4.3BSD-Reno/share/man/cat1/telnet.0
TELNET(1) UNIX Reference Manual TELNET(1)
NNAAMMEE
tteellnneett - User interface to the TELNET protocol
SSYYNNOOPPSSIISS
tteellnneett [--dd] [--aa] [--nn _t_r_a_c_e_f_i_l_e] [--ee _e_s_c_a_p_e_c_h_a_r] [[--ll _u_s_e_r] _h_o_s_t [port]]
DDEESSCCRRIIPPTTIIOONN
The tteellnneett command is used to communicate with another host using the
TELNET protocol. If tteellnneett is invoked without the _h_o_s_t argument, it
enters command mode, indicated by its prompt (tteellnneett>>). In this mode, it
accepts and executes the commands listed below. If it is invoked with
arguments, it performs an ooppeenn command with those arguments.
Options:
--dd Sets the initial value of the ddeebbuugg toggle to TRUE
--aa 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.
--nn _t_r_a_c_e_f_i_l_e
Opens _t_r_a_c_e_f_i_l_e for recording trace information. See the sseett
ttrraacceeffiillee command below.
--ll _u_s_e_r When connecting to the remote system, if the remote system
understands the ENVIRON option, then _u_s_e_r will be sent to the
remote system as the value for the variable USER. This option
implies the --aa option. This option may also be used with the
ooppeenn command.
--ee _e_s_c_a_p_e _c_h_a_r
Sets the initial tteellnneett escape character to _e_s_c_a_p_e _c_h_a_r. If
_e_s_c_a_p_e _c_h_a_r is ommitted, then there will be no escape charac-
ter.
_h_o_s_t Indicates the official name, an alias, or the Internet address
of a remote host.
_p_o_r_t Indicates a port number (address of an application). If a
number is not specified, the default tteellnneett port is used.
Once a connection has been opened, tteellnneett will attempt to enable the
TELNET LINEMODE option. If this fails, then tteellnneett 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 sys-
tem, under the control of the remote system. When input editing or char-
acter echoing is to be disabled, the remote system will relay that infor-
mation. The remote system will also relay changes to any special charac-
ters 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 char-
acter'' (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 llooccaallcchhaarrss toggle is TRUE
(the default for ``old line by line``; see below), the user's qquuiitt, iinnttrr,
and fflluusshh characters are trapped locally, and sent as TELNET protocol se-
quences to the remote side. If LINEMODE has ever been enabled, then the
user's ssuusspp and eeooff are also sent as TELNET protocol sequences, and qquuiitt
is sent as a TELNET ABORT instead of BREAK There are options (see ttooggggllee
aauuttoofflluusshh and ttooggggllee aauuttoossyynncchh 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 qquuiitt
and iinnttrr).
While connected to a remote host, tteellnneett command mode may be entered by
typing the tteellnneett ``escape character'' (initially ``^ When in command
mode, the normal terminal editing conventions are available.
The following .Nm telnet commands are available. Only enough of each
command to uniquely identify it need be typed (this is also true for ar-
guments to the mmooddee, sseett, ttooggggllee, uunnsseett, ssllcc, eennvviirroonn, and ddiissppllaayy com-
mands).
cclloossee Close a TELNET session and return to command mode.
ddiissppllaayy _a_r_g_u_m_e_n_t ...
Displays all, or some, of the sseett and ttooggggllee values (see
below).
mmooddee _t_y_p_e
_T_y_p_e 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.
cchhaarraacctteerr Disable the TELNET LINEMODE option, or, if the re-
mote side does not understand the LINEMODE option,
then enter ``character at a time`` mode.
lliinnee Enable the TELNET LINEMODE option, or, if the re-
mote side does not understand the LINEMODE option,
then attempt to enter ``old-line-by-line`` mode.
iissiigg (--iissiigg)
Attempt to enable (disable) the TRAPSIG mode of the
LINEMODE option. This requires that the LINEMODE
option be enabled.
eeddiitt (--eeddiitt)
Attempt to enable (disable) the EDIT mode of the
LINEMODE option. This requires that the LINEMODE
option be enabled.
ssooffttttaabbss (--ssooffttttaabbss)
Attempt to enable (disable) the SOFT_TAB mode of
the LINEMODE option. This requires that the
LINEMODE option be enabled.
lliitteecchhoo (--lliitteecchhoo)
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 mmooddee command.
ooppeenn _h_o_s_t [[--ll] _u_s_e_r][[--] _p_o_r_t]
Open a connection to the named host. If no port number is
specified, tteellnneett 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 [--ll] 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, tteellnneett
omits any automatic initiation of TELNET options. When the
port number is preceeded by a minus sign, the inital option
negotiation is done. After establishing a connection, the file
._t_e_l_n_e_t_r_c in the users home directory is opened. Lines begin-
ing 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 succes-
sive lines that begin with whitespace are assumed to be tteellnneett
commands and are processed as if they had been typed in manual-
ly to the tteellnneett command prompt.
qquuiitt Close any open TELNET session and exit tteellnneett. An end of file
(in command mode) will also close a session and exit.
sseenndd _a_r_g_u_m_e_n_t_s
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):
aabboorrtt
Sends the TELNET ABORT (ABORT processes) sequence.
aaoo Sends the TELNET AO (Abort Output) sequence, which should
cause the remote system to flush all output _f_r_o_m the re-
mote system _t_o the user's terminal.
aayytt Sends the TELNET AYT (Are You There) sequence, to which
the remote system may or may not choose to respond.
bbrrkk Sends the TELNET BRK (Break) sequence, which may have
significance to the remote system.
eecc Sends the TELNET EC (Erase Character) sequence, which
should cause the remote system to erase the last charac-
ter entered.
eell Sends the TELNET EL (Erase Line) sequence, which should
cause the remote system to erase the line currently being
entered.
eeooff Sends the TELNET EOF (End Of File) sequence.
eeoorr Sends the TELNET EOR (End of Record) sequence.
eessccaappee
Sends the current tteellnneett escape character (initially
``^'').
ggaa Sends the TELNET GA (Go Ahead) sequence, which likely has
no significance to the remote system.
ggeettssttaattuuss
If the remote side supports the TELNET STATUS command,
ggeettssttaattuuss will send the subnegotiation to request that
the server send its current option status.
iipp Sends the TELNET IP (Interrupt Process) sequence, which
should cause the remote system to abort the currently
running process.
nnoopp Sends the TELNET NOP (No OPeration) sequence.
ssuusspp
Sends the TELNET SUSP (SUSPend process) sequence.
ssyynncchh
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 4.2 BSD
system -- if it doesn't work, a lower case ``r'' may be
echoed on the terminal).
?? Prints out help information for the sseenndd command.
sseett _a_r_g_u_m_e_n_t _v_a_l_u_e
uunnsseett _a_r_g_u_m_e_n_t _v_a_l_u_e
The sseett command will set any one of a number of tteellnneett vari-
ables to a specific value or to TRUE. The special value ooffff
turns off the function associated with the variable, this is
equivalent to using the uunnsseett command. The uunnsseett command will
disable or set to FALSE any of the specified functions. The
values of variables may be interrogated with the ddiissppllaayy com-
mand. The variables which may be set or unset, but not tog-
gled, are listed here. In addition, any of the variables for
the ttooggggllee command may be explicitly set or unset using the sseett
and uunnsseett commands.
eecchhoo This is the value (initially ``^E'') which, when in
``line by line'' mode, toggles between doing local
echoing of entered characters (for normal process-
ing), and suppressing echoing of entered characters
(for entering, say, a password).
eeooff If tteellnneett 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 eeooff char-
acter.
eerraassee If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee
llooccaallcchhaarrss below), aanndd if tteellnneett is operating in
``character at a time'' mode, then when this charac-
ter is typed, a TELNET EC sequence (see sseenndd eecc
above) is sent to the remote system. The initial
value for the erase character is taken to be the
terminal's eerraassee character.
eessccaappee This is the tteellnneett escape character (initially
``^['') which causes entry into tteellnneett command mode
(when connected to a remote system).
fflluusshhoouuttppuutt
If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee
llooccaallcchhaarrss below) and the fflluusshhoouuttppuutt character is
typed, a TELNET AO sequence (see sseenndd aaoo above) is
sent to the remote host. The initial value for the
flush character is taken to be the terminal's fflluusshh
character.
iinntteerrrruupptt
If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee
llooccaallcchhaarrss below) and the iinntteerrrruupptt character is
typed, a TELNET IP sequence (see sseenndd iipp above) is
sent to the remote host. The initial value for the
interrupt character is taken to be the terminal's
iinnttrr character.
kkiillll If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee
llooccaallcchhaarrss below), aanndd if tteellnneett is operating in
``character at a time'' mode, then when this charac-
ter is typed, a TELNET EL sequence (see sseenndd eell
above) is sent to the remote system. The initial
value for the kill character is taken to be the
terminal's kkiillll character.
llnneexxtt If tteellnneett is operating in LINEMODE or ``old line by
line`` mode, then this character is taken to be the
terminal's llnneexxtt character. The initial value for
the lnext character is taken to be the terminal's
llnneexxtt character.
qquuiitt If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee
llooccaallcchhaarrss below) and the qquuiitt character is typed, a
TELNET BRK sequence (see sseenndd bbrrkk above) is sent to
the remote host. The initial value for the quit
character is taken to be the terminal's qquuiitt charac-
ter.
rreepprriinntt If tteellnneett is operating in LINEMODE or ``old line by
line`` mode, then this character is taken to be the
terminal's rreepprriinntt character. The initial value for
the reprint character is taken to be the terminal's
rreepprriinntt character.
ssttaarrtt If the TELNET TOGGLE-FLOW-CONTROL option has been en-
abled, then this character is taken to be the
terminal's ssttaarrtt character. The initial value for
the kill character is taken to be the terminal's
ssttaarrtt character.
ssttoopp If the TELNET TOGGLE-FLOW-CONTROL option has been en-
abled, then this character is taken to be the
terminal's ssttoopp character. The initial value for the
kill character is taken to be the terminal's ssttoopp
character.
ssuusspp If tteellnneett is in llooccaallcchhaarrss mode, or LINEMODE is en-
abled, and the ssuussppeenndd character is typed, a TELNET
SUSP sequence (see sseenndd ssuusspp above) is sent to the
remote host. The initial value for the suspend char-
acter is taken to be the terminal's ssuussppeenndd charac-
ter.
ttrraacceeffiillee
Thi is the file to which the output, caused by
nneettddaattaa or ooppttiioonn tracing being TRUE, will be writ-
ten. If it is set to ``--'', then tracing information
will be written to standard output (the default).
wwoorrddeerraassee
If tteellnneett is operating in LINEMODE or ``old line by
line`` mode, then this character is taken to be the
terminal's wwoorrddeerraassee character. The initial value
for the worderase character is taken to be the
terminal's wwoorrddeerraassee character.
?? Displays the legal sseett (uunnsseett) commands.
ssllcc _s_t_a_t_e
The ssllcc command (Set Local Characters) is used to set or change
the state of the the special characters when the TELNET
LINEMODE option has been enabled. Special characters are char-
acters that get mapped to TELNET commands sequences (like iipp or
qquuiitt) or line editing characters (like eerraassee and kkiillll). By de-
fault, the local special characters are exported.
eexxppoorrtt Switch to the local defaults for the special charac-
ters. The local default characters are those of the
local terminal at the time when tteellnneett was started.
iimmppoorrtt Switch to the remote defaults for the special charac-
ters. The remote default characters are those of the
remote system at the time when the TELNET connection
was established.
cchheecckk 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 discrepencies with the local side, the local
side will switch to the remote value.
?? Prints out help information for the ssllcc command.
eennvviirroonn _a_r_g_u_m_e_n_t_s...
The eennvviirroonn command is used to manipulate the the variables
that my 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 --aa or --ll options are
used.
Valid arguments for the eennvviirroonn command are:
ddeeffiinnee _v_a_r_i_a_b_l_e _v_a_l_u_e
Define the variable _v_a_r_i_a_b_l_e to have a value of
_v_a_l_u_e. Any variables defined by this command are au-
tomatically exported. The _v_a_l_u_e may be enclosed in
single or double quotes so that tabs and spaces may
be included.
uunnddeeffiinnee _v_a_r_i_a_b_l_e
Remove _v_a_r_i_a_b_l_e from the list of environment vari-
ables.
eexxppoorrtt _v_a_r_i_a_b_l_e
Mark the variable _v_a_r_i_a_b_l_e to be exported to the re-
mote side.
uunneexxppoorrtt _v_a_r_i_a_b_l_e
Mark the variable _v_a_r_i_a_b_l_e to not be exported unless
explicitly asked for by the remote side.
lliisstt 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 eennvviirroonn command.
ttooggggllee _a_r_g_u_m_e_n_t_s ...
Toggle (between TRUE and FALSE) various flags that control how
tteellnneett responds to events. These flags may be set explicitly
to TRUE or FALSE using the sseett and uunnsseett commands listed above.
More than one argument may be specified. The state of these
flags may be interrogated with the ddiissppllaayy command. Valid ar-
guments are:
aauuttoofflluusshh If aauuttoofflluusshh and llooccaallcchhaarrss are both TRUE, then
when the aaoo, or qquuiitt characters are recognized (and
transformed into TELNET sequences; see sseett above
for details), tteellnneett refuses to display any data on
the user's terminal until the remote system ack-
nowledges (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)).
aauuttoossyynncchh If aauuttoossyynncchh and llooccaallcchhaarrss are both TRUE, then
when either the iinnttrr or qquuiitt characters is typed
(see sseett above for descriptions of the iinnttrr and
qquuiitt characters), the resulting TELNET sequence
sent is followed by the TELNET SYNCH sequence.
This procedure sshhoouulldd cause the remote system to
begin throwing away all previously typed input un-
til both of the TELNET sequences have been read and
acted upon. The initial value of this toggle is
FALSE.
bbiinnaarryy Enable or disable the TELNET BINARY option on both
input and output.
iinnbbiinnaarryy Enable or disable the TELNET BINARY option on in-
put.
oouuttbbiinnaarryy Enable or disable the TELNET BINARY option on out-
put.
ccrrllff If this is TRUE, then carriage returns will be sent
as <CR><LF>. If this is FALSE, then carriage re-
turns will be send as <CR><NUL>. The initial value
for this toggle is FALSE.
ccrrmmoodd Toggle carriage return mode. When this mode is en-
abled, 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 feed. The initial
value for this toggle is FALSE.
ddeebbuugg Toggles socket level debugging (useful only to the
ssuuppeerr uusseerr). The initial value for this toggle is
FALSE.
llooccaallcchhaarrss
If this is TRUE, then the fflluusshh, iinntteerrrruupptt, qquuiitt,
eerraassee, and kkiillll characters (see sseett above) are
recognized locally, and transformed into (hopeful-
ly) appropriate TELNET control sequences (respec-
tively aaoo, iipp, bbrrkk, eecc, and eell; see sseenndd 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 llooccaallcchhaarrss is ignored, and assumed to
always be TRUE. If LINEMODE has ever been enabled,
then qquuiitt is sent as aabboorrtt, and eeooff aanndd are sent as
eeooff aanndd ssuusspp, see sseenndd above).
nneettddaattaa Toggles the display of all network data (in hexade-
cimal format). The initial value for this toggle
is FALSE.
ooppttiioonnss Toggles the display of some internal tteellnneett proto-
col processing (having to do with TELNET options).
The initial value for this toggle is FALSE.
pprreettttyydduummpp
When the nneettddaattaa toggle is enabled, if pprreettttyydduummpp
is enabled the output from the nneettddaattaa command will
be formated in a more user readable format. Spaces
are put between each character in the output, and
the begining of any TELNET escape sequence is pre-
ceeded by a '*' to aid in locating them.
?? Displays the legal ttooggggllee commands.
zz Suspend tteellnneett. This command only works when the user is using
the csh(1).
!! [_c_o_m_m_a_n_d]
Execute a single command in a subshell on the local system. If
ccoommmmaanndd is ommitted, then an interactive subshell is invoked.
ssttaattuuss Show the current status of tteellnneett. This includes the peer one
is connected to, as well as the current mode.
?? [_c_o_m_m_a_n_d]
Get help. With no arguments, tteellnneett prints a help summary. If
a command is specified, tteellnneett will print the help information
for just that command.
EENNVVIIRROONNMMEENNTT
TTeellnneett uses at least the HOME, SHELL, DISPLAY, and TERM environent vari-
ables. Other envirnoment variables may be propogated to the other side
via the TELNET ENVIRON option.
FFIILLEESS
~/._t_e_l_n_e_t_r_c user customized telnet startup values
HHIISSTTOORRYY
TTeellnneett appeared in 4.2 BSD.
NNOOTTEESS
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 eeooff character is
only recognized (and sent to the remote system) when it is the first
character on a line.