telnet(1C) telnet(1C) NAME telnet - user interface to the TELNET protocol SYNOPSIS telnet [-d] [-n tracefile] [-l user | -a] [-e escape-char] [-4 | -6] [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 performs an open command (see below) with those arguments. Options: -d Sets the initial value of the debug toggle to TRUE. -n tracefile Opens tracefile for recording trace information. See the set tracefile command below. -l user When connecting to the remote system, if the remote system understands the ENVIRON option, user is sent to the remote system as the value for the variable USER. This option can also be used with the open command. -a Auto-login. Same as specifying -l with your user name. This option can also be used with the open command. -e escape-char Sets the initial telnet escape character to escape-char. If escape-char is the null character (specified by "" or ''), there is no escape character. -4 Forces to use IPv4 addresses only. -6 Forces to use IPv6 addresses only. 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. Once a connection has been opened, telnet attempts to enable the TELNET LINEMODE option. If this fails, telnet reverts 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 relays that information. The remote system relays 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) can 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, 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) that 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 can 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 needs to be typed (this is also true for arguments to the mode, set, toggle, unset, slc, environ, and display commands). close Close a TELNET session and return to command mode. display [ argument... ] Display all, or some, of the set and toggle values (see below). 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 is entered. character Disable the TELNET LINEMODE option, or, if the remote side does not understand the LINEMODE option, enter "character at a time" mode. line Enable the TELNET LINEMODE option, or, if the remote side does not understand the LINEMODE option, 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. ? Print out help information for the mode command. open host [ [-l user | -a] [-]port ] Open a connection to the named host. If no port number is specified, telnet attempts to contact a TELNET server at the default port. The host specification can be either a hostname (see hosts(4)) or an IPv4 address specified in the "dot notation" (see inet(3N)), or an IPv6 address specified in "colon-hexadecimal" notation. The -l option can be used to specify the user name to be passed to the remote system via the ENVIRON option. The -a option sends your user name 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 establishing a connection, the .telnetrc file in the user's home directory is opened. Lines beginning with a # are comment lines. Blank lines are ignored. Lines that begin without whitespace 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 whitespace, 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) also closes a session and exits. send arguments Send one or more special character sequences to the remote host. The following are the arguments that can be specified (more than one argument can be specified at a time): abort Send the TELNET ABORT (ABORT processes) sequence. ao Send 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 Send the TELNET AYT (Are You There) sequence, to which the remote system may or may not choose to respond. brk Send the TELNET BRK (Break) sequence, which may have significance to the remote system. ec Send the TELNET EC (Erase Character) sequence, which should cause the remote system to erase the last character entered. el Send the TELNET EL (Erase Line) sequence, which should cause the remote system to erase the line currently being entered. eof Send the TELNET EOF (End Of File) sequence. eor Send the TELNET EOR (End of Record) sequence. escape Send the current telnet escape character (initially ^]). ga Send 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 sends the subnegotiation to request that the server send its current option status. ip Send the TELNET IP (Interrupt Process) sequence, which should cause the remote system to abort the currently running process. nop Send the TELNET NOP (No OPeration) sequence. susp Send the TELNET SUSP (SUSPend process) sequence. synch Send 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 4.2 BSD system -- if it doesn't work, a lower case r may be echoed on the terminal). ? Print out help information for the send command. set argument value unset arguments... The set command sets 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 disables or sets to FALSE any of the specified functions. The values of variables can be interrogated with the display command. The variables that can be set or unset, but not toggled, are listed here. In addition, any of the variables for the toggle command can be explicitly set or unset using the set and unset commands. echo 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 causes 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, 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 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. 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, 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, 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, this character is taken to be the terminal's reprint character. The initial value for the reprint character is taken to be the terminal's reprint character. start If the TELNET TOGGLE-FLOW-CONTROL option has been enabled, 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, 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 The file to which the output, caused by netdata or option tracing being TRUE, is written. If it is set to -, tracing information is written to standard output (the default). worderase If telnet is operating in LINEMODE or "old line by line" mode, 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. 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 characters that get mapped to TELNET commands sequences (like ip or quit) or line editing characters (like erase and kill). By default, the local special characters are exported. export Switch to the local defaults for the special characters. The local default characters are those of the local terminal at the time when telnet was started. import Switch to the remote defaults for the special characters. The remote default characters are those of the remote system at the time when the TELNET connection was established. check Verify the current settings for the current special characters. The remote side is requested to send all the current special character settings, and if there are any discrepancies with the local side, the local side switches to the remote value. ? Print out help information for the slc command. environ arguments... The environ command is used to manipulate the variables that can be sent through the ENVIRON option. The initial set of variables is taken from the user's environment with only the DISPLAY and PRINTER variables being exported by default. 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 can be enclosed in single or double quotes so that tabs and spaces can 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. send variable Send the variable variable to the remote side. list List the current set of environment variables. Those marked with a * are sent automatically, other variables are sent only if explicitly requested. ? Print out help information for the environ command. ? Display the legal set (unset) commands. toggle arguments... Toggle (between TRUE and FALSE) various flags that control how telnet responds to events. These flags can be set explicitly to TRUE or FALSE using the set and unset commands listed above. More than one argument can be specified. The state of these flags can be interrogated with the display command. Valid arguments are: autoflush If autoflush and localchars are both TRUE, when the ao, intr, 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)). autosynch If autosynch and localchars are both TRUE, 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, carriage returns are sent as <CR><LF>. If this is FALSE, carriage returns are sent 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 are mapped into a carriage return followed by a linefeed. 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 linefeed. The initial value for this toggle is FALSE. debug Toggle socket level debugging (useful only to the superuser). The initial value for this toggle is FALSE. localchars If this is TRUE, 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, quit is sent as abort, and eofand suspend are sent as eofand susp, see send above). netdata Toggle the display of all network data (in hexadecimal format). The initial value for this toggle is FALSE. options Toggle 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 is 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. ? Display 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, an interactive subshell is invoked. status Show the current status of telnet. This includes the peer one is connected to, as well as the current mode. ? [ command ] Get help. With no arguments, telnet prints a help summary. If a command is specified, telnet prints the help information for just that command. ENVIRONMENT telnet uses at least the HOME, SHELL, USER, DISPLAY, and TERM environment variables. Other environment variables can be propagated to the other side via the TELNET ENVIRON option. FILES ~/.telnetrc user customized telnet startup values 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. In a Trusted IRIX environment, a user can telnet at a different MAC label (see dominance(5)) and/or capability set (see capability(4)) by specifying the label and capability set after the username at the login prompt. See login(1) for more details. However, the label and capability set can not be specified using command line options. SEE ALSO login(1), capability(4), dominance(5), Page 11