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telnet(1c) telnet(1c) Name telnet - user interface to the TELNET protocol Syntax telnet [host[port]] Description The interface is used to communicate with another host using the TELNET protocol. If is invoked without arguments, it enters command mode, which is indicated by the prompt, telnet>. In this mode, accepts and executes the commands listed below. If it is invoked with arguments, it performs an open command (see below) with those arguments. Once a connection is opened, enters input mode. The input mode is either character-at-a-time or line-by-line, depending on what the remote system supports. In character-at-a-time mode, text is sent to the remote host as it is typed. In line-by-line mode, text is echoed locally and only completed lines are sent to the remote host. The local-echo-character, initially ^E. turns the local echo on and off, which is useful when you want to enter passwords without them echoing to the screen. In either mode, if the localchars toggle is TRUE (the default in line mode), then the user's quit, intr, and flush characters are trapped locally and sent as TELNET protocol sequences to the remote side. Options such as toggle autoflush and toggle autosynch flush previous terminal input, as in quit and intr, in addition to flushing subsequent output to the terminal until the remote host acknowledges the TEL- NET sequence. To issue commands when in input mode, precede them with the escape character, initially the control character followed by a right bracket (^]). When in command mode, use the normal terminal editing conventions. The following commands are available: open host [ port ] Opens a connection to the named host. If no port number is specified, attempts to contact a TELNET server at the default port. The host specification may be either a host name or an Internet address specified in the dot notation. For further information, see and close Closes a TELNET session and returns to command mode. quit Closes any open TELNET session and exits z Suspends This command only works when the user is using the mode type The type is either line, for line-by-line mode, or character, for character-at-a-time mode. The local host asks the remote host for permission to go into one or the other mode. The remote host enters the requested mode if it is capable of it. status Shows the current status of This includes the peer one is connected to, as well as the state of debugging. display [ argument... ] Displays all, or some, of the set and toggle values (see below). ? [ command ] Accesses on-line help. With no arguments, prints a help summary. If a command is specified, prints the help information for that command. send argument(s) Sends one or more special character sequences to the remote host. One or more of the following arguments can be specified: escape Sends the current escape character (initially the control character followed by a right bracket, ^]). synch Sends the TELNET SYNCH sequence. This sequence causes the remote system to discard input that was previously entered but that it has not yet read. This sequence is sent as TCP urgent data and may not work if the remote system is a 4.2 BSD system. If it does not work, a lower case r may be echoed on the terminal screen. brk Sends the TELNET BRK (Break) sequence, which may have significance to the remote system. ip Sends the TELNET IP (Interrupt Process) sequence, which causes the remote system to abort the currently running process. ao Sends the TELNET AO (Abort Output) sequence, which causes the remote system to flush all output from the remote sys- tem to the user's terminal. ayt Sends the TELNET AYT (Are You There) sequence. The remote system may or may not respond. ec Sends the TELNET EC (Erase Character) sequence, which causes the remote system to erase the last character entered. el Sends the TELNET EL (Erase Line) sequence, which causes the remote system to erase the line currently being entered. ga Sends the TELNET GA (Go Ahead) sequence. Often this sequence has no significance to the remote system. nop Sends the TELNET NOP (No OPeration) sequence. ? Prints out help information for the send command. set argument value Sets a variable to a specific value. The off value turns off the function associated with the variable. The current values of variables can be displayed with the display command. The following variables that can be specified: echo Toggles between local echoing of entered characters, and suppressing echoing of entered characters when in line-by-line mode. The value is initially ^E. escape Enters the command mode when you are connected to a remote system. The value is initially the control character followed by a left bracket (^[). interrupt Sends a TELNET IP sequence (see send ip above) to the remote host if is in localchars mode (see toggle localchars below) and the interrupt character is typed. The initial value for the interrupt character is the terminal's intr character. quit Sends a TELNET BRK sequence (see send brk above) to the remote host if is in localchars mode (see toggle localchars below) and the quit character is typed. The initial value for the quit character is the terminal's quit character. flushoutput Sends a TELNET AO sequence (see send ao above) to the remote host if telnet is in localchars mode (see toggle localchars below) and the flushoutput character is typed. The initial value for the flush character is the terminal's flush character. erase Sends a TELNET EC sequence (see send ec above) to the remote system if telnet is in localchars mode (see toggle localchars below), and if telnet is operating in character-at-time mode. The initial value for the erase character is the terminal's erase character. kill Sends a TELNET EL sequence (see send el above) to the remote system if is in localchars mode (see toggle localchars below) and if is operating in character-at-a-time mode. The initial value for the kill character is the terminal's kill character. eof Sends this character to the remote system if is operating in line-by-line mode and this character is entered as the first character on a line. The initial value of the eof character is the terminal's eof character. toggle arguments... Toggles (between TRUE and FALSE) flags that control how responds to events. More than one argument may be specified and the current value of these flags can be displayed with the display command. Valid arguments for the command are the following: localchars Causes the flush, interrupt, quit, erase, and kill characters to be recognized locally and transformed into appropriate TEL- NET control sequences if this flag is set to TRUE. (See set above). The appropriate TELNET control sequences are: ao, ip, brk, ec, and el, respectively. For more information see the command. The initial value for this toggle is TRUE in line-by- line mode, and FALSE in character-at-a-time mode. autoflush Causes the command to not display any data on the user's terminal until the remote system acknowledges (via a TELNET Timing Mark option) that it recognized and processed the following TELNET sequences: ao, intr, or quit. Both autoflush and localchars must be TRUE for autoflush to work in this manner. The initial value for this toggle is TRUE if the terminal user did not specify Otherwise it is FALSE. For further information, see autosynch Causes the TELNET SYNCH sequence to follow the TELNET sequence that is initiated when either the intr or quit character is typed. The autosynch flag works in this manner when both the autosynch and localchars are TRUE. 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. crmod Toggles carriage return mode. When this mode is enabled, most carriage return characters received from the remote host are mapped into a carriage return followed by a line feed. It is useful only when the remote host sends carriage returns but never line feeds. The initial value for this toggle is FALSE. debug Toggles socket level debugging which is useful only to the superuser. The initial value for this toggle is FALSE. options Toggles the display of internal protocol processing that deals with TELNET options. The initial value for this toggle is FALSE. netdata Toggles the display of all network data (in hexadecimal format). The initial value for this toggle is FALSE. ? Displays the legal toggle commands. Restrictions In line-by-line mode, the terminal's EOF character is only recognized and sent to the remote system when it is the first character on a line. telnet(1c)