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 command?prompt?("telnet>").
If?telnet?is invoked with a?host?argument, it performs an?open?command implicitly (see the?Commands?section below for details).
Request?8-bit?operation. This option causes an attempt to negotiate the?TELNET BINARY?option for both input and output. By default,?telnet?is not "8-bit clean" (it does not recognize 8-bit?character encodings?such as?Unicode).
-E
Disables the?escape?character?functionality; that is, sets the escape character to "no character".
-L
Specifies an 8-bit data path on output. This option causes the?TELNET BINARY?option to be negotiated on output.
-a
Attempt automatic?login. Currently, this sends the username via the?USER?variable of the?ENVIRON?option if supported by the remote system. The username is retrieved via the?getlogin?system call.
-b?address
Use?bind?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. 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?(Control-Z) instead of a dot suspends?telnet, and a?^]?(Control-close bracket, 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?TOS (type-of-service) 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. 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.
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 is 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.
Note that the current version of?telnet?does not support 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).
encrypt?argument?...
The?encrypt?command controls the?TELNET ENCRYPT?protocol option. If?telnet?was?compiled?without?encryption, the?encrypt?command will not be supported.
Valid arguments are as follows:
disable?type?[input|output]
Disable the specified type of encryption. If you do not specify?input?or?output, encryption of both is disabled. To obtain a list of available types, use "encrypt disable ?".
enable?type?[input|output]
Enable the specified type of encryption. If you do not specify?input?or?output, encryption of both is enabled. To obtain a list of available types, use "encrypt enable ?".
input
This argument is the same as "encrypt start input".
-input
This argument is the same as "encrypt stop input".
output
This argument is the same as "encrypt start output".
-output
This argument is the same as "encrypt stop output".
start?[input|output]
Attempt to begin encrypting. If you do not specify?input?or?output, encryption of both input and output is started.
status
Display the current status of the encryption module.
stop?[input|output]
Stop encrypting. If you do not specify?input?or?output, encryption of both is stopped.
type?type
Sets the default type of encryption to be used with later "encrypt start" or "encrypt stop" commands.
Note that the current version of?telnet?does not support encryption.
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?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 an?asterisk?("*") 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
The?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. Options for?type?are as follows:
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?hostname?or?IP address. The?-l?option may be used to specify a username 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 method of connecting 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 treated as?comments?(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):
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 [rocess) 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?(duspend 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 4.2?BSD?system -- if it doesn't work, a lowercase "r" may be?echoed?on the terminal).
do?cmd
Sends the?TELNET DO?cmd?sequence. The?cmd?can be either a?decimal?number between?0?and?255, or a symbolic name for a specific?TELNET?command. The?cmd?can also be either?help?or???to print out help information, including a list of known symbolic names.
dont?cmd,?will?cmd,?wont?cmd
Similar to?do.
?
Prints out help information for the?send?command.
set?argument?value,?unset?argument?value
The?set?command will set any one of the telnet variables to a specific value or as?TRUE. The special value?off?turns off the function associated with the variable. This command 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. Also, 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 variable 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 variable 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 variable is the?rlogin mode?escape character. Setting it enables?rlogin mode, as with the?r?command-line option (see above).
start
If the?TELNET TOGGLE-FLOW-CONTROL?option is 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 is 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 variable 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 (this is 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?(or?unset) commands.
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 is 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.
state?may be one of the following:
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 command 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).
autoencrypt,?autodecrypt
When the?TELNET ENCRYPT?option is negotiated, by default the actual encryption (or decryption) of the data stream does not start automatically. The?autoencrypt?(or?autodecrypt) command states that encryption of the output (input) stream should be enabled as soon as possible.
Note that this flag exists only if encryption support is enabled.
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?superuser). The initial value for this toggle is?FALSE.
encdebug
Turns on?debugging?information for the encryption code. Note that this flag only exists if encryption support is available.
localchars
If this is?TRUE, then the?flush,?interrupt,?quit,?erase, and?kill?characters (see?set?above) are recognized locally, and transformed into (hopefully) appropriate TELNET control sequences (respectively?ao,?ip,?brk,?ec, and?el; see?send?above). The initial value for this toggle is?TRUE?in "old line by line" mode, and?FALSE?in "character at a time" mode. When the?LINEMODE?option is enabled, the value of?localchars?is ignored, and assumed to always be?TRUE. If?LINEMODE?has ever been enabled, then?quit?is sent as?abort, and?eof and?are sent as?eof?and?susp; see?send?above).
netdata
Toggles the display of all network data (in?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 an asterisk ("*") 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.
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. This flag only exists if encryption support is available.
?
Displays the legal toggle commands.
z
Suspend?telnet. This command only works when the user is using the C Shell (csh).
!?[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 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.
Attempts to open a connection to the remote host?myhost.com. If a connection is established, the host will prompt for a login name and password.
telnet -l myusername myhost.com 5555
Attempts to open a connection to the remote host?myhost.com?on port?5555, using the login name?myusername. If successful, the host will prompt for?myusername's password.
telnet
Opens a local?telnet>?prompt, where you can enter any of the commands listed?above. For example, entering the following command at the prompt:
telnet> open myhost.com
...will attempt to open a connection to?myhost.com, as in our first example.
telnet (TELNET協議的用戶界面)
telnet程序是TELNET協議的用戶界面。
The telnet program is a user interface to the TELNET protocol.
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1 telnet 運行系統環境
2 telnet 說明
3 telnet 語法
4 telnet 例子
telnet 運行系統環境
Linux
telnet 說明
telnet命令用于使用TELNET協議與另一個主機進行交互通信。 它以命令模式開始，在此模式下將打印telnet命令提示符（“ telnet>”）。
如果使用主機參數調用telnet，它將隱式執行打開命令（有關詳細信息，請參見下面的“命令”部分）。
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 command?prompt?("telnet>").
If?telnet?is invoked with a?host?argument, it performs an?open?command implicitly (see the?Commands?section below for details).
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telnet 語法
telnet [-468ELadr] [-S tos] [-b address] [-e escapechar] [-l user] [-n tracefile] [host [port]]選件
協議
打開連接后，telnet將嘗試啟用TELNET LINEMODE選項。如果失敗，則telnet將恢復為兩種輸入模式之一：“一次輸入字符”或“逐行刪除”，具體取決于遠程系統支持的模式。
當LINEMODE啟用，字符處理在本地系統上完成的，遠程系統的控制下。當要禁用輸入編輯或字符回顯時，遠程系統將中繼該信息。遠程系統還將中繼對遠程系統上發生的任何特殊字符的更改，以便它們可以在本地系統上生效。
在“一次字符”模式下，大多數鍵入的文本會立即發送到遠程主機進行處理。
在“逐行舊模式”模式下，所有文本都在本地回顯，并且（通常）僅將完成的行發送到遠程主機?！氨镜鼗仫@字符”（最初為“ ^ E ”）可用于關閉和打開本地回顯（這通常用于輸入密碼而不回顯密碼）。
如果啟用了LINEMODE選項，或者localchars切換為TRUE（默認為“逐行”；請參見下文），則用戶的quit，intr和flush字符將被本地捕獲，并作為TELNET協議序列發送到偏遠的一面。如果已啟用LINEMODE，則用戶的susp和eof也將作為TELNET協議序列發送，而退出將作為TELNET ABORT而不是BREAK發送。有一些選項（請參閱切換自動刷新和切換自動同步，如下所示），這會導致此操作刷新后續的輸出到終端（直到遠程主機確認TELNET序列）并刷新先前的終端輸入（在quit和intr的情況下）。
指令
以下telnet命令可用。唯一前綴被理解為縮寫。
auth命令控制TELNET AUTHENTICATE協議選項。 如果telnet是在未經身份驗證的情況下編譯的，則將不支持auth命令。 有效參數如下：
crypto命令控制TELNET ENCRYPT協議選項。 如果telnet是在未加密的情況下編譯的，則將不支持加密命令。
有效參數如下：
該ENVIRON命令用于跨越繁殖的環境變量的telnet使用鏈路TELNET ENVIRON協議選項。從外殼導出的所有變量均已定義，但默認情況下僅將DISPLAY和PRINTER變量標記為要發送。在USER變量被標記，如果要被發送-a或-l 命令行中使用的選項。
environ命令的有效參數為：
該類型是幾個選項之一，這取決于會議的狀態。telnet要求遠程主機進入請求的模式。如果遠程主機說可以，則該模式生效。類型選項如下：
打開與命名主機的連接。如果未指定端口號，則telnet將嘗試在標準端口（23）上聯系telnet 守護程序。該主機規格可以是主機名或IP地址。該-l選項可用于指定用戶名傳遞到遠程系統，如-l命令行選項。
當連接到telnet端口以外的端口時，telnet不會嘗試telnet協議協商。這種連接方法使連接到不支持telnet協議的服務成為可能。可以通過在端口號前加一個破折號來強制協議協商。
建立連接后，將按該順序執行/ etc / telnetrc中與遠程主機關聯的所有命令以及用戶的.telnetrc文件。
telnetrc文件的格式如下：以＃開頭的行和空白行被視為注釋（忽略）。該文件的其余部分應由主機名和要用于該主機的telnet命令序列組成。命令應該每行一個，以空格縮進；以空格開頭的行將被解釋為主機名。以特殊主機名“ DEFAULT ” 開頭的行將適用于所有主機。主機名（包括“ DEFAULT ”）后可以緊跟冒號，端口號或字符串。如果指定了端口，則它必須與命令行上指定的端口完全匹配。如果在命令行上未指定端口，則值'使用telnet '。連接到特定主機后，將執行與該主機關聯的命令。
將一個或多個特殊的telnet協議字符序列發送到遠程主機。以下是可以指定的代碼（在一個命令中可以使用多個代碼）：
該組命令將設置的telnet變量為特定的值或作為中任一項TRUE。特殊值off關閉與變量關聯的功能。此命令等效于使用unset命令。在未設置命令將禁用或設置為FALSE的任何特定變量?？梢允褂胐isplay命令查詢變量的值。此處列出了可以設置或未設置但不能切換的變量。另外，toggle命令的任何變量都可以顯式設置或取消設置。
該SLC的命令（設置本地字符）用于設置或更改時，特殊字符的狀態TELNET LINEMODE啟用選項。特殊字符是映射到TELNET命令序列的字符（例如ip或quit）或行編輯字符（例如delete和kill）。默認情況下，將導出本地特殊字符。
狀態可能是以下之一：
切換（在TRUE和FALSE之間）控制telnet如何響應事件的各種標志。可以使用set和unset命令將這些標志顯式設置為TRUE或FALSE。一次可以切換多個標志。這些標志的狀態可以用display命令檢查。有效標志是：
請注意，只有啟用了加密支持，此標志才存在。
環境
telnet至少使用HOME，SHELL，DISPLAY和TERM 環境變量。其他環境變量可以通過TELNET ENVIRON選項傳播到另一端。
檔案
telnet [-468ELadr] [-S tos] [-b address] [-e escapechar] [-l user] [-n tracefile] [host [port]]Options
Protocol
Once a connection is 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.
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:
The?encrypt?command controls the?TELNET ENCRYPT?protocol option. If?telnet?was?compiled?without?encryption, the?encrypt?command will not be supported.
Valid arguments are as follows:
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:
The?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. Options for?type?are as follows:
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?hostname?or?IP address. The?-l?option may be used to specify a username 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 method of connecting 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 treated as?comments?(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.
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):
The?set?command will set any one of the telnet variables to a specific value or as?TRUE. The special value?off?turns off the function associated with the variable. This command 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. Also, any of the variables for the toggle command may be explicitly?set?or?unset.
The?slc?command (set local characters) is used to set or change the state of the special characters when the?TELNET LINEMODE?option is 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.
state?may be one of the following:
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:
Note that this flag exists only if encryption support is enabled.
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
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telnet 例子
嘗試打開與遠程主機myhost.com的連接。如果建立連接，主機將提示輸入登錄名和密碼。
嘗試使用登錄名myusername在端口5555上打開到遠程主機myhost.com的連接。如果成功，主機將提示輸入myusername的密碼。
打開本地telnet>提示符，您可以在其中輸入上面列出的任何命令。例如，在提示符下輸入以下命令：
...將嘗試打開與myhost.com的連接，如第一個示例所示。
Attempts to open a connection to the remote host?myhost.com. If a connection is established, the host will prompt for a login name and password.
Attempts to open a connection to the remote host?myhost.com?on port?5555, using the login name?myusername. If successful, the host will prompt for?myusername's password.
Opens a local?telnet>?prompt, where you can enter any of the commands listed?above. For example, entering the following command at the prompt:
...will attempt to open a connection to?myhost.com, as in our first example.
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其他命令行
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