telnet(1tcp)
telnet --
user interface to a remote system using the TELNET protocol
Synopsis
telnet
[ -8ELacdr ]
[ -e escape_char ] [ -l user ]
[ -n tracefile ]
[ host [ -port | port ]
Description
The telnet command communicates with another host
using the TELNET protocol. If telnet
is invoked without the host argument, it will
enter command mode as indicated by its prompt
telnet>
. In this mode, telnet will
accept and execute the commands listed below; if
telnet is invoked with arguments, it will perform
an open command with those arguments.
The following options are available:
-8-
Use an eight bit data path. This will cause
an attempt to negotiate the BINARY option on both
input and output.
Binary mode is enabled by default if the LANG environment variable is set
to one of the following Asian locales:
-
ja, ja_JP, or ja_JP.EUC (Japanese)
-
ko (Korean)
-
zh_cn (Simplified Chinese)
-
zh_tw (Traditional Chinese)
-E-
Stop any character from being recognized as an escape character.
-L-
Use an eight bit data path on output.
This causes the BINARY option to be negotiated on output.
-a-
Automatic login into the remote system. If the remote system
understands the
ENVIRON option, then the USER variable
is exported to the remote system.
This option may also be used with the open command.
-c-
Do not process the user's ~/.telnetrc file
(see the toggle skiprc command below).
-d-
Toggles socket level debugging (useful only to root).
Sets the initial value of the
debug
toggle to
TRUE.
-e escape_char-
Sets the initial TELNET escape character to
escape_char. If escape_char is
the null string (""), then there is no pre-defined escape
character.
-l user -
When connecting to the remote
system and if the remote system understands the
ENVIRON option, then user is exported
to the remote system as the value for the USER variable.
This option may also be used with the open command.
-n tracefile-
Opens tracefile for recording the trace
information. (See the set tracefile
command below.)
-r-
Use a user interface similar to
rlogin(1tcp).
In this mode, the escape character is set to the tilde (~)
character, unless modified with the -e option.
host-
Indicates the host's official name, an
alias, or the Internet address of a remote host.
host may be specified as an IPv4
or IPv6 loose source route (where each element
does not need to be a neighbor)
or strict source route (where each element must be a neighbor).
An IPv4 loose source route takes the form:
@addr[@addr...]:dest
An IPv4 strict source route takes the form:
!@addr[@addr...]:dest
An IPv6 loose source route takes the form:
@addr[@addr...]@dest
An IPv6 strict source route takes the form:
!@addr[@addr...]@dest
Additionally, IPv6 allows the specification of a mixed
strict and loose source route:
@addr[!][@addr[!]...]@dest[!]
In this case, strict elements specify a trailing ``!'';
loose elements do not specify a trailing ``!''.
IPv4 allows up to 9 intermediate addresses
to be specified in the route to the destination.
IPv6 allows up to 23 intermediate addresses
to be specified in the route to the destination.
See RFC 791 and RFC 1883 for more information about
source routing in IPv4 and IPv6.
NOTE:
This exists primarily for debugging
or for use when network connectivity is problematic. Use
of source routing is not usually recommended.
port-
Indicates a port number (that is, the address of an
application). If a number is not specified, the default
TELNET port is used.
When a port number is specified,
telnet
will omit the automatic initiation of any
TELNET options,
unless
the port number is preceded by a minus sign.
After establishing a connection, file
.telnetrc file
in the user's home directory is opened.
Lines beginning with a ``#'' are treated as 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 the host is connecting to.
The rest of the line (and successive
lines which begin with whitespace) are assumed to be
telnet
commands, and are processed as if they had been entered
manually in response to the telnet command prompt.
Once a connection has been opened, TELNET will
enter the input mode. TELNET will attempt
to enable the TELNET LINEMODE option. If this
fails, then TELNET will revert to one of two
input modes: either the character-at-a-time mode or
the old line-by-line mode, depending on what the remote
system supports.
When LINEMODE is enabled, character processing
is done on the local system while 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 the character at a time mode, most entered text will
be sent immediately to the remote host for processing.
In the old line-by-line mode, all text is echoed
locally, but usually only completed lines are sent
to the remote host. The local echo character
(initially ``^E'') may be used to enable and disable the
local echo mode; normally, this would be used only for
entering passwords so that the password will not be echoed.
If the LINEMODE option is enabled or if the
localchars toggle is TRUE (the
default value for the old line-by-line mode; see
below), the user's quit, intr, and
flush characters are trapped locally and sent
as TELNET protocol sequences to the remote
machine. If LINEMODE had been enabled at any
earlier time, then the user's susp and
eof characters will also be sent as
TELNET protocol sequences; quit are
sent as a TELNET ABORT instead of
<Break>. There are options (see toggle autoflush and
toggle autosynch below) which cause this action to flush
any subsequent output to the terminal (until the remote
host acknowledges the TELNET sequence) and to
flush previous terminal input (in the case of
quit and intr).
While connected to a remote host, the
telnet
command mode may be entered by typing the
TELNET <Esc> sequence (initially ``^]'').
When in command mode, the normal terminal editing conventions
are available.
The following TELNET commands are available, but
only enough of each command need be typed to uniquely
identify it (this is also true for arguments pertaining to
the mode, toggle, set,
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 description below).
environ [ argument [...] ]-
Manipulate
the variables that may be sent through the
TELNET ENVIRON option.
The initial set of variables is taken from the user's environment;
only the DISPLAY, LANG,
and PRINTER variables are automatically exported,
although USER is also exported
if the -a or -l options are used.
The 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 exported.
The value
may be enclosed in single or double quotes so
that tabs and embedded spaces may be included.
undefine variable-
Remove variable
from the list of environment variables.
export variable-
Mark the variable
to be exported to the remote side.
unexport variable-
Mark the variable
not to be exported unless explicitly requested by the remote side.
list-
List the current set of environment variables.
Those marked with a ``'' are sent automatically;
any other variables are sent only if explicitly requested.
send variable-
Send environment variable.
?-
Prints out help information for the environ command.
logout-
Send the TELNET LOGOUT option to the remote site.
This command is similar to the close command. However,
nothing will happen if the remote site does not support the
LOGOUT option.
If the remote site does support this option,
then it should cause the remote site to close the TELNET
connection.
Additionally, if a user's session can be suspended for future
attachment, the logout option indicates that you
should terminate the session immediately.
mode [ type ]-
Depending on the state of the TELNET session, the
type argument is one of several available options.
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
TELNET LINEMODE
option, then enter the character-at-a-time mode.
line-
Enable the TELNET LINEMODE
option; or, if the remote side does not understand the
TELNET LINEMODE
option, then attempt to enter the old line-by-line mode.
isig
-isig-
Attempt to enable (disable) the
TRAPSIG mode of the TELNET 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 [ -l user ] [ -a ] host [ [ - ] port ]-
Open a connection to the named host.
If host is ``?'' then the help information for
the open command is displayed.
If no port number is specified,
telnet will attempt 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 (see
inet(3N)).
quit-
Close any open TELNET session and exit telnet.
When in command mode, an End-of-File (EOF) will also close a session
and exit.
send arguments-
Send one (or more) special character sequences to the remote host.
The following are the arguments which may be specified
(more than one argument may be specified at a given 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; the remote system may or may not respond to this
transmission.
brk-
Send the
TELNET BRK
(Break) sequence which may have significance for 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 probably has no significance to the remote system.
getstatus-
If the remote side supports the
TELNET STATUS
command,
send the subnegotiation request to the server for
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 does not work, a lowercase ``l'' may be echoed on the terminal).
do cmd
dont cmd
will cmd
wont cmd-
Send the TELNET DO, DONT, WILL
or WONT command sequence. cmd can be either a decimal
number between 0 and 255, or a symbolic name for a specific TELNET
command. cmd may also be help or ? which
prints help information, including the list of symbolic names.
?-
Print out help information 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; this is equivalent to using the
unset command.
The unset command will disable (or set to
FALSE) any of the specified functions.
The values of variables may be interrogated with the aid of 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 enabled or disabled using the
set and unset commands.
ayt-
If telnet is in localchars mode, or LINEMODE
is enabled, and the status character is 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 the
line-by-line mode, will toggle between doing local echoing
of entered characters (for normal processing) and suppressing
echoing of entered characters (for example, for entering a password).
eof-
If telnet is operating in
LINEMODE
or in the 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 the character at a time mode, then when this
character is entered, a
TELNET EC sequence (see send ec above)
are 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 the
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 entered, a
TELNET AO sequence (see send ao above)
are 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 entered, a
TELNET IP sequence (see send ip above)
are 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 the character at a time mode, then when this
character is entered, a TELNET EL
sequence (see send el above)
are 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 in the 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 entered, a
TELNET BRK sequence (see send brk above)
are 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 in the 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 escape character.
If set, the normal TELNET escape character is ignored, unless
preceded by this character at the beginning of a line.
If the character is followed by a ``.'', then the connection
is closed.
If the character is followed by a ``^Z'', then the telnet
command is suspended.
The initial state is to disable the rlogin escape character.
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 start
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 stop
character is taken to be the terminal's
stop character.
susp-
If telnet is in the localchars
mode or if the LINEMODE
is enabled and the suspend character is entered, a
TELNET SUSP sequence (see send susp above)
are 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.
The default value is ``-'', which sends tracing information to
the standard output.
worderase-
If telnet is operating in LINEMODE
or in the 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.
?-
Display the legal set and unset commands.
slc [ state ]-
The slc command (Set Local Characters) sets
(or changes) the state of the special characters when the
TELNET LINEMODE option has been enabled.
The 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;
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.
?-
Print out help information for the slc
command.
status-
Show the current status of telnet.
This includes the peer to which one is connected, as well as the current mode.
toggle arguments [...]-
Toggle various flags (between TRUE
and FALSE) that control how
TELNET responds to events.
These flags may be set explicitly to TRUE
or FALSE using the set
and unset commands listed above.
More than one argument may be specified.
The state of these flags may be interrogated using
display.
The valid arguments are:
autoflush-
If autoflush and localchars
are both TRUE, then when the
ao or the quit
characters are recognized (and transformed into
TELNET sequences; see set
above for details), telnet
will refuse 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 executed an stty noflsh;
otherwise FALSE (see
stty(1)).
autosynch-
If autosynch and localchars are both
TRUE, then when either the
intr or quit
character is entered (see set
above for descriptions of the intr
and quit characters), the resulting TELNET
sequence sent are followed by the
TELNET SYNCH sequence.
This procedure should cause the remote system to begin throwing away
all previously entered 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 the 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 toggle value is TRUE,
then carriage returns are sent as
<CR><LF>.
If this is FALSE,
then carriage returns are sent as
<CR><NUL>.
The initial value for this toggle is
FALSE.
crmod-
Toggle the 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.
This mode does not affect those characters entered by the user,
but only those received from the remote host.
This mode is not very useful unless the remote host
only sends carriage return, but never any line feeds.
The initial value for this toggle is FALSE.
debug-
Toggle the socket level debugging mode (useful only to root).
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 then transformed into 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; eof
and suspend are sent as eof
and 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 which pertain to
TELNET options.
The initial value for this toggle is
FALSE.
prettydump-
When the netdata toggle is enabled and if
prettydump is enabled, the output from the
netdata command are reorganized into a more user-friendly format.
Spaces are put between each character in the output and the
beginning of any TELNET
escape sequence are preceded by a ``'' to aid in locating them.
skiprc-
If this is TRUE, then telnet does
not process the ~/.telnetrc file.
The initial value is set to
FALSE.
termdata-
Toggle printing of hexadecimal terminal data.
The initial value for this toggle is
FALSE.
?-
Display the legal toggle commands.
<Ctrl>Z-
Suspend telnet.
This command will work only when the user is using
csh(1)
or
ksh(1).
! [ command ]-
Execute a single command in a subshell on the local system.
If command
is omitted, then an interactive subshell are invoked.
? [ command ]-
Get help.
When no command is specified, telnet
will print a summary for the help command.
If a command is specified, telnet
will print the help information for just that
command.
Environment variables
If set, the telnet command exports at least the
following environment variables to the remote machine:
DISPLAY,
LANG,
and
PRINTER.
Note that
DISPLAY are set to
local_hostname:0.0
if DISPLAY is
set to :0.0
or to unix:0.0
locally.
Other environment variables may be propagated to the remote
side via the TELNET ENVIRON option.
USER is set to
LOGNAME if LOGNAME is set locally
but USER is not.
By default, USER is not set.
Files
$HOME/.telnetrc-
user-customized telnet startup values
References
telnetd(1Mtcp)
RFC 727,
RFC 854,
RFC 856,
RFC 857,
RFC 858,
RFC 859,
RFC 860,
RFC 1073,
RFC 1079,
RFC 1091,
RFC 1096,
RFC 1123,
RFC 1184,
RFC 1372,
RFC 1572
Notices
On some remote systems, the echo
command has to be turned off manually when
in the old line-by-line mode.
When in the old line-by-line mode or in
LINEMODE, the terminal's eof character
is only recognized (and sent to the remote system) when it
is the first character in a line.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004