\versionid $Id: config.but 4787 2004-11-16 15:27:00Z simon $

\C{config} Configuring PuTTY

This chapter describes all the configuration options in PuTTY.

PuTTY is configured using the control panel that comes up before you
start a session. Some options can also be changed in the middle of a
session, by selecting \q{Change Settings} from the window menu.

\H{config-session} The Session panel

The Session configuration panel contains the basic options you need
to specify in order to open a session at all, and also allows you to
save your settings to be reloaded later.

\S{config-hostname} The host name section

\cfg{winhelp-topic}{session.hostname}

The top box on the Session panel, labelled \q{Specify your
connection by host name}, contains the details that need to be
filled in before PuTTY can open a session at all.

\b The \q{Host Name} box is where you type the name, or the IP
address, of the server you want to connect to.

\b The \q{Protocol} radio buttons let you choose what type of
connection you want to make: a raw connection, a Telnet connection, an
rlogin connection or an SSH connection. (See \k{which-one} for a
summary of the differences between SSH, Telnet and rlogin, and
\k{using-rawprot} for an explanation of \q{raw} connections.)

\b The \q{Port} box lets you specify which port number on the server
to connect to. If you select Telnet, Rlogin, or SSH, this box will
be filled in automatically to the usual value, and you will only
need to change it if you have an unusual server. If you select Raw
mode, you will almost certainly need to fill in the \q{Port} box.

\S{config-saving} Loading and storing saved sessions

\cfg{winhelp-topic}{session.saved}

The next part of the Session configuration panel allows you to save
your preferred PuTTY options so they will appear automatically the
next time you start PuTTY. It also allows you to create \e{saved
sessions}, which contain a full set of configuration options plus a
host name and protocol. A saved session contains all the information
PuTTY needs to start exactly the session you want.

\b To save your default settings: first set up the settings the way
you want them saved. Then come back to the Session panel. Select the
\q{Default Settings} entry in the saved sessions list, with a single
click. Then press the \q{Save} button.

Note that PuTTY does not allow you to save a host name into the
Default Settings entry. This ensures that when PuTTY is started up,
the host name box is always empty, so a user can always just type in
a host name and connect.

If there is a specific host you want to store the details of how to
connect to, you should create a saved session, which will be
separate from the Default Settings.

\b To save a session: first go through the rest of the configuration
box setting up all the options you want. Then come back to the
Session panel. Enter a name for the saved session in the \q{Saved
Sessions} input box. (The server name is often a good choice for a
saved session name.) Then press the \q{Save} button. Your saved
session name should now appear in the list box.

\b To reload a saved session: single-click to select the session
name in the list box, and then press the \q{Load} button. Your saved
settings should all appear in the configuration panel.

\b To modify a saved session: first load it as described above. Then
make the changes you want. Come back to the Session panel, and press
the \q{Save} button. The new settings will be saved over the top of
the old ones

\lcont{
To save the new settings under a different name, you can enter the new
name in the \q{Saved Sessions} box, or single-click to select a
session name in the list box to overwrite that session. To save
\q{Default Settings}, you must single-click the name before saving.
}

\b To start a saved session immediately: double-click on the session
name in the list box.

\b To delete a saved session: single-click to select the session
name in the list box, and then press the \q{Delete} button.

Each saved session is independent of the Default Settings
configuration. If you change your preferences and update Default
Settings, you must also update every saved session separately.

Saved sessions are stored in the Registry, at the location

\c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\Sessions

If you need to store them in a file, you could try the method
described in \k{config-file}.

\S{config-closeonexit} \q{Close Window on Exit}

\cfg{winhelp-topic}{session.coe}

Finally in the Session panel, there is an option labelled \q{Close
Window on Exit}. This controls whether the PuTTY session window
disappears as soon as the session inside it terminates. If you are
likely to want to copy and paste text out of the session after it
has terminated, or restart the session, you should arrange for this
option to be off.

\q{Close Window On Exit} has three settings. \q{Always} means always
close the window on exit; \q{Never} means never close on exit
(always leave the window open, but \I{inactive window}inactive). The
third setting, and the default one, is \q{Only on clean exit}. In this
mode, a session which terminates normally will cause its window to
close, but one which is aborted unexpectedly by network trouble or a
confusing message from the server will leave the window up.

\H{config-logging} The Logging panel

\cfg{winhelp-topic}{logging.main}

The Logging configuration panel allows you to save log files of your
PuTTY sessions, for debugging, analysis or future reference.

The main option is a radio-button set that specifies whether PuTTY
will log anything at all. The options are

\b \q{Logging turned off completely}. This is the default option; in
this mode PuTTY will not create a log file at all.

\b \q{Log printable output only}. In this mode, a log file will be
created and written to, but only printable text will be saved into
it. The various terminal control codes that are typically sent down
an interactive session alongside the printable text will be omitted.
This might be a useful mode if you want to read a log file in a text
editor and hope to be able to make sense of it.

\b \q{Log all session output}. In this mode, \e{everything} sent by
the server into your terminal session is logged. If you view the log
file in a text editor, therefore, you may well find it full of
strange control characters. This is a particularly useful mode if
you are experiencing problems with PuTTY's terminal handling: you
can record everything that went to the terminal, so that someone
else can replay the session later in slow motion and watch to see
what went wrong.

\b \q{Log SSH packet data}. In this mode (which is only used by SSH
connections), the SSH message packets sent over the encrypted
connection are written to the log file. You might need this to debug
a network-level problem, or more likely to send to the PuTTY authors
as part of a bug report. \e{BE WARNED} that if you log in using a
password, the password can appear in the log file; see
\k{config-logssh} for options that may help to remove sensitive
material from the log file before you send it to anyone else.

\S{config-logfilename} \q{Log file name}

\cfg{winhelp-topic}{logging.filename}

In this edit box you enter the name of the file you want to log the
session to. The \q{Browse} button will let you look around your file
system to find the right place to put the file; or if you already
know exactly where you want it to go, you can just type a pathname
into the edit box.

There are a few special features in this box. If you use the \c{&}
character in the file name box, PuTTY will insert details of the
current session in the name of the file it actually opens. The
precise replacements it will do are:

\b \c{&Y} will be replaced by the current year, as four digits.

\b \c{&M} will be replaced by the current month, as two digits.

\b \c{&D} will be replaced by the current day of the month, as two
digits.

\b \c{&T} will be replaced by the current time, as six digits
(HHMMSS) with no punctuation.

\b \c{&H} will be replaced by the host name you are connecting to.

For example, if you enter the host name
\c{c:\\puttylogs\\log-&h-&y&m&d-&t.dat}, you will end up with files looking
like

\c log-server1.example.com-20010528-110859.dat
\c log-unixbox.somewhere.org-20010611-221001.dat

\S{config-logfileexists} \q{What to do if the log file already exists}

\cfg{winhelp-topic}{logging.exists}

This control allows you to specify what PuTTY should do if it tries
to start writing to a log file and it finds the file already exists.
You might want to automatically destroy the existing log file and
start a new one with the same name. Alternatively, you might want to
open the existing log file and add data to the \e{end} of it.
Finally (the default option), you might not want to have any
automatic behaviour, but to ask the user every time the problem
comes up.

\S{config-logssh} Options specific to SSH packet logging

These options only apply if SSH packet data is being logged.

The following options allow particularly sensitive portions of
unencrypted packets to be automatically left out of the log file.
They are only intended to deter casual nosiness; an attacker could
glean a lot of useful information from even these obfuscated logs
(e.g., length of password).

\S2{config-logssh-omitpw} \q{Omit known password fields}

\cfg{winhelp-topic}{logging.ssh.omitpassword}

When checked, password fields are removed from the log of transmitted
packets. (This includes any user responses to challenge-response
authentication methods such as \q{keyboard-interactive}.) This does
not include X11 authentication data if using X11 forwarding.

Note that this will only omit data that PuTTY \e{knows} to be a
password. However, if you start another login session within your
PuTTY session, for instance, any password used will appear in the
clear in the packet log. The next option may be of use to protect
against this.

This option is enabled by default.

\S2{config-logssh-omitdata} \q{Omit session data}

\cfg{winhelp-topic}{logging.ssh.omitdata}

When checked, all \q{session data} is omitted; this is defined as data
in terminal sessions and in forwarded channels (TCP, X11, and
authentication agent). This will usually substantially reduce the size
of the resulting log file.

This option is disabled by default.

\H{config-terminal} The Terminal panel

The Terminal configuration panel allows you to control the behaviour
of PuTTY's terminal emulation.

\S{config-autowrap} \q{Auto wrap mode initially on}

\cfg{winhelp-topic}{terminal.autowrap}

Auto wrap mode controls what happens when text printed in a PuTTY
window reaches the right-hand edge of the window.

With auto wrap mode on, if a long line of text reaches the
right-hand edge, it will wrap over on to the next line so you can
still see all the text. With auto wrap mode off, the cursor will
stay at the right-hand edge of the screen, and all the characters in
the line will be printed on top of each other.

If you are running a full-screen application and you occasionally
find the screen scrolling up when it looks as if it shouldn't, you
could try turning this option off.

Auto wrap mode can be turned on and off by control sequences sent by
the server. This configuration option controls the \e{default}
state, which will be restored when you reset the terminal (see
\k{reset-terminal}). However, if you modify this option in
mid-session using \q{Change Settings}, it will take effect
immediately.

\S{config-decom} \q{DEC Origin Mode initially on}

\cfg{winhelp-topic}{terminal.decom}

DEC Origin Mode is a minor option which controls how PuTTY
interprets cursor-position control sequences sent by the server.

The server can send a control sequence that restricts the scrolling
region of the display. For example, in an editor, the server might
reserve a line at the top of the screen and a line at the bottom,
and might send a control sequence that causes scrolling operations
to affect only the remaining lines.

With DEC Origin Mode on, cursor coordinates are counted from the top
of the scrolling region. With it turned off, cursor coordinates are
counted from the top of the whole screen regardless of the scrolling
region.

It is unlikely you would need to change this option, but if you find
a full-screen application is displaying pieces of text in what looks
like the wrong part of the screen, you could try turning DEC Origin
Mode on to see whether that helps.

DEC Origin Mode can be turned on and off by control sequences sent
by the server. This configuration option controls the \e{default}
state, which will be restored when you reset the terminal (see
\k{reset-terminal}). However, if you modify this option in
mid-session using \q{Change Settings}, it will take effect
immediately.

\S{config-crlf} \q{Implicit CR in every LF}

\cfg{winhelp-topic}{terminal.lfhascr}

Most servers send two control characters, CR and LF, to start a new
line of the screen. The CR character makes the cursor return to the
left-hand side of the screen. The LF character makes the cursor move
one line down (and might make the screen scroll).

Some servers only send LF, and expect the terminal to move the
cursor over to the left automatically. If you come across a server
that does this, you will see a stepped effect on the screen, like
this:

\c First line of text
\c                   Second line
\c                              Third line

If this happens to you, try enabling the \q{Implicit CR in every LF}
option, and things might go back to normal:

\c First line of text
\c Second line
\c Third line

\S{config-erase} \q{Use background colour to erase screen}

\cfg{winhelp-topic}{terminal.bce}

Not all terminals agree on what colour to turn the screen when the
server sends a \q{clear screen} sequence. Some terminals believe the
screen should always be cleared to the \e{default} background
colour. Others believe the screen should be cleared to whatever the
server has selected as a background colour.

There exist applications that expect both kinds of behaviour.
Therefore, PuTTY can be configured to do either.

With this option disabled, screen clearing is always done in the
default background colour. With this option enabled, it is done in
the \e{current} background colour.

Background-colour erase can be turned on and off by control
sequences sent by the server. This configuration option controls the
\e{default} state, which will be restored when you reset the
terminal (see \k{reset-terminal}). However, if you modify this
option in mid-session using \q{Change Settings}, it will take effect
immediately.

\S{config-blink} \q{Enable blinking text}

\cfg{winhelp-topic}{terminal.blink}

The server can ask PuTTY to display text that blinks on and off.
This is very distracting, so PuTTY allows you to turn blinking text
off completely.

When blinking text is disabled and the server attempts to make some
text blink, PuTTY will instead display the text with a bolded
background colour.

Blinking text can be turned on and off by control sequences sent by
the server. This configuration option controls the \e{default}
state, which will be restored when you reset the terminal (see
\k{reset-terminal}). However, if you modify this option in
mid-session using \q{Change Settings}, it will take effect
immediately.

\S{config-answerback} \q{Answerback to ^E}

\cfg{winhelp-topic}{terminal.answerback}

This option controls what PuTTY will send back to the server if the
server sends it the ^E enquiry character. Normally it just sends
the string \q{PuTTY}.

If you accidentally write the contents of a binary file to your
terminal, you will probably find that it contains more than one ^E
character, and as a result your next command line will probably read
\q{PuTTYPuTTYPuTTY...} as if you had typed the answerback string
multiple times at the keyboard. If you set the answerback string to
be empty, this problem should go away, but doing so might cause
other problems.

Note that this is \e{not} the feature of PuTTY which the server will
typically use to determine your terminal type. That feature is the
\q{Terminal-type string} in the Connection panel; see
\k{config-termtype} for details.

You can include control characters in the answerback string using
\c{^C} notation. (Use \c{^~} to get a literal \c{^}.)

\S{config-localecho} \q{Local echo}

\cfg{winhelp-topic}{terminal.localecho}

With local echo disabled, characters you type into the PuTTY window
are not echoed in the window \e{by PuTTY}. They are simply sent to
the server. (The \e{server} might choose to echo them back to you;
this can't be controlled from the PuTTY control panel.)

Some types of session need local echo, and many do not. In its
default mode, PuTTY will automatically attempt to deduce whether or
not local echo is appropriate for the session you are working in. If
you find it has made the wrong decision, you can use this
configuration option to override its choice: you can force local
echo to be turned on, or force it to be turned off, instead of
relying on the automatic detection.

\S{config-localedit} \q{Local line editing}

\cfg{winhelp-topic}{terminal.localedit}

Normally, every character you type into the PuTTY window is sent
immediately to the server the moment you type it.

If you enable local line editing, this changes. PuTTY will let you
edit a whole line at a time locally, and the line will only be sent
to the server when you press Return. If you make a mistake, you can
use the Backspace key to correct it before you press Return, and the
server will never see the mistake.

Since it is hard to edit a line locally without being able to see
it, local line editing is mostly used in conjunction with local echo
(\k{config-localecho}). This makes it ideal for use in raw mode
\#{FIXME} or when connecting to MUDs or talkers. (Although some more
advanced MUDs do occasionally turn local line editing on and turn
local echo off, in order to accept a password from the user.)

Some types of session need local line editing, and many do not. In
its default mode, PuTTY will automatically attempt to deduce whether
or not local line editing is appropriate for the session you are
working in. If you find it has made the wrong decision, you can use
this configuration option to override its choice: you can force
local line editing to be turned on, or force it to be turned off,
instead of relying on the automatic detection.

\S{config-printing} Remote-controlled printing

\cfg{winhelp-topic}{terminal.printing}

A lot of VT100-compatible terminals support printing under control
of the remote server. PuTTY supports this feature as well, but it is
turned off by default.

To enable remote-controlled printing, choose a printer from the
\q{Printer to send ANSI printer output to} drop-down list box. This
should allow you to select from all the printers you have installed
drivers for on your computer. Alternatively, you can type the
network name of a networked printer (for example,
\c{\\\\printserver\\printer1}) even if you haven't already
installed a driver for it on your own machine.

When the remote server attempts to print some data, PuTTY will send
that data to the printer \e{raw} - without translating it,
attempting to format it, or doing anything else to it. It is up to
you to ensure your remote server knows what type of printer it is
talking to.

Since PuTTY sends data to the printer raw, it cannot offer options
such as portrait versus landscape, print quality, or paper tray
selection. All these things would be done by your PC printer driver
(which PuTTY bypasses); if you need them done, you will have to find
a way to configure your remote server to do them.

To disable remote printing again, choose \q{None (printing
disabled)} from the printer selection list. This is the default
state.

\H{config-keyboard} The Keyboard panel

The Keyboard configuration panel allows you to control the behaviour
of the keyboard in PuTTY.

\S{config-backspace} Changing the action of the Backspace key

\cfg{winhelp-topic}{keyboard.backspace}

Some terminals believe that the Backspace key should send the same
thing to the server as Control-H (ASCII code 8). Other terminals
believe that the Backspace key should send ASCII code 127 (usually
known as Control-?) so that it can be distinguished from Control-H.
This option allows you to choose which code PuTTY generates when you
press Backspace.

If you are connecting to a Unix system, you will probably find that
the Unix \c{stty} command lets you configure which the server
expects to see, so you might not need to change which one PuTTY
generates. On other systems, the server's expectation might be fixed
and you might have no choice but to configure PuTTY.

If you do have the choice, we recommend configuring PuTTY to
generate Control-? and configuring the server to expect it, because
that allows applications such as \c{emacs} to use Control-H for
help.

(Typing \i{Shift-Backspace} will cause PuTTY to send whichever code
isn't configured here as the default.)

\S{config-homeend} Changing the action of the Home and End keys

\cfg{winhelp-topic}{keyboard.homeend}

The Unix terminal emulator \c{rxvt} disagrees with the rest of the
world about what character sequences should be sent to the server by
the Home and End keys.

\c{xterm}, and other terminals, send \c{ESC [1~} for the Home key,
and \c{ESC [4~} for the End key. \c{rxvt} sends \c{ESC [H} for the
Home key and \c{ESC [Ow} for the End key.

If you find an application on which the Home and End keys aren't
working, you could try switching this option to see if it helps.

\S{config-funkeys} Changing the action of the function keys and keypad

\cfg{winhelp-topic}{keyboard.funkeys}

This option affects the function keys (F1 to F12) and the top row of
the numeric keypad.

\b In the default mode, labelled \c{ESC [n~}, the function keys
generate sequences like \c{ESC [11~}, \c{ESC [12~} and so on. This
matches the general behaviour of Digital's terminals.

\b In Linux mode, F6 to F12 behave just like the default mode, but
F1 to F5 generate \c{ESC [[A} through to \c{ESC [[E}. This mimics the
Linux virtual console.

\b In Xterm R6 mode, F5 to F12 behave like the default mode, but F1
to F4 generate \c{ESC OP} through to \c{ESC OS}, which are the
sequences produced by the top row of the \e{keypad} on Digital's
terminals.

\b In VT400 mode, all the function keys behave like the default
mode, but the actual top row of the numeric keypad generates \c{ESC
OP} through to \c{ESC OS}.

\b In VT100+ mode, the function keys generate \c{ESC OP} through to
\c{ESC O[}

\b In SCO mode, the function keys F1 to F12 generate \c{ESC [M}
through to \c{ESC [X}.  Together with shift, they generate \c{ESC [Y}
through to \c{ESC [j}.  With control they generate \c{ESC [k} through
to \c{ESC [v}, and with shift and control together they generate
\c{ESC [w} through to \c{ESC [\{}.

If you don't know what any of this means, you probably don't need to
fiddle with it.

\S{config-appcursor} Controlling Application Cursor Keys mode

\cfg{winhelp-topic}{keyboard.appcursor}

Application Cursor Keys mode is a way for the server to change the
control sequences sent by the arrow keys. In normal mode, the arrow
keys send \c{ESC [A} through to \c{ESC [D}. In application mode,
they send \c{ESC OA} through to \c{ESC OD}.

Application Cursor Keys mode can be turned on and off by the server,
depending on the application. PuTTY allows you to configure the
initial state.

You can also disable application cursor keys mode completely, using
the \q{Features} configuration panel; see
\k{config-features-application}.

\S{config-appkeypad} Controlling Application Keypad mode

\cfg{winhelp-topic}{keyboard.appkeypad}

Application Keypad mode is a way for the server to change the
behaviour of the numeric keypad.

In normal mode, the keypad behaves like a normal Windows keypad:
with NumLock on, the number keys generate numbers, and with NumLock
off they act like the arrow keys and Home, End etc.

In application mode, all the keypad keys send special control
sequences, \e{including} Num Lock. Num Lock stops behaving like Num
Lock and becomes another function key.

Depending on which version of Windows you run, you may find the Num
Lock light still flashes on and off every time you press Num Lock,
even when application mode is active and Num Lock is acting like a
function key. This is unavoidable.

Application keypad mode can be turned on and off by the server,
depending on the application. PuTTY allows you to configure the
initial state.

You can also disable application keypad mode completely, using the
\q{Features} configuration panel; see
\k{config-features-application}.

\S{config-nethack} Using NetHack keypad mode

\cfg{winhelp-topic}{keyboard.nethack}

PuTTY has a special mode for playing NetHack. You can enable it by
selecting \q{NetHack} in the \q{Initial state of numeric keypad}
control.

In this mode, the numeric keypad keys 1-9 generate the NetHack
movement commands (\cw{hjklyubn}). The 5 key generates the \c{.}
command (do nothing).

Better still, pressing Shift with the keypad keys generates the
capital forms of the commands (\cw{HJKLYUBN}), which tells NetHack
to keep moving you in the same direction until you encounter
something interesting.

For some reason, this feature only works properly when Num Lock is
on. We don't know why.

\S{config-compose} Enabling a DEC-like Compose key

\cfg{winhelp-topic}{keyboard.compose}

DEC terminals have a Compose key, which provides an easy-to-remember
way of typing accented characters. You press Compose and then type
two more characters. The two characters are \q{combined} to produce
an accented character. The choices of character are designed to be
easy to remember; for example, composing \q{e} and \q{`} produces
the \q{\u00e8{e-grave}} character.

If your keyboard has a Windows Application key, it acts as a Compose
key in PuTTY. Alternatively, if you enable the \q{AltGr acts as
Compose key} option, the AltGr key will become a Compose key.

\S{config-ctrlalt} \q{Control-Alt is different from AltGr}

\cfg{winhelp-topic}{keyboard.ctrlalt}

Some old keyboards do not have an AltGr key, which can make it
difficult to type some characters. PuTTY can be configured to treat
the key combination Ctrl + Left Alt the same way as the AltGr key.

By default, this checkbox is checked, and the key combination Ctrl +
Left Alt does something completely different. PuTTY's usual handling
of the left Alt key is to prefix the Escape (Control-\cw{[})
character to whatever character sequence the rest of the keypress
would generate. For example, Alt-A generates Escape followed by
\c{a}. So Alt-Ctrl-A would generate Escape, followed by Control-A.

If you uncheck this box, Ctrl-Alt will become a synonym for AltGr,
so you can use it to type extra graphic characters if your keyboard
has any.

(However, Ctrl-Alt will never act as a Compose key, regardless of the
setting of \q{AltGr acts as Compose key} described in
\k{config-compose}.)

\H{config-bell} The Bell panel

The Bell panel controls the terminal bell feature: the server's
ability to cause PuTTY to beep at you.

In the default configuration, when the server sends the character
with ASCII code 7 (Control-G), PuTTY will play the Windows Default
Beep sound. This is not always what you want the terminal bell
feature to do; the Bell panel allows you to configure alternative
actions.

\S{config-bellstyle} \q{Set the style of bell}

\cfg{winhelp-topic}{bell.style}

This control allows you to select various different actions to occur
on a terminal bell:

\b Selecting \q{None} disables the bell completely. In this mode,
the server can send as many Control-G characters as it likes and
nothing at all will happen.

\b \q{Make default system alert sound} is the default setting. It
causes the Windows \q{Default Beep} sound to be played. To change
what this sound is, or to test it if nothing seems to be happening,
use the Sound configurer in the Windows Control Panel.

\b \q{Visual bell} is a silent alternative to a beeping computer. In
this mode, when the server sends a Control-G, the whole PuTTY window
will flash white for a fraction of a second.

\b \q{Beep using the PC speaker} is self-explanatory.

\b \q{Play a custom sound file} allows you to specify a particular
sound file to be used by PuTTY alone, or even by a particular
individual PuTTY session. This allows you to distinguish your PuTTY
beeps from any other beeps on the system. If you select this option,
you will also need to enter the name of your sound file in the edit
control \q{Custom sound file to play as a bell}.

\S{config-belltaskbar} \q{Taskbar/caption indication on bell}

\cfg{winhelp-topic}{bell.taskbar}

This feature controls what happens to the PuTTY window's entry in
the Windows Taskbar if a bell occurs while the window does not have
the input focus.

In the default state (\q{Disabled}) nothing unusual happens.

If you select \q{Steady}, then when a bell occurs and the window is
not in focus, the window's Taskbar entry and its title bar will
change colour to let you know that PuTTY session is asking for your
attention. The change of colour will persist until you select the
window, so you can leave several PuTTY windows minimised in your
terminal, go away from your keyboard, and be sure not to have missed
any important beeps when you get back.

\q{Flashing} is even more eye-catching: the Taskbar entry will
continuously flash on and off until you select the window.

\S{config-bellovl} \q{Control the bell overload behaviour}

\cfg{winhelp-topic}{bell.overload}

A common user error in a terminal session is to accidentally run the
Unix command \c{cat} (or equivalent) on an inappropriate file type,
such as an executable, image file, or ZIP file. This produces a huge
stream of non-text characters sent to the terminal, which typically
includes a lot of bell characters. As a result of this the terminal
often doesn't stop beeping for ten minutes, and everybody else in
the office gets annoyed.

To try to avoid this behaviour, or any other cause of excessive
beeping, PuTTY includes a bell overload management feature. In the
default configuration, receiving more than five bell characters in a
two-second period will cause the overload feature to activate. Once
the overload feature is active, further bells will have no effect at
all, so the rest of your binary file will be sent to the screen in
silence. After a period of five seconds during which no further
bells are received, the overload feature will turn itself off again
and bells will be re-enabled.

If you want this feature completely disabled, you can turn it off
using the checkbox \q{Bell is temporarily disabled when over-used}.

Alternatively, if you like the bell overload feature but don't agree
with the settings, you can configure the details: how many bells
constitute an overload, how short a time period they have to arrive
in to do so, and how much silent time is required before the
overload feature will deactivate itself.

Bell overload mode is always deactivated by any keypress in the
terminal. This means it can respond to large unexpected streams of
data, but does not interfere with ordinary command-line activities
that generate beeps (such as filename completion).

\H{config-features} The Features panel

PuTTY's terminal emulation is very highly featured, and can do a lot
of things under remote server control. Some of these features can
cause problems due to buggy or strangely configured server
applications.

The Features configuration panel allows you to disable some of
PuTTY's more advanced terminal features, in case they cause trouble.

\S{config-features-application} Disabling application keypad and cursor keys

\cfg{winhelp-topic}{features.application}

Application keypad mode (see \k{config-appkeypad}) and application
cursor keys mode (see \k{config-appcursor}) alter the behaviour of
the keypad and cursor keys. Some applications enable these modes but
then do not deal correctly with the modified keys. You can force
these modes to be permanently disabled no matter what the server
tries to do.

\S{config-features-mouse} Disabling \cw{xterm}-style mouse reporting

\cfg{winhelp-topic}{features.mouse}

PuTTY allows the server to send control codes that let it take over
the mouse and use it for purposes other than copy and paste.
Applications which use this feature include the text-mode web
browser \c{links}, the Usenet newsreader \c{trn} version 4, and the
file manager \c{mc} (Midnight Commander).

If you find this feature inconvenient, you can disable it using the
\q{Disable xterm-style mouse reporting} control. With this box
ticked, the mouse will \e{always} do copy and paste in the normal
way.

Note that even if the application takes over the mouse, you can
still manage PuTTY's copy and paste by holding down the Shift key
while you select and paste, unless you have deliberately turned this
feature off (see \k{config-mouseshift}).

\S{config-features-resize} Disabling remote terminal resizing

\cfg{winhelp-topic}{features.resize}

PuTTY has the ability to change the terminal's size and position in
response to commands from the server. If you find PuTTY is doing
this unexpectedly or inconveniently, you can tell PuTTY not to
respond to those server commands.

\S{config-features-altscreen} Disabling switching to the alternate screen

\cfg{winhelp-topic}{features.altscreen}

Many terminals, including PuTTY, support an \q{alternate screen}.
This is the same size as the ordinary terminal screen, but separate.
Typically a screen-based program such as a text editor might switch
the terminal to the alternate screen before starting up. Then at the
end of the run, it switches back to the primary screen, and you see
the screen contents just as they were before starting the editor.

Some people prefer this not to happen. If you want your editor to
run in the same screen as the rest of your terminal activity, you
can disable the alternate screen feature completely.

\S{config-features-retitle} Disabling remote window title changing

\cfg{winhelp-topic}{features.retitle}

PuTTY has the ability to change the window title in response to
commands from the server. If you find PuTTY is doing this
unexpectedly or inconveniently, you can tell PuTTY not to respond to
those server commands.

\S{config-features-qtitle} Disabling remote window title querying

\cfg{winhelp-topic}{features.qtitle}

PuTTY can optionally provide the xterm service of allowing server
applications to find out the local window title. This feature is
disabled by default, but you can turn it on if you really want it.

NOTE that this feature is a \e{potential security hazard}. If a
malicious application can write data to your terminal (for example,
if you merely \c{cat} a file owned by someone else on the server
machine), it can change your window title (unless you have disabled
this as mentioned in \k{config-features-retitle}) and then use this
service to have the new window title sent back to the server as if
typed at the keyboard. This allows an attacker to fake keypresses
and potentially cause your server-side applications to do things you
didn't want. Therefore this feature is disabled by default, and we
recommend you do not turn it on unless you \e{really} know what you
are doing.

\S{config-features-dbackspace} Disabling destructive backspace

\cfg{winhelp-topic}{features.dbackspace}

Normally, when PuTTY receives character 127 (^?) from the server, it
will perform a \q{destructive backspace}: move the cursor one space
left and delete the character under it. This can apparently cause
problems in some applications, so PuTTY provides the ability to
configure character 127 to perform a normal backspace (without
deleting a character) instead.

\S{config-features-charset} Disabling remote character set
configuration

\cfg{winhelp-topic}{features.charset}

PuTTY has the ability to change its character set configuration in
response to commands from the server. Some programs send these
commands unexpectedly or inconveniently. In particular, BitchX (an
IRC client) seems to have a habit of reconfiguring the character set
to something other than the user intended.

If you find that accented characters are not showing up the way you
expect them to, particularly if you're running BitchX, you could try
disabling the remote character set configuration commands.

\H{config-window} The Window panel

The Window configuration panel allows you to control aspects of the
PuTTY window.

\S{config-winsize} Setting the size of the PuTTY window

\cfg{winhelp-topic}{window.size}

The \q{Rows} and \q{Columns} boxes let you set the PuTTY window to a
precise size. Of course you can also drag the window to a new size
while a session is running.

\S{config-winsizelock} What to do when the window is resized

\cfg{winhelp-topic}{window.resize}

These options allow you to control what happens when the user tries
to resize the PuTTY window using its window furniture.

There are four options here:

\b \q{Change the number of rows and columns}: the font size will not
change. (This is the default.)

\b \q{Change the size of the font}: the number of rows and columns in
the terminal will stay the same, and the font size will change.

\b \q{Change font size when maximised}: when the window is resized,
the number of rows and columns will change, \e{except} when the window
is maximised (or restored), when the font size will change.

\b \q{Forbid resizing completely}: the terminal will refuse to be
resized at all.

\S{config-scrollback} Controlling scrollback

\cfg{winhelp-topic}{window.scrollback}

These options let you configure the way PuTTY keeps text after it
scrolls off the top of the screen (see \k{using-scrollback}).

The \q{Lines of scrollback} box lets you configure how many lines of
text PuTTY keeps. The \q{Display scrollbar} options allow you to
hide the scrollbar (although you can still view the scrollback using
the keyboard as described in \k{using-scrollback}). You can separately
configure whether the scrollbar is shown in full-screen mode and in
normal modes.

If you are viewing part of the scrollback when the server sends more
text to PuTTY, the screen will revert to showing the current
terminal contents. You can disable this behaviour by turning off
\q{Reset scrollback on display activity}. You can also make the
screen revert when you press a key, by turning on \q{Reset
scrollback on keypress}.

\S{config-erasetoscrollback} \q{Push erased text into scrollback}

\cfg{winhelp-topic}{window.erased}

When this option is enabled, the contents of the terminal screen
will be pushed into the scrollback when a server-side application
clears the screen, so that your scrollback will contain a better
record of what was on your screen in the past.

If the application switches to the alternate screen (see
\k{config-features-altscreen} for more about this), then the
contents of the primary screen will be visible in the scrollback
until the application switches back again.

This option is enabled by default.

\H{config-appearance} The Appearance panel

The Appearance configuration panel allows you to control aspects of
the appearance of PuTTY's window.

\S{config-cursor} Controlling the appearance of the cursor

\cfg{winhelp-topic}{appearance.cursor}

The \q{Cursor appearance} option lets you configure the cursor to be
a block, an underline, or a vertical line. A block cursor becomes an
empty box when the window loses focus; an underline or a vertical
line becomes dotted.

The \q{Cursor blinks} option makes the cursor blink on and off. This
works in any of the cursor modes.

\S{config-font} Controlling the font used in the terminal window

\cfg{winhelp-topic}{appearance.font}

This option allows you to choose what font, in what size, the PuTTY
terminal window uses to display the text in the session. You will be
offered a choice from all the fixed-width fonts installed on the
system. (VT100-style terminal handling can only deal with fixed-
width fonts.)

\S{config-mouseptr} \q{Hide mouse pointer when typing in window}

\cfg{winhelp-topic}{appearance.hidemouse}

If you enable this option, the mouse pointer will disappear if the
PuTTY window is selected and you press a key. This way, it will not
obscure any of the text in the window while you work in your
session. As soon as you move the mouse, the pointer will reappear.

This option is disabled by default, so the mouse pointer remains
visible at all times.

\S{config-winborder} Controlling the window border

\cfg{winhelp-topic}{appearance.border}

PuTTY allows you to configure the appearance of the window border to
some extent.

The checkbox marked \q{Sunken-edge border} changes the appearance of
the window border to something more like a DOS box: the inside edge
of the border is highlighted as if it sank down to meet the surface
inside the window. This makes the border a little bit thicker as
well. It's hard to describe well. Try it and see if you like it.

You can also configure a completely blank gap between the text in
the window and the border, using the \q{Gap between text and window
edge} control. By default this is set at one pixel. You can reduce
it to zero, or increase it further.

\H{config-behaviour} The Behaviour panel

The Behaviour configuration panel allows you to control aspects of
the behaviour of PuTTY's window.

\S{config-title} Controlling the window title

\cfg{winhelp-topic}{appearance.title}

The \q{Window title} edit box allows you to set the title of the
PuTTY window. By default the window title will contain the host name
followed by \q{PuTTY}, for example \c{server1.example.com - PuTTY}.
If you want a different window title, this is where to set it.

PuTTY allows the server to send \c{xterm} control sequences which
modify the title of the window in mid-session (unless this is disabled -
see \k{config-features-retitle}); the title string set here
is therefore only the \e{initial} window title.

As well as the \e{window} title, there is also an
\c{xterm} sequence to modify the title of the window's \e{icon}.
This makes sense in a windowing system where the window becomes an
icon when minimised, such as Windows 3.1 or most X Window System
setups; but in the Windows 95-like user interface it isn't as
applicable.

By default, PuTTY only uses the server-supplied \e{window} title, and
ignores the icon title entirely. If for some reason you want to see
both titles, check the box marked \q{Separate window and icon titles}.
If you do this, PuTTY's window title and Taskbar caption will
change into the server-supplied icon title if you minimise the PuTTY
window, and change back to the server-supplied window title if you
restore it. (If the server has not bothered to supply a window or
icon title, none of this will happen.)

\S{config-warnonclose} \q{Warn before closing window}

\cfg{winhelp-topic}{behaviour.closewarn}

If you press the Close button in a PuTTY window that contains a
running session, PuTTY will put up a warning window asking if you
really meant to close the window. A window whose session has already
terminated can always be closed without a warning.

If you want to be able to close a window quickly, you can disable
the \q{Warn before closing window} option.

\S{config-altf4} \q{Window closes on ALT-F4}

\cfg{winhelp-topic}{behaviour.altf4}

By default, pressing ALT-F4 causes the window to close (or a warning
box to appear; see \k{config-warnonclose}). If you disable the
\q{Window closes on ALT-F4} option, then pressing ALT-F4 will simply
send a key sequence to the server.

\S{config-altspace} \q{System menu appears on ALT-Space}

\cfg{winhelp-topic}{behaviour.altspace}

If this option is enabled, then pressing ALT-Space will bring up the
PuTTY window's menu, like clicking on the top left corner. If it is
disabled, then pressing ALT-Space will just send \c{ESC SPACE} to
the server.

Some accessibility programs for Windows may need this option
enabling to be able to control PuTTY's window successfully. For
instance, Dragon NaturallySpeaking requires it both to open the
system menu via voice, and to close, minimise, maximise and restore
the window.

\S{config-altonly} \q{System menu appears on Alt alone}

\cfg{winhelp-topic}{behaviour.altonly}

If this option is enabled, then pressing and releasing ALT will
bring up the PuTTY window's menu, like clicking on the top left
corner. If it is disabled, then pressing and releasing ALT will have
no effect.

\S{config-alwaysontop} \q{Ensure window is always on top}

\cfg{winhelp-topic}{behaviour.alwaysontop}

If this option is enabled, the PuTTY window will stay on top of all
other windows.

\S{config-fullscreen} \q{Full screen on Alt-Enter}

\cfg{winhelp-topic}{behaviour.altenter}

If this option is enabled, then pressing Alt-Enter will cause the
PuTTY window to become full-screen. Pressing Alt-Enter again will
restore the previous window size.

The full-screen feature is also available from the System menu, even
when it is configured not to be available on the Alt-Enter key. See
\k{using-fullscreen}.

\H{config-translation} The Translation panel

The Translation configuration panel allows you to control the
translation between the character set understood by the server and
the character set understood by PuTTY.

\S{config-charset} Controlling character set translation

\cfg{winhelp-topic}{translation.codepage}

During an interactive session, PuTTY receives a stream of 8-bit
bytes from the server, and in order to display them on the screen it
needs to know what character set to interpret them in.

There are a lot of character sets to choose from. The \q{Received
data assumed to be in which character set} option lets you select
one. By default PuTTY will attempt to choose a character set that is
right for your locale as reported by Windows; if it gets it wrong,
you can select a different one using this control.

A few notable character sets are:

\b The ISO-8859 series are all standard character sets that include
various accented characters appropriate for different sets of
languages.

\b The Win125x series are defined by Microsoft, for similar
purposes. In particular Win1252 is almost equivalent to ISO-8859-1,
but contains a few extra characters such as matched quotes and the
Euro symbol.

\b If you want the old IBM PC character set with block graphics and
line-drawing characters, you can select \q{CP437}.

\b PuTTY also supports Unicode mode, in which the data coming from
the server is interpreted as being in the UTF-8 encoding of Unicode.
If you select \q{UTF-8} as a character set you can use this mode.
Not all server-side applications will support it.

If you need support for a numeric code page which is not listed in
the drop-down list, such as code page 866, then you can try entering
its name manually (\c{CP866} for example) in the list box. If the
underlying version of Windows has the appropriate translation table
installed, PuTTY will use it.

\S{config-cyr} \q{Caps Lock acts as Cyrillic switch}

\cfg{winhelp-topic}{translation.cyrillic}

This feature allows you to switch between a US/UK keyboard layout
and a Cyrillic keyboard layout by using the Caps Lock key, if you
need to type (for example) Russian and English side by side in the
same document.

Currently this feature is not expected to work properly if your
native keyboard layout is not US or UK.

\S{config-linedraw} Controlling display of line drawing characters

\cfg{winhelp-topic}{translation.linedraw}

VT100-series terminals allow the server to send control sequences that
shift temporarily into a separate character set for drawing simple
lines and boxes. However, there are a variety of ways in which PuTTY
can attempt to find appropriate characters, and the right one to use
depends on the locally configured font. In general you should probably
try lots of options until you find one that your particular font
supports.

\b \q{Use Unicode line drawing code points} tries to use the box
characters that are present in Unicode. For good Unicode-supporting
fonts this is probably the most reliable and functional option.

\b \q{Poor man's line drawing} assumes that the font \e{cannot}
generate the line and box characters at all, so it will use the
\c{+}, \c{-} and \c{|} characters to draw approximations to boxes.
You should use this option if none of the other options works.

\b \q{Font has XWindows encoding} is for use with fonts that have a
special encoding, where the lowest 32 character positions (below the
ASCII printable range) contain the line-drawing characters. This is
unlikely to be the case with any standard Windows font; it will
probably only apply to custom-built fonts or fonts that have been
automatically converted from the X Window System.

\b \q{Use font in both ANSI and OEM modes} tries to use the same
font in two different character sets, to obtain a wider range of
characters. This doesn't always work; some fonts claim to be a
different size depending on which character set you try to use.

\b \q{Use font in OEM mode only} is more reliable than that, but can
miss out other characters from the main character set.

\S{config-linedrawpaste} Controlling copy and paste of line drawing
characters

\cfg{winhelp-topic}{selection.linedraw}

By default, when you copy and paste a piece of the PuTTY screen that
contains VT100 line and box drawing characters, PuTTY will paste
them in the form they appear on the screen: either Unicode line
drawing code points, or the \q{poor man's} line-drawing characters
\c{+}, \c{-} and \c{|}. The checkbox \q{Copy and paste VT100 line
drawing chars as lqqqk} disables this feature, so line-drawing
characters will be pasted as the ASCII characters that were printed
to produce them. This will typically mean they come out mostly as
\c{q} and \c{x}, with a scattering of \c{jklmntuvw} at the corners.
This might be useful if you were trying to recreate the same box
layout in another program, for example.

Note that this option only applies to line-drawing characters which
\e{were} printed by using the VT100 mechanism. Line-drawing
characters that were received as Unicode code points will paste as
Unicode always.

\H{config-selection} The Selection panel

The Selection panel allows you to control the way copy and paste
work in the PuTTY window.

\S{config-rtfpaste} Pasting in Rich Text Format

\cfg{winhelp-topic}{selection.rtf}

If you enable \q{Paste to clipboard in RTF as well as plain text},
PuTTY will write formatting information to the clipboard as well as
the actual text you copy. Currently the only effect of this will be
that if you paste into (say) a word processor, the text will appear
in the word processor in the same font PuTTY was using to display
it. In future it is likely that other formatting information (bold,
underline, colours) will be copied as well.

This option can easily be inconvenient, so by default it is
disabled.

\S{config-mouse} Changing the actions of the mouse buttons

\cfg{winhelp-topic}{selection.buttons}

PuTTY's copy and paste mechanism is by default modelled on the Unix
\c{xterm} application. The X Window System uses a three-button mouse,
and the convention is that the left button selects, the right button
extends an existing selection, and the middle button pastes.

Windows often only has two mouse buttons, so in PuTTY's default
configuration (\q{Compromise}), the \e{right} button pastes, and the
\e{middle} button (if you have one) extends a selection.

If you have a three-button mouse and you are already used to the
\c{xterm} arrangement, you can select it using the \q{Action of
mouse buttons} control.

Alternatively, with the \q{Windows} option selected, the middle
button extends, and the right button brings up a context menu (on
which one of the options is \q{Paste}). (This context menu is always
available by holding down Ctrl and right-clicking, regardless of the
setting of this option.)

\S{config-mouseshift} \q{Shift overrides application's use of mouse}

\cfg{winhelp-topic}{selection.shiftdrag}

PuTTY allows the server to send control codes that let it take over
the mouse and use it for purposes other than copy and paste.
Applications which use this feature include the text-mode web
browser \c{links}, the Usenet newsreader \c{trn} version 4, and the
file manager \c{mc} (Midnight Commander).

When running one of these applications, pressing the mouse buttons
no longer performs copy and paste. If you do need to copy and paste,
you can still do so if you hold down Shift while you do your mouse
clicks.

However, it is possible in theory for applications to even detect
and make use of Shift + mouse clicks. We don't know of any
applications that do this, but in case someone ever writes one,
unchecking the \q{Shift overrides application's use of mouse}
checkbox will cause Shift + mouse clicks to go to the server as well
(so that mouse-driven copy and paste will be completely disabled).

If you want to prevent the application from taking over the mouse at
all, you can do this using the Features control panel; see
\k{config-features-mouse}.

\S{config-rectselect} Default selection mode

\cfg{winhelp-topic}{selection.rect}

As described in \k{using-selection}, PuTTY has two modes of
selecting text to be copied to the clipboard. In the default mode
(\q{Normal}), dragging the mouse from point A to point B selects to
the end of the line containing A, all the lines in between, and from
the very beginning of the line containing B. In the other mode
(\q{Rectangular block}), dragging the mouse between two points
defines a rectangle, and everything within that rectangle is copied.

Normally, you have to hold down Alt while dragging the mouse to
select a rectangular block. Using the \q{Default selection mode}
control, you can set rectangular selection as the default, and then
you have to hold down Alt to get the \e{normal} behaviour.

\S{config-charclasses} Configuring word-by-word selection

\cfg{winhelp-topic}{selection.charclasses}

PuTTY will select a word at a time in the terminal window if you
double-click to begin the drag. This panel allows you to control
precisely what is considered to be a word.

Each character is given a \e{class}, which is a small number
(typically 0, 1 or 2). PuTTY considers a single word to be any
number of adjacent characters in the same class. So by modifying the
assignment of characters to classes, you can modify the word-by-word
selection behaviour.

In the default configuration, the character classes are:

\b Class 0 contains white space and control characters.

\b Class 1 contains most punctuation.

\b Class 2 contains letters, numbers and a few pieces of punctuation
(the double quote, minus sign, period, forward slash and
underscore).

So, for example, if you assign the \c{@} symbol into character class
2, you will be able to select an e-mail address with just a double
click.

In order to adjust these assignments, you start by selecting a group
of characters in the list box. Then enter a class number in the edit
box below, and press the \q{Set} button.

This mechanism currently only covers ASCII characters, because it
isn't feasible to expand the list to cover the whole of Unicode.

Character class definitions can be modified by control sequences
sent by the server. This configuration option controls the
\e{default} state, which will be restored when you reset the
terminal (see \k{reset-terminal}). However, if you modify this
option in mid-session using \q{Change Settings}, it will take effect
immediately.

\H{config-colours} The Colours panel

The Colours panel allows you to control PuTTY's use of colour.

\S{config-boldcolour} \q{Bolded text is a different colour}

\cfg{winhelp-topic}{colours.bold}

When the server sends a control sequence indicating that some text
should be displayed in bold, PuTTY can handle this two ways. It can
either change the font for a bold version, or use the same font in a
brighter colour. This control lets you choose which.

By default the box is checked, so non-bold text is displayed in
light grey and bold text is displayed in bright white (and similarly
in other colours). If you uncheck the box, bold and non-bold text
will be displayed in the same colour, and instead the font will
change to indicate the difference.

\S{config-logpalette} \q{Attempt to use logical palettes}

\cfg{winhelp-topic}{colours.logpal}

Logical palettes are a mechanism by which a Windows application
running on an 8-bit colour display can select precisely the colours
it wants instead of going with the Windows standard defaults.

If you are not getting the colours you ask for on an 8-bit display,
you can try enabling this option. However, be warned that it's never
worked very well.

\S{config-syscolour} \q{Use system colours}

\cfg{winhelp-topic}{colours.system}

Enabling this option will cause PuTTY to ignore the configured colours
for \q{Default Background/Foreground} and \q{Cursor Colour/Text} (see
\k{config-colourcfg}), instead going with the system-wide defaults.

Note that non-bold and bold text will be the same colour if this
option is enabled. You might want to change to indicating bold text
by font changes (see \k{config-boldcolour}).

\S{config-colourcfg} Adjusting the colours in the terminal window

\cfg{winhelp-topic}{colours.config}

The main colour control allows you to specify exactly what colours
things should be displayed in. To modify one of the PuTTY colours,
use the list box to select which colour you want to modify. The RGB
values for that colour will appear on the right-hand side of the
list box. Now, if you press the \q{Modify} button, you will be
presented with a colour selector, in which you can choose a new
colour to go in place of the old one.

PuTTY allows you to set the cursor colour, the default foreground
and background, and the precise shades of all the ANSI configurable
colours (black, red, green, yellow, blue, magenta, cyan, and white).
You can also modify the precise shades used for the bold versions of
these colours; these are used to display bold text if you have
selected \q{Bolded text is a different colour}, and can also be used
if the server asks specifically to use them. (Note that \q{Default
Bold Background} is \e{not} the background colour used for bold text;
it is only used if the server specifically asks for a bold
background.)

\H{config-connection} The Connection panel

The Connection panel allows you to configure options that apply to
more than one type of connection.

\S{config-termtype} \q{Terminal-type string}

\cfg{winhelp-topic}{connection.termtype}

Most servers you might connect to with PuTTY are designed to be
connected to from lots of different types of terminal. In order to
send the right control sequences to each one, the server will need
to know what type of terminal it is dealing with. Therefore, each of
the SSH, Telnet and Rlogin protocols allow a text string to be sent
down the connection describing the terminal.

PuTTY attempts to emulate the Unix \c{xterm} program, and by default
it reflects this by sending \c{xterm} as a terminal-type string. If
you find this is not doing what you want - perhaps the remote
system reports \q{Unknown terminal type} - you could try setting
this to something different, such as \c{vt220}.

If you're not sure whether a problem is due to the terminal type
setting or not, you probably need to consult the manual for your
application or your server.

\S{config-termspeed} \q{Terminal speeds}

\cfg{winhelp-topic}{connection.termspeed}

The Telnet, Rlogin, and SSH protocols allow the client to specify
terminal speeds to the server.

This parameter does \e{not} affect the actual speed of the connection,
which is always \q{as fast as possible}; it is just a hint that is
sometimes used by server software to modify its behaviour. For
instance, if a slow speed is indicated, the server may switch to a
less bandwidth-hungry display mode.

The value is usually meaningless in a network environment, but
PuTTY lets you configure it, in case you find the server is reacting
badly to the default value.

The format is a pair of numbers separated by a comma, for instance,
\c{38400,38400}. The first number represents the output speed
(\e{from} the server) in bits per second, and the second is the input
speed (\e{to} the server). (Only the first is used in the Rlogin
protocol.)

This option has no effect on Raw connections.

\S{config-username} \q{Auto-login username}

\cfg{winhelp-topic}{connection.username}

All three of the SSH, Telnet and Rlogin protocols allow you to
specify what user name you want to log in as, without having to type
it explicitly every time. (Some Telnet servers don't support this.)

In this box you can type that user name.

\S{config-environ} Setting environment variables on the server

\cfg{winhelp-topic}{telnet.environ}

The Telnet protocol provides a means for the client to pass
environment variables to the server. Many Telnet servers have
stopped supporting this feature due to security flaws, but PuTTY
still supports it for the benefit of any servers which have found
other ways around the security problems than just disabling the
whole mechanism.

Version 2 of the SSH protocol also provides a similar mechanism,
which is easier to implement without security flaws. Newer SSH2
servers are more likely to support it than older ones.

This configuration data is not used in the SSHv1, rlogin or raw
protocols.

To add an environment variable to the list transmitted down the
connection, you enter the variable name in the \q{Variable} box,
enter its value in the \q{Value} box, and press the \q{Add} button.
To remove one from the list, select it in the list box and press
\q{Remove}.

\S{config-keepalive} Using keepalives to prevent disconnection

\cfg{winhelp-topic}{connection.keepalive}

If you find your sessions are closing unexpectedly (\q{Connection
reset by peer}) after they have been idle for a while, you might
want to try using this option.

Some network routers and firewalls need to keep track of all
connections through them. Usually, these firewalls will assume a
connection is dead if no data is transferred in either direction
after a certain time interval. This can cause PuTTY sessions to be
unexpectedly closed by the firewall if no traffic is seen in the
session for some time.

The keepalive option (\q{Seconds between keepalives}) allows you to
configure PuTTY to send data through the session at regular
intervals, in a way that does not disrupt the actual terminal
session. If you find your firewall is cutting idle connections off,
you can try entering a non-zero value in this field. The value is
measured in seconds; so, for example, if your firewall cuts
connections off after ten minutes then you might want to enter 300
seconds (5 minutes) in the box.

Note that keepalives are not always helpful. They help if you have a
firewall which drops your connection after an idle period; but if
the network between you and the server suffers from breaks in
connectivity then keepalives can actually make things worse. If a
session is idle, and connectivity is temporarily lost between the
endpoints, but the connectivity is restored before either side tries
to send anything, then there will be no problem - neither endpoint
will notice that anything was wrong. However, if one side does send
something during the break, it will repeatedly try to re-send, and
eventually give up and abandon the connection. Then when
connectivity is restored, the other side will find that the first
side doesn't believe there is an open connection any more.
Keepalives can make this sort of problem worse, because they
increase the probability that PuTTY will attempt to send data during
a break in connectivity. Therefore, you might find they help
connection loss, or you might find they make it worse, depending on
what \e{kind} of network problems you have between you and the
server.

Keepalives are only supported in Telnet and SSH; the Rlogin and Raw
protocols offer no way of implementing them. (For an alternative, see
\k{config-tcp-keepalives}.)

Note that if you are using SSH1 and the server has a bug that makes
it unable to deal with SSH1 ignore messages (see
\k{config-ssh-bug-ignore1}), enabling keepalives will have no effect.

\S{config-nodelay} \q{Disable Nagle's algorithm}

\cfg{winhelp-topic}{connection.nodelay}

Nagle's algorithm is a detail of TCP/IP implementations that tries
to minimise the number of small data packets sent down a network
connection. With Nagle's algorithm enabled, PuTTY's bandwidth usage
will be slightly more efficient; with it disabled, you may find you
get a faster response to your keystrokes when connecting to some
types of server.

The Nagle algorithm is disabled by default.

\S{config-tcp-keepalives} \q{Enable TCP keepalives}

\cfg{winhelp-topic}{connection.tcpkeepalive}

\e{NOTE:} TCP keepalives should not be confused with the
application-level keepalives described in \k{config-keepalive}. If in
doubt, you probably want application-level keepalives; TCP keepalives
are provided for completeness.

The idea of TCP keepalives is similar to application-level keepalives,
and the same caveats apply. The main differences are:

\b TCP keepalives are available on \e{all} connection types, including
Raw and Rlogin.

\b The interval between TCP keepalives is usually much longer,
typically two hours; this is set by the operating system, and cannot
be configured within PuTTY.

\b If the operating system does not receive a response to a keepalive,
it may send out more in quick succession and if terminate the connection
if no response is received.

TCP keepalives may be more useful for ensuring that half-open connections
are terminated than for keeping a connection alive.

TCP keepalives are disabled by default.

\H{config-proxy} The Proxy panel

\cfg{winhelp-topic}{proxy.main}

The Proxy panel allows you to configure PuTTY to use various types
of proxy in order to make its network connections. The settings in
this panel affect the primary network connection forming your PuTTY
session, but also any extra connections made as a result of SSH port
forwarding (see \k{using-port-forwarding}).

\S{config-proxy-type} Setting the proxy type

\cfg{winhelp-topic}{proxy.type}

The \q{Proxy type} radio buttons allow you to configure what type of
proxy you want PuTTY to use for its network connections. The default
setting is \q{None}; in this mode no proxy is used for any
connection.

\b Selecting \q{HTTP} allows you to proxy your connections through a
web server supporting the HTTP \cw{CONNECT} command, as documented
in \W{http://www.ietf.org/rfc/rfc2817.txt}{RFC 2817}.

\b Selecting \q{SOCKS 4} or \q{SOCKS 5} allows you to proxy your
connections through a SOCKS server.

\b Many firewalls implement a less formal type of proxy in which a
user can make a Telnet connection directly to the firewall machine
and enter a command such as \c{connect myhost.com 22} to connect
through to an external host. Selecting \q{Telnet} allows you to tell
PuTTY to use this type of proxy.

\S{config-proxy-exclude} Excluding parts of the network from proxying

\cfg{winhelp-topic}{proxy.exclude}

Typically you will only need to use a proxy to connect to non-local
parts of your network; for example, your proxy might be required for
connections outside your company's internal network. In the
\q{Exclude Hosts/IPs} box you can enter ranges of IP addresses, or
ranges of DNS names, for which PuTTY will avoid using the proxy and
make a direct connection instead.

The \q{Exclude Hosts/IPs} box may contain more than one exclusion
range, separated by commas. Each range can be an IP address or a DNS
name, with a \c{*} character allowing wildcards. For example:

\c *.example.com

This excludes any host with a name ending in \c{.example.com} from
proxying.

\c 192.168.88.*

This excludes any host with an IP address starting with 192.168.88
from proxying.

\c 192.168.88.*,*.example.com

This excludes both of the above ranges at once.

Connections to the local host (the host name \c{localhost}, and any
loopback IP address) are never proxied, even if the proxy exclude
list does not explicitly contain them. It is very unlikely that this
behaviour would ever cause problems, but if it does you can change
it by enabling \q{Consider proxying local host connections}.

Note that if you are doing DNS at the proxy (see
\k{config-proxy-dns}), you should make sure that your proxy
exclusion settings do not depend on knowing the IP address of a
host. If the name is passed on to the proxy without PuTTY looking it
up, it will never know the IP address and cannot check it against
your list.

\S{config-proxy-dns} Name resolution when using a proxy

\cfg{winhelp-topic}{proxy.dns}

If you are using a proxy to access a private network, it can make a
difference whether DNS name resolution is performed by PuTTY itself
(on the client machine) or performed by the proxy.

The \q{Do DNS name lookup at proxy end} configuration option allows
you to control this. If you set it to \q{No}, PuTTY will always do
its own DNS, and will always pass an IP address to the proxy. If you
set it to \q{Yes}, PuTTY will always pass host names straight to the
proxy without trying to look them up first.

If you set this option to \q{Auto} (the default), PuTTY will do
something it considers appropriate for each type of proxy. Telnet
and HTTP proxies will have host names passed straight to them; SOCKS
proxies will not.

Note that if you are doing DNS at the proxy, you should make sure
that your proxy exclusion settings (see \k{config-proxy-exclude}) do
not depend on knowing the IP address of a host. If the name is
passed on to the proxy without PuTTY looking it up, it will never
know the IP address and cannot check it against your list.

The original SOCKS 4 protocol does not support proxy-side DNS. There
is a protocol extension (SOCKS 4A) which does support it, but not
all SOCKS 4 servers provide this extension. If you enable proxy DNS
and your SOCKS 4 server cannot deal with it, this might be why.

\S{config-proxy-auth} Username and password

\cfg{winhelp-topic}{proxy.auth}

If your proxy requires authentication, you can enter a username and
a password in the \q{Username} and \q{Password} boxes.

Note that if you save your session, the proxy password will be
saved in plain text, so anyone who can access your PuTTY
configuration data will be able to discover it.

Authentication is not fully supported for all forms of proxy:

\b Username and password authentication is supported for HTTP
proxies and SOCKS 5 proxies.

\lcont{

\b With SOCKS 5, authentication is via \i{CHAP} if the proxy
supports it (this is not supported in \i{PuTTYtel}); otherwise the
password is sent to the proxy in plain text.

\b With HTTP proxying, the only currently supported authentication
method is \q{basic}, where the password is sent to the proxy in plain
text.

}

\b SOCKS 4 can use the \q{Username} field, but does not support
passwords.

\b You can specify a way to include a username and password in the
Telnet proxy command (see \k{config-proxy-command}).

\S{config-proxy-command} Specifying the Telnet proxy command

\cfg{winhelp-topic}{proxy.command}

If you are using the Telnet proxy type, the usual command required
by the firewall's Telnet server is \c{connect}, followed by a host
name and a port number. If your proxy needs a different command,
you can enter an alternative here.

In this string, you can use \c{\\n} to represent a new-line, \c{\\r}
to represent a carriage return, \c{\\t} to represent a tab
character, and \c{\\x} followed by two hex digits to represent any
other character. \c{\\\\} is used to encode the \c{\\} character
itself.

Also, the special strings \c{%host} and \c{%port} will be replaced
by the host name and port number you want to connect to. The strings
\c{%user} and \c{%pass} will be replaced by the proxy username and 
password you specify. To get a literal \c{%} sign, enter \c{%%}.

If the Telnet proxy server prompts for a username and password
before commands can be sent, you can use a command such as:

\c %user\n%pass\nconnect %host %port\n

This will send your username and password as the first two lines to 
the proxy, followed by a command to connect to the desired host and 
port. Note that if you do not include the \c{%user} or \c{%pass}
tokens in the Telnet command, then the \q{Username} and \q{Password}
configuration fields will be ignored.

\H{config-telnet} The Telnet panel

The Telnet panel allows you to configure options that only apply to
Telnet sessions.

\S{config-oldenviron} \q{Handling of OLD_ENVIRON ambiguity}

\cfg{winhelp-topic}{telnet.oldenviron}

The original Telnet mechanism for passing environment variables was
badly specified. At the time the standard (RFC 1408) was written,
BSD telnet implementations were already supporting the feature, and
the intention of the standard was to describe the behaviour the BSD
implementations were already using.

Sadly there was a typing error in the standard when it was issued,
and two vital function codes were specified the wrong way round. BSD
implementations did not change, and the standard was not corrected.
Therefore, it's possible you might find either BSD or RFC-compliant
implementations out there. This switch allows you to choose which
one PuTTY claims to be.

The problem was solved by issuing a second standard, defining a new
Telnet mechanism called \cw{NEW_ENVIRON}, which behaved exactly like
the original \cw{OLD_ENVIRON} but was not encumbered by existing
implementations. Most Telnet servers now support this, and it's
unambiguous. This feature should only be needed if you have trouble
passing environment variables to quite an old server.

\S{config-ptelnet} Passive and active Telnet negotiation modes

\cfg{winhelp-topic}{telnet.passive}

In a Telnet connection, there are two types of data passed between
the client and the server: actual text, and \e{negotiations} about
which Telnet extra features to use.

PuTTY can use two different strategies for negotiation:

\b In \e{active} mode, PuTTY starts to send negotiations as soon as
the connection is opened.

\b In \e{passive} mode, PuTTY will wait to negotiate until it sees a
negotiation from the server.

The obvious disadvantage of passive mode is that if the server is
also operating in a passive mode, then negotiation will never begin
at all. For this reason PuTTY defaults to active mode.

However, sometimes passive mode is required in order to successfully
get through certain types of firewall and Telnet proxy server. If
you have confusing trouble with a firewall, you could try enabling
passive mode to see if it helps.

\S{config-telnetkey} \q{Keyboard sends Telnet special commands}

\cfg{winhelp-topic}{telnet.specialkeys}

If this box is checked, several key sequences will have their normal
actions modified:

\b the Backspace key on the keyboard will send the \I{Erase Character,
Telnet special command}Telnet special backspace code;

\b Control-C will send the Telnet special \I{Interrupt Process, Telnet
special command}Interrupt Process code;

\b Control-Z will send the Telnet special \I{Suspend Process, Telnet
special command}Suspend Process code.

You probably shouldn't enable this
unless you know what you're doing.

\S{config-telnetnl} \q{Return key sends Telnet New Line instead of ^M}

\cfg{winhelp-topic}{telnet.newline}

Unlike most other remote login protocols, the Telnet protocol has a
special \q{new line} code that is not the same as the usual line
endings of Control-M or Control-J. By default, PuTTY sends the
Telnet New Line code when you press Return, instead of sending
Control-M as it does in most other protocols.

Most Unix-style Telnet servers don't mind whether they receive
Telnet New Line or Control-M; some servers do expect New Line, and
some servers prefer to see ^M. If you are seeing surprising
behaviour when you press Return in a Telnet session, you might try
turning this option off to see if it helps.

\H{config-rlogin} The Rlogin panel

The Rlogin panel allows you to configure options that only apply to
Rlogin sessions.

\S{config-rlogin-localuser} \q{Local username}

\cfg{winhelp-topic}{rlogin.localuser}

Rlogin allows an automated (password-free) form of login by means of
a file called \c{.rhosts} on the server. You put a line in your
\c{.rhosts} file saying something like \c{jbloggs@pc1.example.com},
and then when you make an Rlogin connection the client transmits the
username of the user running the Rlogin client. The server checks
the username and hostname against \c{.rhosts}, and if they match it
does not ask for a password.

This only works because Unix systems contain a safeguard to stop a
user from pretending to be another user in an Rlogin connection.
Rlogin connections have to come from port numbers below 1024, and
Unix systems prohibit this to unprivileged processes; so when the
server sees a connection from a low-numbered port, it assumes the
client end of the connection is held by a privileged (and therefore
trusted) process, so it believes the claim of who the user is.

Windows does not have this restriction: \e{any} user can initiate an
outgoing connection from a low-numbered port. Hence, the Rlogin
\c{.rhosts} mechanism is completely useless for securely
distinguishing several different users on a Windows machine. If you
have a \c{.rhosts} entry pointing at a Windows PC, you should assume
that \e{anyone} using that PC can spoof your username in an Rlogin
connection and access your account on the server.

The \q{Local username} control allows you to specify what user name
PuTTY should claim you have, in case it doesn't match your Windows
user name (or in case you didn't bother to set up a Windows user
name).

\H{config-ssh} The SSH panel

The SSH panel allows you to configure options that only apply to
SSH sessions.

\S{config-command} Executing a specific command on the server

\cfg{winhelp-topic}{ssh.command}

In SSH, you don't have to run a general shell session on the server.
Instead, you can choose to run a single specific command (such as a
mail user agent, for example). If you want to do this, enter the
command in the \q{Remote command} box.

\S{config-ssh-pty} \q{Don't allocate a pseudo-terminal}

\cfg{winhelp-topic}{ssh.nopty}

When connecting to a Unix system, most interactive shell sessions
are run in a \e{pseudo-terminal}, which allows the Unix system to
pretend it's talking to a real physical terminal device but allows
the SSH server to catch all the data coming from that fake device
and send it back to the client.

Occasionally you might find you have a need to run a session \e{not}
in a pseudo-terminal. In PuTTY, this is generally only useful for
very specialist purposes; although in Plink (see \k{plink}) it is
the usual way of working.

\S{config-ssh-noshell} \q{Don't start a shell or command at all}

\cfg{winhelp-topic}{ssh.noshell}

If you tick this box, PuTTY will not attempt to run a shell or
command after connecting to the remote server. You might want to use
this option if you are only using the SSH connection for port
forwarding, and your user account on the server does not have the
ability to run a shell.

This feature is only available in SSH protocol version 2 (since the
version 1 protocol assumes you will always want to run a shell).

This feature can also be enabled using the \c{-N} command-line
option; see \k{using-cmdline-noshell}.

If you use this feature in Plink, you will not be able to terminate
the Plink process by any graceful means; the only way to kill it
will be by pressing Control-C or sending a kill signal from another
program.

\S{config-ssh-comp} \q{Enable compression}

\cfg{winhelp-topic}{ssh.compress}

This enables data compression in the SSH connection: data sent by
the server is compressed before sending, and decompressed at the
client end. Likewise, data sent by PuTTY to the server is compressed
first and the server decompresses it at the other end. This can help
make the most of a low-bandwidth connection.

\S{config-ssh-prot} \q{Preferred SSH protocol version}

\cfg{winhelp-topic}{ssh.protocol}

This allows you to select whether you would like to use SSH protocol
version 1 or version 2. \#{FIXME: say something about this elsewhere?}

PuTTY will attempt to use protocol 1 if the server you connect to
does not offer protocol 2, and vice versa.

If you select \q{1 only} or \q{2 only} here, PuTTY will only connect
if the server you connect to offers the SSH protocol version you
have specified.

\S{config-ssh-encryption} Encryption algorithm selection

\cfg{winhelp-topic}{ssh.ciphers}

PuTTY supports a variety of different encryption algorithms, and
allows you to choose which one you prefer to use. You can do this by
dragging the algorithms up and down in the list box (or moving them
using the Up and Down buttons) to specify a preference order. When
you make an SSH connection, PuTTY will search down the list from the
top until it finds an algorithm supported by the server, and then
use that.

PuTTY currently supports the following algorithms:

\b AES (Rijndael) - 256, 192, or 128-bit CBC (SSH-2 only)

\b Blowfish - 128-bit CBC

\b Triple-DES - 168-bit CBC

\b Single-DES - 56-bit CBC (see below for SSH-2)

If the algorithm PuTTY finds is below the \q{warn below here} line,
you will see a warning box when you make the connection:

\c The first cipher supported by the server
\c is single-DES, which is below the configured
\c warning threshold.
\c Do you want to continue with this connection?

This warns you that the first available encryption is not a very
secure one. Typically you would put the \q{warn below here} line
between the encryptions you consider secure and the ones you
consider substandard. By default, PuTTY supplies a preference order
intended to reflect a reasonable preference in terms of security and
speed.

In SSH-2, the encryption algorithm is negotiated independently for
each direction of the connection, although PuTTY does not support
separate configuration of the preference orders. As a result you may
get two warnings similar to the one above, possibly with different
encryptions.

Single-DES is not recommended in the SSH 2 draft protocol
standards, but one or two server implementations do support it.
PuTTY can use single-DES to interoperate with
these servers if you enable the \q{Enable legacy use of single-DES in
SSH 2} option; by default this is disabled and PuTTY will stick to
recommended ciphers.

\H{config-ssh-auth} The Auth panel

The Auth panel allows you to configure authentication options for
SSH sessions.

\S{config-ssh-tis} \q{Attempt TIS or CryptoCard authentication}

\cfg{winhelp-topic}{ssh.auth.tis}

TIS and CryptoCard authentication are simple challenge/response
forms of authentication available in SSH protocol version 1 only.
You might use them if you were using S/Key one-time passwords, for
example, or if you had a physical security token that generated
responses to authentication challenges.

With this switch enabled, PuTTY will attempt these forms of
authentication if the server is willing to try them. You will be
presented with a challenge string (which will be different every
time) and must supply the correct response in order to log in. If
your server supports this, you should talk to your system
administrator about precisely what form these challenges and
responses take.

\S{config-ssh-ki} \q{Attempt keyboard-interactive authentication}

\cfg{winhelp-topic}{ssh.auth.ki}

The SSH 2 equivalent of TIS authentication is called
\q{keyboard-interactive}. It is a flexible authentication method
using an arbitrary sequence of requests and responses; so it is not
only useful for challenge/response mechanisms such as S/Key, but it
can also be used for (for example) asking the user for a new
password when the old one has expired.

PuTTY leaves this option enabled by default, but supplies a switch
to turn it off in case you should have trouble with it.

\S{config-ssh-agentfwd} \q{Allow agent forwarding}

\cfg{winhelp-topic}{ssh.auth.agentfwd}

This option allows the SSH server to open forwarded connections back
to your local copy of Pageant. If you are not running Pageant, this
option will do nothing.

See \k{pageant} for general information on Pageant, and
\k{pageant-forward} for information on agent forwarding. Note that
there is a security risk involved with enabling this option; see
\k{pageant-security} for details.

\S{config-ssh-changeuser} \q{Allow attempted changes of username in SSH2}

\cfg{winhelp-topic}{ssh.auth.changeuser}

In the SSH 1 protocol, it is impossible to change username after
failing to authenticate. So if you mis-type your username at the
PuTTY \q{login as:} prompt, you will not be able to change it except
by restarting PuTTY.

The SSH 2 protocol \e{does} allow changes of username, in principle,
but does not make it mandatory for SSH 2 servers to accept them. In
particular, OpenSSH does not accept a change of username; once you
have sent one username, it will reject attempts to try to
authenticate as another user. (Depending on the version of OpenSSH,
it may quietly return failure for all login attempts, or it may send
an error message.)

For this reason, PuTTY will by default not prompt you for your
username more than once, in case the server complains. If you know
your server can cope with it, you can enable the \q{Allow attempted
changes of username} option to modify PuTTY's behaviour.

\S{config-ssh-privkey} \q{Private key file for authentication}

\cfg{winhelp-topic}{ssh.auth.privkey}

This box is where you enter the name of your private key file if you
are using public key authentication. See \k{pubkey} for information
about public key authentication in SSH.

This key must be in PuTTY's native format (\c{*.PPK}).

\H{config-ssh-tunnels} The Tunnels panel

The Tunnels panel allows you to configure tunnelling of other
connection types through an SSH connection.

\S{config-ssh-x11} X11 forwarding

\cfg{winhelp-topic}{ssh.tunnels.x11}

If your server lets you run X Window System applications, X11
forwarding allows you to securely give those applications access to
a local X display on your PC.

To enable X11 forwarding, check the \q{Enable X11 forwarding} box.
If your X display is somewhere unusual, you will need to enter its
location in the \q{X display location} box; if this is left blank,
PuTTY try to find a sensible default in the environment, or use the
primary local display (\c{:0}) if that fails.

See \k{using-x-forwarding} for more information about X11
forwarding.

\S2{config-ssh-x11auth} Remote X11 authentication

\cfg{winhelp-topic}{ssh.tunnels.x11auth}

If you are using X11 forwarding, the virtual X server created on the
SSH server machine will be protected by authorisation data. This
data is invented, and checked, by PuTTY.

The usual authorisation method used for this is called
\cw{MIT-MAGIC-COOKIE-1}. This is a simple password-style protocol:
the X client sends some cookie data to the server, and the server
checks that it matches the real cookie. The cookie data is sent over
an unencrypted X11 connection; so if you allow a client on a third
machine to access the virtual X server, then the cookie will be sent
in the clear.

PuTTY offers the alternative protocol \cw{XDM-AUTHORIZATION-1}. This
is a cryptographically authenticated protocol: the data sent by the
X client is different every time, and it depends on the IP address
and port of the client's end of the connection and is also stamped
with the current time. So an eavesdropper who captures an
\cw{XDM-AUTHORIZATION-1} string cannot immediately re-use it for
their own X connection.

PuTTY's support for \cw{XDM-AUTHORIZATION-1} is a somewhat
experimental feature, and may encounter several problems:

\b Some X clients probably do not even support
\cw{XDM-AUTHORIZATION-1}, so they will not know what to do with the
data PuTTY has provided.

\b This authentication mechanism will only work in SSH v2. In SSH
v1, the SSH server does not tell the client the source address of
a forwarded connection in a machine-readable format, so it's
impossible to verify the \cw{XDM-AUTHORIZATION-1} data.

\b You may find this feature causes problems with some SSH servers,
which will not clean up \cw{XDM-AUTHORIZATION-1} data after a
session, so that if you then connect to the same server using
a client which only does \cw{MIT-MAGIC-COOKIE-1} and are allocated
the same remote display number, you might find that out-of-date
authentication data is still present on your server and your X
connections fail.

PuTTY's default is \cw{MIT-MAGIC-COOKIE-1}. If you change it, you
should be sure you know what you're doing.

\S{config-ssh-portfwd} Port forwarding

\cfg{winhelp-topic}{ssh.tunnels.portfwd}

Port forwarding allows you to tunnel other types of network
connection down an SSH session. See \k{using-port-forwarding} for a
general discussion of port forwarding and how it works.

The port forwarding section in the Tunnels panel shows a list of all
the port forwardings that PuTTY will try to set up when it connects
to the server. By default no port forwardings are set up, so this
list is empty.

To add a port forwarding:

\b Set one of the \q{Local} or \q{Remote} radio buttons, depending
on whether you want to forward a local port to a remote destination
(\q{Local}) or forward a remote port to a local destination
(\q{Remote}). Alternatively, select \q{Dynamic} if you want PuTTY to
provide a local SOCKS 4/4A/5 proxy on a local port.

\b Enter a source port number into the \q{Source port} box. For
local forwardings, PuTTY will listen on this port of your PC. For
remote forwardings, your SSH server will listen on this port of the
remote machine. Note that most servers will not allow you to listen
on port numbers less than 1024.

\b If you have selected \q{Local} or \q{Remote} (this step is not
needed with \q{Dynamic}), enter a hostname and port number separated
by a colon, in the \q{Destination} box. Connections received on the
source port will be directed to this destination. For example, to
connect to a POP-3 server, you might enter
\c{popserver.example.com:110}.

\b Click the \q{Add} button. Your forwarding details should appear
in the list box.

To remove a port forwarding, simply select its details in the list
box, and click the \q{Remove} button.

In the \q{Source port} box, you can also optionally enter an IP
address to listen on, by specifying (for instance) \c{127.0.0.5:79}.
See \k{using-port-forwarding} for more information on how this
works and its restrictions.

\S{config-ssh-portfwd-localhost} Controlling the visibility of
forwarded ports

\cfg{winhelp-topic}{ssh.tunnels.portfwd.localhost}

The source port for a forwarded connection usually does not accept
connections from any machine except the SSH client or server machine
itself (for local and remote forwardings respectively). There are
controls in the Tunnels panel to change this:

\b The \q{Local ports accept connections from other hosts} option
allows you to set up local-to-remote port forwardings in such a way
that machines other than your client PC can connect to the forwarded
port. (This also applies to dynamic SOCKS forwarding.)

\b The \q{Remote ports do the same} option does the same thing for
remote-to-local port forwardings (so that machines other than the
SSH server machine can connect to the forwarded port.) Note that
this feature is only available in the SSH 2 protocol, and not all
SSH 2 servers support it (OpenSSH 3.0 does not, for example).

\H{config-ssh-bugs} The Bugs panel

Not all SSH servers work properly. Various existing servers have
bugs in them, which can make it impossible for a client to talk to
them unless it knows about the bug and works around it.

Since most servers announce their software version number at the
beginning of the SSH connection, PuTTY will attempt to detect which
bugs it can expect to see in the server and automatically enable
workarounds. However, sometimes it will make mistakes; if the server
has been deliberately configured to conceal its version number, or
if the server is a version which PuTTY's bug database does not know
about, then PuTTY will not know what bugs to expect.

The Bugs panel allows you to manually configure the bugs PuTTY
expects to see in the server. Each bug can be configured in three
states:

\b \q{Off}: PuTTY will assume the server does not have the bug.

\b \q{On}: PuTTY will assume the server \e{does} have the bug.

\b \q{Auto}: PuTTY will use the server's version number announcement
to try to guess whether or not the server has the bug.

\S{config-ssh-bug-ignore1} \q{Chokes on SSH1 ignore messages}

\cfg{winhelp-topic}{ssh.bugs.ignore1}

An ignore message (SSH_MSG_IGNORE) is a message in the SSH protocol
which can be sent from the client to the server, or from the server
to the client, at any time. Either side is required to ignore the
message whenever it receives it. PuTTY uses ignore messages to hide
the password packet in SSH1, so that a listener cannot tell the
length of the user's password; it also uses ignore messages for
connection keepalives (see \k{config-keepalive}).

If this bug is detected, PuTTY will stop using ignore messages. This
means that keepalives will stop working, and PuTTY will have to fall
back to a secondary defence against SSH1 password-length
eavesdropping. See \k{config-ssh-bug-plainpw1}. If this bug is
enabled when talking to a correct server, the session will succeed,
but keepalives will not work and the session might be more
vulnerable to eavesdroppers than it could be.

This is an SSH1-specific bug. No known SSH2 server fails to deal
with SSH2 ignore messages.

\S{config-ssh-bug-plainpw1} \q{Refuses all SSH1 password camouflage}

\cfg{winhelp-topic}{ssh.bugs.plainpw1}

When talking to an SSH1 server which cannot deal with ignore
messages (see \k{config-ssh-bug-ignore1}), PuTTY will attempt to
disguise the length of the user's password by sending additional
padding \e{within} the password packet. This is technically a
violation of the SSH1 specification, and so PuTTY will only do it
when it cannot use standards-compliant ignore messages as
camouflage. In this sense, for a server to refuse to accept a padded
password packet is not really a bug, but it does make life
inconvenient if the server can also not handle ignore messages.

If this \q{bug} is detected, PuTTY will have no choice but to send
the user's password with no form of camouflage, so that an
eavesdropping user will be easily able to find out the exact length
of the password. If this bug is enabled when talking to a correct
server, the session will succeed, but will be more vulnerable to
eavesdroppers than it could be.

This is an SSH1-specific bug. SSH2 is secure against this type of
attack.

\S{config-ssh-bug-rsa1} \q{Chokes on SSH1 RSA authentication}

\cfg{winhelp-topic}{ssh.bugs.rsa1}

Some SSH1 servers cannot deal with RSA authentication messages at
all. If Pageant is running and contains any SSH1 keys, PuTTY will
normally automatically try RSA authentication before falling back to
passwords, so these servers will crash when they see the RSA attempt.

If this bug is detected, PuTTY will go straight to password
authentication. If this bug is enabled when talking to a correct
server, the session will succeed, but of course RSA authentication
will be impossible.

This is an SSH1-specific bug.

\S{config-ssh-bug-hmac2} \q{Miscomputes SSH2 HMAC keys}

\cfg{winhelp-topic}{ssh.bugs.hmac2}

Versions 2.3.0 and below of the SSH server software from
\cw{ssh.com} compute the keys for their HMAC message authentication
codes incorrectly. A typical symptom of this problem is that PuTTY
dies unexpectedly at the beginning of the session, saying
\q{Incorrect MAC received on packet}.

If this bug is detected, PuTTY will compute its HMAC keys in the
same way as the buggy server, so that communication will still be
possible. If this bug is enabled when talking to a correct server,
communication will fail.

This is an SSH2-specific bug.

\S{config-ssh-bug-derivekey2} \q{Miscomputes SSH2 encryption keys}

\cfg{winhelp-topic}{ssh.bugs.derivekey2}

Versions below 2.0.11 of the SSH server software from \cw{ssh.com}
compute the keys for the session encryption incorrectly. This
problem can cause various error messages, such as \q{Incoming packet
was garbled on decryption}, or possibly even \q{Out of memory}.

If this bug is detected, PuTTY will compute its encryption keys in
the same way as the buggy server, so that communication will still
be possible. If this bug is enabled when talking to a correct
server, communication will fail.

This is an SSH2-specific bug.

\S{config-ssh-bug-sig} \q{Requires padding on SSH2 RSA signatures}

\cfg{winhelp-topic}{ssh.bugs.rsapad2}

Versions below 3.3 of OpenSSH require SSH2 RSA signatures to be
padded with zero bytes to the same length as the RSA key modulus.
The SSH2 draft specification says that an unpadded signature MUST be
accepted, so this is a bug. A typical symptom of this problem is
that PuTTY mysteriously fails RSA authentication once in every few
hundred attempts, and falls back to passwords.

If this bug is detected, PuTTY will pad its signatures in the way
OpenSSH expects. If this bug is enabled when talking to a correct
server, it is likely that no damage will be done, since correct
servers usually still accept padded signatures because they're used
to talking to OpenSSH.

This is an SSH2-specific bug.

\S{config-ssh-bug-dhgex} \q{Chokes on Diffie-Hellman group exchange}

\cfg{winhelp-topic}{ssh.bugs.dhgex2}

We have anecdotal evidence that some SSH servers claim to be able to
perform Diffie-Hellman group exchange, but fail to actually do so
when PuTTY tries to. If your SSH2 sessions spontaneously close
immediately after opening the PuTTY window, it might be worth
enabling the workaround for this bug to see if it helps.

We have no hard evidence that any specific version of specific
server software reliably demonstrates this bug. Therefore, PuTTY
will never \e{assume} a server has this bug; if you want the
workaround, you need to enable it manually.

This is an SSH2-specific bug.

\S{config-ssh-bug-pksessid2} \q{Misuses the session ID in PK auth}

\cfg{winhelp-topic}{ssh.bugs.pksessid2}

Versions below 2.3 of OpenSSH require SSH2 public-key authentication
to be done slightly differently: the data to be signed by the client
contains the session ID formatted in a different way. If public-key
authentication mysteriously does not work but the Event Log (see
\k{using-eventlog}) thinks it has successfully sent a signature, it
might be worth enabling the workaround for this bug to see if it
helps.

If this bug is detected, PuTTY will sign data in the way OpenSSH
expects. If this bug is enabled when talking to a correct server,
SSH2 public-key authentication will fail.

This is an SSH2-specific bug.

\H{config-file} Storing configuration in a file

PuTTY does not currently support storing its configuration in a file
instead of the Registry. However, you can work around this with a
couple of batch files.

You will need a file called (say) \c{PUTTY.BAT} which imports the
contents of a file into the Registry, then runs PuTTY, exports the
contents of the Registry back into the file, and deletes the
Registry entries. This can all be done using the Regedit command
line options, so it's all automatic. Here is what you need in
\c{PUTTY.BAT}:

\c @ECHO OFF
\c regedit /s putty.reg
\c regedit /s puttyrnd.reg
\c start /w putty.exe
\c regedit /ea new.reg HKEY_CURRENT_USER\Software\SimonTatham\PuTTY
\c copy new.reg putty.reg
\c del new.reg
\c regedit /s puttydel.reg

This batch file needs two auxiliary files: \c{PUTTYRND.REG} which
sets up an initial safe location for the \c{PUTTY.RND} random seed
file, and \c{PUTTYDEL.REG} which destroys everything in the Registry
once it's been successfully saved back to the file.

Here is \c{PUTTYDEL.REG}:

\c REGEDIT4
\c  
\c [-HKEY_CURRENT_USER\Software\SimonTatham\PuTTY]

Here is an example \c{PUTTYRND.REG} file:

\c REGEDIT4
\c  
\c [HKEY_CURRENT_USER\Software\SimonTatham\PuTTY]
\c "RandSeedFile"="a:\\putty.rnd"

You should replace \c{a:\\putty.rnd} with the location where you
want to store your random number data. If the aim is to carry around
PuTTY and its settings on one floppy, you probably want to store it
on the floppy.
