telnet - user interface to the TELNET protocol
telnet [-468EFKLacdfrx] [-X authtype] [-b hostalias] [-e
escapechar]
[-k realm] [-l user] [-n tracefile] [host [port]]
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:
-4 Forces telnet to use IPv4 addresses only.
-6 Forces telnet to use IPv6 addresses only.
-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.
-F If Kerberos 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.
-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 hostalias
Uses bind(2) on the local socket to bind it to an
aliased address
(see ifconfig(8) and the ``alias'' specifier) or to
the 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 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.
-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. In
this mode, the
escape character is set to the tilde (~) character,
unless modified
by the -e option.
-x Turn on encryption of the data stream. When this
option is
turned on, telnet will exit with an error if authentication cannot
be negotiated or if encryption cannot be turned
on.
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 that's available when
Kerberos is
used.
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 users environment, with only
the DISPLAY and PRINTER variables being exported by default.
The USER variable is also exported if the
-a or -l options
are used.
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
Mark the variable variable to be exported to the
remote side.
unexport variable
Mark the variable variable to not be
exported unless
explicitly asked for by the remote side.
list List the current set of environment
variables.
Those marked with a * will be sent
automatically,
other variables will only be sent if
explicitly
requested.
? Prints out help information for the
environ command.
logout Sends the TELNET LOGOUT option to the remote
side. This command
is similar to a close command; however, if
the remote
side does not support the LOGOUT option, nothing
happens. If,
however, the remote side does support the LOGOUT
option, this
command should cause the remote side to close the
TELNET connection.
If the remote side also supports the
concept of suspending
a user's session for later reattachment,
the logout
argument indicates that you should terminate the
session immediately.
mode type type is one of several options, depending on the
state of the
TELNET session. The remote host is asked for
permission to go
into the requested mode. If the remote host is
capable of entering
that mode, the requested mode will be entered.
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 ``oldline-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 server at
the default port. The host specification may be
either a host
name (see hosts(5)) or an Internet address specified in the
``dot notation'' (see inet(3)). The -l option
may be used to
specify the user name to be passed to the remote
system via
the ENVIRON option. When connecting to a nonstandard 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
is opened.
Lines beginning with a ``#'' are comment lines.
Blank lines
are ignored. Lines that begin without whitespace
are the
start of a machine entry. The first thing on the
line is the
name of the machine that is being connected to.
The rest of
the line, and successive lines that begin with
whitespace are
assumed to be telnet commands and are processed
as if they had
been typed in manually to the telnet command
prompt.
quit Close any open TELNET session and exit telnet.
An end-of-file
(in command mode) will also close a session and
exit.
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
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, 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
(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 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 is
sent as TCP urgent
data (and may not work if the remote
system is a
4.2BSD system -- if it doesn't work, a
lower case
``r'' may be echoed on the 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 information for the send
command.
set argument value
unset argument value
The set command will set 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
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 set or unset
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 preceding) 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.
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 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 is the rlogin escape character. If
set, the normal
TELNET escape character is ignored
unless it is
preceded by this character at the beginning of a line.
This character, at the beginning of a
line, followed
by a "." closes the connection; when followed by a ^Z
it suspends the telnet command. 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 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 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 (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 (unset) commands.
skey sequence challenge
The skey command computes a response to the S/Key
challenge.
See skey(1) for more information on the S/Key
system.
slc state The slc command (Set Local Characters) is used to
set or
change the state of the special characters when
the TELNET
LINEMODE option has been enabled. Special characters are
characters that get mapped to TELNET commands sequences (like
ip or quit) or line editing characters (like
erase and kill).
By default, the local special characters are exported.
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 includes
the peer one
is connected to, 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
listed
above. More than one argument may be specified.
The state of
these flags may be interrogated with the display
command.
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 are
recognized
(and transformed into TELNET sequences; see set
above for details), telnet refuses
to display
any data on the user's terminal until the remote
system acknowledges (via a TELNET
TIMING MARK
option) that it has processed those
TELNET sequences.
The initial value for
this toggle is
TRUE if the terminal user had not
done an "stty
noflsh", otherwise FALSE (see
stty(1)).
autodecrypt When the TELNET ENCRYPT option is
negotiated, by
default the actual encryption (decryption) of
the data stream does not start automatically.
The autoencrypt (autodecrypt) command states
that encryption of the output (input) stream
should be enabled as soon as possible.
autologin If the remote side supports the
TELNET
AUTHENTICATION option TELNET attempts to use it
to perform automatic authentication. If the
AUTHENTICATION option is not supported, the user's
login name is 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 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 sent as
<CR><NUL>. The
initial value for this toggle is
FALSE.
crmod Toggle carriage return mode. When
this mode is
enabled, most carriage return characters received
from the remote host 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 feeds. 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.
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 suspend
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
any TELNET escape sequence is preceded by a '*'
to aid in locating them.
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. 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.
? Displays the legal toggle commands.
z Suspend telnet. This command only works when the
user is using
the csh(1).
! [command]
Execute a single command in a subshell on the local system.
If command is omitted, 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 just that command.
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.
~/.telnetrc user customized telnet startup values
The telnet command appeared in 4.2BSD.
On some remote systems, echo has to be turned off manually
when in ``old
line by line'' mode.
In ``old line by line'' mode or LINEMODE the terminal's eof
character is
only recognized (and sent to the remote system) when it is
the first
character on a line.
Source routing is not supported yet for IPv6.
OpenBSD 3.6 February 3, 1994
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