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.

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 4.11.3). 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 4.11.6.) 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 4.11.5 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.

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. 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.

If you click the left mouse button on the icon in the top left corner of PuTTY's 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.

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 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 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.
• 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.

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).

3.1.3.4 Copy All to Clipboard

This system menu option provides a convenient way to copy the whole contents of the terminal screen and scrollback to the clipboard in one go.

3.1.3.5 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.

3.1.3.6 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) 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. Now all you need is to find out which of them you want!

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 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 4.19.1) before starting your SSH session. The "X display location" box reads localhost:0 by default, 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 authors and give details.

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.
• Now, before you start your SSH connection, go to the Tunnels panel (see section 4.19.2). 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).

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 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 support it (OpenSSH 3.0 does not, for example).

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 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).

3.7.1 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 3.7.3.2).

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 3.7.3.1).

putty.exe -load "session name"


3.7.2 -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).

3.7.3 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.

3.7.3.1 -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 (although Plink still requires an explicitly specified host name).

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.)

3.7.3.2 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).

3.7.3.3 -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.

3.7.3.4 -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 4.13.2).

3.7.3.5 -L and -R: set up port forwardings

As well as setting up port forwardings in the PuTTY configuration (see section 4.19.2), 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


And 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


For general information on port forwarding, see section 3.5.

These options are not available in the file transfer tools PSCP and PSFTP.

3.7.3.6 -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 4.17.1). However, the -m option expects to be given a file name, and it will read a command from that file. On most Unix systems, you can even put multiple lines in this file and execute more than one command in sequence, or a whole shell script.

This option is not available in the file transfer tools PSCP and PSFTP.

3.7.3.7 -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


(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.)

These options are equivalent to the protocol selection buttons in the Session panel of the PuTTY configuration box (see section 4.1.1).

3.7.3.8 -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.

3.7.3.9 -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 4.18.3).

These options are not available in the file transfer tools PSCP and PSFTP.

3.7.3.10 -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 4.19.1).

These options are not available in the file transfer tools PSCP and PSFTP.

3.7.3.11 -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 4.17.2).

These options are not available in the file transfer tools PSCP and PSFTP.

3.7.3.12 -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 4.17.3).

3.7.3.13 -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 4.17.4).

3.7.3.14 -i: specify an SSH private key

The -i option allows you to specify the name of a private key file 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 4.18.5).

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