrypt
                              When the verbose_encrypt toggle is TRUE, telnet prints out a message each time
                              encryption is enabled or disabled.  The initial value for this toggle is
                              FALSE.

                ?             Displays the legal toggle commands.

     z          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 invoked.

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

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

SEE ALSO
     rlogin(1), rsh(1), hosts(5), nologin(5), telnetd(8)

FILES
     ~/.telnetrc  user customized telnet startup values

HISTORY
     The telnet command appeared in 4.2BSD.

     IPv6 support was added by WIDE/KAME project.

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.

BSD                            January 27, 2000                            BSD

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