TELNET(1)

📦
version 1.2 · 7 versions
, in opensuse-leap 16.0

🌸 NAME 🌸

TELNET(1) — General Commands Manual vibes, and bestie, this is the page for telnet, aka your user interface to the TELNET protocol. ✨ It’s giving “classic network icon” and we’re gonna read every single bite. 🫶

✨ SYNOPSIS ✨

telnet [-8] [-E] [-F] [-K] [-L] [-S tos] [-X authtype] [-a]
       [-b hostalias] [-c] [-d] [-e escapechar] [-f] [-k realm]
       [-l user] [-n tracefile] [-r] [-x] [host [port]]

💅 DESCRIPTION 💅

Okay so 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 with those arguments. 💖

🎀 The options are as follows 🎀

  • -8 — specifies an 8-bit data path. This causes an attempt to negotiate the TELNET BINARY option on both input and output. 🦋
  • -E — stops any character from being recognized as an escape character. no cap.
  • -F — if Kerberos V5 authentication is being used, the -F option allows the local credentials to be forwarded to the remote system, including any credentials that have already been forwarded into the local environment. 🔥
  • -K — specifies no automatic login to the remote system.
  • -L — specifies an 8-bit data path on output. This causes the BINARY option to be negotiated on output.
  • -S tos — sets the IP type-of-service (TOS) option for the telnet connection to the value tos, which can be a numeric TOS value or, on systems that support it, a symbolic TOS name found in the /etc/iptos file. 💅
  • -X atype — disables the atype type of authentication.
  • -a — attempt automatic login. Currently, this sends the user name via the USER variable of the ENVIRON option if supported by the remote system. The name used is that of the current user as returned by getlogin(2) if it agrees with the current user ID, otherwise it is the name associated with the user ID. 🫶
  • -b ip_address — uses bind(2) on the local socket to bind it to an aliased ip address or to the ip address of another interface than the one naturally chosen by connect(2). This can be useful when connecting to services which use IP addresses for authentication and reconfiguration of the server is undesirable (or impossible). 😭
  • -c — disables the reading of the user's .telnetrc file. (See the toggle skiprc command on this man page.) 🙈
  • -d — sets the initial value of the debug toggle to TRUE.
  • -e escapechar — sets the initial telnet escape character to escapechar. If escapechar is omitted, then there will be no escape character. 💀
  • -f — if Kerberos V5 authentication is being used, the -f option allows the local credentials to be forwarded to the remote system.
  • -k realm — if Kerberos authentication is being used, the -k option requests that telnet obtain tickets for the remote host in realm realm instead of the remote host's realm, as determined by krb_realmofhost(3). 🎟️
  • -l user — when connecting to the remote system, if the remote system understands the ENVIRON option, then user will be sent to the remote system as the value for the variable USER. This option implies the -a option. This option may also be used with the open command. 👑
  • -n tracefile — opens tracefile for recording trace information. See the set tracefile command below. 🍓
  • -r — specifies a user interface similar to rlogin(1). In this mode, the escape character is set to the tilde (~) character, unless modified by the -e option. 🌈
  • -x — turns on encryption of the data stream if possible.
  • 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. 🔌

When in rlogin mode, a line of the form ~. disconnects from the remote host; ~ is the telnet escape character. Similarly, the line ~^Z suspends the telnet session. The line ~^] escapes to the normal telnet escape prompt. 💫

Once a connection has been opened, telnet will attempt to enable the TELNET LINEMODE option. If this fails, 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). 🔥

While connected to a remote host, telnet command mode may be entered by typing the telnet "escape character" (initially "^]"). When in command mode, the normal terminal editing conventions are available. Note that the escape character will return to the command mode of the initial invocation of telnet that has the controlling terminal. Use the send escape command to switch to command mode in subsequent telnet processes on remote hosts. 💅

🌟 The following telnet commands are available 🌟

Only enough of each command to uniquely identify it need be typed (this is also true for arguments to the mode, set, toggle, unset, slc, environ, and display commands).

auth argument [...]

The auth command manipulates the information sent through the TELNET AUTHENTICATE option. Valid arguments for the auth command are as follows:

  • disable type — disables the specified type of authentication. To obtain a list of available types, use the auth disable ? command. 🎀
  • enable type — enables the specified type of authentication. To obtain a list of available types, use the auth enable ? command.
  • status — lists the current status of the various types of authentication. ✨

close

Close a TELNET session and return to command mode.

display argument [...]

Displays all, or some, of the set and toggle values (see below). 💖

encrypt argument [...]

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

Valid arguments for the encrypt command are as follows:

  • disable type [input|output] — disables the specified type of encryption. If you omit input and output, both input and output are disabled. To obtain a list of available types, use the encrypt disable ? command. 🔐
  • enable type [input|output] — enables the specified type of encryption. If you omit input and output, both input and output are enabled. To obtain a list of available types, use the encrypt enable ? command.
  • input — this is the same as the encrypt start input command.
  • -input — this is the same as the encrypt stop input command.
  • output — this is the same as the encrypt start output command.
  • -output — this is the same as the encrypt stop output command.
  • start [input|output] — attempts to start encryption. If you omit input and output, both input and output are enabled. To obtain a list of available types, use the encrypt enable ? command. 🫶
  • status — lists the current status of encryption.
  • stop [input|output] — stops encryption. If you omit input and output, encryption is on both input and output.
  • type type — sets the default type of encryption to be used with later encrypt start or encrypt stop commands. 💅

environ arguments [...]

The environ command is used to manipulate the variables that may be sent through the TELNET ENVIRON option. The initial set of variables is taken from the user's environment, with only the DISPLAY, PRINTER, and XAUTHORITY variables being exported by default. The USER variable is also exported if the -a or -l options are used. Additionally, the value of the TERM variable is by default available to be queried by the server. 🌱

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 may be enclosed in single or double quotes so that tabs and spaces may be included. ✨
  • undefine variable — remove variable from the list of environment variables. 🦋
  • export variable — flags variable as "yes ship this one to the remote side bestie" 💌
    • unexport variable — un-flags variable, so it stays home and does NOT get exported.
    • list — shows you the current roster of environment variables. The tea on the little markers: a * means it gets sent automatically, a + means it only goes if the server explicitly asks for it, and anything else is staying in the vault — it won't be revealed to the server even if they request it. 🙈
    • ? — prints out help info for the environ command.

logout — sends the TELNET LOGOUT option over to the remote side. It's giving close energy, but with a twist: if the remote side doesn't support the LOGOUT option, literally nothing happens. But if it does support it, this command should make the remote side close the TELNET connection. And if the remote side also does the whole "suspending a user's session for later reattachment" thing, the logout argument is you saying "no, terminate this session right now, immediately, periodt." 💀

mode type — type is one of several options, depending on what state your TELNET session is in. The remote host gets asked for permission to enter the mode you want. If the remote host can actually do that mode, the requested mode is entered. 🤝

  • character — disable the TELNET LINEMODE option, or, if the remote side doesn't understand LINEMODE, then enter "character at a time" mode.
  • line — enable the TELNET LINEMODE option, or, if the remote side doesn't understand LINEMODE, then attempt to enter "old-line-by-line" mode.
  • isig (-isig) — attempt to enable (disable) the TRAPSIG mode of the LINEMODE option. Requires that the LINEMODE option be enabled.
  • edit (-edit) — attempt to enable (disable) the EDIT mode of the LINEMODE option. Requires that the LINEMODE option be enabled.
  • softtabs (-softtabs) — attempt to enable (disable) the SOFT_TAB mode of the LINEMODE option. Requires that the LINEMODE option be enabled.
  • litecho (-litecho) — attempt to enable (disable) the LIT_ECHO mode of the LINEMODE option. Requires that the LINEMODE option be enabled.
  • ? — prints out help info for the mode command.

open host [-l user] [[-] port] — opens a connection to the named host. If you don't give a port number, telnet will try to hit a TELNET server at the default port. The host can be either a host name (peep hosts(5)) or an Internet address in "dot notation" (peep inet(3)). The -l option lets you specify the user name to pass to the remote system via the ENVIRON option. When you connect 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 file .telnetrc in the user's home directory gets opened. Lines beginning with a # are comment lines. Blank lines are ignored. Lines that begin without white space are the start of a machine entry — use DEFAULT as the machine name to match every connection. The first thing on the line is the name of the machine being connected to. The rest of the line, plus successive lines that begin with white space, are assumed to be telnet commands and get processed as if you'd typed them in manually at the telnet command prompt. 🫶

quit — close any open TELNET session and exit telnet. An end-of-file (in command mode) will also close a session and exit. 👋

send arguments — sends one or more special character sequences to the remote host. Here's the full menu of arguments you can specify (and yes, you can stack more than one at a time):

  • abort — sends the TELNET ABORT (Abort processes) sequence.
  • ao — sends the TELNET AO (Abort Output) sequence, which should make the remote system flush all output from the remote system to your terminal.
  • ayt — sends the TELNET AYT (Are You There) sequence. The remote system may or may not choose to respond — no cap, it's their call.
  • 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 make the remote system erase the last character entered.
  • el — sends the TELNET EL (Erase Line) sequence, which should make the remote system erase the line currently being entered.
  • eof — sends the TELNET EOF (End Of File) sequence.
  • eor — sends the TELNET EOR (End of Record) sequence.
  • escape — sends the current telnet escape character (initially ^]).
  • ga — sends the TELNET GA (Go Ahead) sequence, which likely has no significance to the remote system. 😭
  • getstatus — if the remote side supports the TELNET STATUS command, getstatus will send the subnegotiation to request that the server send its current option status.
  • ip — sends the TELNET IP (Interrupt Process) sequence, which should make the remote system 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 one makes the remote system discard all previously typed (but not yet read) input. Heads up: it's sent as TCP urgent data, and it may not work if the remote system is a 4.2BSD system — if it doesn't work, a lower case r may get echoed on your terminal. 💀
  • do 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.
  • dont cmd — sends the TELNET DONT 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.
  • will cmd — sends the TELNET WILL 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.
  • wont cmd — sends the TELNET WONT 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 info for the send command.

set argument value

unset argument value

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 — that's equivalent to using the unset command. The unset command disables, or sets to FALSE, any of the specified functions. You can interrogate the values of variables with the display command. 👀

The variables that may be set or unset (but NOT toggled) are listed here. Also, any of the variables for the toggle command can be explicitly set or unset using set and unset.

  • ayt — if TELNET is in localchars mode, or LINEMODE is enabled, and the status character gets typed, a TELNET AYT sequence (see send ayt above) 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.
okay bestie we're mid-list, no big intro, just vibes and characters 💅
  • erase — if telnet is in localchars mode (peep toggle localchars below ok) and telnet is doing that "character at a time" thing, then the second you type this char, a TELNET EC sequence (that's send ec from up above, mwah) gets yeeted to the remote system. The starting value for the erase character is literally whatever your terminal's erase character is. ✨
  • escape — this is the telnet escape character (starts out as ^[) and it's the one that yeets you into telnet command mode while you're connected to a remote system. main character energy honestly 👑
  • flushoutput — if telnet is in localchars mode (again: toggle localchars below) and you type the flushoutput character, a TELNET AO sequence (send ao, you know her) goes to the remote host. The starting value comes from your terminal's flush character.
  • forw1
  • forw2 — if TELNET is in LINEMODE, these are the characters that, when typed, cause partial lines to be forwarded to the remote system (yes, partial, she's sending the draft 🫶). Starting values come from your terminal's eol and eol2 characters.
  • interrupt — if telnet is in localchars mode (see toggle localchars below, iykyk) and you hit the interrupt character, a TELNET IP sequence (send ip) gets sent to the remote host. Starting value = the terminal's intr character.
  • kill — if telnet is in localchars mode (see toggle localchars below) and telnet is in "character at a time" mode, then typing this bad girl sends a TELNET EL sequence (send el) to the remote system. Starting value = the terminal's kill character. lowkey iconic 💀
  • lnext — if telnet is in LINEMODE or old line by line mode, this character is taken to be the terminal's lnext character. And yes, the starting value is taken to be the terminal's lnext character. she's consistent fr fr
  • quit — if telnet is in localchars mode (again! toggle localchars below!) and you type quit, a TELNET BRK sequence (send brk) gets sent to the remote host. Starting value = the terminal's quit character.
  • reprint — if telnet is in LINEMODE or old line by line mode, then this character is taken to be the terminal's reprint character. Starting value = the terminal's reprint character. 🌸
  • rlogin — okay this one's the rlogin escape character. If you set it, the normal TELNET escape character is ignored unless it's preceded by this character at the beginning of a line. This character, at the beginning of a line, followed by a . closes the connection. Followed by a ^Z? It suspends the telnet command. The initial state is to have the rlogin escape character disabled. 🙈
  • start — if the TELNET TOGGLE-FLOW-CONTROL option is enabled, this character is taken to be the terminal's start character. Starting value = the terminal's start character.
  • stop — if the TELNET TOGGLE-FLOW-CONTROL option is enabled, this character is taken to be the terminal's stop character. Starting value = the terminal's stop character. (yes they're a matching set, we love a coordinated duo 🎀)
  • susp — if telnet is in localchars mode, or LINEMODE is enabled, and you type the suspend character, a TELNET SUSP sequence (send susp) goes to the remote host. Starting value = the terminal's suspend character.
  • tracefile — this is the file where all the output goes when netdata or option tracing is TRUE. Set it to - and the tracing info gets written to standard output instead (and that's the default btw). ⭐
  • worderase — if telnet is in LINEMODE or old line by line mode, this character is taken to be the terminal's worderase character. Starting value = the terminal's worderase character.
  • ? — displays the legal set (unset) commands. short king. thank you for your service 🫶

🦋 skey, slc, status & toggle 🦋

  • skey sequence challenge — the skey command computes a response to the S/Key challenge. Wanna know more about the S/Key system? Go read skey(1), she explains it better than me ngl.
  • slc state — the slc command (Set Local Characters, see what they did there 💅) is used to set or change the state of the special characters when the TELNET LINEMODE option has been enabled. And what even are special characters? They're the characters that get mapped to TELNET command sequences (like ip or quit) or to line editing characters (like erase and kill). By default, the local special characters are exported. k slay, here's the states:
    • check — verify the current settings for the current special characters. The remote side is asked to send all the current special character settings, and if there's any discrepancy with the local side, the local side switches over to the remote value. vibe check, but for characters 🌈
    • export — switch to the local defaults for the special characters. "Local defaults" = whatever your local terminal had going on at the time telnet was started.
    • import — switch to the remote defaults for the special characters. "Remote defaults" = whatever the remote system had at the time the TELNET connection was established.
    • ? — prints out help info for the slc command. 🎀
  • status — shows the current status of telnet. This includes the peer you're connected to, plus the current mode. a whole little report card, obsessed
  • toggle arguments [...] — toggles (between TRUE and FALSE, the classic duo) all the flags that control how telnet responds to events. You can also set these explicitly to TRUE or FALSE using the set and unset commands listed above. You can pass more than one argument, go off 👑. Wanna interrogate the state of these flags? That's what the display command is for. Valid arguments are:
    • authdebug — turns on debugging information for the authentication code. 🔍
    • autoflush — if autoflush and localchars are both TRUE, then when the ao or quit characters get recognized (and transformed into TELNET sequences; see set above for the deets), telnet refuses to display any data on your terminal until the remote system acknowledges (via a TELNET TIMING MARK option) that it processed those TELNET sequences. Initial value for this toggle is TRUE if the terminal user hadn't done an stty noflsh, otherwise it's FALSE (see stty(1)). no cap, she will simply not show you anything until she gets her confirmation 🫶
    • autodecrypt — when the TELNET ENCRYPT option is negotiated, by default the actual encryption (decryption) of the data stream doesn't start automatically. The autoencrypt (autodecrypt) command says that encryption of the output (input) stream should be enabled as soon as possible. yeah, the parentheticals are doing a lot of work here, iykyk 😭
    • autologin — if the remote side supports the TELNET AUTHENTICATION option, TELNET attempts to use it to perform automatic authentication. If the AUTHENTICATION option isn't supported, the user's login name are propagated through the TELNET ENVIRON option. This command is the same as specifying a option on the open command. ✨
    • autosynch — if autosynch and localchars are both TRUE, then when either the intr or quit character is typed (see set above for the descriptions of the intr and quit characters), the resulting TELNET sequence that gets sent is followed by the TELNET SYNCH sequence. This procedure should cause the remote system to start throwing away all previously typed input until both 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. both! at once! equal opportunity 💜
    • 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> (yes "send", that's what it says, we're keeping it 💀). The initial value for this toggle is FALSE.
  • crmod — toggles carriage return mode. When it's enabled, most carriage return characters coming in from the remote host get mapped into a carriage return followed by a line feed. Lowkey important: this mode does not touch the characters you type — only the ones the remote host sends back. It's not super useful unless the remote host only ever sends carriage returns and never line feeds. Initial value for this toggle is FALSE.
  • debug — toggles socket level debugging (useful only to the super-user, so like, root energy only 👑). Initial value is FALSE.
  • encdebug — turns on debugging information for the encryption code.
  • localchars — the big one 🫶. 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). 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. And 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). Initial value is FALSE.
  • options — toggles the display of some internal telnet protocol processing (the stuff having to do with TELNET options). Initial value is FALSE.
  • prettydump — when the netdata toggle is enabled, if prettydump is enabled the output from the netdata command gets formatted in a more user readable format. Spaces go between each character in the output, and the beginning of any TELNET escape sequence is preceded by a '*' to aid in locating them. So cute, so readable ✨.
  • skiprc — when the skiprc toggle is TRUE, TELNET skips the reading of the .telnetrc file in the user's home directory when connections are opened. Initial value is FALSE.
  • termdata — toggles the display of all terminal data (in hexadecimal format). Initial value is FALSE.
  • verbose_encrypt — when the verbose_encrypt toggle is TRUE, telnet prints out a message each time encryption is enabled or disabled. Initial value is FALSE.
  • ? — displays the legal toggle commands. Your little cheat sheet 💅.

🦋 and now the actual commands, not toggles 🦋

  • z — suspend telnet. Heads up though: this command only works when the user is using csh(1), so if you're on another shell it's just gonna sit there.
  • ! [command] — execute a single command in a subshell on the local system. If command is omitted, then an interactive subshell is invoked (main character energy, you get a whole shell 🐚).
  • ? [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. We love a targeted answer.

🌸 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 — so yeah, your env can literally travel 🧳.

🎀 FILES 🎀

  • ~/.telnetrc — user customized telnet startup values

💜 HISTORY 💜

The telnet command appeared in 4.2BSD. Ancient. Iconic. Both 🫶.

⭐ NOTES ⭐

On some remote systems, echo has to be turned off manually when in ``old line by line'' mode. No cap, it just does.

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. So like — beginning of the line only, bestie, that's the vibe check.

Source routing is not supported yet for IPv6. Not a bug, just a "we haven't gotten there yet" 💀.

okay that's the whole page, you made it 🎉 this was the Debian build of TELNET(1), dated February 3, 1994 — yeah, it's older than most of us, and it's still serving. go forth and telnet responsibly, ily, bye 💖✨

📦 where this page comes from