Provided by: telnet-ssl_0.17.24+0.1-19_i386 bug

NAME

     telnet - user interface to the TELNET protocol

SYNOPSIS

     telnet [-468EKLadr] [-S tos] [-X authtype] [-b address] [-e escapechar]
            [-l user] [-n tracefile] [-z option] [host [port]]

DESCRIPTION

     The telnet command is used for interactive communication with another
     host using the TELNET protocol. It begins in command mode, where it
     prints a telnet prompt ("telnet> "). If telnet is invoked with a host
     argument, it performs an open command implicitly; see the description
     below.

     Options:

     -4      Force IPv4 address resolution.

     -6      Force IPv6 address resolution.

     -8      Request 8-bit operation. This causes an attempt to negotiate the
             TELNET BINARY option for both input and output. By default telnet
             is not 8-bit clean.

     -E      Disables the escape character functionality; that is, sets the
             escape character to ‘‘no character’’.

     -K      Specifies no automatic login to the remote system.

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

     -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
             remote system. The username is retrieved via getlogin(3).

     -b address
             Use bind(2) on the local socket to bind it to a specific local
             address.

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

     -r      Emulate rlogin(1).  In this mode, the default escape character is
             a tilde. Also, the interpretation of the escape character is
             changed: an escape character followed by a dot causes telnet to
             disconnect from the remote host. A ^Z instead of a dot suspends
             telnet, and a ^] (the default telnet escape character) generates
             a normal telnet prompt. These codes are accepted only at the
             beginning of a line.

     -S tos  Sets the IP type-of-service (TOS) option for the telnet
             connection to the value tos.

     -e escapechar
             Sets the escape character to escapechar. If no character is
             supplied, no escape character will be used.  Entering the escape
             character while connected causes telnet to drop to command mode.

     -l user
             Specify user as the user to log in as on the remote system. This
             is accomplished by sending the specified name as the USER
             environment variable, so it requires that the remote system
             support the TELNET ENVIRON option. This option implies the -a
             option, and may also be used with the open command.

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

     -z option
             Set SSL (Secure Socket Layer) parameters. The default is to
             negotiate via telnet protocol if SSL is available at server side
             and then to switch it on. In this mode you can connect to both
             conventional and SSL enhanced telnetd’s. If the connection is
             made to localhost and -z secure is not set, then SSL is not
             enabled.

             The SSL parameters are:

             debug       Send SSL related debugging information to stderr.

             authdebug   Enable authentication debugging.

             ssl         Negotiate SSL at first, then use telnet protocol. In
                         this mode you can connect to any server supporting
                         directly SSL like Apache-SSL. Use telnet -z ssl
                         ssl3.netscape.com https for example. telnet protocol
                         negotiation goes encrypted.

             nossl, !ssl
                         switch off SSL negotiation

             certrequired
                         server certificate is mandatory

             secure      Don’t switch back to unencrypted mode (no SSL) if SSL
                         is not available.

             verbose     Be verbose about certificates etc.

             verify=int  Set the SSL verify flags (SSL_VERIFY_* in ssl/ssl.h
                         ).

             cert=cert_file
                         Use the certificate(s) in cert_file.

             key=key_file
                         Use the key(s) in key_file.

             cipher=ciph_list
                         Set the preferred ciphers to ciph_list.  (See
                         ssl/ssl.h ).

     host    Specifies a host to contact over the network.

     port    Specifies a port number or service name to contact. If not
             specified, the telnet port (23) is used.

     Protocol:

     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 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).

     Commands:

     The following telnet commands are available. Unique prefixes are
     understood as abbreviations.

     auth argument ...
                The auth command controls the TELNET AUTHENTICATE protocol
                option.  If telnet was compiled without authentication, the
                auth command will not be supported.  Valid arguments are as
                follows:

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

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

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

     close      Close the connection to the remote host, if any, and return to
                command mode.

     display argument ...
                Display all, or some, of the set and toggle values (see
                below).

     environ arguments...
                The environ command is used to propagate environment variables
                across the telnet link using the TELNET ENVIRON protocol
                option.  All variables exported from the shell are defined,
                but only the DISPLAY and PRINTER variables are marked to be
                sent by default.  The USER variable is marked to be sent if
                the -a or -l command-line options were 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 marked for propagation
                            (‘‘exported’’).  The value may be enclosed in
                            single or double quotes so that tabs and spaces
                            may be included.

                undefine variable
                            Remove any existing definition of variable.

                export variable
                            Mark the specified variable for propagation to the
                            remote host.

                unexport variable
                            Do not mark the specified variable for propagation
                            to the remote host. The remote host may still ask
                            explicitly for variables that are not exported.

                list        List the current set of environment variables.
                            Those marked with a * will be propagated to the
                            remote host. The remote host may still ask
                            explicitly for the rest.

                ?           Prints out help information for the environ
                            command.

     logout     Send the TELNET LOGOUT protocol option to the remote host.
                This command is similar to a close command. If the remote host
                does not support the LOGOUT option, nothing happens.  But if
                it does, this command should cause it to close the connection.
                If the remote side also supports the concept of suspending a
                user’s session for later reattachment, the logout command
                indicates that the session should be terminated immediately.

     mode type  Type is one of several options, depending on the state of the
                session.  Telnet asks the remote host to go into the requested
                mode. If the remote host says it can, that mode takes effect.

                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 daemon at
                the standard port (23).  The host specification may be a host
                name or IP address.  The -l option may be used to specify a
                user name to be passed to the remote system, like the -l
                command-line option.

                When connecting to ports other than the telnet port, telnet
                does not attempt telnet protocol negotiations. This makes it
                possible to connect to services that do not support the telnet
                protocol without making a mess. Protocol negotiation can be
                forced by placing a dash before the port number.

                After establishing a connection, any commands associated with
                the remote host in /etc/telnetrc and the user’s .telnetrc file
                are executed, in that order.

                The format of the telnetrc files is as follows: Lines
                beginning with a #, and blank lines, are ignored.  The rest of
                the file should consist of hostnames and sequences of telnet
                commands to use with that host. Commands should be one per
                line, indented by whitespace; lines beginning without
                whitespace are interpreted as hostnames.  Lines beginning with
                the special hostname ‘DEFAULT’ will apply to all hosts.
                Hostnames including ‘DEFAULT’ may be followed immediately by a
                colon and a port number or string.  If a port is specified it
                must match exactly with what is specified on the command line.
                If no port was specified on the command line, then the value
                ‘telnet’ is used.  Upon connecting to a particular host, the
                commands associated with that host are executed.

     quit       Close any open session and exit telnet.  An end of file
                condition on input, when in command mode, will trigger this
                operation as well.

     send arguments
                Send one or more special telnet protocol character sequences
                to the remote host.  The following are the codes which may be
                specified (more than one may be used in one command):

                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.

                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
                        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 variables.
                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.

                ayt     If telnet is in localchars mode, or LINEMODE is
                        enabled, and the status character is typed, a TELNET
                        AYT sequence is sent to the remote 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
                        entering, 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
                        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 forwarding 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 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 mode escape character. Setting it
                        enables rlogin mode, as with the r command-line option
                        (q.v.)

                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
                        kill 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
                        kill 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.

     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
                            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.

     startssl   Attempt to negotiate telnet-over-SSL (as with the -z ssl
                option). This is useful when connecting to non-telnetds such
                as imapd (with the STARTTLS command). To control SSL when
                connecting to a SSL-enabled telnetd, use the auth command
                instead.

     status     Show the current status of telnet.  This includes the name of
                the remote host, if any, 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.  More than
                one flag may be toggled at once.  The state of these flags may
                be examined with the display command.  Valid flags are:

                authdebug     Turns on debugging for the authentication code.
                              This flag only exists if authentication support
                              is enabled.

                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
                              sequences.  The initial value for this toggle is
                              TRUE if the terminal user had not done an "stty
                              noflsh", otherwise FALSE (see stty(1)).

                autologin     If the remote side supports the TELNET
                              AUTHENTICATION option, telnet attempts to use it
                              to perform automatic authentication.  If the
                              TELNET AUTHENTICATION option is not supported,
                              the user’s login name is propagated using the
                              TELNET ENVIRON option.  Setting this flag is the
                              same as specifying the a option to the open
                              command or on the command line.

                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
                              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.

                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 telnet escape sequences are preceded by a ’*’
                              to aid in locating them.

                skiprc        When the skiprc toggle is TRUE, telnet does not
                              read the telnetrc files.  The initial value for
                              this toggle is FALSE.

                termdata      Toggles the display of all terminal data (in
                              hexadecimal format).  The initial value for this
                              toggle is FALSE.

                ?             Displays the legal toggle commands.

     z          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 a 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 variables may be propagated to the other
     side via the TELNET ENVIRON option.

FILES

     /etc/telnetrc  global telnet startup values
     ~/.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.

BUGS

     The source code is not comprehensible.