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NAME
telnet - user interface to a remote system using the TELNET
protocol
SYNOPSIS
telnet [-8EFKLacdfrx] [-X atype] [-e escape_char]
[-k realm] [-l user] [-n file]
[ [ [!] @hop1 [@hop2...] @] host [port]]
DESCRIPTION
The telnet utility communicates with another host using the
TELNET protocol. If telnet is invoked without arguments, it
enters command mode, indicated by its prompt, telnet>. In
this mode, it accepts and executes its associated commands.
See , , below. If it is invoked with arguments, it performs
an open command with those arguments.
If, for example, a host is specified as @hop1@hop2@host, the
connection goes through hosts hop1 and hop2, using loose
source routing to end at host. If a leading ! is used, the
connection follows strict source routing. Notice that when
telnet uses IPv6, it can only use loose source routing, and
the connection ignores the !.
Once a connection has been opened, telnet enters input mode.
In this mode, text typed is sent to the remote host. The
input mode entered will be either "line mode", "character at
a time", or "old line by line", depending upon what the
remote system supports.
In "line mode", 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 immedi-
ately 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. (Use this mostly to enter
passwords without the password being echoed.).
If the "line mode" option is enabled, or if the localchars
toggle is TRUE (the default in "old line by line" mode), the
user's quit, intr, and flush characters are trapped locally,
and sent as TELNET protocol sequences to the remote side. If
"line mode" has ever been enabled, then the user's susp and
eof are also sent as TELNET protocol sequences. quit is then
sent as a TELNET ABORT instead of BREAK. The options toggle
autoflush and toggle autosynch cause this action to flush
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 user can enter telnet
command mode by typing the telnet escape character (ini-
tially ^]). When in command mode, the normal terminal edit-
ing conventions are available. Pressing RETURN at the telnet
command prompt causes telnet to exit command mode.
OPTIONS
The following options are supported:
-8 Specifies an 8-bit data path. Negotiating
the TELNET BINARY option is attempted for
both input and output.
-a Attempts automatic login. This sends the
user name by means of 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(3C) if it agrees with the current
user ID. Otherwise, it is the name associ-
ated with the user ID.
-c Disables the reading of the user's tel-
netrc file. (See the toggle skiprc command
on this reference page.)
-d Sets the initial value of the debug toggle
to TRUE.
-e escape_char Sets the initial escape character to
escape_char. escape_char may also be a two
character sequence consisting of ^ (Con-
trol key) followed by one character. If
the second character is ?, the DEL charac-
ter is selected. Otherwise, the second
character is converted to a control char-
acter and used as the escape character. If
escape_char is defined as the null string
(that is, -e ''), this is equivalent to -e
'^@' (Control-@). To specify that no
character can be the escape character, use
the -E option.
-E Stops any character from being recognized
as an escape character.
-f Forwards a copy of the local credentials
to the remote system.
-F Forwards a forwardable copy of the local
credentials to the remote system.
-k realm If Kerberos authentication is being used,
requests that telnet obtain tickets for
the remote host in realm instead of the
remote host's default realm as determined
inkrb5.conf(4).
-K Specifies no automatic login to the remote
system.
-l user When connecting to a remote system that
understands the ENVIRON option, then user
will be sent to the remote system as the
value for the ENVIRON variable USER.
-L Specifies an 8-bit data path on output.
This causes the BINARY option to be nego-
tiated on output.
-n tracefile Opens tracefile for recording trace infor-
mation. See the set tracefile command
below.
-r Specifies a user interface similar to rlo-
gin. In this mode, the escape character is
set to the tilde (~) character, unless
modified by the -e option. The rlogin
escape character is only recognized when
it is preceded by a carriage return. In
this mode, the telnet escape character,
normally '^]', must still precede a telnet
command. The rlogin escape character can
also be followed by '.\r' or '^Z', and,
like rlogin(1), closes or suspends the
connection, respectively. This option is
an uncommitted interface and may change in
the future.
-x Turns on encryption of the data stream.
When this option is turned on, telnet will
exit with an error if authentication can-
not be negotiated or if encryption cannot
be turned on.
-X atype Disables the atype type of authentication.
USAGE
telnet Commands
The commands described in this section are available with
telnet. It is necessary to type only enough of each command
to uniquely identify it. (This is also true for arguments to
the mode, set, toggle, unset, environ, and display com-
mands.)
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 authenti-
cation. To obtain a list of available
types, use the auth disable ? command.
enable type Enables the specified type of authenti-
cation. To obtain a list of available
types, use the auth enable ? command.
status Lists the current status of the various
types of authentication.
open [-l user ] [ [!] @hop1 [@hop2 ...]@host [ 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(4)) or an Internet
address specified in the "dot notation" (see inet( 7P)
or inet6( 7P)). If the host is specified as
@hop1@hop2@host, the connection goes through hosts hop1
and hop2, using loose source routing to end at host. The
@ symbol is required as a separator between the hosts
specified. If a leading ! is used with IPv4, the connec-
tion follows strict source routing.
The -l option passes the user as the value of the
ENVIRON variable USER to the remote system.
close
Close any open TELNET session and exit telnet. An EOF
(in command mode) will also close a session and exit.
encrypt
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 the 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 com-
mand.
-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.
quit
Same as close.
z
Suspend telnet. This command only works when the user is
using a shell that supports job control, such as sh(1).
mode type
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.
The argument type is one of the following:
character Disable the TELNET LINEMODE
option, or, if the remote side
does not understand the LINEMODE
option, then enter "character at
a time" mode.
line Enable the TELNET LINEMODE
option, or, if the remote side
does not understand the LINEMODE
option, then attempt to enter
"old-line-by-line" mode.
isig (-isig) Attempt to enable (disable) the
TRAPSIG mode of the LINEMODE
option. This requires that the
LINEMODE option be enabled.
edit (-edit) Attempt to enable (disable) the
EDIT mode of the LINEMODE
option. This requires that the
LINEMODE option be enabled.
softtabs (-softtabs) Attempt to enable (disable) the
SOFT_TAB mode of the LINEMODE
option. This requires that the
LINEMODE option be enabled.
litecho (-litecho) Attempt to enable (disable) the
LIT_ECHO mode of the LINEMODE
option. This requires that the
LINEMODE option be enabled.
? Prints out help information for
the mode command.
status
Show the current status of telnet. This includes the
peer one is connected to, as well as the current mode.
display
[argument...] Display all, or some, of the set and tog-
gle values (see toggle argument...).
?
[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.
send argument...
Send one or more special character sequences to the
remote host. The following are the arguments that can be
specified (more than one argument may be specified at a
time):
escape Send the current telnet escape character
(initially ^]).
synch Send the TELNET SYNCH sequence. This
sequence discards all previously typed,
but not yet read, input on the remote
system. 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 "r" may be
echoed on the terminal.
brk or break Send the TELNET BRK (Break) sequence,
which may have significance to the
remote system.
ip Send the TELNET IP (Interrupt Process)
sequence, which aborts the currently
running process on the remote system.
abort Send the TELNET ABORT (Abort Process)
sequence.
ao Send the TELNET AO (Abort Output)
sequence, which flushes all output from
the remote system to the user's termi-
nal.
ayt Send the TELNET AYT (Are You There)
sequence, to which the remote system may
or may not respond.
ec Send the TELNET EC (Erase Character)
sequence, which erases the last charac-
ter 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.
ga Send the TELNET GA (Go Ahead) sequence,
which probably has no significance for
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.
nop Send the TELNET NOP (No Operation)
sequence.
susp Send the TELNET SUSP (Suspend Process)
sequence.
do option Send the TELNET protocol option negotia-
dont option tion indicated. Option may be the text
will option name of the protocol option, or the
wont option number corresponding to the option. The
command will be silently ignored if the
option negotiation indicated is not
valid in the current state. If the
option is given as help or ?, the list
of option names known is listed. This
command is mostly useful for unusual
debugging situations.
? Print out help information for the send
command.
set argument [value]
unset argument
Set any one of a number of telnet variables to a
specific value. The special value off turns off the
function associated with the variable. The values of
variables may be interrogated with the display command.
If value is omitted, the value is taken to be true, or
"on". If the unset form is used, the value is taken to
be false, or off. The variables that may be specified
are:
echo This is the value (initially ^E) that,
when in "line by line" mode, toggles
between local echoing of entered charac-
ters for normal processing, and suppress-
ing echoing of entered characters, for
example, entering a password.
escape This is the telnet escape character (ini-
tially ^]) that enters telnet command
mode when connected to a remote system.
interrupt If telnet is in localchars mode (see tog-
gle, localchars) and the interrupt char-
acter is typed, a TELNET IP sequence (see
send and ip) is sent to the remote host.
The initial value for the interrupt char-
acter is taken to be the terminal's intr
character.
quit If telnet is in localchars mode and the
quit character is typed, a TELNET BRK
sequence (see send, brk) is sent to the
remote host. The initial value for the
quit character is taken to be the
terminal's quit character.
flushoutput If telnet is in localchars mode and the
flushoutput character is typed, a TELNET
AO sequence (see send, ao) is sent to the
remote host. The initial value for the
flush character is taken to be the
terminal's flush character.
erase If telnet is in localchars mode and
operating in "character at a time" mode,
then when the erase character is typed, a
TELNET EC sequence (see send, ec) is sent
to the remote system. The initial value
for the erase character is taken to be
the terminal's erase character.
kill If telnet is in localchars mode and
operating in "character at a time" mode,
then when the kill character is typed, a
TELNET EL sequence (see send, el) is sent
to the remote system. The initial value
for the kill character is taken to be the
terminal's kill character.
eof If telnet is operating in "line by line"/
mode, entering the eof character as the
first character on a line sends this
character to the remote system. The ini-
tial value of eof is taken to be the
terminal's eof character.
ayt If telnet is in localchars mode, or
LINEMODE is enabled, and the status char-
acter is typed, a TELNET AYT ("Are You
There") sequence is sent to the remote
host. (See send, ayt above.) The initial
value for ayt is the terminal's status
character.
forw1 If telnet is operating in LINEMODE, and
forw2 the forw1 or forw2 characters are typed,
this causes the forwarding of partial
lines to the remote system. The initial
values for the forwarding characters come
from the terminal's eol and eol2 charac-
ters.
lnext If telnet is operating in LINEMODE or
"old line by line" mode, then the lnext
character is assumed to be the terminal's
lnext character. The initial value for
the lnext character is taken to be the
terminal's lnext character.
reprint If telnet is operating in LINEMODE or
"old line by line" mode, then the reprint
character is assumed to be the terminal's
reprint character. The initial value for
reprint 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. The
rlogin character, at the beginning of a
line followed by a "." closes the connec-
tion. When followed by a ^Z, the rlogin
command 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 the start charac-
ter is taken to be the terminal's start
character. The initial value for the kill
character is taken to be the terminal's
start character.
stop If the TELNET TOGGLE-FLOW-CONTROL option
has been enabled, then the stop character
is taken to be the terminal's stop char-
acter. The initial value for the kill
character is taken to be the terminal's
stop character.
susp If telnet is in localchars mode, or
LINEMODE is enabled, and the suspend
character is typed, a TELNET SUSP
sequence (see send, susp above) is sent
to the remote host. The initial value for
the suspend character is taken to be the
terminal's suspend character.
tracefile This is the file to which the output,
generated when the netdata or the debug
option is TRUE, will be written. If tra-
cefile is set to "-", then tracing infor-
mation will be written to standard output
(the default).
worderase If telnet is operating in LINEMODE or
"old line by line" mode, then this char-
acter is taken to be the terminal's wor-
derase character. The initial value for
the worderase character is taken to be
the terminal's worderase character.
? Displays the legal set and unset com-
mands.
slc state
The slc (Set Local Characters) command is used to set or
change the state of 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. The following values for state are valid:
check Verifies the settings for the current special
characters. The remote side is requested to
send all the current special character set-
tings. If there are any discrepancies with the
local side, the local settings will switch to
the remote values.
export Switches 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 Switches to the remote defaults for the spe-
cial 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 com-
mand.
toggle argument...
Toggle between TRUE and FALSE the various flags that
control how telnet responds to events. More than one
argument may be specified. The state of these flags may
be interrogated with the display command. Valid argu-
ments are:
authdebug Turns on debugging information for
the authentication code.
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 TEL-
NET AUTHENTICATION option, telnet
attempts to use it to perform
automatic authentication. If the
AUTHENTICATION option is not sup-
ported, the user's login name is pro-
pagated through the TELNET ENVIRON
option. This command is the same as
specifying the -a option on the open
command.
autoflush If autoflush and localchars are both
TRUE, then when the ao, intr, or quit
characters are recognized (and
transformed into TELNET sequences;
see set for details), telnet refuses
to display any data on the user's
terminal until the remote system ack-
nowledges (using a TELNET Timing Mark
option) that it has processed those
TELNET sequences. The initial value
for this toggle is TRUE if the termi-
nal user has not done an "stty
noflsh". Otherwise, the value is
FALSE (see stty(1)).
autosynch If autosynch and localchars are both
TRUE, then when either the interrupt
or quit characters are typed (see set
for descriptions of interrupt and
quit), 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 Determines how carriage returns are
sent. If the value is TRUE, then car-
riage returns will be sent as
<CR><LF>. If the value is FALSE, then
carriage returns will be send as
<CR><NUL>. The initial value for this
toggle is FALSE.
crmod Toggle RETURN mode. When this mode is
enabled, most RETURN characters
received from the remote host will be
mapped into a 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 useful only for
remote hosts that send RETURN but
never send LINEFEED. The initial
value for this toggle is FALSE.
debug Toggle socket level debugging (only
available to the super-user). The
initial value for this toggle is
FALSE.
encdebug Turns on debugging information for
the encryption code.
localchars If this toggle is TRUE, then the
flush, interrupt, quit, erase, and
kill characters (see set) are recog-
nized locally, and transformed into
appropriate TELNET control sequences,
respectively ao, ip, brk, ec, and el
(see send). The initial value for
this toggle is TRUE in "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 always to 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 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 (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 for-
matted in a more user readable for-
mat. Spaces are put between each
character in the output. The begin-
ning of any TELNET escape sequence is
preceded by an asterisk (*) to aid in
locating them.
skiprc When the skiprc toggle is TRUE, TEL-
NET skips the reading of the .tel-
netrc file in the user's home direc-
tory 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 flag is
TRUE, TELNET prints out a message
each time encryption is enabled or
disabled. The initial value for this
toggle is FALSE.
? Display the legal toggle commands.
environ argument...
The environ command is used to manipulate variables that
may be sent through the TELNET ENVIRON option. The ini-
tial set of variables is taken from the users environ-
ment. Only the DISPLAY and PRINTER variables are
exported by default. Valid arguments for the environ
command are:
define variable value Define variable to have a value
of value. Any variables defined
by this command are automati-
cally 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 to be
exported to the remote side.
unexport variable Mark the variable to not be
exported unless explicitly
requested by the remote side.
list List the current set of
environment variables. Those
marked with an asterisk (*)
will be sent automatically.
Other variables will be sent
only 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
the remote side should terminate the session immedi-
ately.
FILES
$HOME/.telnetrc file that contains commands to be exe-
cuted before initiating a telnet session
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWtnetc |
|_____________________________|_____________________________|
SEE ALSO
rlogin(1), sh(1), stty(1), getlogin(3C), hosts(4),
krb5.conf(4), nologin(4), telnetrc(4), attributes(5),
inet(7P), inet6(7P)
DIAGNOSTICS
NO LOGINS: System going down in N minutes
The machine is in the process of being shut down and
logins have been disabled.
NOTES
On some remote systems, echo has to be turned off manually
when in "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.
The telnet protocol only uses single DES for session
protection-clients request service tickets with single DES
session keys. The KDC must know that host service principals
that offer the telnet service support single DES, which, in
practice, means that such principals must have single DES
keys in the KDC database.