telnet(TC)
telnet --
user interface to a remote system using the TELNET protocol
Syntax
telnet [ -8 ] [ -E ]
[ -K ]
[ -L ]
[ -X atype ]
[ -a ] [ -d ]
[ -e escape_char ] [ -l user ]
[ -k realm ]
[ -n tracefile ]
[ -r ] [ host [ port ] ]
Description
The telnet command communicates with another host
using the TELNET protocol. If telnet
is invoked without the host argument, it will
enter command mode as indicated by its prompt
telnet>
. In this mode, telnet will
accept and execute the commands listed below; if
telnet is invoked with arguments, it will perform
an open command with those arguments.
The following options are available:
-8-
Use an eight bit data path. This will cause
an attempt to negotiate the BINARY option on both
input and output.
-E-
Option stops any character from being recognized as an escape character.
-K-
Disable automatic login.
-L-
Use an eight bit data path on output.
This causes the BINARY option to be negotiated on output.
-X atype-
Disable authentication type atype. Currently, the only type
supported is KERBEROS_V5.
-a-
Automatic login into the remote system. If the remote system
understands the
ENVIRON option, then the variable USER
will be exported to the remote system.
This option may also be used with the open command.
-d-
Toggles socket level debugging (useful only to root).
Sets the initial value of the
debug
toggle to
``TRUE''.
-e [ escape_char ]-
Sets the initial TELNET escape character to
escape_char. If escape_char is
omitted, then there will be no pre-defined escape
character.
-k realm-
Used to connect to a Kerberos Version 4 realm.
This is not currently supported.
-l user -
When connecting to the remote
system and if the remote system understands the
ENVIRON option, then user will be exported
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 settracefile
command below.)
-r-
Use a user interface similar to
rlogin(TC).
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.
host may be specified as an IP source-route.
This takes the form
of
[!]@addr@addr@addr:dest.
If the source-route is prefixed with the ``!''
character, it is interpreted as a strict source route.
Otherwise, it is interpreted as a loose source route. See
the IP specification for more information about
source routing. Note: This exists primarily for debugging
or for use when network connectivity is problematic. Use
of source-routing is not normally recommended.
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.
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 <Esc> (initially ``^]'').
When in command mode, the normal terminal editing conventions
will be available.
The following TELNET commands are available, but
only enough of each command need be typed to uniquely
identify it (this is also true for arguments pertaining to
the mode, toggle, set,
unset, slc, environ, and
display commands).
auth argument-
This command controls authentication according to the value of
argument:
enable type-
Enable authentication type type.
Currently, the only type supported is KERBEROS_V5.
disable type-
Disable authentication type type.
Currently, the only type supported is KERBEROS_V5.
help-
Display help information about the auth command.
status-
Display the current types of authentication,
and whether they are enabled or disabled.
?-
Same as help
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
TELNET LINEMODE
option, then enter the character at a time mode.
line-
Enable the TELNET LINEMODE
option; or, if the remote side does not understand the
TELNET LINEMODE
option, then attempt to enter the old line by line mode.
isig
-isig-
Attempt to enable (disable) the
TRAPSIG mode of the TELNET LINEMODE option.
This requires that the LINEMODE
option be enabled.
edit
-edit-
Attempt to enable (disable) the
EDIT mode of the LINEMODE option.
This requires that the LINEMODE option be enabled.
softtabs
-softtabs-
Attempt to enable (disable) the SOFT_TAB
mode of the LINEMODE option.
This requires that the LINEMODE option be enabled.
litecho
-litecho-
Attempt to enable (disable) the LIT_ECHO
mode of the LINEMODE option.
This requires that the LINEMODE
option be enabled.
?-
Prints out help information for the mode command.
open host [ user ] [ [ - ] port ] [ -a ] [ -l user ]-
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(SFF))
or an Internet address specified in the ``dot notation'' (see
inet(SLIB)).
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.
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 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 does not work, a lowercase ``|'' may be echoed on the terminal).
?-
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
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 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 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.
kill-
If TELNET is in localchars
mode (see toggle localchars
below), and if TELNET
is operating in the character at a time mode, then when this
character is entered, a TELNET EL
sequence (see send el above)
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 is operating in LINEMODE
or in the old line by line mode, then this character is taken to
be the terminal's lnext character.
The initial value for the lnext character is taken to be
the terminal's lnext character.
quit-
If TELNET is in
localchars mode (see toggle localchars below)
and the quit character is entered, a
TELNET BRK sequence (see send brk above)
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 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.
forw1-
If TELNET is in the localchars mode, then this
character is taken to be an alternate end of line character.
forw2-
If TELNET is in the localchars mode, then this
character is taken to be an alternate end of line character.
ayt-
If TELNET is in the localchars mode, then this
character is taken to be the
alternate AYT character.
susp-
If TELNET is in the localchars
mode or if the LINEMODE
is enabled and the suspend character is entered, a
TELNET SUSP sequence (see send susp above)
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 legal set and unset commands.
slc [ state ]-
The slc command (Set Local Characters) sets
(or changes) the state of the special characters when the
TELNET LINEMODE option has been enabled.
The ``Special Characters'' are characters that get mapped to
TELNET commands sequences (like ip or quit)
or line-editing characters (like erase and
kill).
By default, the ``local special characters'' are exported.
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.
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.
?-
Prints out help information for the slc
command.
environ [ argument [ ... ] ]-
The environ command manipulates
the variables that may be sent through the
TELNET ENVIRON option.
The initial set of variables is taken from the user's environment;
only the DISPLAY, LANG,
and PRINTER variables are automatically exported
although USER may also be exported in some circumstances.
The valid arguments for the environ command are:
define variable value-
Define the variable
to have a value of
value.
Any variables defined by this command are automatically exported.
The value
may be enclosed in single or double quotes so
that tabs and embedded spaces may be included.
undefine variable-
Remove variable
from the list of environment variables.
export variable-
Mark the variable
to be exported to the remote side.
unexport variable-
Mark the variable
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.
send variable-
Send environment variable.
?-
Prints out 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(C)).
autologin-
Same as the -a option on the command line.
toggle authdebug-
authdebug-
Display verbose debugging information about authentication.
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.
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 root).
The initial value for this toggle is
``FALSE''.
localchars-
If this is ``TRUE'', then the
flush, interrupt, quit, erase,
and kill characters (see set
above) are recognized locally and then transformed into appropriate
TELNET control sequences (respectively ao,
ip, brk, ec, and el; see
send above).
The initial value for this toggle is
``TRUE''
in old line by line mode and ``FALSE''
in character at a time mode.
When the LINEMODE
option is enabled, the value of
localchars is ignored and assumed to always be
``TRUE''.
If LINEMODE has ever been enabled, then
quit will be sent as abort; eof
and suspend will be 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 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.
skiprc-
Toggle
does not process ~/.telnetrc file.
The initial value for this toggle is
``FALSE''.
termdata-
Toggles printing of hexadecimal terminal data.
The initial value for this toggle is
``FALSE''.
?-
Displays the legal toggle commands.
<Ctrl>Z-
Suspend telnet.
This command will work only when the user is using
csh(C)
or
ksh(C).
! [ 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.
Environment variables
If set, the telnet command exports at least the
following environment variables to the remote machine:
DISPLAY,
LANG,
and
PRINTER.
Note that
DISPLAY will be set to
local_hostname:0.0
if DISPLAY is
set to :0.0
or to unix:0.0
locally.
Other environment variables may be propagated to the remote
side via the TELNET ENVIRON option.
USER is set to
LOGNAME if LOGNAME is set locally
but USER is not.
By default, USER is not set.
Authenticated telnet using Kerberos
If telnet succeeds
in reaching an authenticated telnetd server,
telnet attempts to establish authentication.
If it cannot establish authentication, telnet
tries to connect without authentication if this is permitted
by the telnetd server.
The user executing telnet is logged in on the
remote host without entering a password,
provided the -a or
-l user options are used
(these send a user name to the telnetd service daemon),
the user has network credentials,
and the user's principal name appears in the
$HOME/.k5login file on the remote host.
Limitations
On some remote systems, the echo
command has to be turned off manually when
in the old line by line mode.
When in the old line by line mode or in
LINEMODE, the terminal's eof character
is only recognized (and sent to the remote system) when it
is the first character in a line.
Authentication is based on Version 5 of the
Kerberos Network Authentication Service protocol.
Only this version of the protocol is supported.
Data encryption is not supported.
Using
telnet(TC)
to log into a
machine running SCO UNIX
System V/386 Release 3.2 Operating System Version 4.2
can give the error
message bad login user id
.
This message appears when a user, already logged in as a
non-root user, recursively logs in as
root and runs tcp stop followed by
tcp start -- see the
tcp(ADMN)
manual page.
To avoid this error, start TCP/IP using the
sd(ADM)
command while logged in as root.
To do so, enter the following command:
sd tcp start
Only root and other users with
the sysadmin authorization are permitted to run
sd.
Files
$HOME/.telnetrc-
user-customized telnet startup values
$HOME/.k5login-
equivalent users for authenticated rcmd
/krb5/v5srvtab-
local default service key table
See also
telnetd(ADMN),
k5login(SFF)
Standards conformance
Authenticated telnet is not part of any currently supported standard.
It is an extension of AT&T UNIX System V provided by
The Santa Cruz Operation, Inc.
telnet is conformant with:
RFC 727,
RFC 854,
RFC 856 (STD 27),
RFC 857 (STD 28),
RFC 858 (STD 29),
RFC 859 (STD 30),
RFC 860 (STD 31),
RFC 1073,
RFC 1079,
RFC 1080,
RFC 1091,
RFC 1096,
RFC 1123,
RFC 1184
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003