1 \versionid $Id: using.but,v 1.19 2004/02/08 00:14:57 jacob Exp $
5 This chapter provides a general introduction to some more advanced
6 features of PuTTY. For extreme detail and reference purposes,
7 \k{config} is likely to contain more information.
9 \H{using-session} During your session
11 A lot of PuTTY's complexity and features are in the configuration
12 panel. Once you have worked your way through that and started
13 a session, things should be reasonably simple after that.
14 Nevertheless, there are a few more useful features available.
16 \S{using-selection} Copying and pasting text
18 Often in a PuTTY session you will find text on your terminal screen
19 which you want to type in again. Like most other terminal emulators,
20 PuTTY allows you to copy and paste the text rather than having to
21 type it again. Also, copy and paste uses the Windows clipboard, so
22 that you can paste (for example) URLs into a web browser, or paste
23 from a word processor or spreadsheet into your terminal session.
25 PuTTY's copy and paste works entirely with the mouse. In order to
26 copy text to the clipboard, you just click the left mouse button in
27 the terminal window, and drag to select text. When you let go of the
28 button, the text is \e{automatically} copied to the clipboard. You
29 do not need to press Ctrl-C or Ctrl-Ins; in fact, if you do press
30 Ctrl-C, PuTTY will send a Ctrl-C character down your session to the
31 server where it will probably cause a process to be interrupted.
33 Pasting is done using the right button (or the middle mouse button,
34 if you have a three-button mouse and have set it up; see
35 \k{config-mouse}). (Pressing Shift-Ins, or selecting \q{Paste} from
36 the Ctrl+right-click context menu, have the same effect.)
37 When you click the right mouse button, PuTTY will
38 read whatever is in the Windows Clipboard and paste it into your
39 session, \e{exactly} as if it had been typed at the keyboard.
40 (Therefore, be careful of pasting formatted text into an editor that
41 does automatic indenting; you may find that the spaces pasted from
42 the clipboard plus the spaces added by the editor add up to too many
43 spaces and ruin the formatting. There is nothing PuTTY can do about
46 If you double-click the left mouse button, PuTTY will select a whole
47 word. If you double-click, hold down the second click, and drag the
48 mouse, PuTTY will select a sequence of whole words. (You can adjust
49 precisely what PuTTY considers to be part of a word; see
50 \k{config-charclasses}.) If you \e{triple}-click, or triple-click
51 and drag, then PuTTY will select a whole line or sequence of lines.
53 If you want to select a rectangular region instead of selecting to
54 the end of each line, you can do this by holding down Alt when you
55 make your selection. (You can also configure rectangular selection
56 to be the default, and then holding down Alt gives the normal
57 behaviour instead. See \k{config-rectselect} for details.)
59 If you have a middle mouse button, then you can use it to adjust an
60 existing selection if you selected something slightly wrong. (If you
61 have configured the middle mouse button to paste, then the right
62 mouse button does this instead.) Click the button on the screen, and
63 you can pick up the nearest end of the selection and drag it to
66 It's possible for the server to ask to handle mouse clicks in the
67 PuTTY window itself. If this happens, the mouse cursor will turn
68 into an arrow, and copy and paste will only work if you hold down
69 Shift. See \k{config-features-mouse} and \k{config-mouseshift} for
70 details of this feature and how to configure it.
72 \S{using-scrollback} Scrolling the screen back
74 PuTTY keeps track of text that has scrolled up off the top of the
75 terminal. So if something appears on the screen that you want to
76 read, but it scrolls too fast and it's gone by the time you try to
77 look for it, you can use the scrollbar on the right side of the
78 window to look back up the session history and find it again.
80 As well as using the scrollbar, you can also page the scrollback up
81 and down by pressing Shift-PgUp and Shift-PgDn. You can scroll a
82 line at a time using Ctrl-PgUp and Ctrl-PgDn. These are still
83 available if you configure the scrollbar to be invisible.
85 By default the last 200 lines scrolled off the top are
86 preserved for you to look at. You can increase (or decrease) this
87 value using the configuration box; see \k{config-scrollback}.
89 \S{using-sysmenu} The System menu
91 If you click the left mouse button on the icon in the top left
92 corner of PuTTY's window, or click the right mouse button on the
93 title bar, you will see the standard Windows system menu containing
94 items like Minimise, Move, Size and Close.
96 PuTTY's system menu contains extra program features in addition to
97 the Windows standard options. These extra menu commands are
100 (These options are also available in a context menu brought up
101 by holding Ctrl and clicking with the right mouse button anywhere
102 in the PuTTY window.)
104 \S2{using-eventlog} The PuTTY Event Log
106 If you choose \q{Event Log} from the system menu, a small window
107 will pop up in which PuTTY logs significant events during the
108 connection. Most of the events in the log will probably take place
109 during session startup, but a few can occur at any point in the
110 session, and one or two occur right at the end.
112 You can use the mouse to select one or more lines of the Event Log,
113 and hit the Copy button to copy them to the clipboard. If you are
114 reporting a bug, it's often useful to paste the contents of the
115 Event Log into your bug report.
117 \S2{using-specials} Special commands
119 Depending on the protocol used for the current session, there may be a
120 submenu of \q{special commands}. These are protocol-specific tokens,
121 such as a \q{break} signal, that can be sent down a connection in
122 addition to normal data. Currently only Telnet and SSH have special
125 \S2{using-newsession} Starting new sessions
127 PuTTY's system menu provides some shortcut ways to start new
130 \b Selecting \q{New Session} will start a completely new instance of
131 PuTTY, and bring up the configuration box as normal.
133 \b Selecting \q{Duplicate Session} will start a session with
134 precisely the same options as your current one - connecting to the
135 same host using the same protocol, with all the same terminal
136 settings and everything.
138 \b The \q{Saved Sessions} submenu gives you quick access to any
139 sets of stored session details you have previously saved. See
140 \k{config-saving} for details of how to create saved sessions.
142 \S2{using-changesettings} Changing your session settings
144 If you select \q{Change Settings} from the system menu, PuTTY will
145 display a cut-down version of its initial configuration box. This
146 allows you to adjust most properties of your current session. You
147 can change the terminal size, the font, the actions of various
148 keypresses, the colours, and so on.
150 Some of the options that are available in the main configuration box
151 are not shown in the cut-down Change Settings box. These are usually
152 options which don't make sense to change in the middle of a session
153 (for example, you can't switch from SSH to Telnet in mid-session).
155 \S2{using-copyall} Copy All to Clipboard
157 This system menu option provides a convenient way to copy the whole
158 contents of the terminal screen and scrollback to the clipboard in
161 \S2{reset-terminal} Clearing and resetting the terminal
163 The \q{Clear Scrollback} option on the system menu tells PuTTY to
164 discard all the lines of text that have been kept after they
165 scrolled off the top of the screen. This might be useful, for
166 example, if you displayed sensitive information and wanted to make
167 sure nobody could look over your shoulder and see it. (Note that
168 this only prevents a casual user from using the scrollbar to view
169 the information; the text is not guaranteed not to still be in
172 The \q{Reset Terminal} option causes a full reset of the terminal
173 emulation. A VT-series terminal is a complex piece of software and
174 can easily get into a state where all the text printed becomes
175 unreadable. (This can happen, for example, if you accidentally
176 output a binary file to your terminal.) If this happens, selecting
177 Reset Terminal should sort it out.
179 \S2{using-fullscreen} Full screen mode
181 If you find the title bar on a maximised window to be ugly or
182 distracting, you can select Full Screen mode to maximise PuTTY
183 \q{even more}. When you select this, PuTTY will expand to fill the
184 whole screen and its borders, title bar and scrollbar will
185 disappear. (You can configure the scrollbar not to disappear in
186 full-screen mode if you want to keep it; see \k{config-scrollback}.)
188 When you are in full-screen mode, you can still access the system
189 menu if you click the left mouse button in the \e{extreme} top left
190 corner of the screen.
192 \H{using-logging} Creating a log file of your session
194 For some purposes you may find you want to log everything that
195 appears on your screen. You can do this using the \q{Logging} panel
196 in the configuration box.
198 To begin a session log, select \q{Change Settings} from the system
199 menu and go to the Logging panel. Enter a log file name, and select
200 a logging mode. (You can log all session output including the
201 terminal control sequences, or you can just log the printable text.
202 It depends what you want the log for.) Click \q{Apply} and your log
203 will be started. Later on, you can go back to the Logging panel and
204 select \q{Logging turned off completely} to stop logging; then PuTTY
205 will close the log file and you can safely read it.
207 See \k{config-logging} for more details and options.
209 \H{using-translation} Altering your character set configuration
211 If you find that special characters (accented characters, for
212 example) are not being displayed correctly in your PuTTY session, it
213 may be that PuTTY is interpreting the characters sent by the server
214 according to the wrong \e{character set}. There are a lot of
215 different character sets available, so it's entirely possible for
218 If you click \q{Change Settings} and look at the \q{Translation}
219 panel, you should see a large number of character sets which you can
220 select. Now all you need is to find out which of them you want!
222 \H{using-x-forwarding} Using X11 forwarding in SSH
224 The SSH protocol has the ability to securely forward X Window System
225 applications over your encrypted SSH connection, so that you can run
226 an application on the SSH server machine and have it put its windows
227 up on your local machine without sending any X network traffic in
230 In order to use this feature, you will need an X display server for
231 your Windows machine, such as X-Win32 or Exceed. This will probably
232 install itself as display number 0 on your local machine; if it
233 doesn't, the manual for the X server should tell you what it does
236 You should then tick the \q{Enable X11 forwarding} box in the
237 Tunnels panel (see \k{config-ssh-x11}) before starting your SSH
238 session. The \q{X display location} box reads \c{localhost:0} by
239 default, which is the usual display location where your X server
240 will be installed. If that needs changing, then change it.
242 Now you should be able to log in to the SSH server as normal. To
243 check that X forwarding has been successfully negotiated during
244 connection startup, you can check the PuTTY Event Log (see
245 \k{using-eventlog}). It should say something like this:
247 \c 2001-12-05 17:22:01 Requesting X11 forwarding
248 \c 2001-12-05 17:22:02 X11 forwarding enabled
250 If the remote system is Unix or Unix-like, you should also be able
251 to see that the \c{DISPLAY} environment variable has been set to
252 point at display 10 or above on the SSH server machine itself:
254 \c fred@unixbox:~$ echo $DISPLAY
257 If this works, you should then be able to run X applications in the
258 remote session and have them display their windows on your PC.
260 Note that if your PC X server requires authentication to connect,
261 then PuTTY cannot currently support it. If this is a problem for
262 you, you should mail the PuTTY authors \#{FIXME} and give details
265 \H{using-port-forwarding} Using port forwarding in SSH
267 The SSH protocol has the ability to forward arbitrary network
268 connections over your encrypted SSH connection, to avoid the network
269 traffic being sent in clear. For example, you could use this to
270 connect from your home computer to a POP-3 server on a remote
271 machine without your POP-3 password being visible to network
274 In order to use port forwarding to connect from your local machine
275 to a port on a remote server, you need to:
277 \b Choose a port number on your local machine where PuTTY should
278 listen for incoming connections. There are likely to be plenty of
279 unused port numbers above 3000. (You can also use a local loopback
280 address here; see below for more details.)
282 \b Now, before you start your SSH connection, go to the Tunnels
283 panel (see \k{config-ssh-portfwd}). Make sure the \q{Local} radio
284 button is set. Enter the local port number into the \q{Source port}
285 box. Enter the destination host name and port number into the
286 \q{Destination} box, separated by a colon (for example,
287 \c{popserver.example.com:110} to connect to a POP-3 server).
289 \b Now click the \q{Add} button. The details of your port forwarding
290 should appear in the list box.
292 Now start your session and log in. (Port forwarding will not be
293 enabled until after you have logged in; otherwise it would be easy
294 to perform completely anonymous network attacks, and gain access to
295 anyone's virtual private network). To check that PuTTY has set up
296 the port forwarding correctly, you can look at the PuTTY Event Log
297 (see \k{using-eventlog}). It should say something like this:
299 \c 2001-12-05 17:22:10 Local port 3110 forwarding to
300 \c popserver.example.com:110
302 Now if you connect to the source port number on your local PC, you
303 should find that it answers you exactly as if it were the service
304 running on the destination machine. So in this example, you could
305 then configure an e-mail client to use \c{localhost:3110} as a POP-3
306 server instead of \c{popserver.example.com:110}. (Of course, the
307 forwarding will stop happening when your PuTTY session closes down.)
309 You can also forward ports in the other direction: arrange for a
310 particular port number on the \e{server} machine to be forwarded
311 back to your PC as a connection to a service on your PC or near it.
312 To do this, just select the \q{Remote} radio button instead of the
313 \q{Local} one. The \q{Source port} box will now specify a port
314 number on the \e{server} (note that most servers will not allow you
315 to use port numbers under 1024 for this purpose).
317 An alternative way to forward local connections to remote hosts is
318 to use dynamic SOCKS proxying. For this, you will need to select the
319 \q{Dynamic} radio button instead of \q{Local}, and then you should
320 not enter anything into the \q{Destination} box (it will be
321 ignored). This will cause PuTTY to listen on the port you have
322 specified, and provide a SOCKS proxy service to any programs which
323 connect to that port. So, in particular, you can forward other PuTTY
324 connections through it by setting up the Proxy control panel (see
325 \k{config-proxy} for details).
327 The source port for a forwarded connection usually does not accept
328 connections from any machine except the SSH client or server machine
329 itself (for local and remote forwardings respectively). There are
330 controls in the Tunnels panel to change this:
332 \b The \q{Local ports accept connections from other hosts} option
333 allows you to set up local-to-remote port forwardings (including
334 dynamic port forwardings) in such a way that machines other than
335 your client PC can connect to the forwarded port.
337 \b The \q{Remote ports do the same} option does the same thing for
338 remote-to-local port forwardings (so that machines other than the
339 SSH server machine can connect to the forwarded port.) Note that
340 this feature is only available in the SSH 2 protocol, and not all
341 SSH 2 servers support it (OpenSSH 3.0 does not, for example).
343 You can also specify an IP address to listen on. Typically a
344 Windows machine can be asked to listen on any single IP address in
345 the \cw{127.*.*.*} range, and all of these are loopback addresses
346 available only to the local machine. So if you forward (for
347 example) \c{127.0.0.5:79} to a remote machine's \cw{finger} port,
348 then you should be able to run commands such as \c{finger
349 fred@127.0.0.5}. This can be useful if the program connecting to
350 the forwarded port doesn't allow you to change the port number it
351 uses. This feature is available for local-to-remote forwarded
352 ports; SSH1 is unable to support it for remote-to-local ports,
353 while SSH2 can support it in theory but servers will not
354 necessarily cooperate.
356 \H{using-rawprot} Making raw TCP connections
358 A lot of Internet protocols are composed of commands and responses
359 in plain text. For example, SMTP (the protocol used to transfer
360 e-mail), NNTP (the protocol used to transfer Usenet news), and HTTP
361 (the protocol used to serve Web pages) all consist of commands in
364 Sometimes it can be useful to connect directly to one of these
365 services and speak the protocol \q{by hand}, by typing protocol
366 commands and watching the responses. On Unix machines, you can do
367 this using the system's \c{telnet} command to connect to the right
368 port number. For example, \c{telnet mailserver.example.com 25} might
369 enable you to talk directly to the SMTP service running on a mail
372 Although the Unix \c{telnet} program provides this functionality,
373 the protocol being used is not really Telnet. Really there is no
374 actual protocol at all; the bytes sent down the connection are
375 exactly the ones you type, and the bytes shown on the screen are
376 exactly the ones sent by the server. Unix \c{telnet} will attempt to
377 detect or guess whether the service it is talking to is a real
378 Telnet service or not; PuTTY prefers to be told for certain.
380 In order to make a debugging connection to a service of this type,
381 you simply select the fourth protocol name, \q{Raw}, from the
382 \q{Protocol} buttons in the \q{Session} configuration panel. (See
383 \k{config-hostname}.) You can then enter a host name and a port
384 number, and make the connection.
386 \H{using-cmdline} The PuTTY command line
388 PuTTY can be made to do various things without user intervention by
389 supplying command-line arguments (e.g., from a command prompt window,
390 or a Windows shortcut).
392 \S{using-cmdline-session} Starting a session from the command line
394 These options allow you to bypass the configuration window and launch
395 straight into a session.
397 To start a connection to a server called \c{host}:
399 \c putty.exe [-ssh | -telnet | -rlogin | -raw] [user@]host
401 If this syntax is used, settings are taken from the Default Settings
402 (see \k{config-saving}); \c{user} overrides these settings if
403 supplied. Also, you can specify a protocol, which will override the
404 default protocol (see \k{using-cmdline-protocol}).
406 For telnet sessions, the following alternative syntax is supported
407 (this makes PuTTY suitable for use as a URL handler for telnet URLs in
410 \c putty.exe telnet://host[:port]/
412 In order to start an existing saved session called \c{sessionname},
413 use the \c{-load} option (described in \k{using-cmdline-load}).
415 \c putty.exe -load "session name"
417 \S{using-cleanup} \c{-cleanup}
419 If invoked with the \c{-cleanup} option, rather than running as
420 normal, PuTTY will remove its registry entries and random seed file
421 from the local machine (after confirming with the user).
423 \S{using-general-opts} Standard command-line options
425 PuTTY and its associated tools support a range of command-line
426 options, most of which are consistent across all the tools. This
427 section lists the available options in all tools. Options which are
428 specific to a particular tool are covered in the chapter about that
431 \S2{using-cmdline-load} \c{-load}: load a saved session
433 The \c{-load} option causes PuTTY to load configuration details out
434 of a saved session. If these details include a host name, then this
435 option is all you need to make PuTTY start a session (although Plink
436 still requires an explicitly specified host name).
438 You need double quotes around the session name if it contains spaces.
440 If you want to create a Windows shortcut to start a PuTTY saved
441 session, this is the option you should use: your shortcut should
444 \c d:\path\to\putty.exe -load "my session"
446 (Note that PuTTY itself supports an alternative form of this option,
447 for backwards compatibility. If you execute \c{putty @sessionname}
448 it will have the same effect as \c{putty -load "sessionname"}. With
449 the \c{@} form, no double quotes are required, and the \c{@} sign
450 must be the very first thing on the command line. This form of the
451 option is deprecated.)
453 \S2{using-cmdline-protocol} Selecting a protocol: \c{-ssh},
454 \c{-telnet}, \c{-rlogin}, \c{-raw}
456 To choose which protocol you want to connect with, you can use one
459 \b \c{-ssh} selects the SSH protocol.
461 \b \c{-telnet} selects the Telnet protocol.
463 \b \c{-rlogin} selects the Rlogin protocol.
465 \b \c{-raw} selects the raw protocol.
467 These options are not available in the file transfer tools PSCP and
468 PSFTP (which only work with the SSH protocol).
470 These options are equivalent to the protocol selection buttons in
471 the Session panel of the PuTTY configuration box (see
472 \k{config-hostname}).
474 \S2{using-cmdline-v} \c{-v}: increase verbosity
476 Most of the PuTTY tools can be made to tell you more about what they
477 are doing by supplying the \c{-v} option. If you are having trouble
478 when making a connection, or you're simply curious, you can turn
479 this switch on and hope to find out more about what is happening.
481 \S2{using-cmdline-l} \c{-l}: specify a login name
483 You can specify the user name to log in as on the remote server
484 using the \c{-l} option. For example, \c{plink login.example.com -l
487 These options are equivalent to the username selection box in the
488 Connection panel of the PuTTY configuration box (see
489 \k{config-username}).
491 \S2{using-cmdline-portfwd} \c{-L}, \c{-R} and \c{-D}: set up port forwardings
493 As well as setting up port forwardings in the PuTTY configuration
494 (see \k{config-ssh-portfwd}), you can also set up forwardings on the
495 command line. The command-line options work just like the ones in
496 Unix \c{ssh} programs.
498 To forward a local port (say 5110) to a remote destination (say
499 \cw{popserver.example.com} port 110), you can write something like
502 \c putty -L 5110:popserver.example.com:110 -load mysession
503 \c plink mysession -L 5110:popserver.example.com:110
505 To forward a remote port to a local destination, just use the \c{-R}
506 option instead of \c{-L}:
508 \c putty -R 5023:mytelnetserver.myhouse.org:23 -load mysession
509 \c plink mysession -R 5023:mytelnetserver.myhouse.org:23
511 To specify an IP address for the listening end of the tunnel,
512 prepend it to the argument:
514 \c plink -L 127.0.0.5:23:localhost:23 myhost
516 To set up SOCKS-based dynamic port forwarding on a local port, use
517 the \c{-D} option. For this one you only have to pass the port
520 \c putty -D 4096 -load mysession
522 For general information on port forwarding, see
523 \k{using-port-forwarding}.
525 These options are not available in the file transfer tools PSCP and
528 \S2{using-cmdline-m} \c{-m}: read a remote command or script from a
531 The \c{-m} option performs a similar function to the \q{Remote
532 command} box in the SSH panel of the PuTTY configuration box (see
533 \k{config-command}). However, the \c{-m} option expects to be given
534 a local file name, and it will read a command from that file. On most Unix
535 systems, you can even put multiple lines in this file and execute
536 more than one command in sequence, or a whole shell script.
538 This option is not available in the file transfer tools PSCP and
541 \S2{using-cmdline-p} \c{-P}: specify a port number
543 The \c{-P} option is used to specify the port number to connect to. If
544 you have a Telnet server running on port 9696 of a machine instead of
545 port 23, for example:
547 \c putty -telnet -P 9696 host.name
548 \c plink -telnet -P 9696 host.name
550 (Note that this option is more useful in Plink than in PuTTY,
551 because in PuTTY you can write \c{putty -telnet host.name 9696} in
554 These options are equivalent to the protocol selection buttons in
555 the Session panel of the PuTTY configuration box (see
556 \k{config-hostname}).
558 \S2{using-cmdline-pw} \c{-pw}: specify a password
560 A simple way to automate a remote login is to supply your password
561 on the command line. This is \e{not recommended} for reasons of
562 security. If you possibly can, we recommend you set up public-key
563 authentication instead. See \k{pubkey} for details.
565 Note that the \c{-pw} option only works when you are using the SSH
566 protocol. Due to fundamental limitations of Telnet and Rlogin, these
567 protocols do not support automated password authentication.
569 \S2{using-cmdline-agent} \c{-A} and \c{-a}: control agent forwarding
571 The \c{-A} option turns on SSH agent forwarding, and \c{-a} turns it
572 off. These options are only meaningful if you are using SSH.
574 See \k{pageant} for general information on Pageant, and
575 \k{pageant-forward} for information on agent forwarding. Note that
576 there is a security risk involved with enabling this option; see
577 \k{pageant-security} for details.
579 These options are equivalent to the agent forwarding checkbox in the
580 Auth panel of the PuTTY configuration box (see \k{config-ssh-agentfwd}).
582 These options are not available in the file transfer tools PSCP and
585 \S2{using-cmdline-x11} \c{-X} and \c{-x}: control X11 forwarding
587 The \c{-X} option turns on X11 forwarding in SSH, and \c{-x} turns
588 it off. These options are only meaningful if you are using SSH.
590 For information on X11 forwarding, see \k{using-x-forwarding}.
592 These options are equivalent to the X11 forwarding checkbox in the
593 Tunnels panel of the PuTTY configuration box (see
596 These options are not available in the file transfer tools PSCP and
599 \S2{using-cmdline-pty} \c{-t} and \c{-T}: control pseudo-terminal
602 The \c{-t} option ensures PuTTY attempts to allocate a
603 pseudo-terminal at the server, and \c{-T} stops it from allocating
604 one. These options are only meaningful if you are using SSH.
606 These options are equivalent to the \q{Don't allocate a
607 pseudo-terminal} checkbox in the SSH panel of the PuTTY
608 configuration box (see \k{config-ssh-pty}).
610 These options are not available in the file transfer tools PSCP and
613 \S2{using-cmdline-compress} \c{-C}: enable compression
615 The \c{-C} option enables compression of the data sent across the
616 network. This option is only meaningful if you are using SSH.
618 This option is equivalent to the \q{Enable compression} checkbox in
619 the SSH panel of the PuTTY configuration box (see
620 \k{config-ssh-comp}).
622 \S2{using-cmdline-sshprot} \c{-1} and \c{-2}: specify an SSH protocol
625 The \c{-1} and \c{-2} options force PuTTY to use version 1 or
626 version 2 of the SSH protocol. These options are only meaningful if
629 These options are equivalent to selecting your preferred SSH
630 protocol version as \q{1 only} or \q{2 only} in the SSH panel of the
631 PuTTY configuration box (see \k{config-ssh-prot}).
633 \S2{using-cmdline-identity} \c{-i}: specify an SSH private key
635 The \c{-i} option allows you to specify the name of a private key
636 file in \c{*.PPK} format which PuTTY will use to authenticate with the
637 server. This option is only meaningful if you are using SSH.
639 For general information on public-key authentication, see \k{pubkey}.
641 This option is equivalent to the \q{Private key file for
642 authentication} box in the Auth panel of the PuTTY configuration box
643 (see \k{config-ssh-privkey}).