telnet(1)
NAME
telnet - user interface to a remote system using the TELNET
protocol
SYNOPSIS
telnet [-8ELcdr] [-e escape_char] [-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 USAGE, telnet Commands, 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. Note 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.
-c Disables the reading of the user's telnetrc 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 '^' followed by one character. If
the second character is '?', the DEL character is
selected. Otherwise, the second character is con-
verted to a control character and used as the
escape character. If the escape character is the
null string (that is, -e ''), it is disabled.
-E Stops any character from being recognized as an
escape character.
-l user
When connecting to a remote system that under-
stands 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 negotiated on out-
put.
-n tracefile
Opens tracefile for recording trace information.
See the set tracefile command below.
-r Specifies a user interface similar to rlogin. In
this mode, the escape character is set to the
tilde (~) character, unless modified by the -e
option. The rlogin escape character is only
recognized when it is preceded by a carriage
return. In this mode, the telnet escape charac-
ter, normally '^]', must still precede a telnet
command. The rlogin escape character can also
be followed by '.\r' or '^Z', and, like rlo-
gin(1), closes or suspends the connection,
respectively. This option is an uncommitted
interface and may change in the future.
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.)
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), ipnodes(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 connection follows strict source rout-
ing.
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.
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 com-
mand.
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
toggle 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 (ini-
tially ^]).
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 lower case "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 terminal.
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 character 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 sys-
tem.
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
dont option
will option
wont option
Send the TELNET protocol option negotiation
indicated. Option may be the text name of the
protocol option, or the 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 com-
mand. 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 echo-
ing of entered characters for normal processing,
and suppressing echoing of entered characters,
for example, entering a password.
escape
This is the telnet escape character (initially
^]) that enters telnet command mode when con-
nected to a remote system.
interrupt
If telnet is in localchars mode (see toggle,
localchars) and the interrupt character is
typed, a TELNET IP sequence (see send and ip) is
sent to the remote host. The initial value for
the interrupt character 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 ini-
tial 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 ini-
tial 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 ini-
tial 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 charac-
ter on a line sends this character to the
remote system. The initial 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 character is typed, a
TELNET AYT ("Are You There") sequence is sent to
the remote host. (See send, ayt above.) The ini-
tial value for ayt is the terminal's status
character.
forw1
forw2 If telnet is operating in LINEMODE, and 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 characters.
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 connection. When followed by a ^Z, the rlo-
gin 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 character is taken
to be the terminal's start character. The ini-
tial 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 character. 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 tracefile 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 ini-
tial 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 (Set Local Characters) command is used to set
or change the state of special characters when the
TELNET LINEMODE option has been enabled. Special char-
acters are characters that get mapped to TELNET com-
mands 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 settings. 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 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.
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
arguments are:
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 acknowledges (using a TELNET
Timing Mark option) that it has processed those
TELNET sequences. The initial value for this
toggle is TRUE if the terminal 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 carriage 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 use-
ful 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 tog-
gle is FALSE.
localchars
If this toggle is TRUE, then the flush, inter-
rupt, quit, erase, and kill characters (see set)
are recognized locally, and transformed into
appropriate TELNET control sequences, respec-
tively 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 hexa-
decimal format). The initial value for this tog-
gle is FALSE.
options
Toggle the display of some internal TELNET pro-
tocol processing (having to do with telnet
options). The initial value for this toggle is
FALSE.
prettydump
When the netdata toggle is enabled, if pret-
tydump is enabled, the output from the netdata
command will be formatted in a more user read-
able format. Spaces are put between each charac-
ter in the output. The beginning of any TELNET
escape sequence is preceded by an asterisk (*)
to aid in locating them.
skiprc
When the skiprc toggle is TRUE, TELNET skips
the reading of the .telnetrc file in the user's
home directory when connections are opened. The
initial value for this toggle is FALSE.
termdata
Toggles the display of all terminal data (in
hexadecimal format). The initial value for this
toggle is FALSE.
? 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 initial set of variables is taken from the users
environment. 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 com-
mand.
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 ter-
minate the session immediately.
FILES
$HOME/.telnetrc
file that contains commands to be executed before ini-
tiating 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), hosts(4), ipnodes(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.
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