1 \define{versionidfaq} \versionid $Id$
5 This FAQ is published on the PuTTY web site, and also provided as an
6 appendix in the manual.
8 \H{faq-intro} Introduction
10 \S{faq-what}{Question} What is PuTTY?
12 PuTTY is a client program for the SSH, Telnet and Rlogin network
15 These protocols are all used to run a remote session on a computer,
16 over a network. PuTTY implements the client end of that session: the
17 end at which the session is displayed, rather than the end at which
20 In really simple terms: you run PuTTY on a Windows machine, and tell
21 it to connect to (for example) a Unix machine. PuTTY opens a window.
22 Then, anything you type into that window is sent straight to the
23 Unix machine, and everything the Unix machine sends back is
24 displayed in the window. So you can work on the Unix machine as if
25 you were sitting at its console, while actually sitting somewhere
28 \H{faq-support} Features supported in PuTTY
30 \I{supported features}In general, if you want to know if PuTTY supports
31 a particular feature, you should look for it on the
32 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/}{PuTTY web site}.
36 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html}{changes
37 page}, and see if you can find the feature on there. If a feature is
38 listed there, it's been implemented. If it's listed as a change made
39 \e{since} the latest version, it should be available in the
40 development snapshots, in which case testing will be very welcome.
43 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/}{Wishlist
44 page}, and see if you can find the feature there. If it's on there,
45 and not in the \q{Recently fixed} section, it probably \e{hasn't} been
48 \S{faq-ssh2}{Question} Does PuTTY support SSH-2?
50 Yes. SSH-2 support has been available in PuTTY since version 0.50.
52 Public key authentication (both RSA and DSA) in SSH-2 is new in
55 \S{faq-ssh2-keyfmt}{Question} Does PuTTY support reading OpenSSH or
56 \cw{ssh.com} SSH-2 private key files?
58 PuTTY doesn't support this natively (see
59 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/key-formats-natively.html}{the wishlist entry}
60 for reasons why not), but as of 0.53
61 PuTTYgen can convert both OpenSSH and \cw{ssh.com} private key
62 files into PuTTY's format.
64 \S{faq-ssh1}{Question} Does PuTTY support SSH-1?
66 Yes. SSH-1 support has always been available in PuTTY.
68 \S{faq-localecho}{Question} Does PuTTY support \i{local echo}?
70 Yes. Version 0.52 has proper support for local echo.
72 In version 0.51 and before, local echo could not be separated from
73 local line editing (where you type a line of text locally, and it is
74 not sent to the server until you press Return, so you have the
75 chance to edit it and correct mistakes \e{before} the server sees
76 it). New in version 0.52, local echo and local line editing are
77 separate options, and by default PuTTY will try to determine
78 automatically whether to enable them or not, based on which protocol
79 you have selected and also based on hints from the server. If you
80 have a problem with PuTTY's default choice, you can force each
81 option to be enabled or disabled as you choose. The controls are in
82 the Terminal panel, in the section marked \q{Line discipline
85 \S{faq-savedsettings}{Question} Does PuTTY support storing settings,
86 so I don't have to change them every time?
88 Yes, all of PuTTY's settings can be saved in named session profiles.
89 You can also change the default settings that are used for new sessions.
90 See \k{config-saving} in the documentation for how to do this.
92 \S{faq-disksettings}{Question} Does PuTTY support storing its
93 settings in a disk file?
95 Not at present, although \k{config-file} in the documentation gives
96 a method of achieving the same effect.
98 \S{faq-fullscreen}{Question} Does PuTTY support full-screen mode,
101 Yes; this is a new feature in version 0.52.
103 \S{faq-password-remember}{Question} Does PuTTY have the ability to
104 \i{remember my password} so I don't have to type it every time?
108 Remembering your password is a bad plan for obvious security
109 reasons: anyone who gains access to your machine while you're away
110 from your desk can find out the remembered password, and use it,
111 abuse it or change it.
113 In addition, it's not even \e{possible} for PuTTY to automatically
114 send your password in a Telnet session, because Telnet doesn't give
115 the client software any indication of which part of the login
116 process is the password prompt. PuTTY would have to guess, by
117 looking for words like \q{password} in the session data; and if your
118 login program is written in something other than English, this won't
121 In SSH, remembering your password would be possible in theory, but
122 there doesn't seem to be much point since SSH supports public key
123 authentication, which is more flexible and more secure. See
124 \k{pubkey} in the documentation for a full discussion of public key
127 \S{faq-hostkeys}{Question} Is there an option to turn off the
128 \I{verifying the host key}annoying host key prompts?
130 No, there isn't. And there won't be. Even if you write it yourself
131 and send us the patch, we won't accept it.
133 Those annoying host key prompts are the \e{whole point} of SSH.
134 Without them, all the cryptographic technology SSH uses to secure
135 your session is doing nothing more than making an attacker's job
136 slightly harder; instead of sitting between you and the server with
137 a packet sniffer, the attacker must actually subvert a router and
138 start modifying the packets going back and forth. But that's not all
139 that much harder than just sniffing; and without host key checking,
140 it will go completely undetected by client or server.
142 Host key checking is your guarantee that the encryption you put on
143 your data at the client end is the \e{same} encryption taken off the
144 data at the server end; it's your guarantee that it hasn't been
145 removed and replaced somewhere on the way. Host key checking makes
146 the attacker's job \e{astronomically} hard, compared to packet
147 sniffing, and even compared to subverting a router. Instead of
148 applying a little intelligence and keeping an eye on Bugtraq, the
149 attacker must now perform a brute-force attack against at least one
150 military-strength cipher. That insignificant host key prompt really
151 does make \e{that} much difference.
153 If you're having a specific problem with host key checking - perhaps
154 you want an automated batch job to make use of PSCP or Plink, and
155 the interactive host key prompt is hanging the batch process - then
156 the right way to fix it is to add the correct host key to the
157 Registry in advance. That way, you retain the \e{important} feature
158 of host key checking: the right key will be accepted and the wrong
159 ones will not. Adding an option to turn host key checking off
160 completely is the wrong solution and we will not do it.
162 If you have host keys available in the common \i\c{known_hosts} format,
163 we have a script called
164 \W{http://www.tartarus.org/~simon-anonsvn/viewcvs.cgi/putty/contrib/kh2reg.py?view=markup}\c{kh2reg.py}
165 to convert them to a Windows .REG file, which can be installed ahead of
166 time by double-clicking or using \c{REGEDIT}.
168 \S{faq-server}{Question} Will you write an SSH server for the PuTTY
169 suite, to go with the client?
171 No. The only reason we might want to would be if we could easily
172 re-use existing code and significantly cut down the effort. We don't
173 believe this is the case; there just isn't enough common ground
174 between an SSH client and server to make it worthwhile.
176 If someone else wants to use bits of PuTTY in the process of writing
177 a Windows SSH server, they'd be perfectly welcome to of course, but
178 I really can't see it being a lot less effort for us to do that than
179 it would be for us to write a server from the ground up. We don't
180 have time, and we don't have motivation. The code is available if
181 anyone else wants to try it.
183 \S{faq-pscp-ascii}{Question} Can PSCP or PSFTP transfer files in
188 Until recently, this was a limitation of the file transfer protocols:
189 the SCP and SFTP protocols had no notion of transferring a file in
190 anything other than binary mode. (This is still true of SCP.)
192 The current draft protocol spec of SFTP proposes a means of
193 implementing ASCII transfer. At some point PSCP/PSFTP may implement
196 \H{faq-ports} Ports to other operating systems
198 The eventual goal is for PuTTY to be a multi-platform program, able
199 to run on at least Windows, Mac OS and Unix.
201 Porting will become easier once PuTTY has a generalised porting
202 layer, drawing a clear line between platform-dependent and
203 platform-independent code. The general intention was for this
204 porting layer to evolve naturally as part of the process of doing
205 the first port; a Unix port has now been released and the plan
206 seems to be working so far.
208 \S{faq-ports-general}{Question} What ports of PuTTY exist?
210 Currently, release versions of PuTTY tools only run on full Win32
211 systems and Unix. \q{Win32} includes Windows 95, 98, and ME, and it
212 includes Windows NT, Windows 2000 and Windows XP.
214 In the development code, a partial port to the Mac OS (see
215 \k{faq-mac-port}) is under way.
217 Currently PuTTY does \e{not} run on Windows CE (see \k{faq-wince}),
218 and it does not quite run on the Win32s environment under Windows
219 3.1 (see \k{faq-win31}).
221 We do not have release-quality ports for any other systems at the
222 present time. If anyone told you we had an EPOC port, or an iPaq port,
223 or any other port of PuTTY, they were mistaken. We don't.
225 There are some third-party ports to various platforms, mentioned
226 on the Links page of our website.
228 \S{faq-unix}{Question} \I{Unix version}Is there a port to Unix?
230 As of 0.54, there are Unix ports of most of the traditional PuTTY
231 tools, and also one entirely new application.
233 If you look at the source release, you should find a \c{unix}
234 subdirectory containing \c{Makefile.gtk}, which should build you Unix
235 ports of Plink, PuTTY itself, PuTTYgen, PSCP, PSFTP, and also
236 \i\c{pterm} - an \cw{xterm}-type program which supports the same
237 terminal emulation as PuTTY. We do not yet have a Unix port of
240 If you don't have \i{Gtk}, you should still be able to build the
243 Note that Unix PuTTY has mostly only been tested on Linux so far;
244 portability problems such as BSD-style ptys or different header file
245 requirements are expected.
247 \S{faq-unix-why}{Question} What's the point of the Unix port? Unix
250 All sorts of little things. \c{pterm} is directly useful to anyone
251 who prefers PuTTY's terminal emulation to \c{xterm}'s, which at
252 least some people do. Unix Plink has apparently found a niche among
253 people who find the complexity of OpenSSL makes OpenSSH hard to
254 install (and who don't mind Plink not having as many features). Some
255 users want to generate a large number of SSH keys on Unix and then
256 copy them all into PuTTY, and the Unix PuTTYgen should allow them to
257 automate that conversion process.
259 There were development advantages as well; porting PuTTY to Unix was
260 a valuable path-finding effort for other future ports, and also
261 allowed us to use the excellent Linux tool
262 \W{http://valgrind.kde.org/}{Valgrind} to help with debugging, which
263 has already improved PuTTY's stability on \e{all} platforms.
265 However, if you're a Unix user and you can see no reason to switch
266 from OpenSSH to PuTTY/Plink, then you're probably right. We don't
267 expect our Unix port to be the right thing for everybody.
269 \S{faq-wince}{Question} Will there be a port to Windows CE or PocketPC?
271 It's currently being worked on, but it's only in its early stages yet,
272 and certainly isn't yet useful. PuTTY on portable devices would
273 clearly be a useful thing, so in the long term I hope it can be
274 brought up to release quality.
276 There's also a third-party port at
277 \W{http://www.pocketputty.net/}\c{http://www.pocketputty.net/}.
279 \S{faq-win31}{Question} Is there a port to \i{Windows 3.1}?
281 PuTTY is a 32-bit application from the ground up, so it won't run on
282 Windows 3.1 as a native 16-bit program; and it would be \e{very}
283 hard to port it to do so, because of Windows 3.1's vile memory
284 allocation mechanisms.
286 However, it is possible in theory to compile the existing PuTTY
287 source in such a way that it will run under \i{Win32s} (an extension to
288 Windows 3.1 to let you run 32-bit programs). In order to do this
289 you'll need the right kind of C compiler - modern versions of Visual
290 C at least have stopped being backwards compatible to Win32s. Also,
291 the last time we tried this it didn't work very well.
293 If you're interested in running PuTTY under Windows 3.1, help and
294 testing in this area would be very welcome!
296 \S{faq-mac-port}{Question} Will there be a port to the \I{Mac OS}Mac?
298 There are several answers to this question:
300 \b The Unix/Gtk port is already fully working under Mac OS X as an X11
303 \b A native (Cocoa) Mac OS X port has been started. It's just about
304 usable, but is of nowhere near release quality yet, and is likely to
305 behave in unexpected ways. Currently it's unlikely to be completed
306 unless someone steps in to help.
308 \b A separate port to the classic Mac OS (pre-OSX) is also in
309 progress; it too is not ready yet.
311 \S{faq-epoc}{Question} Will there be a port to EPOC?
313 I hope so, but given that ports aren't really progressing very fast
314 even on systems the developers \e{do} already know how to program
315 for, it might be a long time before any of us get round to learning
316 a new system and doing the port for that.
318 However, some of the work has been done by other people, and a beta
319 port of PuTTY for the Nokia 9200 Communicator series is available
320 from \W{http://s2putty.sourceforge.net/}\cw{http://s2putty.sourceforge.net/}
322 \H{faq-embedding} Embedding PuTTY in other programs
324 \S{faq-dll}{Question} Is the SSH or Telnet code available as a DLL?
326 No, it isn't. It would take a reasonable amount of rewriting for
327 this to be possible, and since the PuTTY project itself doesn't
328 believe in DLLs (they make installation more error-prone) none of us
329 has taken the time to do it.
331 Most of the code cleanup work would be a good thing to happen in
332 general, so if anyone feels like helping, we wouldn't say no.
334 \S{faq-vb}{Question} Is the SSH or Telnet code available as a Visual
337 No, it isn't. None of the PuTTY team uses Visual Basic, and none of
338 us has any particular need to make SSH connections from a Visual
339 Basic application. In addition, all the preliminary work to turn it
340 into a DLL would be necessary first; and furthermore, we don't even
341 know how to write VB components.
343 If someone offers to do some of this work for us, we might consider
344 it, but unless that happens I can't see VB integration being
345 anywhere other than the very bottom of our priority list.
347 \S{faq-ipc}{Question} How can I use PuTTY to make an SSH connection
348 from within another program?
350 Probably your best bet is to use Plink, the command-line connection
351 tool. If you can start Plink as a second Windows process, and
352 arrange for your primary process to be able to send data to the
353 Plink process, and receive data from it, through pipes, then you
354 should be able to make SSH connections from your program.
356 This is what CVS for Windows does, for example.
358 \H{faq-details} Details of PuTTY's operation
360 \S{faq-term}{Question} What \i{terminal type} does PuTTY use?
362 For most purposes, PuTTY can be considered to be an \cw{xterm}
365 PuTTY also supports some terminal \i{control sequences} not supported by
366 the real \cw{xterm}: notably the Linux console sequences that
367 reconfigure the colour palette, and the title bar control sequences
368 used by \i\cw{DECterm} (which are different from the \cw{xterm} ones;
369 PuTTY supports both).
371 By default, PuTTY announces its terminal type to the server as
372 \c{xterm}. If you have a problem with this, you can reconfigure it
373 to say something else; \c{vt220} might help if you have trouble.
375 \S{faq-settings}{Question} Where does PuTTY store its data?
377 On Windows, PuTTY stores most of its data (saved sessions, SSH host
378 keys) in the \i{Registry}. The precise location is
380 \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY
382 and within that area, saved sessions are stored under \c{Sessions}
383 while host keys are stored under \c{SshHostKeys}.
385 PuTTY also requires a random number seed file, to improve the
386 unpredictability of randomly chosen data needed as part of the SSH
387 cryptography. This is stored by default in a file called \i\c{PUTTY.RND}
388 in your Windows home directory (\c{%HOMEDRIVE%\\%HOMEPATH%}), or in
389 the actual Windows directory (such as \c{C:\\WINDOWS}) if the home
390 directory doesn't exist, for example if you're using Win95. If you
391 want to change the location of the random number seed file, you can
392 put your chosen pathname in the Registry, at
394 \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\RandSeedFile
396 On Unix, PuTTY stores all of this data in a directory \cw{~/.putty}.
398 \H{faq-howto} HOWTO questions
400 \S{faq-login}{Question} What login name / password should I use?
402 This is not a question you should be asking \e{us}.
404 PuTTY is a communications tool, for making connections to other
405 computers. We maintain the tool; we \e{don't} administer any computers
406 that you're likely to be able to use, in the same way that the people
407 who make web browsers aren't responsible for most of the content you can
408 view in them. \#{FIXME: less technical analogy?} We cannot help with
409 questions of this sort.
411 If you know the name of the computer you want to connect to, but don't
412 know what login name or password to use, you should talk to whoever
413 administers that computer. If you don't know who that is, see the next
414 question for some possible ways to find out.
416 \# FIXME: some people ask us to provide them with a login name
417 apparently as random members of the public rather than in the
418 belief that we run a server belonging to an organisation they already
419 have some relationship with. Not sure what to say to such people.
421 \S{faq-commands}{Question} \I{commands on the server}What commands
422 can I type into my PuTTY terminal window?
424 Again, this is not a question you should be asking \e{us}. You need
425 to read the manuals, or ask the administrator, of \e{the computer
426 you have connected to}.
428 PuTTY does not process the commands you type into it. It's only a
429 communications tool. It makes a connection to another computer; it
430 passes the commands you type to that other computer; and it passes
431 the other computer's responses back to you. Therefore, the precise
432 range of commands you can use will not depend on PuTTY, but on what
433 kind of computer you have connected to and what software is running
434 on it. The PuTTY team cannot help you with that.
436 (Think of PuTTY as being a bit like a telephone. If you phone
437 somebody up and you don't know what language to speak to make them
438 understand you, it isn't \e{the telephone company}'s job to find
439 that out for you. We just provide the means for you to get in touch;
440 making yourself understood is somebody else's problem.)
442 If you are unsure of where to start looking for the administrator of
443 your server, a good place to start might be to remember how you
444 found out the host name in the PuTTY configuration. If you were
445 given that host name by e-mail, for example, you could try asking
446 the person who sent you that e-mail. If your company's IT department
447 provided you with ready-made PuTTY saved sessions, then that IT
448 department can probably also tell you something about what commands
449 you can type during those sessions. But the PuTTY maintainer team
450 does not administer any server you are likely to be connecting to,
451 and cannot help you with questions of this type.
453 \S{faq-startmax}{Question} How can I make PuTTY start up \i{maximise}d?
455 Create a Windows shortcut to start PuTTY from, and set it as \q{Run
458 \S{faq-startsess}{Question} How can I create a \i{Windows shortcut} to
459 start a particular saved session directly?
461 To run a PuTTY session saved under the name \q{\cw{mysession}},
462 create a Windows shortcut that invokes PuTTY with a command line
465 \c \path\name\to\putty.exe -load "mysession"
467 (Note: prior to 0.53, the syntax was \c{@session}. This is now
468 deprecated and may be removed at some point.)
470 \S{faq-startssh}{Question} How can I start an SSH session straight
471 from the command line?
473 Use the command line \c{putty -ssh host.name}. Alternatively, create
474 a saved session that specifies the SSH protocol, and start the saved
475 session as shown in \k{faq-startsess}.
477 \S{faq-cutpaste}{Question} How do I \i{copy and paste} between PuTTY and
478 other Windows applications?
480 Copy and paste works similarly to the X Window System. You use the
481 left mouse button to select text in the PuTTY window. The act of
482 selection \e{automatically} copies the text to the clipboard: there
483 is no need to press Ctrl-Ins or Ctrl-C or anything else. In fact,
484 pressing Ctrl-C will send a Ctrl-C character to the other end of
485 your connection (just like it does the rest of the time), which may
486 have unpleasant effects. The \e{only} thing you need to do, to copy
487 text to the clipboard, is to select it.
489 To paste the clipboard contents into a PuTTY window, by default you
490 click the right mouse button. If you have a three-button mouse and
491 are used to X applications, you can configure pasting to be done by
492 the middle button instead, but this is not the default because most
493 Windows users don't have a middle button at all.
495 You can also paste by pressing Shift-Ins.
497 \S{faq-options}{Question} How do I use all PuTTY's features (public
498 keys, proxying, cipher selection, etc.) in PSCP, PSFTP and Plink?
500 Most major features (e.g., public keys, port forwarding) are available
501 through command line options. See the documentation.
503 Not all features are accessible from the command line yet, although
504 we'd like to fix this. In the meantime, you can use most of
505 PuTTY's features if you create a PuTTY saved session, and then use
506 the name of the saved session on the command line in place of a
507 hostname. This works for PSCP, PSFTP and Plink (but don't expect
508 port forwarding in the file transfer applications!).
510 \S{faq-pscp}{Question} How do I use PSCP.EXE? When I double-click it
511 gives me a command prompt window which then closes instantly.
513 PSCP is a command-line application, not a GUI application. If you
514 run it without arguments, it will simply print a help message and
517 To use PSCP properly, run it from a Command Prompt window. See
518 \k{pscp} in the documentation for more details.
520 \S{faq-pscp-spaces}{Question} \I{spaces in filenames}How do I use
521 PSCP to copy a file whose name has spaces in?
523 If PSCP is using the traditional SCP protocol, this is confusing. If
524 you're specifying a file at the local end, you just use one set of
525 quotes as you would normally do:
527 \c pscp "local filename with spaces" user@host:
528 \c pscp user@host:myfile "local filename with spaces"
530 But if the filename you're specifying is on the \e{remote} side, you
531 have to use backslashes and two sets of quotes:
533 \c pscp user@host:"\"remote filename with spaces\"" local_filename
534 \c pscp local_filename user@host:"\"remote filename with spaces\""
536 Worse still, in a remote-to-local copy you have to specify the local
537 file name explicitly, otherwise PSCP will complain that they don't
538 match (unless you specified the \c{-unsafe} option). The following
539 command will give an error message:
541 \c c:\>pscp user@host:"\"oo er\"" .
542 \c warning: remote host tried to write to a file called 'oo er'
543 \c when we requested a file called '"oo er"'.
545 Instead, you need to specify the local file name in full:
547 \c c:\>pscp user@host:"\"oo er\"" "oo er"
549 If PSCP is using the newer SFTP protocol, none of this is a problem,
550 and all filenames with spaces in are specified using a single pair
551 of quotes in the obvious way:
553 \c pscp "local file" user@host:
554 \c pscp user@host:"remote file" .
556 \H{faq-trouble} Troubleshooting
558 \S{faq-incorrect-mac}{Question} Why do I see \q{Incorrect MAC
561 One possible cause of this that used to be common is a bug in old
562 SSH-2 servers distributed by \cw{ssh.com}. (This is not the only
563 possible cause; see \k{errors-crc} in the documentation.)
564 Version 2.3.0 and below of their SSH-2 server
565 constructs Message Authentication Codes in the wrong way, and
566 expects the client to construct them in the same wrong way. PuTTY
567 constructs the MACs correctly by default, and hence these old
568 servers will fail to work with it.
570 If you are using PuTTY version 0.52 or better, this should work
571 automatically: PuTTY should detect the buggy servers from their
572 version number announcement, and automatically start to construct
573 its MACs in the same incorrect manner as they do, so it will be able
576 If you are using PuTTY version 0.51 or below, you can enable the
577 workaround by going to the SSH panel and ticking the box labelled
578 \q{Imitate SSH2 MAC bug}. It's possible that you might have to do
579 this with 0.52 as well, if a buggy server exists that PuTTY doesn't
582 In this context MAC stands for \ii{Message Authentication Code}. It's a
583 cryptographic term, and it has nothing at all to do with Ethernet
584 MAC (Media Access Control) addresses.
586 \S{faq-pscp-protocol}{Question} Why do I see \q{Fatal: Protocol
587 error: Expected control record} in PSCP?
589 This happens because PSCP was expecting to see data from the server
590 that was part of the PSCP protocol exchange, and instead it saw data
591 that it couldn't make any sense of at all.
593 This almost always happens because the \i{startup scripts} in your
594 account on the server machine are generating output. This is
595 impossible for PSCP, or any other SCP client, to work around. You
596 should never use startup files (\c{.bashrc}, \c{.cshrc} and so on)
597 which generate output in non-interactive sessions.
599 This is not actually a PuTTY problem. If PSCP fails in this way,
600 then all other SCP clients are likely to fail in exactly the same
601 way. The problem is at the server end.
603 \S{faq-colours}{Question} I clicked on a colour in the \ii{Colours}
604 panel, and the colour didn't change in my terminal.
606 That isn't how you're supposed to use the Colours panel.
608 During the course of a session, PuTTY potentially uses \e{all} the
609 colours listed in the Colours panel. It's not a question of using
610 only one of them and you choosing which one; PuTTY will use them
611 \e{all}. The purpose of the Colours panel is to let you adjust the
612 appearance of all the colours. So to change the colour of the
613 cursor, for example, you would select \q{Cursor Colour}, press the
614 \q{Modify} button, and select a new colour from the dialog box that
615 appeared. Similarly, if you want your session to appear in green,
616 you should select \q{Default Foreground} and press \q{Modify}.
617 Clicking on \q{ANSI Green} won't turn your session green; it will
618 only allow you to adjust the \e{shade} of green used when PuTTY is
619 instructed by the server to display green text.
621 \S{faq-winsock2}{Question} Plink on \i{Windows 95} says it can't find
624 Plink requires the extended Windows network library, WinSock version
625 2. This is installed as standard on Windows 98 and above, and on
626 Windows NT, and even on later versions of Windows 95; but early
627 Win95 installations don't have it.
629 In order to use Plink on these systems, you will need to download
631 \W{http://www.microsoft.com/windows95/downloads/contents/wuadmintools/s_wunetworkingtools/w95sockets2/}{WinSock 2 upgrade}:
633 \c http://www.microsoft.com/windows95/downloads/contents/
634 \c wuadmintools/s_wunetworkingtools/w95sockets2/
636 \S{faq-outofmem}{Question} After trying to establish an SSH-2
637 connection, PuTTY says \q{\ii{Out of memory}} and dies.
639 If this happens just while the connection is starting up, this often
640 indicates that for some reason the client and server have failed to
641 establish a session encryption key. Somehow, they have performed
642 calculations that should have given each of them the same key, but
643 have ended up with different keys; so data encrypted by one and
644 decrypted by the other looks like random garbage.
646 This causes an \q{out of memory} error because the first encrypted
647 data PuTTY expects to see is the length of an SSH message. Normally
648 this will be something well under 100 bytes. If the decryption has
649 failed, PuTTY will see a completely random length in the region of
650 two \e{gigabytes}, and will try to allocate enough memory to store
651 this non-existent message. This will immediately lead to it thinking
652 it doesn't have enough memory, and panicking.
654 If this happens to you, it is quite likely to still be a PuTTY bug
655 and you should report it (although it might be a bug in your SSH
656 server instead); but it doesn't necessarily mean you've actually run
659 \S{faq-outofmem2}{Question} When attempting a file transfer, either
660 PSCP or PSFTP says \q{\ii{Out of memory}} and dies.
662 This is almost always caused by your \i{login scripts} on the server
663 generating output. PSCP or PSFTP will receive that output when they
664 were expecting to see the start of a file transfer protocol, and
665 they will attempt to interpret the output as file-transfer protocol.
666 This will usually lead to an \q{out of memory} error for much the
667 same reasons as given in \k{faq-outofmem}.
669 This is a setup problem in your account on your server, \e{not} a
670 PSCP/PSFTP bug. Your login scripts should \e{never} generate output
671 during non-interactive sessions; secure file transfer is not the
672 only form of remote access that will break if they do.
674 On Unix, a simple fix is to ensure that all the parts of your login
675 script that might generate output are in \c{.profile} (if you use a
676 Bourne shell derivative) or \c{.login} (if you use a C shell).
677 Putting them in more general files such as \c{.bashrc} or \c{.cshrc}
678 is liable to lead to problems.
680 \S{faq-psftp-slow}{Question} PSFTP transfers files much slower than PSCP.
682 The throughput of PSFTP 0.54 should be much better than 0.53b and
683 prior; we've added code to the SFTP backend to queue several blocks
684 of data rather than waiting for an acknowledgement for each. (The
685 SCP backend did not suffer from this performance issue because SCP
686 is a much simpler protocol.)
688 \S{faq-bce}{Question} When I run full-colour applications, I see
689 areas of black space where colour ought to be, or vice versa.
691 You almost certainly need to change the \q{Use \i{background colour} to
692 erase screen} setting in the Terminal panel. If there is too much
693 black space (the commoner situation), you should enable it, while if
694 there is too much colour, you should disable it. (See \k{config-erase}.)
696 In old versions of PuTTY, this was disabled by default, and would not
697 take effect until you reset the terminal (see \k{faq-resetterm}).
698 Since 0.54, it is enabled by default, and changes take effect
701 \S{faq-resetterm}{Question} When I change some terminal settings,
704 Some of the terminal options (notably \ii{Auto Wrap} and
705 background-colour screen erase) actually represent the \e{default}
706 setting, rather than the currently active setting. The server can
707 send sequences that modify these options in mid-session, but when
708 the terminal is reset (by server action, or by you choosing \q{Reset
709 Terminal} from the System menu) the defaults are restored.
711 In versions 0.53b and prior, if you change one of these options in
712 the middle of a session, you will find that the change does not
713 immediately take effect. It will only take effect once you reset
716 In version 0.54, the behaviour has changed - changes to these
717 settings take effect immediately.
719 \S{faq-idleout}{Question} My PuTTY sessions unexpectedly close after
720 they are \I{idle connections}idle for a while.
722 Some types of \i{firewall}, and almost any router doing Network Address
723 Translation (\i{NAT}, also known as IP masquerading), will forget about
724 a connection through them if the connection does nothing for too
725 long. This will cause the connection to be rudely cut off when
728 You can try to combat this by telling PuTTY to send \e{keepalives}:
729 packets of data which have no effect on the actual session, but
730 which reassure the router or firewall that the network connection is
731 still active and worth remembering about.
733 Keepalives don't solve everything, unfortunately; although they
734 cause greater robustness against this sort of router, they can also
735 cause a \e{loss} of robustness against network dropouts. See
736 \k{config-keepalive} in the documentation for more discussion of
739 \S{faq-timeout}{Question} PuTTY's network connections time out too
740 quickly when \I{breaks in connectivity}network connectivity is
743 This is a Windows problem, not a PuTTY problem. The timeout value
744 can't be set on per application or per session basis. To increase
745 the TCP timeout globally, you need to tinker with the Registry.
747 On Windows 95, 98 or ME, the registry key you need to create or
750 \c HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\
751 \c MSTCP\MaxDataRetries
753 (it must be of type DWORD in Win95, or String in Win98/ME).
754 (See MS Knowledge Base article
755 \W{http://support.microsoft.com/default.aspx?scid=kb;en-us;158474}{158474}
756 for more information.)
758 On Windows NT, 2000, or XP, the registry key to create or change is
760 \c HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\
761 \c Parameters\TcpMaxDataRetransmissions
763 and it must be of type DWORD.
764 (See MS Knowledge Base articles
765 \W{http://support.microsoft.com/default.aspx?scid=kb;en-us;120642}{120642}
767 \W{http://support.microsoft.com/default.aspx?scid=kb;en-us;314053}{314053}
768 for more information.)
770 Set the key's value to something like 10. This will cause Windows to
771 try harder to keep connections alive instead of abandoning them.
773 \S{faq-puttyputty}{Question} When I \cw{cat} a binary file, I get
774 \q{PuTTYPuTTYPuTTY} on my command line.
778 This is designed behaviour; when PuTTY receives the character
779 Control-E from the remote server, it interprets it as a request to
780 identify itself, and so it sends back the string \q{\cw{PuTTY}} as
781 if that string had been entered at the keyboard. Control-E should
782 only be sent by programs that are prepared to deal with the
783 response. Writing a binary file to your terminal is likely to output
784 many Control-E characters, and cause this behaviour. Don't do it.
787 To mitigate the effects, you could configure the answerback string
788 to be empty (see \k{config-answerback}); but writing binary files to
789 your terminal is likely to cause various other unpleasant behaviour,
790 so this is only a small remedy.
792 \S{faq-wintitle}{Question} When I \cw{cat} a binary file, my \i{window
793 title} changes to a nonsense string.
797 It is designed behaviour that PuTTY should have the ability to
798 adjust the window title on instructions from the server. Normally
799 the control sequence that does this should only be sent
800 deliberately, by programs that know what they are doing and intend
801 to put meaningful text in the window title. Writing a binary file to
802 your terminal runs the risk of sending the same control sequence by
803 accident, and cause unexpected changes in the window title. Don't do
806 \S{faq-password-fails}{Question} My \i{keyboard} stops working once
807 PuTTY displays the \i{password prompt}.
809 No, it doesn't. PuTTY just doesn't display the password you type, so
810 that someone looking at your screen can't see what it is.
812 Unlike the Windows login prompts, PuTTY doesn't display the password
813 as a row of asterisks either. This is so that someone looking at
814 your screen can't even tell how \e{long} your password is, which
815 might be valuable information.
817 \S{faq-keyboard}{Question} One or more \I{keyboard}\i{function keys}
818 don't do what I expected in a server-side application.
820 If you've already tried all the relevant options in the PuTTY
821 Keyboard panel, you may need to mail the PuTTY maintainers and ask.
823 It is \e{not} usually helpful just to tell us which application,
824 which server operating system, and which key isn't working; in order
825 to replicate the problem we would need to have a copy of every
826 operating system, and every application, that anyone has ever
829 PuTTY responds to function key presses by sending a sequence of
830 control characters to the server. If a function key isn't doing what
831 you expect, it's likely that the character sequence your application
832 is expecting to receive is not the same as the one PuTTY is sending.
833 Therefore what we really need to know is \e{what} sequence the
834 application is expecting.
836 The simplest way to investigate this is to find some other terminal
837 environment, in which that function key \e{does} work; and then
838 investigate what sequence the function key is sending in that
839 situation. One reasonably easy way to do this on a \i{Unix} system is to
840 type the command \i\c{cat}, and then press the function key. This is
841 likely to produce output of the form \c{^[[11~}. You can also do
842 this in PuTTY, to find out what sequence the function key is
843 producing in that. Then you can mail the PuTTY maintainers and tell
844 us \q{I wanted the F1 key to send \c{^[[11~}, but instead it's
845 sending \c{^[OP}, can this be done?}, or something similar.
847 You should still read the
848 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/feedback.html}{Feedback
849 page} on the PuTTY website (also provided as \k{feedback} in the
850 manual), and follow the guidelines contained in that.
852 \S{faq-openssh-bad-openssl}{Question} Since my SSH server was upgraded
853 to \i{OpenSSH} 3.1p1/3.4p1, I can no longer connect with PuTTY.
855 There is a known problem when OpenSSH has been built against an
856 incorrect version of OpenSSL; the quick workaround is to configure
857 PuTTY to use SSH protocol 2 and the Blowfish cipher.
859 For more details and OpenSSH patches, see
860 \W{http://bugzilla.mindrot.org/show_bug.cgi?id=138}{bug 138} in the
863 This is not a PuTTY-specific problem; if you try to connect with
864 another client you'll likely have similar problems. (Although PuTTY's
865 default cipher differs from many other clients.)
867 \e{OpenSSH 3.1p1:} configurations known to be broken (and symptoms):
869 \b SSH-2 with AES cipher (PuTTY says \q{Assertion failed! Expression:
870 (len & 15) == 0} in \cw{sshaes.c}, or \q{Out of memory}, or crashes)
872 \b SSH-2 with 3DES (PuTTY says \q{Incorrect MAC received on packet})
874 \b SSH-1 with Blowfish (PuTTY says \q{Incorrect CRC received on
879 \e{OpenSSH 3.4p1:} as of 3.4p1, only the problem with SSH-1 and
880 Blowfish remains. Rebuild your server, apply the patch linked to from
881 bug 138 above, or use another cipher (e.g., 3DES) instead.
883 \e{Other versions:} we occasionally get reports of the same symptom
884 and workarounds with older versions of OpenSSH, although it's not
885 clear the underlying cause is the same.
887 \S{faq-ssh2key-ssh1conn}{Question} Why do I see \q{Couldn't load
888 private key from ...}? Why can PuTTYgen load my key but not PuTTY?
890 It's likely that you've generated an SSH protocol 2 key with PuTTYgen,
891 but you're trying to use it in an SSH-1 connection. SSH-1 and SSH-2 keys
892 have different formats, and (at least in 0.52) PuTTY's reporting of a
893 key in the wrong format isn't optimal.
895 To connect using SSH-2 to a server that supports both versions, you
896 need to change the configuration from the default (see \k{faq-ssh2}).
898 \S{faq-rh8-utf8}{Question} When I'm connected to a \i{Red Hat Linux} 8.0
899 system, some characters don't display properly.
901 A common complaint is that hyphens in man pages show up as a-acute.
903 With release 8.0, Red Hat appear to have made \i{UTF-8} the default
904 character set. There appears to be no way for terminal emulators such
905 as PuTTY to know this (as far as we know, the appropriate escape
906 sequence to switch into UTF-8 mode isn't sent).
908 A fix is to configure sessions to RH8 systems to use UTF-8
909 translation - see \k{config-charset} in the documentation. (Note that
910 if you use \q{Change Settings}, changes may not take place immediately
911 - see \k{faq-resetterm}.)
913 If you really want to change the character set used by the server, the
914 right place is \c{/etc/sysconfig/i18n}, but this shouldn't be
917 \S{faq-screen}{Question} Since I upgraded to PuTTY 0.54, the
918 scrollback has stopped working when I run \c{screen}.
920 PuTTY's terminal emulator has always had the policy that when the
921 \q{\i{alternate screen}} is in use, nothing is added to the scrollback.
922 This is because the usual sorts of programs which use the alternate
923 screen are things like text editors, which tend to scroll back and
924 forth in the same document a lot; so (a) they would fill up the
925 scrollback with a large amount of unhelpfully disordered text, and
926 (b) they contain their \e{own} method for the user to scroll back to
927 the bit they were interested in. We have generally found this policy
928 to do the Right Thing in almost all situations.
930 Unfortunately, \c{screen} is one exception: it uses the alternate
931 screen, but it's still usually helpful to have PuTTY's scrollback
932 continue working. The simplest solution is to go to the Features
933 control panel and tick \q{Disable switching to alternate terminal
934 screen}. (See \k{config-features-altscreen} for more details.)
935 Alternatively, you can tell \c{screen} itself not to use the
936 alternate screen: the
937 \W{http://www4.informatik.uni-erlangen.de/~jnweiger/screen-faq.html}{\c{screen}
938 FAQ} suggests adding the line \cq{termcapinfo xterm ti@:te@} to your
941 The reason why this only started to be a problem in 0.54 is because
942 \c{screen} typically uses an unusual control sequence to switch to
943 the alternate screen, and previous versions of PuTTY did not support
946 \S{faq-alternate-localhost}{Question} Since I upgraded \i{Windows XP}
947 to Service Pack 2, I can't use addresses like \cw{127.0.0.2}.
949 Some people who ask PuTTY to listen on \i{localhost} addresses other
950 than \cw{127.0.0.1} to forward services such as \i{SMB} and \i{Windows
951 Terminal Services} have found that doing so no longer works since
952 they upgraded to WinXP SP2.
954 This is apparently an issue with SP2 that is acknowledged by Microsoft
955 in MS Knowledge Base article
956 \W{http://support.microsoft.com/default.aspx?scid=kb;en-us;884020}{884020}.
957 The article links to a fix you can download.
959 (\e{However}, we've been told that SP2 \e{also} fixes the bug that
960 means you need to use non-\cw{127.0.0.1} addresses to forward
961 Terminal Services in the first place.)
963 \S{faq-missing-slash}{Question} PSFTP commands seem to be missing a
964 directory separator (slash).
966 Some people have reported the following incorrect behaviour with
971 \c Remote directory is /dir1/dir2
972 \c psftp> get filename.ext
974 \c /dir1/dir2filename.ext: no such file or directory
976 This is not a bug in PSFTP. There is a known bug in some versions of
978 (\W{http://bugzilla.mindrot.org/show_bug.cgi?id=697}{bug 697}) that
979 causes these symptoms; it appears to have been introduced around
980 3.7.x. It manifests only on certain platforms (AIX is what has been
983 There is a patch for OpenSSH attached to that bug; it's also fixed in
984 recent versions of portable OpenSSH (from around 3.8).
986 \S{faq-connaborted}{Question} Do you want to hear about \q{Software
987 caused connection abort}?
989 In the documentation for PuTTY 0.53 and 0.53b, we mentioned that we'd
990 like to hear about any occurrences of this error. Since the release
991 of PuTTY 0.54, however, we've been convinced that this error doesn't
992 indicate that PuTTY's doing anything wrong, and we don't need to hear
993 about further occurrences. See \k{errors-connaborted} for our current
994 documentation of this error.
996 \S{faq-rekey}{Question} My SSH-2 session \I{locking up, SSH-2
997 sessions}locks up for a few seconds every so often.
999 Recent versions of PuTTY automatically initiate \i{repeat key
1000 exchange} once per hour, to improve session security. If your client
1001 or server machine is slow, you may experience this as a delay of
1002 anything up to thirty seconds or so.
1004 These \I{delays, in SSH-2 sessions}delays are inconvenient, but they
1005 are there for your protection. If they really cause you a problem,
1006 you can choose to turn off periodic rekeying using the \q{Kex}
1007 configuration panel (see \k{config-ssh-kex}), but be aware that you
1008 will be sacrificing security for this. (Falling back to SSH-1 would
1009 also remove the delays, but would lose a \e{lot} more security
1010 still. We do not recommend it.)
1012 \S{faq-xpwontrun}{Question} PuTTY fails to start up. Windows claims that
1013 \q{the application configuration is incorrect}.
1015 This is caused by a bug in certain versions of \i{Windows XP} which is
1016 triggered by PuTTY 0.58. It can be avoided by installing
1017 Service Pack 2, by using a different version of PuTTY, or by installing
1018 a special \i{manifest file} alongside the PuTTY executable.
1020 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/xp-wont-run}{\q{xp-wont-run}}
1021 entry in PuTTY's wishlist has more details.
1023 \H{faq-secure} Security questions
1025 \S{faq-publicpc}{Question} Is it safe for me to download PuTTY and
1026 use it on a public PC?
1028 It depends on whether you trust that PC. If you don't trust the
1029 public PC, don't use PuTTY on it, and don't use any other software
1030 you plan to type passwords into either. It might be watching your
1031 keystrokes, or it might tamper with the PuTTY binary you download.
1032 There is \e{no} program safe enough that you can run it on an
1033 actively malicious PC and get away with typing passwords into it.
1035 If you do trust the PC, then it's probably OK to use PuTTY on it
1036 (but if you don't trust the network, then the PuTTY download might
1037 be tampered with, so it would be better to carry PuTTY with you on a
1040 \S{faq-cleanup}{Question} What does PuTTY leave on a system? How can
1041 I \i{clean up} after it?
1043 PuTTY will leave some Registry entries, and a random seed file, on
1044 the PC (see \k{faq-settings}). If you are using PuTTY on a public
1045 PC, or somebody else's PC, you might want to clean these up when you
1046 leave. You can do that automatically, by running the command
1047 \c{putty -cleanup}. (Note that this only removes settings for
1048 the currently logged-in user on \i{multi-user systems}.)
1050 If PuTTY was installed from the installer package, it will also
1051 appear in \q{Add/Remove Programs}. Older versions of the uninstaller
1052 do not remove the above-mentioned registry entries and file.
1054 \S{faq-dsa}{Question} How come PuTTY now supports \i{DSA}, when the
1055 website used to say how insecure it was?
1057 DSA has a major weakness \e{if badly implemented}: it relies on a
1058 random number generator to far too great an extent. If the random
1059 number generator produces a number an attacker can predict, the DSA
1060 private key is exposed - meaning that the attacker can log in as you
1061 on all systems that accept that key.
1063 The PuTTY policy changed because the developers were informed of
1064 ways to implement DSA which do not suffer nearly as badly from this
1065 weakness, and indeed which don't need to rely on random numbers at
1066 all. For this reason we now believe PuTTY's DSA implementation is
1067 probably OK. However, if you have the choice, we still recommend you
1070 \S{faq-virtuallock}{Question} Couldn't Pageant use
1071 \cw{VirtualLock()} to stop private keys being written to disk?
1073 Unfortunately not. The \cw{VirtualLock()} function in the Windows
1074 API doesn't do a proper job: it may prevent small pieces of a
1075 process's memory from being paged to disk while the process is
1076 running, but it doesn't stop the process's memory as a whole from
1077 being swapped completely out to disk when the process is long-term
1078 inactive. And Pageant spends most of its time inactive.
1080 \H{faq-admin} Administrative questions
1082 \S{faq-domain}{Question} Would you like me to register you a nicer
1085 No, thank you. Even if you can find one (most of them seem to have
1086 been registered already, by people who didn't ask whether we
1087 actually wanted it before they applied), we're happy with the PuTTY
1088 web site being exactly where it is. It's not hard to find (just type
1089 \q{putty} into \W{http://www.google.com/}{google.com} and we're the
1090 first link returned), and we don't believe the administrative hassle
1091 of moving the site would be worth the benefit.
1093 In addition, if we \e{did} want a custom domain name, we would want
1094 to run it ourselves, so we knew for certain that it would continue
1095 to point where we wanted it, and wouldn't suddenly change or do
1096 strange things. Having it registered for us by a third party who we
1097 don't even know is not the best way to achieve this.
1099 \S{faq-webhosting}{Question} Would you like free web hosting for the
1102 We already have some, thanks.
1104 \S{faq-link}{Question} Would you link to my web site from the PuTTY
1107 Only if the content of your web page is of definite direct interest
1108 to PuTTY users. If your content is unrelated, or only tangentially
1109 related, to PuTTY, then the link would simply be advertising for
1112 One very nice effect of the Google ranking mechanism is that by and
1113 large, the most popular web sites get the highest rankings. This
1114 means that when an ordinary person does a search, the top item in
1115 the search is very likely to be a high-quality site or the site they
1116 actually wanted, rather than the site which paid the most money for
1119 The PuTTY web site is held in high esteem by Google, for precisely
1120 this reason: lots of people have linked to it simply because they
1121 like PuTTY, without us ever having to ask anyone to link to us. We
1122 feel that it would be an abuse of this esteem to use it to boost the
1123 ranking of random advertisers' web sites. If you want your web site
1124 to have a high Google ranking, we'd prefer that you achieve this the
1125 way we did - by being good enough at what you do that people will
1126 link to you simply because they like you.
1128 In particular, we aren't interested in trading links for money (see
1129 above), and we \e{certainly} aren't interested in trading links for
1130 other links (since we have no advertising on our web site, our
1131 Google ranking is not even directly worth anything to us). If we
1132 don't want to link to you for free, then we probably won't want to
1135 If you have software based on PuTTY, or specifically designed to
1136 interoperate with PuTTY, or in some other way of genuine interest to
1137 PuTTY users, then we will probably be happy to add a link to you on
1138 our Links page. And if you're running a mirror of the PuTTY web
1139 site, we're \e{definitely} interested.
1141 \S{faq-sourceforge}{Question} Why don't you move PuTTY to
1144 Partly, because we don't want to move the web site location (see
1147 Also, security reasons. PuTTY is a security product, and as such it
1148 is particularly important to guard the code and the web site against
1149 unauthorised modifications which might introduce subtle security
1150 flaws. Therefore, we prefer that the Subversion repository, web site and
1151 FTP site remain where they are, under the direct control of system
1152 administrators we know and trust personally, rather than being run
1153 by a large organisation full of people we've never met and which is
1154 known to have had breakins in the past.
1156 No offence to SourceForge; I think they do a wonderful job. But
1157 they're not ideal for everyone, and in particular they're not ideal
1160 \S{faq-mailinglist1}{Question} Why can't I subscribe to the
1161 putty-bugs mailing list?
1163 Because you're not a member of the PuTTY core development team. The
1164 putty-bugs mailing list is not a general newsgroup-like discussion
1165 forum; it's a contact address for the core developers, and an
1166 \e{internal} mailing list for us to discuss things among ourselves.
1167 If we opened it up for everybody to subscribe to, it would turn into
1168 something more like a newsgroup and we would be completely
1169 overwhelmed by the volume of traffic. It's hard enough to keep up
1170 with the list as it is.
1172 \S{faq-mailinglist2}{Question} If putty-bugs isn't a
1173 general-subscription mailing list, what is?
1175 There isn't one, that we know of.
1177 If someone else wants to set up a mailing list or other forum for
1178 PuTTY users to help each other with common problems, that would be
1179 fine with us, though the PuTTY team would almost certainly not have the
1180 time to read it. It's probably better to use one of the established
1181 newsgroups for this purpose (see \k{feedback-other-fora}).
1183 \S{faq-donations}{Question} How can I donate to PuTTY development?
1185 Please, \e{please} don't feel you have to. PuTTY is completely free
1186 software, and not shareware. We think it's very important that
1187 \e{everybody} who wants to use PuTTY should be able to, whether they
1188 have any money or not; so the last thing we would want is for a
1189 PuTTY user to feel guilty because they haven't paid us any money. If
1190 you want to keep your money, please do keep it. We wouldn't dream of
1193 Having said all that, if you still really \e{want} to give us money,
1194 we won't argue :-) The easiest way for us to accept donations is if
1195 you send money to \cw{<anakin@pobox.com>} using PayPal
1196 (\W{http://www.paypal.com/}\cw{www.paypal.com}). Alternatively, if
1197 you don't trust PayPal, you could donate through e-gold
1198 (\W{http://www.e-gold.com}\cw{www.e-gold.com}): deposit your
1199 donation in account number 174769, then send us e-mail to let us
1200 know you've done so (otherwise we might not notice for months!).
1202 Small donations (tens of dollars or tens of euros) will probably be
1203 spent on beer or curry, which helps motivate our volunteer team to
1204 continue doing this for the world. Larger donations will be spent on
1205 something that actually helps development, if we can find anything
1206 (perhaps new hardware, or a copy of Windows XP), but if we can't
1207 find anything then we'll just distribute the money among the
1208 developers. If you want to be sure your donation is going towards
1209 something worthwhile, ask us first. If you don't like these terms,
1210 feel perfectly free not to donate. We don't mind.
1212 \S{faq-permission}{Question} Can I have permission to put PuTTY on a
1213 cover disk / distribute it with other software / etc?
1215 Yes. For most things, you need not bother asking us explicitly for
1216 permission; our licence already grants you permission.
1218 See \k{feedback-permission} for more details.
1220 \S{faq-indemnity}{Question} Can you sign an agreement indemnifying
1221 us against security problems in PuTTY?
1225 A vendor of physical security products (e.g. locks) might plausibly
1226 be willing to accept financial liability for a product that failed
1227 to perform as advertised and resulted in damage (e.g. valuables
1228 being stolen). The reason they can afford to do this is because they
1229 sell a \e{lot} of units, and only a small proportion of them will
1230 fail; so they can meet their financial liability out of the income
1231 from all the rest of their sales, and still have enough left over to
1232 make a profit. Financial liability is intrinsically linked to
1233 selling your product for money.
1235 There are two reasons why PuTTY is not analogous to a physical lock
1236 in this context. One is that software products don't exhibit random
1237 variation: \e{if} PuTTY has a security hole (which does happen,
1238 although we do our utmost to prevent it and to respond quickly when
1239 it does), every copy of PuTTY will have the same hole, so it's
1240 likely to affect all the users at the same time. So even if our
1241 users were all paying us to use PuTTY, we wouldn't be able to
1242 \e{simultaneously} pay every affected user compensation in excess of
1243 the amount they had paid us in the first place. It just wouldn't
1246 The second, much more important, reason is that PuTTY users
1247 \e{don't} pay us. The PuTTY team does not have an income; it's a
1248 volunteer effort composed of people spending their spare time to try
1249 to write useful software. We aren't even a company or any kind of
1250 legally recognised organisation. We're just a bunch of people who
1251 happen to do some stuff in our spare time.
1253 Therefore, to ask us to assume financial liability is to ask us to
1254 assume a risk of having to pay it out of our own \e{personal}
1255 pockets: out of the same budget from which we buy food and clothes
1256 and pay our rent. That's more than we're willing to give. We're
1257 already giving a lot of our spare \e{time} to developing software
1258 for free; if we had to pay our own \e{money} to do it as well, we'd
1259 start to wonder why we were bothering.
1261 Free software fundamentally does not work on the basis of financial
1262 guarantees. Your guarantee of the software functioning correctly is
1263 simply that you have the source code and can check it before you use
1264 it. If you want to be sure there aren't any security holes, do a
1265 security audit of the PuTTY code, or hire a security engineer if you
1266 don't have the necessary skills yourself: instead of trying to
1267 ensure you can get compensation in the event of a disaster, try to
1268 ensure there isn't a disaster in the first place.
1270 If you \e{really} want financial security, see if you can find a
1271 security engineer who will take financial responsibility for the
1272 correctness of their review. (This might be less likely to suffer
1273 from the everything-failing-at-once problem mentioned above, because
1274 such an engineer would probably be reviewing a lot of \e{different}
1275 products which would tend to fail independently.) Failing that, see
1276 if you can persuade an insurance company to insure you against
1277 security incidents, and if the insurer demands it as a condition
1278 then get our code reviewed by a security engineer they're happy
1281 \S{faq-permission-form}{Question} Can you sign this form granting us
1282 permission to use/distribute PuTTY?
1284 If your form contains any clause along the lines of \q{the
1285 undersigned represents and warrants}, we're not going to sign it.
1286 This is particularly true if it asks us to warrant that PuTTY is
1287 secure; see \k{faq-indemnity} for more discussion of this. But it
1288 doesn't really matter what we're supposed to be warranting: even if
1289 it's something we already believe is true, such as that we don't
1290 infringe any third-party copyright, we will not sign a document
1291 accepting any legal or financial liability. This is simply because
1292 the PuTTY development project has no income out of which to satisfy
1293 that liability, or pay legal costs, should it become necessary. We
1294 cannot afford to be sued. We are assuring you that \e{we have done
1295 our best}; if that isn't good enough for you, tough.
1297 The existing PuTTY licence document already gives you permission to
1298 use or distribute PuTTY in pretty much any way which does not
1299 involve pretending you wrote it or suing us if it goes wrong. We
1300 think that really ought to be enough for anybody.
1302 See also \k{faq-permission-general} for another reason why we don't
1303 want to do this sort of thing.
1305 \S{faq-permission-future}{Question} Can you write us a formal notice
1306 of permission to use PuTTY?
1308 We could, in principle, but it isn't clear what use it would be. If
1309 you think there's a serious chance of one of the PuTTY copyright
1310 holders suing you (which we don't!), you would presumably want a
1311 signed notice from \e{all} of them; and we couldn't provide that
1312 even if we wanted to, because many of the copyright holders are
1313 people who contributed some code in the past and with whom we
1314 subsequently lost contact. Therefore the best we would be able to do
1315 \e{even in theory} would be to have the core development team sign
1316 the document, which wouldn't guarantee you that some other copyright
1317 holder might not sue.
1319 See also \k{faq-permission-general} for another reason why we don't
1320 want to do this sort of thing.
1322 \S{faq-permission-general}{Question} Can you sign \e{anything} for
1325 Not unless there's an incredibly good reason.
1327 We are generally unwilling to set a precedent that involves us
1328 having to enter into individual agreements with PuTTY users. We
1329 estimate that we have literally \e{millions} of users, and we
1330 absolutely would not have time to go round signing specific
1331 agreements with every one of them. So if you want us to sign
1332 something specific for you, you might usefully stop to consider
1333 whether there's anything special that distinguishes you from 999,999
1334 other users, and therefore any reason we should be willing to sign
1335 something for you without it setting such a precedent.
1337 If your company policy requires you to have an individual agreement
1338 with the supplier of any software you use, then your company policy
1339 is simply not well suited to using popular free software, and we
1340 urge you to consider this as a flaw in your policy.
1342 \S{faq-permission-assurance}{Question} If you won't sign anything,
1343 can you give us some sort of assurance that you won't make PuTTY
1344 closed-source in future?
1348 If what you want is an assurance that some \e{current version} of
1349 PuTTY which you've already downloaded will remain free, then you
1350 already have that assurance: it's called the PuTTY Licence. It
1351 grants you permission to use, distribute and copy the software to
1352 which it applies; once we've granted that permission (which we
1353 have), we can't just revoke it.
1355 On the other hand, if you want an assurance that \e{future} versions
1356 of PuTTY won't be closed-source, that's more difficult. We could in
1357 principle sign a document stating that we would never release a
1358 closed-source PuTTY, but that wouldn't assure you that we \e{would}
1359 keep releasing \e{open}-source PuTTYs: we would still have the
1360 option of ceasing to develop PuTTY at all, which would surely be
1361 even worse for you than making it closed-source! (And we almost
1362 certainly wouldn't \e{want} to sign a document guaranteeing that we
1363 would actually continue to do development work on PuTTY; we
1364 certainly wouldn't sign it for free. Documents like that are called
1365 contracts of employment, and are generally not signed except in
1366 return for a sizeable salary.)
1368 If we \e{were} to stop developing PuTTY, or to decide to make all
1369 future releases closed-source, then you would still be free to copy
1370 the last open release in accordance with the current licence, and in
1371 particular you could start your own fork of the project from that
1372 release. If this happened, I confidently predict that \e{somebody}
1373 would do that, and that some kind of a free PuTTY would continue to
1374 be developed. There's already precedent for that sort of thing
1375 happening in free software. We can't guarantee that somebody
1376 \e{other than you} would do it, of course; you might have to do it
1377 yourself. But we can assure you that there would be nothing
1378 \e{preventing} anyone from continuing free development if we
1381 (Finally, we can also confidently predict that if we made PuTTY
1382 closed-source and someone made an open-source fork, most people
1383 would switch to the latter. Therefore, it would be pretty stupid of
1386 \S{faq-export-cert}{Question} Can you provide us with export control
1387 information / FIPS certification for PuTTY?
1389 Some people have asked us for an Export Control Classification Number
1390 (ECCN) for PuTTY. We don't know whether we have one, and as a team of
1391 free software developers based in the UK we don't have the time,
1392 money, or effort to deal with US bureaucracy to investigate any
1393 further. We believe that PuTTY falls under 5D002 on the US Commerce
1394 Control List, but that shouldn't be taken as definitive. If you need
1395 to know more you should seek professional legal advice. The same
1396 applies to any other country's legal requirements and restrictions.
1398 Similarly, some people have asked us for FIPS certification of the
1399 PuTTY tools. Unless someone else is prepared to do the necessary work
1400 and pay any costs, we can't provide this.
1402 \H{faq-misc} Miscellaneous questions
1404 \S{faq-openssh}{Question} Is PuTTY a port of \i{OpenSSH}, or based on
1407 No, it isn't. PuTTY is almost completely composed of code written
1408 from scratch for PuTTY. The only code we share with OpenSSH is the
1409 detector for SSH-1 CRC compensation attacks, written by CORE SDI S.A.
1411 \S{faq-sillyputty}{Question} Where can I buy silly putty?
1413 You're looking at the wrong web site; the only PuTTY we know about
1414 here is the name of a computer program.
1416 If you want the kind of putty you can buy as an executive toy, the
1417 PuTTY team can personally recommend Thinking Putty, which you can
1418 buy from Crazy Aaron's Putty World, at
1419 \W{http://www.puttyworld.com}\cw{www.puttyworld.com}.
1421 \S{faq-meaning}{Question} What does \q{PuTTY} mean?
1423 It's the name of a popular SSH and Telnet client. Any other meaning
1424 is in the eye of the beholder. It's been rumoured that \q{PuTTY}
1425 is the antonym of \q{\cw{getty}}, or that it's the stuff that makes your
1426 Windows useful, or that it's a kind of plutonium Teletype. We
1427 couldn't possibly comment on such allegations.
1429 \S{faq-pronounce}{Question} How do I pronounce \q{PuTTY}?
1431 Exactly like the English word \q{putty}, which we pronounce
1432 /\u02C8{'}p\u028C{V}ti/.