telnet(1) telnet(1)
NAME
telnet - user interface to a remote system using the TELNET
protocol
SYNOPSIS
telnet [-8][-E][-L][-a][-d][-e escape_char][-l user][-n tracefile]
[-r][host [port]]
DESCRIPTION
The telnet command is used to communicate with another host
using the TELNET protocol.
Files
$HOME/.telnetrc
user-customized telnet startup values
/usr/lib/locale/locale/LC_MESSAGES/uxtelnet
language-specific message file [See LANG on environ(5).]
Environment Variables
The telnet command uses at least the following environment
variables: HOME, SHELL, USER, DISPLAY, and TERM. Other
environment variables may be propagated to the other side via
the TELNET ENVIRON option.
USAGE
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 (see the description of the telnet commands
below) with those arguments.
Options
telnet takes the following options:
-8 Use an eight bit data path. This will cause an
attempt to negotiate the BINARY option on both
input and output.
-E Stops 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.
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telnet(1) telnet(1)
-a Automatic login into the remote system. If the
remote system understands the ENVIRON option, then
the variable USER will be sent to the remote
system. This option may also be used with the
open command.
-d Toggles socket level debugging (useful only to the
privileged user). 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 a null string
(""), then there will be no pre-defined escape
character.
-l user When connecting to the remote system, and 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 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(1). In
this mode, the escape character is set to the
tilde (``~'') character, unless modified by the -e
flag.
host Indicates the host's official name: an alias or
the Internet address of a remote host.
port Indicates a port number (that is, the address of
an application). If a number is not specified, the
default TELNET port will be used.
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.
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telnet(1) telnet(1)
When LINEMODE is enabled, character processing will be 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 will be echoed
locally, but (normally) only completed lines will be 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 will
be 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 will be 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 ``escape character''
(initially ``^['').
When in command mode, the normal terminal editing conventions
will be available.
Commands
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, set, toggle,
unset, slc, environ, and display commands).
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telnet(1) telnet(1)
close Close a TELNET session and return to command mode.
display argument ...
Displays all, or some, of the set and toggle
values (see description below).
mode type Depending on the state of the TELNET session, the
type argument is one of several available
options. The remote host will be asked for
permission to go into the requested mode. If the
remote host is capable of entering that mode, the
requested mode will be entered.
character Disable the TELNET LINEMODE option;
or, if the remote side does not
understand the 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.
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telnet(1) telnet(1)
litecho
-litecho Attempt to enable (disable) the
LIT_ECHO mode of the LINEMODE option.
This requires that the LINEMODE option
be enabled.
? Print help information for the mode
command.
open [ -l user ] [ -a ] host [[-]port ]
Open a connection to the named host. Note that
the presence or absence of white space in the
command syntax is significant. 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 [see
hosts(4)] or an Internet address specified in the
``dot notation'' [see inet(3N)].
The -l or the -a option may be used to specify the
user name to be passed to the remote system via
the ENVIRON option.
When connecting to a non-standard port, telnet
will omit the automatic initiation of any TELNET
options. When the port number is preceded by a
minus sign, the initial option negotiation will be
done as follows: After establishing a connection,
the file .telnetrc in the user's home directory
will be opened. Lines beginning with a # will be
treated as comment lines; blank lines will be
ignored. Lines that begin without whitespace will
be the start of a machine entry. The first thing
on the line will be the name of the machine to
which this host is being connected. The rest of
the line - and successive lines which begin with
whitespace - will be assumed to be telnet commands
and will be processed as if they had been entered
manually in response to the telnet command prompt.
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.
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telnet(1) telnet(1)
send arguments
Sends 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 Sends the TELNET ABORT (ABORT processes)
sequence.
ao 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; the remote system may or may not
choose to respond to this transmission.
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
(initially ``^['').
ga Sends 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, getstatus will send
the subnegotiation request that the server
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telnet(1) telnet(1)
send its current option status.
ip Sends the TELNET IP (Interrupt Process)
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 (SUSPend 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 will be 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 ``|'' may be echoed on
the terminal).
? Print help information for the send command.
set argument value
unset argument value
The set command will set anyone of a number of
TELNET variables to a specific value or to TRUE.
The special value off will turn off the function
associated with this 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.
echo This is the value (initially ``^['') 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
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telnet(1) telnet(1)
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) will
be 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) will be sent to the
remote host. The initial value for the
flush character is taken to be the
terminal's flush character.
interrupt
If TELNET AO is in localchars mode (see
toggle localchars below) and the interrupt
character is entered, a TELNET IP sequence
(see send ip above) will be sent to the
remote host. The initial value for the
interrupt character is taken to be the
terminal's intr character.
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telnet(1) telnet(1)
kill If TELNET IP is in localchars mode (see
toggle localchars below), and if TELNET IP
is operating in the ``character at a time''
mode, then when this character is entered, a
TELNET EL sequence (see send el above) will
be sent to the remote system. The initial
value for the kill character is taken to be
the terminal's kill character.
lnext If TELNET EL 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 EL is in localchars mode (see
toggle localchars below) and the quit
character is entered, a TELNET BRK sequence
(see send brk above) will be sent to the
remote host. The initial value for the quit
character is taken to be the terminal's quit
character.
reprint
If TELNET BRK 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.
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.
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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) will be 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
generated by the netdata command will be
written.
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.
? Displays the valid set and 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 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.
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.
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telnet(1) telnet(1)
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 set of remote
values.
? Print help information for the slc command.
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 USER and DISPLAY variables being
exported.
The 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 embedded spaces may
be included.
undefine variable
Remove the variable 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 requested by the
remote side.
list List the current set of environment
variables. Those marked with a * will be
sent automatically; any other variables will
be sent only if requested explicitly.
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telnet(1) telnet(1)
? Print help information for the environ
command.
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 with the aid of
the display command. 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 will be
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.
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telnet(1) telnet(1)
outbinary
Enable or disable the TELNET BINARY option
on output.
crlf If this toggle value is TRUE, then Carriage
Returns will be sent as <CR><LF>. If this
is FALSE, then Carriage Returns will be 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
will be 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 Toggles the socket level debugging mode
(useful only to the privileged user). 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 (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 will be sent as
abort; eof and suspend will be sent as eof
and susp; (see send above).
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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 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 will be reorganized into a
more user-friendly format. Spaces will be
put between each character in the output and
the beginning of any TELNET escape sequence
will be preceded by a '*' to aid in locating
them.
? Displays the valid 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 will be invoked.
status Show the current status of telnet. This includes
the peer to which one is connected, as well as the
current mode.
? [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.
Warnings
On some remote systems, the echo command has to be turned off
manually when in the ``old line by line'' mode.
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telnet(1) telnet(1)
When in the ``old line by line'' mode or in LINEMODE, the
terminal's eof character is recognized (and sent to the remote
system) only when it is the first character in a line.
REFERENCES
hosts(4), inet(7), rlogin(1), sh(1), stty(1)
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