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:
-7
Strip 8th bit on input and output. Telnet is 8-bit clean by default but doesn't send the TELNET BINARY option unless forced.
-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 V5 authentication is being used, the
-F
option allows the local credentials to be forwarded
to the remote system, including any credentials that
have already been forwarded into the local environment.
-K
Specifies no automatic login to the remote system.
-L
Specifies an 8-bit data path on output.
This causes the BINARY option to be negotiated on output.
-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 V5 authentication is being used, the
-f
option allows the local credentials to be forwarded to the remote system.
-k realm
If Kerberos authentication is being used, the
-k
option requests that
telnet
obtain tickets for the remote host in
realm
realm
instead of the remote host's realm, as determined
by
krb_realmofhost3.
-l user
When connecting to the remote system, if the remote system
understands the
ENVIRON
option, then
user
will be sent to the remote system as the value for the variable USER.
This option implies the
-a
option.
This option may also be used with the
open
command.
-n tracefile
Opens
tracefile
for recording trace information.
See the
set tracefile
command below.
-r
Specifies a user interface similar to
rlogin(1).
#include <this>
mode, the escape character is set to the tilde (~) character,
unless modified by the
-e
option.
-x
Turns on encryption of the data stream if possible.
host
Indicates the official name, an alias, or the Internet address
of a remote host.
port
Indicates a port number (address of an application).
If a number is not specified, the default
telnet
port is used.
When in rlogin mode, a line of the form ~.
disconnects from the
remote host; ~ is the telnet escape character.
Similarly, the line ~^Z suspends the telnet session.
The line ~^] escapes to the normal telnet escape prompt.
Once a connection has been opened,
telnet
will attempt to enable the
TELNET LINEMODE
option.
If this fails,
telnet
will revert to one of two input modes:
either ``character at a time''
or ``old line by line''
depending on what the remote system supports.
When
LINEMODE
is enabled, character processing is done on the
local system, under the control of the remote system.
When input
editing or character echoing is to be disabled, the remote system
will relay that information.
The remote system will also relay
changes to any special characters that happen on the remote
system, so that they can take effect on the local system.
In ``character at a time'' mode, most
text typed is immediately sent to the remote host for processing.
In ``old line by line'' mode, all text is echoed locally,
and (normally) only completed lines are sent to the remote host.
The ``local echo character'' (initially ``^E'') may be used
to turn off and on the local echo
(this would mostly be used to enter passwords
without the password being echoed).
If the
LINEMODE
option is enabled, or if the
localchars
toggle is
TRUE
(the default for ``old line by line''; see below),
the user's
quitintr
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
toggleautoflush
and
toggleautosynch
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
modesettoggleunsetslcenviron
and
display
commands).
auth argument [...
]
The
auth
command manipulates the information sent through the
TELNET AUTHENTICATE
option.
Valid arguments for the
auth
command are as follows:
disable type
Disables the specified
type
of authentication.
To obtain a list of available types, use the
auth disable ?
command.
enable type
Enables the specified
type
of authentication.
To obtain a list of available types, use the
auth enable ?
command.
status
Lists the current status of the various types of
authentication.
close
Close a
TELNET
session and return to command mode.
display argument [...
]
Displays all, or some, of the
set
and
toggle
values (see below).
encrypt argument [...
]
The
encrypt
command manipulates the information sent through the
TELNET ENCRYPT
option.
Valid arguments for the encrypt command are as follows:
disable type [input|output]
Disables the specified
type
of encryption.
If you omit
input
and
output
both input and output
are disabled.
To obtain a list of available types, use the
encrypt disable ?
command.
enable type [input|output]
Enables the specified
type
of encryption.
If you omit
input
and
output
both input and output are
enabled.
To obtain a list of available types, use the
encrypt enable ?
command.
input
This is the same as the
encrypt start input
command.
-input
This is the same as the
encrypt stop input
command.
output
This is the same as the
encrypt start output
command.
-output
This is the same as the
encrypt stop output
command.
start [input|output]
Attempts to start encryption.
If you omit
input
and
output
both input and output are enabled.
To obtain a list of available types, use the
encrypt enable ?
command.
status
Lists the current status of encryption.
stop [input|output]
Stops encryption.
If you omit
input
and
output
encryption is on both input and output.
type type
Sets the default type of encryption to be used
with later
encrypt start
or
encrypt stop
commands.
environ arguments [...
]
The
environ
command is used to manipulate the
variables that may be sent through the
TELNET ENVIRON
option.
The initial set of variables is taken from the 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 ``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.
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 non-standard port,
telnet
omits any automatic initiation of
TELNET
options.
When the port number is preceded by a minus sign,
the initial option negotiation is done.
After establishing a connection, the file
.telnetrc
in the
user's home directory 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
BSD 4.2
system -- if
it doesn't work, a lower case ``r'' may be echoed on the terminal).
do cmd
Sends the
TELNET DOcmd
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 DONTcmd
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 WILLcmd
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 WONTcmd
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
togglelocalchars
below),
and if
telnet
is operating in ``character at a time'' mode, then when this
character is typed, a
TELNET EC
sequence (see
sendec
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
togglelocalchars
below)
and the
flushoutput
character is typed, a
TELNET AO
sequence (see
sendao
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
togglelocalchars
below)
and the
interrupt
character is typed, a
TELNET IP
sequence (see
sendip
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
togglelocalchars
below),
and if
telnet
is operating in ``character at a time'' mode, then when this
character is typed, a
TELNET EL
sequence (see
sendel
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
togglelocalchars
below)
and the
quit
character is typed, a
TELNET BRK
sequence (see
sendbrk
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
sendsusp
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 are propagated through the
TELNET ENVIRON
option.
This command is the same as specifying
a
option on the
open
command.
autosynch
If
autosynch
and
localchars
are both
TRUE
then when either the
intr
or
quit
character is typed (see
set
above for 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 send 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
flushinterruptquiterase
and
kill
characters (see
set
above) are recognized locally, and transformed into (hopefully) appropriate
TELNET
control sequences
(respectively
aoipbrkec
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
TRUETELNET
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
TRUEtelnet
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.
ENVIRONMENT
telnet
uses at least the
HOMESHELLDISPLAY
and
TERM
environment variables.
Other environment variables may be propagated
to the other side via the
TELNET ENVIRON
option.
FILES
~/.telnetrc
user customized telnet startup values
HISTORY
The
telnet
command appeared in
BSD 4.2
NOTES
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.
