PuTTY User Manual ================= PuTTY is a free (MIT-licensed) Win32 Telnet and SSH client. This manual documents PuTTY, and its companion utilities PSCP, PSFTP, Plink, Pageant and PuTTYgen. _Note to Unix users:_ this manual currently primarily documents the Windows versions of the PuTTY utilities. Some options are therefore mentioned that are absent from the Unix version; the Unix version has features not described here; and the pterm and command-line puttygen utilities are not described at all. The only Unix-specific documentation that currently exists is the man pages. This manual is copyright 2001-2007 Simon Tatham. All rights reserved. You may distribute this documentation under the MIT licence. See appendix C for the licence text in full. Chapter 1: Introduction to PuTTY -------------------------------- PuTTY is a free SSH, Telnet and Rlogin client for 32-bit Windows systems. 1.1 What are SSH, Telnet and Rlogin? If you already know what SSH, Telnet and Rlogin are, you can safely skip on to the next section. SSH, Telnet and Rlogin are three ways of doing the same thing: logging in to a multi-user computer from another computer, over a network. Multi-user operating systems, such as Unix and VMS, usually present a command-line interface to the user, much like the `Command Prompt' or `MS-DOS Prompt' in Windows. The system prints a prompt, and you type commands which the system will obey. Using this type of interface, there is no need for you to be sitting at the same machine you are typing commands to. The commands, and responses, can be sent over a network, so you can sit at one computer and give commands to another one, or even to more than one. SSH, Telnet and Rlogin are _network protocols_ that allow you to do this. On the computer you sit at, you run a _client_, which makes a network connection to the other computer (the _server_). The network connection carries your keystrokes and commands from the client to the server, and carries the server's responses back to you. These protocols can also be used for other types of keyboard-based interactive session. In particular, there are a lot of bulletin boards, talker systems and MUDs (Multi-User Dungeons) which support access using Telnet. There are even a few that support SSH. You might want to use SSH, Telnet or Rlogin if: - you have an account on a Unix or VMS system which you want to be able to access from somewhere else - your Internet Service Provider provides you with a login account on a web server. (This might also be known as a _shell account_. A _shell_ is the program that runs on the server and interprets your commands for you.) - you want to use a bulletin board system, talker or MUD which can be accessed using Telnet. You probably do _not_ want to use SSH, Telnet or Rlogin if: - you only use Windows. Windows computers have their own ways of networking between themselves, and unless you are doing something fairly unusual, you will not need to use any of these remote login protocols. 1.2 How do SSH, Telnet and Rlogin differ? This list summarises some of the differences between SSH, Telnet and Rlogin. - SSH (which stands for `secure shell') is a recently designed, high-security protocol. It uses strong cryptography to protect your connection against eavesdropping, hijacking and other attacks. Telnet and Rlogin are both older protocols offering minimal security. - SSH and Rlogin both allow you to log in to the server without having to type a password. (Rlogin's method of doing this is insecure, and can allow an attacker to access your account on the server. SSH's method is much more secure, and typically breaking the security requires the attacker to have gained access to your actual client machine.) - SSH allows you to connect to the server and automatically send a command, so that the server will run that command and then disconnect. So you can use it in automated processing. The Internet is a hostile environment and security is everybody's responsibility. If you are connecting across the open Internet, then we recommend you use SSH. If the server you want to connect to doesn't support SSH, it might be worth trying to persuade the administrator to install it. If your client and server are both behind the same (good) firewall, it is more likely to be safe to use Telnet or Rlogin, but we still recommend you use SSH. Chapter 2: Getting started with PuTTY ------------------------------------- This chapter gives a quick guide to the simplest types of interactive login session using PuTTY. 2.1 Starting a session When you start PuTTY, you will see a dialog box. This dialog box allows you to control everything PuTTY can do. See chapter 4 for details of all the things you can control. You don't usually need to change most of the configuration options. To start the simplest kind of session, all you need to do is to enter a few basic parameters. In the `Host Name' box, enter the Internet host name of the server you want to connect to. You should have been told this by the provider of your login account. Now select a login protocol to use, from the `Connection type' buttons. For a login session, you should select Telnet, Rlogin or SSH. See section 1.2 for a description of the differences between the three protocols, and advice on which one to use. The fourth protocol, _Raw_, is not used for interactive login sessions; you would usually use this for debugging other Internet services (see section 3.6). The fifth option, _Serial_, is used for connecting to a local serial line, and works somewhat differently: see section 3.7 for more information on this. When you change the selected protocol, the number in the `Port' box will change. This is normal: it happens because the various login services are usually provided on different network ports by the server machine. Most servers will use the standard port numbers, so you will not need to change the port setting. If your server provides login services on a non-standard port, your system administrator should have told you which one. (For example, many MUDs run Telnet service on a port other than 23.) Once you have filled in the `Host Name', `Protocol', and possibly `Port' settings, you are ready to connect. Press the `Open' button at the bottom of the dialog box, and PuTTY will begin trying to connect you to the server. 2.2 Verifying the host key (SSH only) If you are not using the SSH protocol, you can skip this section. If you are using SSH to connect to a server for the first time, you will probably see a message looking something like this: The server's host key is not cached in the registry. You have no guarantee that the server is the computer you think it is. The server's rsa2 key fingerprint is: ssh-rsa 1024 7b:e5:6f:a7:f4:f9:81:62:5c:e3:1f:bf:8b:57:6c:5a If you trust this host, hit Yes to add the key to PuTTY's cache and carry on connecting. If you want to carry on connecting just once, without adding the key to the cache, hit No. If you do not trust this host, hit Cancel to abandon the connection. This is a feature of the SSH protocol. It is designed to protect you against a network attack known as _spoofing_: secretly redirecting your connection to a different computer, so that you send your password to the wrong machine. Using this technique, an attacker would be able to learn the password that guards your login account, and could then log in as if they were you and use the account for their own purposes. To prevent this attack, each server has a unique identifying code, called a _host key_. These keys are created in a way that prevents one server from forging another server's key. So if you connect to a server and it sends you a different host key from the one you were expecting, PuTTY can warn you that the server may have been switched and that a spoofing attack might be in progress. PuTTY records the host key for each server you connect to, in the Windows Registry. Every time you connect to a server, it checks that the host key presented by the server is the same host key as it was the last time you connected. If it is not, you will see a warning, and you will have the chance to abandon your connection before you type any private information (such as a password) into it. However, when you connect to a server you have not connected to before, PuTTY has no way of telling whether the host key is the right one or not. So it gives the warning shown above, and asks you whether you want to trust this host key or not. Whether or not to trust the host key is your choice. If you are connecting within a company network, you might feel that all the network users are on the same side and spoofing attacks are unlikely, so you might choose to trust the key without checking it. If you are connecting across a hostile network (such as the Internet), you should check with your system administrator, perhaps by telephone or in person. (Some modern servers have more than one host key. If the system administrator sends you more than one fingerprint, you should make sure the one PuTTY shows you is on the list, but it doesn't matter which one it is.) 2.3 Logging in After you have connected, and perhaps verified the server's host key, you will be asked to log in, probably using a username and a password. Your system administrator should have provided you with these. Enter the username and the password, and the server should grant you access and begin your session. If you have mistyped your password, most servers will give you several chances to get it right. If you are using SSH, be careful not to type your username wrongly, because you will not have a chance to correct it after you press Return; many SSH servers do not permit you to make two login attempts using different usernames. If you type your username wrongly, you must close PuTTY and start again. If your password is refused but you are sure you have typed it correctly, check that Caps Lock is not enabled. Many login servers, particularly Unix computers, treat upper case and lower case as different when checking your password; so if Caps Lock is on, your password will probably be refused. 2.4 After logging in After you log in to the server, what happens next is up to the server! Most servers will print some sort of login message and then present a prompt, at which you can type commands which the server will carry out. Some servers will offer you on-line help; others might not. If you are in doubt about what to do next, consult your system administrator. 2.5 Logging out When you have finished your session, you should log out by typing the server's own logout command. This might vary between servers; if in doubt, try `logout' or `exit', or consult a manual or your system administrator. When the server processes your logout command, the PuTTY window should close itself automatically. You _can_ close a PuTTY session using the Close button in the window border, but this might confuse the server - a bit like hanging up a telephone unexpectedly in the middle of a conversation. We recommend you do not do this unless the server has stopped responding to you and you cannot close the window any other way. Chapter 3: Using PuTTY ---------------------- This chapter provides a general introduction to some more advanced features of PuTTY. For extreme detail and reference purposes, chapter 4 is likely to contain more information. 3.1 During your session A lot of PuTTY's complexity and features are in the configuration panel. Once you have worked your way through that and started a session, things should be reasonably simple after that. Nevertheless, there are a few more useful features available. 3.1.1 Copying and pasting text Often in a PuTTY session you will find text on your terminal screen which you want to type in again. Like most other terminal emulators, PuTTY allows you to copy and paste the text rather than having to type it again. Also, copy and paste uses the Windows clipboard, so that you can paste (for example) URLs into a web browser, or paste from a word processor or spreadsheet into your terminal session. PuTTY's copy and paste works entirely with the mouse. In order to copy text to the clipboard, you just click the left mouse button in the terminal window, and drag to select text. When you let go of the button, the text is _automatically_ copied to the clipboard. You do not need to press Ctrl-C or Ctrl-Ins; in fact, if you do press Ctrl-C, PuTTY will send a Ctrl-C character down your session to the server where it will probably cause a process to be interrupted. Pasting is done using the right button (or the middle mouse button, if you have a three-button mouse and have set it up; see section 4.11.2). (Pressing Shift-Ins, or selecting `Paste' from the Ctrl+right-click context menu, have the same effect.) When you click the right mouse button, PuTTY will read whatever is in the Windows clipboard and paste it into your session, _exactly_ as if it had been typed at the keyboard. (Therefore, be careful of pasting formatted text into an editor that does automatic indenting; you may find that the spaces pasted from the clipboard plus the spaces added by the editor add up to too many spaces and ruin the formatting. There is nothing PuTTY can do about this.) If you double-click the left mouse button, PuTTY will select a whole word. If you double-click, hold down the second click, and drag the mouse, PuTTY will select a sequence of whole words. (You can adjust precisely what PuTTY considers to be part of a word; see section 4.11.5.) If you _triple_-click, or triple-click and drag, then PuTTY will select a whole line or sequence of lines. If you want to select a rectangular region instead of selecting to the end of each line, you can do this by holding down Alt when you make your selection. (You can also configure rectangular selection to be the default, and then holding down Alt gives the normal behaviour instead. See section 4.11.4 for details.) If you have a middle mouse button, then you can use it to adjust an existing selection if you selected something slightly wrong. (If you have configured the middle mouse button to paste, then the right mouse button does this instead.) Click the button on the screen, and you can pick up the nearest end of the selection and drag it to somewhere else. It's possible for the server to ask to handle mouse clicks in the PuTTY window itself. If this happens, the mouse pointer will turn into an arrow, and using the mouse to copy and paste will only work if you hold down Shift. See section 4.6.2 and section 4.11.3 for details of this feature and how to configure it. 3.1.2 Scrolling the screen back PuTTY keeps track of text that has scrolled up off the top of the terminal. So if something appears on the screen that you want to read, but it scrolls too fast and it's gone by the time you try to look for it, you can use the scrollbar on the right side of the window to look back up the session history and find it again. As well as using the scrollbar, you can also page the scrollback up and down by pressing Shift-PgUp and Shift-PgDn. You can scroll a line at a time using Ctrl-PgUp and Ctrl-PgDn. These are still available if you configure the scrollbar to be invisible. By default the last 200 lines scrolled off the top are preserved for you to look at. You can increase (or decrease) this value using the configuration box; see section 4.7.3. 3.1.3 The System menu If you click the left mouse button on the icon in the top left corner of PuTTY's terminal window, or click the right mouse button on the title bar, you will see the standard Windows system menu containing items like Minimise, Move, Size and Close. PuTTY's system menu contains extra program features in addition to the Windows standard options. These extra menu commands are described below. (These options are also available in a context menu brought up by holding Ctrl and clicking with the right mouse button anywhere in the PuTTY window.) 3.1.3.1 The PuTTY Event Log If you choose `Event Log' from the system menu, a small window will pop up in which PuTTY logs significant events during the connection. Most of the events in the log will probably take place during session startup, but a few can occur at any point in the session, and one or two occur right at the end. You can use the mouse to select one or more lines of the Event Log, and hit the Copy button to copy them to the clipboard. If you are reporting a bug, it's often useful to paste the contents of the Event Log into your bug report. 3.1.3.2 Special commands Depending on the protocol used for the current session, there may be a submenu of `special commands'. These are protocol-specific tokens, such as a `break' signal, that can be sent down a connection in addition to normal data. Their precise effect is usually up to the server. Currently only Telnet, SSH, and serial connections have special commands. The following special commands are available in Telnet: - Are You There - Break - Synch - Erase Character PuTTY can also be configured to send this when the Backspace key is pressed; see section 4.16.3. - Erase Line - Go Ahead - No Operation Should have no effect. - Abort Process - Abort Output - Interrupt Process PuTTY can also be configured to send this when Ctrl-C is typed; see section 4.16.3. - Suspend Process PuTTY can also be configured to send this when Ctrl-Z is typed; see section 4.16.3. - End Of Record - End Of File In an SSH connection, the following special commands are available: - IGNORE message Should have no effect. - Repeat key exchange Only available in SSH-2. Forces a repeat key exchange immediately (and resets associated timers and counters). For more information about repeat key exchanges, see section 4.19.2. - Break Only available in SSH-2, and only during a session. Optional extension; may not be supported by server. PuTTY requests the server's default break length. - Signals (SIGINT, SIGTERM etc) Only available in SSH-2, and only during a session. Sends various POSIX signals. Not honoured by all servers. With a serial connection, the only available special command is `Break'. 3.1.3.3 Starting new sessions PuTTY's system menu provides some shortcut ways to start new sessions: - Selecting `New Session' will start a completely new instance of PuTTY, and bring up the configuration box as normal. - Selecting `Duplicate Session' will start a session in a new window with precisely the same options as your current one - connecting to the same host using the same protocol, with all the same terminal settings and everything. - In an inactive window, selecting `Restart Session' will do the same as `Duplicate Session', but in the current window. - The `Saved Sessions' submenu gives you quick access to any sets of stored session details you have previously saved. See section 4.1.2 for details of how to create saved sessions. 3.1.3.4 Changing your session settings If you select `Change Settings' from the system menu, PuTTY will display a cut-down version of its initial configuration box. This allows you to adjust most properties of your current session. You can change the terminal size, the font, the actions of various keypresses, the colours, and so on. Some of the options that are available in the main configuration box are not shown in the cut-down Change Settings box. These are usually options which don't make sense to change in the middle of a session (for example, you can't switch from SSH to Telnet in mid-session). You can save the current settings to a saved session for future use from this dialog box. See section 4.1.2 for more on saved sessions. 3.1.3.5 Copy All to Clipboard This system menu option provides a convenient way to copy the whole contents of the terminal screen (up to the last nonempty line) and scrollback to the clipboard in one go. 3.1.3.6 Clearing and resetting the terminal The `Clear Scrollback' option on the system menu tells PuTTY to discard all the lines of text that have been kept after they scrolled off the top of the screen. This might be useful, for example, if you displayed sensitive information and wanted to make sure nobody could look over your shoulder and see it. (Note that this only prevents a casual user from using the scrollbar to view the information; the text is not guaranteed not to still be in PuTTY's memory.) The `Reset Terminal' option causes a full reset of the terminal emulation. A VT-series terminal is a complex piece of software and can easily get into a state where all the text printed becomes unreadable. (This can happen, for example, if you accidentally output a binary file to your terminal.) If this happens, selecting Reset Terminal should sort it out. 3.1.3.7 Full screen mode If you find the title bar on a maximised window to be ugly or distracting, you can select Full Screen mode to maximise PuTTY `even more'. When you select this, PuTTY will expand to fill the whole screen and its borders, title bar and scrollbar will disappear. (You can configure the scrollbar not to disappear in full-screen mode if you want to keep it; see section 4.7.3.) When you are in full-screen mode, you can still access the system menu if you click the left mouse button in the _extreme_ top left corner of the screen. 3.2 Creating a log file of your session For some purposes you may find you want to log everything that appears on your screen. You can do this using the `Logging' panel in the configuration box. To begin a session log, select `Change Settings' from the system menu and go to the Logging panel. Enter a log file name, and select a logging mode. (You can log all session output including the terminal control sequences, or you can just log the printable text. It depends what you want the log for.) Click `Apply' and your log will be started. Later on, you can go back to the Logging panel and select `Logging turned off completely' to stop logging; then PuTTY will close the log file and you can safely read it. See section 4.2 for more details and options. 3.3 Altering your character set configuration If you find that special characters (accented characters, for example, or line-drawing characters) are not being displayed correctly in your PuTTY session, it may be that PuTTY is interpreting the characters sent by the server according to the wrong _character set_. There are a lot of different character sets available, so it's entirely possible for this to happen. If you click `Change Settings' and look at the `Translation' panel, you should see a large number of character sets which you can select, and other related options. Now all you need is to find out which of them you want! (See section 4.10 for more information.) 3.4 Using X11 forwarding in SSH The SSH protocol has the ability to securely forward X Window System applications over your encrypted SSH connection, so that you can run an application on the SSH server machine and have it put its windows up on your local machine without sending any X network traffic in the clear. In order to use this feature, you will need an X display server for your Windows machine, such as Cygwin/X, X-Win32, or Exceed. This will probably install itself as display number 0 on your local machine; if it doesn't, the manual for the X server should tell you what it does do. You should then tick the `Enable X11 forwarding' box in the Tunnels panel (see section 4.22) before starting your SSH session. The `X display location' box is blank by default, which means that PuTTY will try to use a sensible default such as `:0', which is the usual display location where your X server will be installed. If that needs changing, then change it. Now you should be able to log in to the SSH server as normal. To check that X forwarding has been successfully negotiated during connection startup, you can check the PuTTY Event Log (see section 3.1.3.1). It should say something like this: 2001-12-05 17:22:01 Requesting X11 forwarding 2001-12-05 17:22:02 X11 forwarding enabled If the remote system is Unix or Unix-like, you should also be able to see that the `DISPLAY' environment variable has been set to point at display 10 or above on the SSH server machine itself: fred@unixbox:~$ echo $DISPLAY unixbox:10.0 If this works, you should then be able to run X applications in the remote session and have them display their windows on your PC. Note that if your PC X server requires authentication to connect, then PuTTY cannot currently support it. If this is a problem for you, you should mail the PuTTY authors and give details (see appendix B). For more options relating to X11 forwarding, see section 4.22. 3.5 Using port forwarding in SSH The SSH protocol has the ability to forward arbitrary network connections over your encrypted SSH connection, to avoid the network traffic being sent in clear. For example, you could use this to connect from your home computer to a POP-3 server on a remote machine without your POP-3 password being visible to network sniffers. In order to use port forwarding to connect from your local machine to a port on a remote server, you need to: - Choose a port number on your local machine where PuTTY should listen for incoming connections. There are likely to be plenty of unused port numbers above 3000. (You can also use a local loopback address here; see below for more details.) - Now, before you start your SSH connection, go to the Tunnels panel (see section 4.23). Make sure the `Local' radio button is set. Enter the local port number into the `Source port' box. Enter the destination host name and port number into the `Destination' box, separated by a colon (for example, `popserver.example.com:110' to connect to a POP-3 server). - Now click the `Add' button. The details of your port forwarding should appear in the list box. Now start your session and log in. (Port forwarding will not be enabled until after you have logged in; otherwise it would be easy to perform completely anonymous network attacks, and gain access to anyone's virtual private network.) To check that PuTTY has set up the port forwarding correctly, you can look at the PuTTY Event Log (see section 3.1.3.1). It should say something like this: 2001-12-05 17:22:10 Local port 3110 forwarding to popserver.example.com:110 Now if you connect to the source port number on your local PC, you should find that it answers you exactly as if it were the service running on the destination machine. So in this example, you could then configure an e-mail client to use `localhost:3110' as a POP- 3 server instead of `popserver.example.com:110'. (Of course, the forwarding will stop happening when your PuTTY session closes down.) You can also forward ports in the other direction: arrange for a particular port number on the _server_ machine to be forwarded back to your PC as a connection to a service on your PC or near it. To do this, just select the `Remote' radio button instead of the `Local' one. The `Source port' box will now specify a port number on the _server_ (note that most servers will not allow you to use port numbers under 1024 for this purpose). An alternative way to forward local connections to remote hosts is to use dynamic SOCKS proxying. For this, you will need to select the `Dynamic' radio button instead of `Local', and then you should not enter anything into the `Destination' box (it will be ignored). This will cause PuTTY to listen on the port you have specified, and provide a SOCKS proxy service to any programs which connect to that port. So, in particular, you can forward other PuTTY connections through it by setting up the Proxy control panel (see section 4.15 for details). 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: - The `Local ports accept connections from other hosts' option allows you to set up local-to-remote port forwardings (including dynamic port forwardings) in such a way that machines other than your client PC can connect to the forwarded port. - The `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 honour it (in OpenSSH, for example, it's usually disabled by default). You can also specify an IP address to listen on. Typically a Windows machine can be asked to listen on any single IP address in the 127.*.*.* range, and all of these are loopback addresses available only to the local machine. So if you forward (for example) `127.0.0.5:79' to a remote machine's finger port, then you should be able to run commands such as `finger fred@127.0.0.5'. This can be useful if the program connecting to the forwarded port doesn't allow you to change the port number it uses. This feature is available for local-to-remote forwarded ports; SSH-1 is unable to support it for remote-to-local ports, while SSH-2 can support it in theory but servers will not necessarily cooperate. (Note that if you're using Windows XP Service Pack 2, you may need to obtain a fix from Microsoft in order to use addresses like 127.0.0.5 - see question A.7.20.) 3.6 Making raw TCP connections A lot of Internet protocols are composed of commands and responses in plain text. For example, SMTP (the protocol used to transfer e- mail), NNTP (the protocol used to transfer Usenet news), and HTTP (the protocol used to serve Web pages) all consist of commands in readable plain text. Sometimes it can be useful to connect directly to one of these services and speak the protocol `by hand', by typing protocol commands and watching the responses. On Unix machines, you can do this using the system's `telnet' command to connect to the right port number. For example, `telnet mailserver.example.com 25' might enable you to talk directly to the SMTP service running on a mail server. Although the Unix `telnet' program provides this functionality, the protocol being used is not really Telnet. Really there is no actual protocol at all; the bytes sent down the connection are exactly the ones you type, and the bytes shown on the screen are exactly the ones sent by the server. Unix `telnet' will attempt to detect or guess whether the service it is talking to is a real Telnet service or not; PuTTY prefers to be told for certain. In order to make a debugging connection to a service of this type, you simply select the fourth protocol name, `Raw', from the `Protocol' buttons in the `Session' configuration panel. (See section 4.1.1.) You can then enter a host name and a port number, and make the connection. 3.7 Connecting to a local serial line PuTTY can connect directly to a local serial line as an alternative to making a network connection. In this mode, text typed into the PuTTY window will be sent straight out of your computer's serial port, and data received through that port will be displayed in the PuTTY window. You might use this mode, for example, if your serial port is connected to another computer which has a serial connection. To make a connection of this type, simply select `Serial' from the `Connection type' radio buttons on the `Session' configuration panel (see section 4.1.1). The `Host Name' and `Port' boxes will transform into `Serial line' and `Speed', allowing you to specify which serial line to use (if your computer has more than one) and what speed (baud rate) to use when transferring data. For further configuration options (data bits, stop bits, parity, flow control), you can use the `Serial' configuration panel (see section 4.25). After you start up PuTTY in serial mode, you might find that you have to make the first move, by sending some data out of the serial line in order to notify the device at the other end that someone is there for it to talk to. This probably depends on the device. If you start up a PuTTY serial session and nothing appears in the window, try pressing Return a few times and see if that helps. A serial line provides no well defined means for one end of the connection to notify the other that the connection is finished. Therefore, PuTTY in serial mode will remain connected until you close the window using the close button. 3.8 The PuTTY command line PuTTY can be made to do various things without user intervention by supplying command-line arguments (e.g., from a command prompt window, or a Windows shortcut). 3.8.1 Starting a session from the command line These options allow you to bypass the configuration window and launch straight into a session. To start a connection to a server called `host': putty.exe [-ssh | -telnet | -rlogin | -raw] [user@]host If this syntax is used, settings are taken from the Default Settings (see section 4.1.2); `user' overrides these settings if supplied. Also, you can specify a protocol, which will override the default protocol (see section 3.8.3.2). For telnet sessions, the following alternative syntax is supported (this makes PuTTY suitable for use as a URL handler for telnet URLs in web browsers): putty.exe telnet://host[:port]/ In order to start an existing saved session called `sessionname', use the `-load' option (described in section 3.8.3.1). putty.exe -load "session name" 3.8.2 `-cleanup' If invoked with the `-cleanup' option, rather than running as normal, PuTTY will remove its registry entries and random seed file from the local machine (after confirming with the user). Note that on multi-user systems, `-cleanup' only removes registry entries and files associated with the currently logged-in user. 3.8.3 Standard command-line options PuTTY and its associated tools support a range of command-line options, most of which are consistent across all the tools. This section lists the available options in all tools. Options which are specific to a particular tool are covered in the chapter about that tool. 3.8.3.1 `-load': load a saved session The `-load' option causes PuTTY to load configuration details out of a saved session. If these details include a host name, then this option is all you need to make PuTTY start a session. You need double quotes around the session name if it contains spaces. If you want to create a Windows shortcut to start a PuTTY saved session, this is the option you should use: your shortcut should call something like d:\path\to\putty.exe -load "my session" (Note that PuTTY itself supports an alternative form of this option, for backwards compatibility. If you execute `putty @sessionname' it will have the same effect as `putty -load "sessionname"'. With the `@' form, no double quotes are required, and the `@' sign must be the very first thing on the command line. This form of the option is deprecated.) 3.8.3.2 Selecting a protocol: `-ssh', `-telnet', `-rlogin', `-raw' To choose which protocol you want to connect with, you can use one of these options: - `-ssh' selects the SSH protocol. - `-telnet' selects the Telnet protocol. - `-rlogin' selects the Rlogin protocol. - `-raw' selects the raw protocol. These options are not available in the file transfer tools PSCP and PSFTP (which only work with the SSH protocol). These options are equivalent to the protocol selection buttons in the Session panel of the PuTTY configuration box (see section 4.1.1). 3.8.3.3 `-v': increase verbosity Most of the PuTTY tools can be made to tell you more about what they are doing by supplying the `-v' option. If you are having trouble when making a connection, or you're simply curious, you can turn this switch on and hope to find out more about what is happening. 3.8.3.4 `-l': specify a login name You can specify the user name to log in as on the remote server using the `-l' option. For example, `plink login.example.com - l fred'. These options are equivalent to the username selection box in the Connection panel of the PuTTY configuration box (see section 4.14.1). 3.8.3.5 `-L', `-R' and `-D': set up port forwardings As well as setting up port forwardings in the PuTTY configuration (see section 4.23), you can also set up forwardings on the command line. The command-line options work just like the ones in Unix `ssh' programs. To forward a local port (say 5110) to a remote destination (say popserver.example.com port 110), you can write something like one of these: putty -L 5110:popserver.example.com:110 -load mysession plink mysession -L 5110:popserver.example.com:110 To forward a remote port to a local destination, just use the `-R' option instead of `-L': putty -R 5023:mytelnetserver.myhouse.org:23 -load mysession plink mysession -R 5023:mytelnetserver.myhouse.org:23 To specify an IP address for the listening end of the tunnel, prepend it to the argument: plink -L 127.0.0.5:23:localhost:23 myhost To set up SOCKS-based dynamic port forwarding on a local port, use the `-D' option. For this one you only have to pass the port number: putty -D 4096 -load mysession For general information on port forwarding, see section 3.5. These options are not available in the file transfer tools PSCP and PSFTP. 3.8.3.6 `-m': read a remote command or script from a file The `-m' option performs a similar function to the `Remote command' box in the SSH panel of the PuTTY configuration box (see section 4.18.1). However, the `-m' option expects to be given a local file name, and it will read a command from that file. With some servers (particularly Unix systems), you can even put multiple lines in this file and execute more than one command in sequence, or a whole shell script; but this is arguably an abuse, and cannot be expected to work on all servers. In particular, it is known _not_ to work with certain `embedded' servers, such as Cisco routers. This option is not available in the file transfer tools PSCP and PSFTP. 3.8.3.7 `-P': specify a port number The `-P' option is used to specify the port number to connect to. If you have a Telnet server running on port 9696 of a machine instead of port 23, for example: putty -telnet -P 9696 host.name plink -telnet -P 9696 host.name (Note that this option is more useful in Plink than in PuTTY, because in PuTTY you can write `putty -telnet host.name 9696' in any case.) This option is equivalent to the port number control in the Session panel of the PuTTY configuration box (see section 4.1.1). 3.8.3.8 `-pw': specify a password A simple way to automate a remote login is to supply your password on the command line. This is _not recommended_ for reasons of security. If you possibly can, we recommend you set up public-key authentication instead. See chapter 8 for details. Note that the `-pw' option only works when you are using the SSH protocol. Due to fundamental limitations of Telnet and Rlogin, these protocols do not support automated password authentication. 3.8.3.9 `-agent' and `-noagent': control use of Pageant for authentication The `-agent' option turns on SSH authentication using Pageant, and `-noagent' turns it off. These options are only meaningful if you are using SSH. See chapter 9 for general information on Pageant. These options are equivalent to the agent authentication checkbox in the Auth panel of the PuTTY configuration box (see section 4.20.2). 3.8.3.10 `-A' and `-a': control agent forwarding The `-A' option turns on SSH agent forwarding, and `-a' turns it off. These options are only meaningful if you are using SSH. See chapter 9 for general information on Pageant, and section 9.4 for information on agent forwarding. Note that there is a security risk involved with enabling this option; see section 9.5 for details. These options are equivalent to the agent forwarding checkbox in the Auth panel of the PuTTY configuration box (see section 4.20.5). These options are not available in the file transfer tools PSCP and PSFTP. 3.8.3.11 `-X' and `-x': control X11 forwarding The `-X' option turns on X11 forwarding in SSH, and `-x' turns it off. These options are only meaningful if you are using SSH. For information on X11 forwarding, see section 3.4. These options are equivalent to the X11 forwarding checkbox in the Tunnels panel of the PuTTY configuration box (see section 4.22). These options are not available in the file transfer tools PSCP and PSFTP. 3.8.3.12 `-t' and `-T': control pseudo-terminal allocation The `-t' option ensures PuTTY attempts to allocate a pseudo-terminal at the server, and `-T' stops it from allocating one. These options are only meaningful if you are using SSH. These options are equivalent to the `Don't allocate a pseudo- terminal' checkbox in the SSH panel of the PuTTY configuration box (see section 4.21.1). These options are not available in the file transfer tools PSCP and PSFTP. 3.8.3.13 `-N': suppress starting a shell or command The `-N' option prevents PuTTY from attempting to start a shell or command on 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 option is equivalent to the `Don't start a shell or command at all' checkbox in the SSH panel of the PuTTY configuration box (see section 4.18.2). This option is not available in the file transfer tools PSCP and PSFTP. 3.8.3.14 `-nc': make a remote network connection in place of a remote shell or command The `-nc' option prevents Plink (or PuTTY) from attempting to start a shell or command on the remote server. Instead, it will instruct the remote server to open a network connection to a host name and port number specified by you, and treat that network connection as if it were the main session. You specify a host and port as an argument to the `-nc' option, with a colon separating the host name from the port number, like this: plink host1.example.com -nc host2.example.com:1234 You might want to use this feature if you needed to make an SSH connection to a target host which you can only reach by going through a proxy host, and rather than using port forwarding you prefer to use the local proxy feature (see section 4.15.1 for more about local proxies). In this situation you might select `Local' proxy type, set your local proxy command to be `plink %proxyhost - nc %host:%port', enter the target host name on the Session panel, and enter the directly reachable proxy host name on the Proxy panel. This feature is only available in SSH protocol version 2 (since the version 1 protocol assumes you will always want to run a shell). It is not available in the file transfer tools PSCP and PSFTP. It is available in PuTTY itself, although it is unlikely to be very useful in any tool other than Plink. Also, `-nc' uses the same server functionality as port forwarding, so it will not work if your server administrator has disabled port forwarding. (The option is named `-nc' after the Unix program `nc', short for `netcat'. The command `plink host1 -nc host2:port' is very similar in functionality to `plink host1 nc host2 port', which invokes `nc' on the server and tells it to connect to the specified destination. However, Plink's built-in `-nc' option does not depend on the `nc' program being installed on the server.) 3.8.3.15 `-C': enable compression The `-C' option enables compression of the data sent across the network. This option is only meaningful if you are using SSH. This option is equivalent to the `Enable compression' checkbox in the SSH panel of the PuTTY configuration box (see section 4.18.3). 3.8.3.16 `-1' and `-2': specify an SSH protocol version The `-1' and `-2' options force PuTTY to use version 1 or version 2 of the SSH protocol. These options are only meaningful if you are using SSH. These options are equivalent to selecting your preferred SSH protocol version as `1 only' or `2 only' in the SSH panel of the PuTTY configuration box (see section 4.18.4). 3.8.3.17 `-4' and `-6': specify an Internet protocol version The `-4' and `-6' options force PuTTY to use the older Internet protocol IPv4 or the newer IPv6. These options are equivalent to selecting your preferred Internet protocol version as `IPv4' or `IPv6' in the Connection panel of the PuTTY configuration box (see section 4.13.4). 3.8.3.18 `-i': specify an SSH private key The `-i' option allows you to specify the name of a private key file in `*.PPK' format which PuTTY will use to authenticate with the server. This option is only meaningful if you are using SSH. For general information on public-key authentication, see chapter 8. This option is equivalent to the `Private key file for authentication' box in the Auth panel of the PuTTY configuration box (see section 4.20.7). 3.8.3.19 `-pgpfp': display PGP key fingerprints This option causes the PuTTY tools not to run as normal, but instead to display the fingerprints of the PuTTY PGP Master Keys, in order to aid with verifying new versions. See appendix E for more information. Chapter 4: 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 `Change Settings' from the window menu. 4.1 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. 4.1.1 The host name section The top box on the Session panel, labelled `Specify your connection by host name', contains the details that need to be filled in before PuTTY can open a session at all. - The `Host Name' box is where you type the name, or the IP address, of the server you want to connect to. - The `Connection type' radio buttons let you choose what type of connection you want to make: a raw connection, a Telnet connection, an Rlogin connection, an SSH connection, or a connection to a local serial line. (See section 1.2 for a summary of the differences between SSH, Telnet and rlogin; see section 3.6 for an explanation of `raw' connections; see section 3.7 for information about using a serial line.) - The `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 `Port' box yourself. If you select `Serial' from the `Connection type' radio buttons, the `Host Name' and `Port' boxes are replaced by `Serial line' and `Speed'; see section 4.25 for more details of these. 4.1.2 Loading and storing saved sessions 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 _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. - 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 `Default Settings' entry in the saved sessions list, with a single click. Then press the `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. - 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 `Saved Sessions' input box. (The server name is often a good choice for a saved session name.) Then press the `Save' button. Your saved session name should now appear in the list box. You can also save settings in mid-session, from the `Change Settings' dialog. Settings changed since the start of the session will be saved with their current values; as well as settings changed through the dialog, this includes changes in window size, window title changes sent by the server, and so on. - To reload a saved session: single-click to select the session name in the list box, and then press the `Load' button. Your saved settings should all appear in the configuration panel. - 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 `Save' button. The new settings will be saved over the top of the old ones. To save the new settings under a different name, you can enter the new name in the `Saved Sessions' box, or single-click to select a session name in the list box to overwrite that session. To save `Default Settings', you must single-click the name before saving. - To start a saved session immediately: double-click on the session name in the list box. - To delete a saved session: single-click to select the session name in the list box, and then press the `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 HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\Sessions If you need to store them in a file, you could try the method described in section 4.26. 4.1.3 `Close Window on Exit' Finally in the Session panel, there is an option labelled `Close Window on Exit'. This controls whether the PuTTY terminal 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. `Close Window On Exit' has three settings. `Always' means always close the window on exit; `Never' means never close on exit (always leave the window open, but inactive). The third setting, and the default one, is `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. 4.2 The Logging panel 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: - `None'. This is the default option; in this mode PuTTY will not create a log file at all. - `Printable output'. 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. - `All session output'. In this mode, _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. - `SSH packets'. 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 (as well as Event Log entries). 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. _BE WARNED_ that if you log in using a password, the password can appear in the log file; see section 4.2.4 for options that may help to remove sensitive material from the log file before you send it to anyone else. - `SSH packets and raw data'. In this mode, as well as the decrypted packets (as in the previous mode), the _raw_ (encrypted, compressed, etc) packets are _also_ logged. This could be useful to diagnose corruption in transit. (The same caveats as the previous mode apply, of course.) Note that the non-SSH logging options (`Printable output' and `All session output') only work with PuTTY proper; in programs without terminal emulation (such as Plink), they will have no effect, even if enabled via saved settings. 4.2.1 `Log file name' In this edit box you enter the name of the file you want to log the session to. The `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 `&' 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: - `&Y' will be replaced by the current year, as four digits. - `&M' will be replaced by the current month, as two digits. - `&D' will be replaced by the current day of the month, as two digits. - `&T' will be replaced by the current time, as six digits (HHMMSS) with no punctuation. - `&H' will be replaced by the host name you are connecting to. For example, if you enter the host name `c:\puttylogs\log-&h-&y&m&d- &t.dat', you will end up with files looking like log-server1.example.com-20010528-110859.dat log-unixbox.somewhere.org-20010611-221001.dat 4.2.2 `What to do if the log file already 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 _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. 4.2.3 `Flush log file frequently' This option allows you to control how frequently logged data is flushed to disc. By default, PuTTY will flush data as soon as it is displayed, so that if you view the log file while a session is still open, it will be up to date; and if the client system crashes, there's a greater chance that the data will be preserved. However, this can incur a performance penalty. If PuTTY is running slowly with logging enabled, you could try unchecking this option. Be warned that the log file may not always be up to date as a result (although it will of course be flushed when it is closed, for instance at the end of a session). 4.2.4 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). 4.2.4.1 `Omit known password fields' When checked, decrypted password fields are removed from the log of transmitted packets. (This includes any user responses to challenge- response authentication methods such as `keyboard-interactive'.) This does not include X11 authentication data if using X11 forwarding. Note that this will only omit data that PuTTY _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. 4.2.4.2 `Omit session data' When checked, all decrypted `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. 4.3 The Terminal panel The Terminal configuration panel allows you to control the behaviour of PuTTY's terminal emulation. 4.3.1 `Auto wrap mode initially on' 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 _default_ state, which will be restored when you reset the terminal (see section 3.1.3.6). However, if you modify this option in mid-session using `Change Settings', it will take effect immediately. 4.3.2 `DEC Origin Mode initially on' 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 _default_ state, which will be restored when you reset the terminal (see section 3.1.3.6). However, if you modify this option in mid-session using `Change Settings', it will take effect immediately. 4.3.3 `Implicit CR in every LF' 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: First line of text Second line Third line If this happens to you, try enabling the `Implicit CR in every LF' option, and things might go back to normal: First line of text Second line Third line 4.3.4 `Use background colour to erase screen' Not all terminals agree on what colour to turn the screen when the server sends a `clear screen' sequence. Some terminals believe the screen should always be cleared to the _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 _current_ background colour. Background-colour erase can be turned on and off by control sequences sent by the server. This configuration option controls the _default_ state, which will be restored when you reset the terminal (see section 3.1.3.6). However, if you modify this option in mid- session using `Change Settings', it will take effect immediately. 4.3.5 `Enable blinking text' 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 _default_ state, which will be restored when you reset the terminal (see section 3.1.3.6). However, if you modify this option in mid-session using `Change Settings', it will take effect immediately. 4.3.6 `Answerback to ^E' 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 `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 `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 _not_ the feature of PuTTY which the server will typically use to determine your terminal type. That feature is the `Terminal-type string' in the Connection panel; see section 4.14.2 for details. You can include control characters in the answerback string using `^C' notation. (Use `^~' to get a literal `^'.) 4.3.7 `Local echo' With local echo disabled, characters you type into the PuTTY window are not echoed in the window _by PuTTY_. They are simply sent to the server. (The _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. 4.3.8 `Local line editing' 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 (section 4.3.7). This makes it ideal for use in raw mode 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. 4.3.9 Remote-controlled 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 `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, `\\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 _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 `None (printing disabled)' from the printer selection list. This is the default state. 4.4 The Keyboard panel The Keyboard configuration panel allows you to control the behaviour of the keyboard in PuTTY. The correct state for many of these settings depends on what the server to which PuTTY is connecting expects. With a Unix server, this is likely to depend on the `termcap' or `terminfo' entry it uses, which in turn is likely to be controlled by the `Terminal-type string' setting in the Connection panel; see section 4.14.2 for details. If none of the settings here seems to help, you may find question A.7.15 to be useful. 4.4.1 Changing the action of the Backspace key 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 over SSH, PuTTY by default tells the server the value of this option (see section 4.21.2), so you may find that the Backspace key does the right thing either way. Similarly, if you are connecting to a Unix system, you will probably find that the Unix `stty' command lets you configure which the server expects to see, so again 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 `emacs' to use Control-H for help. (Typing Shift-Backspace will cause PuTTY to send whichever code isn't configured here as the default.) 4.4.2 Changing the action of the Home and End keys The Unix terminal emulator `rxvt' disagrees with the rest of the world about what character sequences should be sent to the server by the Home and End keys. `xterm', and other terminals, send `ESC [1~' for the Home key, and `ESC [4~' for the End key. `rxvt' sends `ESC [H' for the Home key and `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. 4.4.3 Changing the action of the function keys and keypad This option affects the function keys (F1 to F12) and the top row of the numeric keypad. - In the default mode, labelled `ESC [n~', the function keys generate sequences like `ESC [11~', `ESC [12~' and so on. This matches the general behaviour of Digital's terminals. - In Linux mode, F6 to F12 behave just like the default mode, but F1 to F5 generate `ESC [[A' through to `ESC [[E'. This mimics the Linux virtual console. - In Xterm R6 mode, F5 to F12 behave like the default mode, but F1 to F4 generate `ESC OP' through to `ESC OS', which are the sequences produced by the top row of the _keypad_ on Digital's terminals. - In VT400 mode, all the function keys behave like the default mode, but the actual top row of the numeric keypad generates `ESC OP' through to `ESC OS'. - In VT100+ mode, the function keys generate `ESC OP' through to `ESC O[' - In SCO mode, the function keys F1 to F12 generate `ESC [M' through to `ESC [X'. Together with shift, they generate `ESC [Y' through to `ESC [j'. With control they generate `ESC [k' through to `ESC [v', and with shift and control together they generate `ESC [w' through to `ESC [{'. If you don't know what any of this means, you probably don't need to fiddle with it. 4.4.4 Controlling Application Cursor Keys mode 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 `ESC [A' through to `ESC [D'. In application mode, they send `ESC OA' through to `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 `Features' configuration panel; see section 4.6.1. 4.4.5 Controlling Application Keypad mode 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, _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 `Features' configuration panel; see section 4.6.1. 4.4.6 Using NetHack keypad mode PuTTY has a special mode for playing NetHack. You can enable it by selecting `NetHack' in the `Initial state of numeric keypad' control. In this mode, the numeric keypad keys 1-9 generate the NetHack movement commands (hjklyubn). The 5 key generates the `.' command (do nothing). In addition, pressing Shift or Ctrl with the keypad keys generate the Shift- or Ctrl-keys you would expect (e.g. keypad-7 generates `y', so Shift-keypad-7 generates `Y' and Ctrl-keypad-7 generates Ctrl-Y); these commands tell 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. 4.4.7 Enabling a DEC-like Compose key 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 `combined' to produce an accented character. The choices of character are designed to be easy to remember; for example, composing `e' and ``' produces the `e-grave' character. If your keyboard has a Windows Application key, it acts as a Compose key in PuTTY. Alternatively, if you enable the `AltGr acts as Compose key' option, the AltGr key will become a Compose key. 4.4.8 `Control-Alt is different from AltGr' 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-[) character to whatever character sequence the rest of the keypress would generate. For example, Alt-A generates Escape followed by `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 `AltGr acts as Compose key' described in section 4.4.7.) 4.5 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. 4.5.1 `Set the style of bell' This control allows you to select various different actions to occur on a terminal bell: - Selecting `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. - `Make default system alert sound' is the default setting. It causes the Windows `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. - `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. - `Beep using the PC speaker' is self-explanatory. - `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 `Custom sound file to play as a bell'. 4.5.2 `Taskbar/caption indication on bell' 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 (`Disabled') nothing unusual happens. If you select `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. `Flashing' is even more eye-catching: the Taskbar entry will continuously flash on and off until you select the window. 4.5.3 `Control the bell overload behaviour' A common user error in a terminal session is to accidentally run the Unix command `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 `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). 4.6 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. 4.6.1 Disabling application keypad and cursor keys Application keypad mode (see section 4.4.5) and application cursor keys mode (see section 4.4.4) 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. 4.6.2 Disabling xterm-style mouse reporting 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 `links', the Usenet newsreader `trn' version 4, and the file manager `mc' (Midnight Commander). If you find this feature inconvenient, you can disable it using the `Disable xterm-style mouse reporting' control. With this box ticked, the mouse will _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 section 4.11.3). 4.6.3 Disabling remote terminal resizing 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. 4.6.4 Disabling switching to the alternate screen Many terminals, including PuTTY, support an `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. 4.6.5 Disabling remote window title changing 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. 4.6.6 Response to remote window title querying 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 _potential security hazard_. If a malicious application can write data to your terminal (for example, if you merely `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 section 4.6.5) 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 set it to `Window title' unless you _really_ know what you are doing. There are three settings for this option: `None' PuTTY makes no response whatsoever to the relevant escape sequence. This may upset server-side software that is expecting some sort of response. `Empty string' PuTTY makes a well-formed response, but leaves it blank. Thus, server-side software that expects a response is kept happy, but an attacker cannot influence the response string. This is probably the setting you want if you have no better ideas. `Window title' PuTTY responds with the actual window title. This is dangerous for the reasons described above. 4.6.7 Disabling destructive backspace Normally, when PuTTY receives character 127 (^?) from the server, it will perform a `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. 4.6.8 Disabling remote character set configuration 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, (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. 4.6.9 Disabling Arabic text shaping PuTTY supports shaping of Arabic text, which means that if your server sends text written in the basic Unicode Arabic alphabet then it will convert it to the correct display forms before printing it on the screen. If you are using full-screen software which was not expecting this to happen (especially if you are not an Arabic speaker and you unexpectedly find yourself dealing with Arabic text files in applications which are not Arabic-aware), you might find that the display becomes corrupted. By ticking this box, you can disable Arabic text shaping so that PuTTY displays precisely the characters it is told to display. You may also find you need to disable bidirectional text display; see section 4.6.10. 4.6.10 Disabling bidirectional text display PuTTY supports bidirectional text display, which means that if your server sends text written in a language which is usually displayed from right to left (such as Arabic or Hebrew) then PuTTY will automatically flip it round so that it is displayed in the right direction on the screen. If you are using full-screen software which was not expecting this to happen (especially if you are not an Arabic speaker and you unexpectedly find yourself dealing with Arabic text files in applications which are not Arabic-aware), you might find that the display becomes corrupted. By ticking this box, you can disable bidirectional text display, so that PuTTY displays text from left to right in all situations. You may also find you need to disable Arabic text shaping; see section 4.6.9. 4.7 The Window panel The Window configuration panel allows you to control aspects of the PuTTY window. 4.7.1 Setting the size of the PuTTY window The `Rows' and `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. 4.7.2 What to do when the window is resized 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: - `Change the number of rows and columns': the font size will not change. (This is the default.) - `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. - `Change font size when maximised': when the window is resized, the number of rows and columns will change, _except_ when the window is maximised (or restored), when the font size will change. - `Forbid resizing completely': the terminal will refuse to be resized at all. 4.7.3 Controlling scrollback These options let you configure the way PuTTY keeps text after it scrolls off the top of the screen (see section 3.1.2). The `Lines of scrollback' box lets you configure how many lines of text PuTTY keeps. The `Display scrollbar' options allow you to hide the scrollbar (although you can still view the scrollback using the keyboard as described in section 3.1.2). 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 `Reset scrollback on display activity'. You can also make the screen revert when you press a key, by turning on `Reset scrollback on keypress'. 4.7.4 `Push erased text into scrollback' 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 section 4.6.4 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. 4.8 The Appearance panel The Appearance configuration panel allows you to control aspects of the appearance of PuTTY's window. 4.8.1 Controlling the appearance of the cursor The `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 `Cursor blinks' option makes the cursor blink on and off. This works in any of the cursor modes. 4.8.2 Controlling the font used in the terminal window 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.) 4.8.3 `Hide mouse pointer when typing in window' 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. 4.8.4 Controlling the window border PuTTY allows you to configure the appearance of the window border to some extent. The checkbox marked `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 `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. 4.9 The Behaviour panel The Behaviour configuration panel allows you to control aspects of the behaviour of PuTTY's window. 4.9.1 Controlling the window title The `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 `PuTTY', for example `server1.example.com - PuTTY'. If you want a different window title, this is where to set it. PuTTY allows the server to send `xterm' control sequences which modify the title of the window in mid-session (unless this is disabled - see section 4.6.5); the title string set here is therefore only the _initial_ window title. As well as the _window_ title, there is also an `xterm' sequence to modify the title of the window's _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 _window_ title, and ignores the icon title entirely. If for some reason you want to see both titles, check the box marked `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.) 4.9.2 `Warn before closing window' 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 `Warn before closing window' option. 4.9.3 `Window closes on ALT-F4' By default, pressing ALT-F4 causes the window to close (or a warning box to appear; see section 4.9.2). If you disable the `Window closes on ALT-F4' option, then pressing ALT-F4 will simply send a key sequence to the server. 4.9.4 `System menu appears on ALT-Space' 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 `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. 4.9.5 `System menu appears on Alt alone' 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. 4.9.6 `Ensure window is always on top' If this option is enabled, the PuTTY window will stay on top of all other windows. 4.9.7 `Full screen on Alt-Enter' 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 section 3.1.3.7. 4.10 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. 4.10.1 Controlling character set translation 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 `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: - The ISO-8859 series are all standard character sets that include various accented characters appropriate for different sets of languages. - 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. - If you want the old IBM PC character set with block graphics and line-drawing characters, you can select `CP437'. - 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 `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 (`CP866' for example) in the list box. If the underlying version of Windows has the appropriate translation table installed, PuTTY will use it. 4.10.2 `Treat CJK ambiguous characters as wide' There are some Unicode characters whose width is not well-defined. In most contexts, such characters should be treated as single- width for the purposes of wrapping and so on; however, in some CJK contexts, they are better treated as double-width for historical reasons, and some server-side applications may expect them to be displayed as such. Setting this option will cause PuTTY to take the double-width interpretation. If you use legacy CJK applications, and you find your lines are wrapping in the wrong places, or you are having other display problems, you might want to play with this setting. This option only has any effect in UTF-8 mode (see section 4.10.1). 4.10.3 `Caps Lock acts as Cyrillic switch' 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. 4.10.4 Controlling display of line-drawing characters 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. - `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. - `Poor man's line drawing' assumes that the font _cannot_ generate the line and box characters at all, so it will use the `+', `-' and `|' characters to draw approximations to boxes. You should use this option if none of the other options works. - `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. - `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. - `Use font in OEM mode only' is more reliable than that, but can miss out other characters from the main character set. 4.10.5 Controlling copy and paste of line drawing characters 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 `poor man's' line-drawing characters `+', `-' and `|'. The checkbox `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 `q' and `x', with a scattering of `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 _were_ printed by using the VT100 mechanism. Line-drawing characters that were received as Unicode code points will paste as Unicode always. 4.11 The Selection panel The Selection panel allows you to control the way copy and paste work in the PuTTY window. 4.11.1 Pasting in Rich Text Format If you enable `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. The effect of this is that if you paste into (say) a word processor, the text will appear in the word processor in the same font, colour, and style (e.g. bold, underline) PuTTY was using to display it. This option can easily be inconvenient, so by default it is disabled. 4.11.2 Changing the actions of the mouse buttons PuTTY's copy and paste mechanism is by default modelled on the Unix `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 (`Compromise'), the _right_ button pastes, and the _middle_ button (if you have one) extends a selection. If you have a three-button mouse and you are already used to the `xterm' arrangement, you can select it using the `Action of mouse buttons' control. Alternatively, with the `Windows' option selected, the middle button extends, and the right button brings up a context menu (on which one of the options is `Paste'). (This context menu is always available by holding down Ctrl and right-clicking, regardless of the setting of this option.) 4.11.3 `Shift overrides application's use of 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 `links', the Usenet newsreader `trn' version 4, and the file manager `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 `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 section 4.6.2. 4.11.4 Default selection mode As described in section 3.1.1, PuTTY has two modes of selecting text to be copied to the clipboard. In the default mode (`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 (`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 `Default selection mode' control, you can set rectangular selection as the default, and then you have to hold down Alt to get the _normal_ behaviour. 4.11.5 Configuring word-by-word selection 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 _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: - Class 0 contains white space and control characters. - Class 1 contains most punctuation. - 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 `@' 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 `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 _default_ state, which will be restored when you reset the terminal (see section 3.1.3.6). However, if you modify this option in mid-session using `Change Settings', it will take effect immediately. 4.12 The Colours panel The Colours panel allows you to control PuTTY's use of colour. 4.12.1 `Allow terminal to specify ANSI colours' This option is enabled by default. If it is disabled, PuTTY will ignore any control sequences sent by the server to request coloured text. If you have a particularly garish application, you might want to turn this option off and make PuTTY only use the default foreground and background colours. 4.12.2 `Allow terminal to use xterm 256-colour mode' This option is enabled by default. If it is disabled, PuTTY will ignore any control sequences sent by the server which use the extended 256-colour mode supported by recent versions of xterm. If you have an application which is supposed to use 256-colour mode and it isn't working, you may find you need to tell your server that your terminal supports 256 colours. On Unix, you do this by ensuring that the setting of TERM describes a 256-colour-capable terminal. You can check this using a command such as `infocmp': $ infocmp | grep colors colors#256, cols#80, it#8, lines#24, pairs#256, If you do not see `colors#256' in the output, you may need to change your terminal setting. On modern Linux machines, you could try `xterm-256color'. 4.12.3 `Bolded text is a different colour' 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. 4.12.4 `Attempt to use logical palettes' 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. 4.12.5 `Use system colours' Enabling this option will cause PuTTY to ignore the configured colours for `Default Background/Foreground' and `Cursor Colour/Text' (see section 4.12.6), 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 section 4.12.3). 4.12.6 Adjusting the colours in the terminal window 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 `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. (You may also edit the RGB values directly in the edit boxes, if you wish; each value is an integer from 0 to 255.) 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 `Bolded text is a different colour', and can also be used if the server asks specifically to use them. (Note that `Default Bold Background' is _not_ the background colour used for bold text; it is only used if the server specifically asks for a bold background.) 4.13 The Connection panel The Connection panel allows you to configure options that apply to more than one type of connection. 4.13.1 Using keepalives to prevent disconnection If you find your sessions are closing unexpectedly (most often with `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 (`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. (Other types of periodic network activity can cause this behaviour; in particular, SSH-2 re-keys can have this effect. See section 4.19.2.) Therefore, you might find that keepalives help connection loss, or you might find they make it worse, depending on what _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 section 4.13.3.) Note that if you are using SSH-1 and the server has a bug that makes it unable to deal with SSH-1 ignore messages (see section 4.24.1), enabling keepalives will have no effect. 4.13.2 `Disable Nagle's algorithm' 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 for interactive connections. 4.13.3 `Enable TCP keepalives' _NOTE:_ TCP keepalives should not be confused with the application- level keepalives described in section 4.13.1. 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: - TCP keepalives are available on _all_ connection types, including Raw and Rlogin. - 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. - If the operating system does not receive a response to a keepalive, it may send out more in quick succession and 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. 4.13.4 `Internet protocol' This option allows the user to select between the old and new Internet protocols and addressing schemes (IPv4 and IPv6). The default setting is `Auto', which means PuTTY will do something sensible and try to guess which protocol you wanted. (If you specify a literal Internet address, it will use whichever protocol that address implies. If you provide a hostname, it will see what kinds of address exist for that hostname; it will use IPv6 if there is an IPv6 address available, and fall back to IPv4 if not.) If you need to force PuTTY to use a particular protocol, you can explicitly set this to `IPv4' or `IPv6'. 4.14 The Data panel The Data panel allows you to configure various pieces of data which can be sent to the server to affect your connection at the far end. Each option on this panel applies to more than one protocol. Options which apply to only one protocol appear on that protocol's configuration panels. 4.14.1 `Auto-login 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. 4.14.2 `Terminal-type string' 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. On a Unix server, this selects an entry from the `termcap' or `terminfo' database that tells applications what control sequences to send to the terminal, and what character sequences to expect the keyboard to generate. PuTTY attempts to emulate the Unix `xterm' program, and by default it reflects this by sending `xterm' as a terminal-type string. If you find this is not doing what you want - perhaps the remote system reports `Unknown terminal type' - you could try setting this to something different, such as `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. 4.14.3 `Terminal speeds' The Telnet, Rlogin, and SSH protocols allow the client to specify terminal speeds to the server. This parameter does _not_ affect the actual speed of the connection, which is always `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, `38400,38400'. The first number represents the output speed (_from_ the server) in bits per second, and the second is the input speed (_to_ the server). (Only the first is used in the Rlogin protocol.) This option has no effect on Raw connections. 4.14.4 Setting environment variables on the server 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 SSH-2 servers are more likely to support it than older ones. This configuration data is not used in the SSH-1, rlogin or raw protocols. To add an environment variable to the list transmitted down the connection, you enter the variable name in the `Variable' box, enter its value in the `Value' box, and press the `Add' button. To remove one from the list, select it in the list box and press `Remove'. 4.15 The Proxy panel 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, and also any extra connections made as a result of SSH port forwarding (see section 3.5). 4.15.1 Setting the proxy type The `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 `None'; in this mode no proxy is used for any connection. - Selecting `HTTP' allows you to proxy your connections through a web server supporting the HTTP CONNECT command, as documented in RFC 2817. - Selecting `SOCKS 4' or `SOCKS 5' allows you to proxy your connections through a SOCKS server. - 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 `connect myhost.com 22' to connect through to an external host. Selecting `Telnet' allows you to tell PuTTY to use this type of proxy. - Selecting `Local' allows you to specify an arbitrary command on the local machine to act as a proxy. When the session is started, instead of creating a TCP connection, PuTTY runs the command (specified in section 4.15.5), and uses its standard input and output streams. This could be used, for instance, to talk to some kind of network proxy that PuTTY does not natively support; or you could tunnel a connection over something other than TCP/IP entirely. If you want your local proxy command to make a secondary SSH connection to a proxy host and then tunnel the primary connection over that, you might well want the `-nc' command-line option in Plink. See section 3.8.3.14 for more information. 4.15.2 Excluding parts of the network from proxying Typically you will only need to use a proxy to connect to non-local parts of your netw