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 In general, if you want to know if PuTTY supports a particular
31 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 v2?
50 Yes. SSH v2 support has been available in PuTTY since version 0.50.
52 Public key authentication (both RSA and DSA) in SSH v2 is new in
55 \S{faq-ssh2-keyfmt}{Question} Does PuTTY support reading OpenSSH or
56 \cw{ssh.com} SSHv2 private key files?
58 PuTTY doesn't support this natively, but as of 0.53
59 PuTTYgen can convert both OpenSSH and \cw{ssh.com} private key
60 files into PuTTY's format.
62 \S{faq-ssh1}{Question} Does PuTTY support SSH v1?
64 Yes. SSH 1 support has always been available in PuTTY.
66 \S{faq-localecho}{Question} Does PuTTY support local echo?
68 Yes. Version 0.52 has proper support for local echo.
70 In version 0.51 and before, local echo could not be separated from
71 local line editing (where you type a line of text locally, and it is
72 not sent to the server until you press Return, so you have the
73 chance to edit it and correct mistakes \e{before} the server sees
74 it). New in version 0.52, local echo and local line editing are
75 separate options, and by default PuTTY will try to determine
76 automatically whether to enable them or not, based on which protocol
77 you have selected and also based on hints from the server. If you
78 have a problem with PuTTY's default choice, you can force each
79 option to be enabled or disabled as you choose. The controls are in
80 the Terminal panel, in the section marked \q{Line discipline
83 \S{faq-savedsettings}{Question} Does PuTTY support storing settings,
84 so I don't have to change them every time?
86 Yes, all of PuTTY's settings can be saved in named session profiles.
87 See \k{config-saving} in the documentation for how to do this.
89 \S{faq-disksettings}{Question} Does PuTTY support storing its
90 settings in a disk file?
92 Not at present, although \k{config-file} in the documentation gives
93 a method of achieving the same effect.
95 \S{faq-fullscreen}{Question} Does PuTTY support full-screen mode,
98 Yes; this is a new feature in version 0.52.
100 \S{faq-password-remember}{Question} Does PuTTY have the ability to
101 remember my password so I don't have to type it every time?
105 Remembering your password is a bad plan for obvious security
106 reasons: anyone who gains access to your machine while you're away
107 from your desk can find out the remembered password, and use it,
108 abuse it or change it.
110 In addition, it's not even \e{possible} for PuTTY to automatically
111 send your password in a Telnet session, because Telnet doesn't give
112 the client software any indication of which part of the login
113 process is the password prompt. PuTTY would have to guess, by
114 looking for words like \q{password} in the session data; and if your
115 login program is written in something other than English, this won't
118 In SSH, remembering your password would be possible in theory, but
119 there doesn't seem to be much point since SSH supports public key
120 authentication, which is more flexible and more secure. See
121 \k{pubkey} in the documentation for a full discussion of public key
124 \S{faq-hostkeys}{Question} Is there an option to turn off the
125 annoying host key prompts?
127 No, there isn't. And there won't be. Even if you write it yourself
128 and send us the patch, we won't accept it.
130 Those annoying host key prompts are the \e{whole point} of SSH.
131 Without them, all the cryptographic technology SSH uses to secure
132 your session is doing nothing more than making an attacker's job
133 slightly harder; instead of sitting between you and the server with
134 a packet sniffer, the attacker must actually subvert a router and
135 start modifying the packets going back and forth. But that's not all
136 that much harder than just sniffing; and without host key checking,
137 it will go completely undetected by client or server.
139 Host key checking is your guarantee that the encryption you put on
140 your data at the client end is the \e{same} encryption taken off the
141 data at the server end; it's your guarantee that it hasn't been
142 removed and replaced somewhere on the way. Host key checking makes
143 the attacker's job \e{astronomically} hard, compared to packet
144 sniffing, and even compared to subverting a router. Instead of
145 applying a little intelligence and keeping an eye on Bugtraq, the
146 attacker must now perform a brute-force attack against at least one
147 military-strength cipher. That insignificant host key prompt really
148 does make \e{that} much difference.
150 If you're having a specific problem with host key checking - perhaps
151 you want an automated batch job to make use of PSCP or Plink, and
152 the interactive host key prompt is hanging the batch process - then
153 the right way to fix it is to add the correct host key to the
154 Registry in advance. That way, you retain the \e{important} feature
155 of host key checking: the right key will be accepted and the wrong
156 ones will not. Adding an option to turn host key checking off
157 completely is the wrong solution and we will not do it.
159 If you have host keys available in the common \c{known_hosts} format,
160 we have a script called
161 \W{http://www.tartarus.org/~simon-anonsvn/viewcvs.cgi/putty/contrib/kh2reg.py?view=markup}\c{kh2reg.py}
162 to convert them to a Windows .REG file, which can be installed ahead of
163 time by double-clicking or using \c{REGEDIT}.
165 \S{faq-server}{Question} Will you write an SSH server for the PuTTY
166 suite, to go with the client?
168 No. The only reason we might want to would be if we could easily
169 re-use existing code and significantly cut down the effort. We don't
170 believe this is the case; there just isn't enough common ground
171 between an SSH client and server to make it worthwhile.
173 If someone else wants to use bits of PuTTY in the process of writing
174 a Windows SSH server, they'd be perfectly welcome to of course, but
175 I really can't see it being a lot less effort for us to do that than
176 it would be for us to write a server from the ground up. We don't
177 have time, and we don't have motivation. The code is available if
178 anyone else wants to try it.
180 \S{faq-pscp-ascii}{Question} Can PSCP or PSFTP transfer files in
185 Until recently, this was a limitation of the file transfer protocols:
186 the SCP and SFTP protocols had no notion of transferring a file in
187 anything other than binary mode. (This is still true of SCP.)
189 The current draft protocol spec of SFTP proposes a means of
190 implementing ASCII transfer. At some point PSCP/PSFTP may implement
193 \H{faq-ports} Ports to other operating systems
195 The eventual goal is for PuTTY to be a multi-platform program, able
196 to run on at least Windows, Mac OS and Unix.
198 Porting will become easier once PuTTY has a generalised porting
199 layer, drawing a clear line between platform-dependent and
200 platform-independent code. The general intention was for this
201 porting layer to evolve naturally as part of the process of doing
202 the first port; a Unix port has now been released and the plan
203 seems to be working so far.
205 \S{faq-ports-general}{Question} What ports of PuTTY exist?
207 Currently, release versions of PuTTY tools only run on full Win32
208 systems and Unix. \q{Win32} includes Windows 95, 98, and ME, and it
209 includes Windows NT, Windows 2000 and Windows XP.
211 In the development code, a partial port to the Mac OS (see
212 \k{faq-mac-port}) is under way.
214 Currently PuTTY does \e{not} run on Windows CE (see \k{faq-wince}),
215 and it does not quite run on the Win32s environment under Windows
216 3.1 (see \k{faq-win31}).
218 We do not have release-quality ports for any other systems at the
219 present time. If anyone told you we had an EPOC port, or an iPaq port,
220 or any other port of PuTTY, they were mistaken. We don't.
222 There are some third-party ports to various platforms, mentioned
223 on the Links page of our website.
225 \S{faq-unix}{Question} Is there a port to Unix?
227 As of 0.54, there are Unix ports of most of the traditional PuTTY
228 tools, and also one entirely new application.
230 If you look at the source release, you should find a \c{unix}
231 subdirectory containing \c{Makefile.gtk}, which should build you Unix
232 ports of Plink, PuTTY itself, PuTTYgen, PSCP, PSFTP, and also
233 \c{pterm} - an \cw{xterm}-type program which supports the same
234 terminal emulation as PuTTY. We do not yet have a Unix port of
237 If you don't have Gtk, you should still be able to build the
240 Note that Unix PuTTY has mostly only been tested on Linux so far;
241 portability problems such as BSD-style ptys or different header file
242 requirements are expected.
244 \S{faq-unix-why}{Question} What's the point of the Unix port? Unix
247 All sorts of little things. \c{pterm} is directly useful to anyone
248 who prefers PuTTY's terminal emulation to \c{xterm}'s, which at
249 least some people do. Unix Plink has apparently found a niche among
250 people who find the complexity of OpenSSL makes OpenSSH hard to
251 install (and who don't mind Plink not having as many features). Some
252 users want to generate a large number of SSH keys on Unix and then
253 copy them all into PuTTY, and the Unix PuTTYgen should allow them to
254 automate that conversion process.
256 There were development advantages as well; porting PuTTY to Unix was
257 a valuable path-finding effort for other future ports, and also
258 allowed us to use the excellent Linux tool
259 \W{http://valgrind.kde.org/}{Valgrind} to help with debugging, which
260 has already improved PuTTY's stability on \e{all} platforms.
262 However, if you're a Unix user and you can see no reason to switch
263 from OpenSSH to PuTTY/Plink, then you're probably right. We don't
264 expect our Unix port to be the right thing for everybody.
266 \S{faq-wince}{Question} Will there be a port to Windows CE or PocketPC?
268 It's currently being worked on, but it's only in its early stages yet,
269 and certainly isn't yet useful. PuTTY on portable devices would
270 clearly be a useful thing, so in the long term I hope it can be
271 brought up to release quality.
273 There's also a third-party port at
274 \W{http://pocketputty.duxy.net/}\c{http://pocketputty.duxy.net/}.
276 \S{faq-win31}{Question} Is there a port to Windows 3.1?
278 PuTTY is a 32-bit application from the ground up, so it won't run on
279 Windows 3.1 as a native 16-bit program; and it would be \e{very}
280 hard to port it to do so, because of Windows 3.1's vile memory
281 allocation mechanisms.
283 However, it is possible in theory to compile the existing PuTTY
284 source in such a way that it will run under Win32s (an extension to
285 Windows 3.1 to let you run 32-bit programs). In order to do this
286 you'll need the right kind of C compiler - modern versions of Visual
287 C at least have stopped being backwards compatible to Win32s. Also,
288 the last time we tried this it didn't work very well.
290 If you're interested in running PuTTY under Windows 3.1, help and
291 testing in this area would be very welcome!
293 \S{faq-mac-port}{Question} Will there be a port to the Mac?
295 There are several answers to this question:
297 \b The Unix/Gtk port is already fully working under Mac OS X as an X11
300 \b A native (Cocoa) Mac OS X port is in progress. It's just about
301 usable, but is of nowhere near release quality yet, and is likely to
302 behave in unexpected ways.
304 \b A separate port to the classic Mac OS (pre-OSX) is also in
305 progress; it too is not ready yet.
307 \S{faq-epoc}{Question} Will there be a port to EPOC?
309 I hope so, but given that ports aren't really progressing very fast
310 even on systems the developers \e{do} already know how to program
311 for, it might be a long time before any of us get round to learning
312 a new system and doing the port for that.
314 However, some of the work has been done by other people, and a beta
315 port of PuTTY for the Nokia 9200 Communicator series is available
316 from \W{http://s2putty.sourceforge.net/}\cw{http://s2putty.sourceforge.net/}
318 \H{faq-embedding} Embedding PuTTY in other programs
320 \S{faq-dll}{Question} Is the SSH or Telnet code available as a DLL?
322 No, it isn't. It would take a reasonable amount of rewriting for
323 this to be possible, and since the PuTTY project itself doesn't
324 believe in DLLs (they make installation more error-prone) none of us
325 has taken the time to do it.
327 Most of the code cleanup work would be a good thing to happen in
328 general, so if anyone feels like helping, we wouldn't say no.
330 \S{faq-vb}{Question} Is the SSH or Telnet code available as a Visual
333 No, it isn't. None of the PuTTY team uses Visual Basic, and none of
334 us has any particular need to make SSH connections from a Visual
335 Basic application. In addition, all the preliminary work to turn it
336 into a DLL would be necessary first; and furthermore, we don't even
337 know how to write VB components.
339 If someone offers to do some of this work for us, we might consider
340 it, but unless that happens I can't see VB integration being
341 anywhere other than the very bottom of our priority list.
343 \S{faq-ipc}{Question} How can I use PuTTY to make an SSH connection
344 from within another program?
346 Probably your best bet is to use Plink, the command-line connection
347 tool. If you can start Plink as a second Windows process, and
348 arrange for your primary process to be able to send data to the
349 Plink process, and receive data from it, through pipes, then you
350 should be able to make SSH connections from your program.
352 This is what CVS for Windows does, for example.
354 \H{faq-details} Details of PuTTY's operation
356 \S{faq-term}{Question} What terminal type does PuTTY use?
358 For most purposes, PuTTY can be considered to be an \cw{xterm}
361 PuTTY also supports some terminal control sequences not supported by
362 the real \cw{xterm}: notably the Linux console sequences that
363 reconfigure the colour palette, and the title bar control sequences
364 used by \cw{DECterm} (which are different from the \cw{xterm} ones;
365 PuTTY supports both).
367 By default, PuTTY announces its terminal type to the server as
368 \c{xterm}. If you have a problem with this, you can reconfigure it
369 to say something else; \c{vt220} might help if you have trouble.
371 \S{faq-settings}{Question} Where does PuTTY store its data?
373 On Windows, PuTTY stores most of its data (saved sessions, SSH host
374 keys) in the Registry. The precise location is
376 \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY
378 and within that area, saved sessions are stored under \c{Sessions}
379 while host keys are stored under \c{SshHostKeys}.
381 PuTTY also requires a random number seed file, to improve the
382 unpredictability of randomly chosen data needed as part of the SSH
383 cryptography. This is stored by default in your Windows home
384 directory (\c{%HOMEDRIVE%\\%HOMEPATH%}), or in the actual Windows
385 directory (such as \c{C:\\WINDOWS}) if the home directory doesn't
386 exist, for example if you're using Win95. If you want to change the
387 location of the random number seed file, you can put your chosen
388 pathname in the Registry, at
390 \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\RandSeedFile
392 On Unix, PuTTY stores all of this data in a directory \cw{~/.putty}.
394 \H{faq-howto} HOWTO questions
396 \S{faq-startmax}{Question} How can I make PuTTY start up maximised?
398 Create a Windows shortcut to start PuTTY from, and set it as \q{Run
401 \S{faq-startsess}{Question} How can I create a Windows shortcut to
402 start a particular saved session directly?
404 To run a PuTTY session saved under the name \q{\cw{mysession}},
405 create a Windows shortcut that invokes PuTTY with a command line
408 \c \path\name\to\putty.exe -load mysession
410 (Note: prior to 0.53, the syntax was \c{@session}. This is now
411 deprecated and may be removed at some point.)
413 \S{faq-startssh}{Question} How can I start an SSH session straight
414 from the command line?
416 Use the command line \c{putty -ssh host.name}. Alternatively, create
417 a saved session that specifies the SSH protocol, and start the saved
418 session as shown in \k{faq-startsess}.
420 \S{faq-cutpaste}{Question} How do I copy and paste between PuTTY and
421 other Windows applications?
423 Copy and paste works similarly to the X Window System. You use the
424 left mouse button to select text in the PuTTY window. The act of
425 selection \e{automatically} copies the text to the clipboard: there
426 is no need to press Ctrl-Ins or Ctrl-C or anything else. In fact,
427 pressing Ctrl-C will send a Ctrl-C character to the other end of
428 your connection (just like it does the rest of the time), which may
429 have unpleasant effects. The \e{only} thing you need to do, to copy
430 text to the clipboard, is to select it.
432 To paste the clipboard contents into a PuTTY window, by default you
433 click the right mouse button. If you have a three-button mouse and
434 are used to X applications, you can configure pasting to be done by
435 the middle button instead, but this is not the default because most
436 Windows users don't have a middle button at all.
438 You can also paste by pressing Shift-Ins.
440 \S{faq-options}{Question} How do I use all PuTTY's features (public
441 keys, proxying, cipher selection, etc.) in PSCP, PSFTP and Plink?
443 Most major features (e.g., public keys, port forwarding) are available
444 through command line options. See the documentation.
446 Not all features are accessible from the command line yet, although
447 we'd like to fix this. In the meantime, you can use most of
448 PuTTY's features if you create a PuTTY saved session, and then use
449 the name of the saved session on the command line in place of a
450 hostname. This works for PSCP, PSFTP and Plink (but don't expect
451 port forwarding in the file transfer applications!).
453 \S{faq-pscp}{Question} How do I use PSCP.EXE? When I double-click it
454 gives me a command prompt window which then closes instantly.
456 PSCP is a command-line application, not a GUI application. If you
457 run it without arguments, it will simply print a help message and
460 To use PSCP properly, run it from a Command Prompt window. See
461 \k{pscp} in the documentation for more details.
463 \S{faq-pscp-spaces}{Question} How do I use PSCP to copy a file whose
466 If PSCP is using the traditional SCP protocol, this is confusing. If
467 you're specifying a file at the local end, you just use one set of
468 quotes as you would normally do:
470 \c pscp "local filename with spaces" user@host:
471 \c pscp user@host:myfile "local filename with spaces"
473 But if the filename you're specifying is on the \e{remote} side, you
474 have to use backslashes and two sets of quotes:
476 \c pscp user@host:"\"remote filename with spaces\"" local_filename
477 \c pscp local_filename user@host:"\"remote filename with spaces\""
479 Worse still, in a remote-to-local copy you have to specify the local
480 file name explicitly, otherwise PSCP will complain that they don't
481 match (unless you specified the \c{-unsafe} option). The following
482 command will give an error message:
484 \c c:\>pscp user@host:"\"oo er\"" .
485 \c warning: remote host tried to write to a file called 'oo er'
486 \c when we requested a file called '"oo er"'.
488 Instead, you need to specify the local file name in full:
490 \c c:\>pscp user@host:"\"oo er\"" "oo er"
492 If PSCP is using the newer SFTP protocol, none of this is a problem,
493 and all filenames with spaces in are specified using a single pair
494 of quotes in the obvious way:
496 \c pscp "local file" user@host:
497 \c pscp user@host:"remote file" .
499 \H{faq-trouble} Troubleshooting
501 \S{faq-incorrect-mac}{Question} Why do I see \q{Incorrect MAC
504 One possible cause of this that used to be common is a bug in old
505 SSH 2 servers distributed by \cw{ssh.com}. (This is not the only
506 possible cause; see \k{errors-crc} in the documentation.)
507 Version 2.3.0 and below of their SSH 2 server
508 constructs Message Authentication Codes in the wrong way, and
509 expects the client to construct them in the same wrong way. PuTTY
510 constructs the MACs correctly by default, and hence these old
511 servers will fail to work with it.
513 If you are using PuTTY version 0.52 or better, this should work
514 automatically: PuTTY should detect the buggy servers from their
515 version number announcement, and automatically start to construct
516 its MACs in the same incorrect manner as they do, so it will be able
519 If you are using PuTTY version 0.51 or below, you can enable the
520 workaround by going to the SSH panel and ticking the box labelled
521 \q{Imitate SSH 2 MAC bug}. It's possible that you might have to do
522 this with 0.52 as well, if a buggy server exists that PuTTY doesn't
525 In this context MAC stands for Message Authentication Code. It's a
526 cryptographic term, and it has nothing at all to do with Ethernet
527 MAC (Media Access Control) addresses.
529 \S{faq-pscp-protocol}{Question} Why do I see \q{Fatal: Protocol
530 error: Expected control record} in PSCP?
532 This happens because PSCP was expecting to see data from the server
533 that was part of the PSCP protocol exchange, and instead it saw data
534 that it couldn't make any sense of at all.
536 This almost always happens because the startup scripts in your
537 account on the server machine are generating output. This is
538 impossible for PSCP, or any other SCP client, to work around. You
539 should never use startup files (\c{.bashrc}, \c{.cshrc} and so on)
540 which generate output in non-interactive sessions.
542 This is not actually a PuTTY problem. If PSCP fails in this way,
543 then all other SCP clients are likely to fail in exactly the same
544 way. The problem is at the server end.
546 \S{faq-colours}{Question} I clicked on a colour in the Colours
547 panel, and the colour didn't change in my terminal.
549 That isn't how you're supposed to use the Colours panel.
551 During the course of a session, PuTTY potentially uses \e{all} the
552 colours listed in the Colours panel. It's not a question of using
553 only one of them and you choosing which one; PuTTY will use them
554 \e{all}. The purpose of the Colours panel is to let you adjust the
555 appearance of all the colours. So to change the colour of the
556 cursor, for example, you would select \q{Cursor Colour}, press the
557 \q{Modify} button, and select a new colour from the dialog box that
558 appeared. Similarly, if you want your session to appear in green,
559 you should select \q{Default Foreground} and press \q{Modify}.
560 Clicking on \q{ANSI Green} won't turn your session green; it will
561 only allow you to adjust the \e{shade} of green used when PuTTY is
562 instructed by the server to display green text.
564 \S{faq-winsock2}{Question} Plink on Windows 95 says it can't find
567 Plink requires the extended Windows network library, WinSock version
568 2. This is installed as standard on Windows 98 and above, and on
569 Windows NT, and even on later versions of Windows 95; but early
570 Win95 installations don't have it.
572 In order to use Plink on these systems, you will need to download
574 \W{http://www.microsoft.com/windows95/downloads/contents/wuadmintools/s_wunetworkingtools/w95sockets2/}{WinSock 2 upgrade}:
576 \c http://www.microsoft.com/windows95/downloads/contents/
577 \c wuadmintools/s_wunetworkingtools/w95sockets2/
579 \S{faq-outofmem}{Question} After trying to establish an SSH 2
580 connection, PuTTY says \q{Out of memory} and dies.
582 If this happens just while the connection is starting up, this often
583 indicates that for some reason the client and server have failed to
584 establish a session encryption key. Somehow, they have performed
585 calculations that should have given each of them the same key, but
586 have ended up with different keys; so data encrypted by one and
587 decrypted by the other looks like random garbage.
589 This causes an \q{out of memory} error because the first encrypted
590 data PuTTY expects to see is the length of an SSH message. Normally
591 this will be something well under 100 bytes. If the decryption has
592 failed, PuTTY will see a completely random length in the region of
593 two \e{gigabytes}, and will try to allocate enough memory to store
594 this non-existent message. This will immediately lead to it thinking
595 it doesn't have enough memory, and panicking.
597 If this happens to you, it is quite likely to still be a PuTTY bug
598 and you should report it (although it might be a bug in your SSH
599 server instead); but it doesn't necessarily mean you've actually run
602 \S{faq-outofmem2}{Question} When attempting a file transfer, either
603 PSCP or PSFTP says \q{Out of memory} and dies.
605 This is almost always caused by your login scripts on the server
606 generating output. PSCP or PSFTP will receive that output when they
607 were expecting to see the start of a file transfer protocol, and
608 they will attempt to interpret the output as file-transfer protocol.
609 This will usually lead to an \q{out of memory} error for much the
610 same reasons as given in \k{faq-outofmem}.
612 This is a setup problem in your account on your server, \e{not} a
613 PSCP/PSFTP bug. Your login scripts should \e{never} generate output
614 during non-interactive sessions; secure file transfer is not the
615 only form of remote access that will break if they do.
617 On Unix, a simple fix is to ensure that all the parts of your login
618 script that might generate output are in \c{.profile} (if you use a
619 Bourne shell derivative) or \c{.login} (if you use a C shell).
620 Putting them in more general files such as \c{.bashrc} or \c{.cshrc}
621 is liable to lead to problems.
623 \S{faq-psftp-slow}{Question} PSFTP transfers files much slower than PSCP.
625 The throughput of PSFTP 0.54 should be much better than 0.53b and
626 prior; we've added code to the SFTP backend to queue several blocks
627 of data rather than waiting for an acknowledgement for each. (The
628 SCP backend did not suffer from this performance issue because SCP
629 is a much simpler protocol.)
631 \S{faq-bce}{Question} When I run full-colour applications, I see
632 areas of black space where colour ought to be, or vice versa.
634 You almost certainly need to change the \q{Use background colour to
635 erase screen} setting in the Terminal panel. If there is too much
636 black space (the commoner situation), you should enable it, while if
637 there is too much colour, you should disable it. (See \k{config-erase}.)
639 In old versions of PuTTY, this was disabled by default, and would not
640 take effect until you reset the terminal (see \k{faq-resetterm}).
641 Since 0.54, it is enabled by default, and changes take effect
644 \S{faq-resetterm}{Question} When I change some terminal settings,
647 Some of the terminal options (notably Auto Wrap and
648 background-colour screen erase) actually represent the \e{default}
649 setting, rather than the currently active setting. The server can
650 send sequences that modify these options in mid-session, but when
651 the terminal is reset (by server action, or by you choosing \q{Reset
652 Terminal} from the System menu) the defaults are restored.
654 In versions 0.53b and prior, if you change one of these options in
655 the middle of a session, you will find that the change does not
656 immediately take effect. It will only take effect once you reset
659 In version 0.54, the behaviour has changed - changes to these
660 settings take effect immediately.
662 \S{faq-idleout}{Question} My PuTTY sessions unexpectedly close after
663 they are idle for a while.
665 Some types of firewall, and almost any router doing Network Address
666 Translation (NAT, also known as IP masquerading), will forget about
667 a connection through them if the connection does nothing for too
668 long. This will cause the connection to be rudely cut off when
671 You can try to combat this by telling PuTTY to send \e{keepalives}:
672 packets of data which have no effect on the actual session, but
673 which reassure the router or firewall that the network connection is
674 still active and worth remembering about.
676 Keepalives don't solve everything, unfortunately; although they
677 cause greater robustness against this sort of router, they can also
678 cause a \e{loss} of robustness against network dropouts. See
679 \k{config-keepalive} in the documentation for more discussion of
682 \S{faq-timeout}{Question} PuTTY's network connections time out too
683 quickly when network connectivity is temporarily lost.
685 This is a Windows problem, not a PuTTY problem. The timeout value
686 can't be set on per application or per session basis. To increase
687 the TCP timeout globally, you need to tinker with the Registry.
689 On Windows 95, 98 or ME, the registry key you need to create or
692 \c HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\
693 \c MSTCP\MaxDataRetries
695 (it must be of type DWORD in Win95, or String in Win98/ME).
696 (See MS Knowledge Base article
697 \W{http://support.microsoft.com/default.aspx?scid=kb;en-us;158474}{158474}
698 for more information.)
700 On Windows NT or 2000, the registry key is
702 \c HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\
703 \c Parameters\TcpMaxDataRetransmissions
705 and it must be of type DWORD.
706 (See MS Knowledge Base article
707 \W{http://support.microsoft.com/default.aspx?scid=kb;en-us;120642}{120642}
708 for more information.)
710 Set the key's value to something like 10. This will cause Windows to
711 try harder to keep connections alive instead of abandoning them.
713 \S{faq-puttyputty}{Question} When I \cw{cat} a binary file, I get
714 \q{PuTTYPuTTYPuTTY} on my command line.
718 This is designed behaviour; when PuTTY receives the character
719 Control-E from the remote server, it interprets it as a request to
720 identify itself, and so it sends back the string \q{\cw{PuTTY}} as
721 if that string had been entered at the keyboard. Control-E should
722 only be sent by programs that are prepared to deal with the
723 response. Writing a binary file to your terminal is likely to output
724 many Control-E characters, and cause this behaviour. Don't do it.
727 To mitigate the effects, you could configure the answerback string
728 to be empty (see \k{config-answerback}); but writing binary files to
729 your terminal is likely to cause various other unpleasant behaviour,
730 so this is only a small remedy.
732 \S{faq-wintitle}{Question} When I \cw{cat} a binary file, my window
733 title changes to a nonsense string.
737 It is designed behaviour that PuTTY should have the ability to
738 adjust the window title on instructions from the server. Normally
739 the control sequence that does this should only be sent
740 deliberately, by programs that know what they are doing and intend
741 to put meaningful text in the window title. Writing a binary file to
742 your terminal runs the risk of sending the same control sequence by
743 accident, and cause unexpected changes in the window title. Don't do
746 \S{faq-password-fails}{Question} My keyboard stops working once
747 PuTTY displays the password prompt.
749 No, it doesn't. PuTTY just doesn't display the password you type, so
750 that someone looking at your screen can't see what it is.
752 Unlike the Windows login prompts, PuTTY doesn't display the password
753 as a row of asterisks either. This is so that someone looking at
754 your screen can't even tell how \e{long} your password is, which
755 might be valuable information.
757 \S{faq-keyboard}{Question} One or more function keys don't do what I
758 expected in a server-side application.
760 If you've already tried all the relevant options in the PuTTY
761 Keyboard panel, you may need to mail the PuTTY maintainers and ask.
763 It is \e{not} usually helpful just to tell us which application,
764 which server operating system, and which key isn't working; in order
765 to replicate the problem we would need to have a copy of every
766 operating system, and every application, that anyone has ever
769 PuTTY responds to function key presses by sending a sequence of
770 control characters to the server. If a function key isn't doing what
771 you expect, it's likely that the character sequence your application
772 is expecting to receive is not the same as the one PuTTY is sending.
773 Therefore what we really need to know is \e{what} sequence the
774 application is expecting.
776 The simplest way to investigate this is to find some other terminal
777 environment, in which that function key \e{does} work; and then
778 investigate what sequence the function key is sending in that
779 situation. One reasonably easy way to do this on a Unix system is to
780 type the command \c{cat}, and then press the function key. This is
781 likely to produce output of the form \c{^[[11~}. You can also do
782 this in PuTTY, to find out what sequence the function key is
783 producing in that. Then you can mail the PuTTY maintainers and tell
784 us \q{I wanted the F1 key to send \c{^[[11~}, but instead it's
785 sending \c{^[OP}, can this be done?}, or something similar.
787 You should still read the
788 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/feedback.html}{Feedback
789 page} on the PuTTY website (also provided as \k{feedback} in the
790 manual), and follow the guidelines contained in that.
792 \S{faq-openssh-bad-openssl}{Question} Since my SSH server was upgraded
793 to OpenSSH 3.1p1/3.4p1, I can no longer connect with PuTTY.
795 There is a known problem when OpenSSH has been built against an
796 incorrect version of OpenSSL; the quick workaround is to configure
797 PuTTY to use SSH protocol 2 and the Blowfish cipher.
799 For more details and OpenSSH patches, see
800 \W{http://bugzilla.mindrot.org/show_bug.cgi?id=138}{bug 138} in the
803 This is not a PuTTY-specific problem; if you try to connect with
804 another client you'll likely have similar problems. (Although PuTTY's
805 default cipher differs from many other clients.)
807 \e{OpenSSH 3.1p1:} configurations known to be broken (and symptoms):
809 \b SSH 2 with AES cipher (PuTTY says "Assertion failed! Expression:
810 (len & 15) == 0" in sshaes.c, or "Out of memory", or crashes)
812 \b SSH 2 with 3DES (PuTTY says "Incorrect MAC received on packet")
814 \b SSH 1 with Blowfish (PuTTY says "Incorrect CRC received on
819 \e{OpenSSH 3.4p1:} as of 3.4p1, only the problem with SSH 1 and
820 Blowfish remains. Rebuild your server, apply the patch linked to from
821 bug 138 above, or use another cipher (e.g., 3DES) instead.
823 \e{Other versions:} we occasionally get reports of the same symptom
824 and workarounds with older versions of OpenSSH, although it's not
825 clear the underlying cause is the same.
827 \S{faq-ssh2key-ssh1conn}{Question} Why do I see "Couldn't load private
828 key from ..."? Why can PuTTYgen load my key but not PuTTY?
830 It's likely that you've generated an SSH protocol 2 key with PuTTYgen,
831 but you're trying to use it in an SSH 1 connection. SSH1 and SSH2 keys
832 have different formats, and (at least in 0.52) PuTTY's reporting of a
833 key in the wrong format isn't optimal.
835 To connect using SSH 2 to a server that supports both versions, you
836 need to change the configuration from the default (see \k{faq-ssh2}).
838 \S{faq-rh8-utf8}{Question} When I'm connected to a Red Hat Linux 8.0
839 system, some characters don't display properly.
841 A common complaint is that hyphens in man pages show up as a-acute.
843 With release 8.0, Red Hat appear to have made UTF-8 the default
844 character set. There appears to be no way for terminal emulators such
845 as PuTTY to know this (as far as we know, the appropriate escape
846 sequence to switch into UTF-8 mode isn't sent).
848 A fix is to configure sessions to RH8 systems to use UTF-8
849 translation - see \k{config-charset} in the documentation. (Note that
850 if you use \q{Change Settings}, changes may not take place immediately
851 - see \k{faq-resetterm}.)
853 If you really want to change the character set used by the server, the
854 right place is \c{/etc/sysconfig/i18n}, but this shouldn't be
857 \S{faq-screen}{Question} Since I upgraded to PuTTY 0.54, the
858 scrollback has stopped working when I run \c{screen}.
860 PuTTY's terminal emulator has always had the policy that when the
861 \q{alternate screen} is in use, nothing is added to the scrollback.
862 This is because the usual sorts of programs which use the alternate
863 screen are things like text editors, which tend to scroll back and
864 forth in the same document a lot; so (a) they would fill up the
865 scrollback with a large amount of unhelpfully disordered text, and
866 (b) they contain their \e{own} method for the user to scroll back to
867 the bit they were interested in. We have generally found this policy
868 to do the Right Thing in almost all situations.
870 Unfortunately, \c{screen} is one exception: it uses the alternate
871 screen, but it's still usually helpful to have PuTTY's scrollback
872 continue working. The simplest solution is to go to the Features
873 control panel and tick \q{Disable switching to alternate terminal
874 screen}. (See \k{config-features-altscreen} for more details.)
876 The reason why this only started to be a problem in 0.54 is because
877 \c{screen} typically uses an unusual control sequence to switch to
878 the alternate screen, and previous versions of PuTTY did not support
881 \S{faq-alternate-localhost}{Question} Since I upgraded Windows XP
882 to Service Pack 2, I can't use addresses like \cw{127.0.0.2}.
884 Some people who ask PuTTY to listen on localhost addresses other
885 than \cw{127.0.0.1} to forward services such as SMB and Windows
886 Terminal Services have found that doing so no longer works since
887 they upgraded to WinXP SP2.
889 This is apparently an issue with SP2 that is acknowledged by Microsoft
890 in MS Knowledge Base article
891 \W{http://support.microsoft.com/default.aspx?scid=kb;en-us;884020}{884020}.
892 The article links to a fix you can download.
894 (\e{However}, we've been told that SP2 \e{also} fixes the bug that
895 means you need to use non-\cw{127.0.0.1} addresses to forward
896 Terminal Services in the first place.)
898 \S{faq-missing-slash}{Question} PSFTP commands seem to be missing a
899 directory separator (slash).
901 Some people have reported the following incorrect behaviour with
906 \c Remote directory is /dir1/dir2
907 \c psftp> get filename.ext
909 \c /dir1/dir2filename.ext: no such file or directory
911 This is not a bug in PSFTP. There is a known bug in some versions of
913 (\W{http://bugzilla.mindrot.org/show_bug.cgi?id=697}{bug 697}) that
914 causes these symptoms; it appears to have been introduced around
915 3.7.x. It manifests only on certain platforms (AIX is what has been
918 There is a patch for OpenSSH attached to that bug; it's also fixed in
919 recent versions of portable OpenSSH (from around 3.8).
921 \S{faq-connaborted}{Question} Do you want to hear about \q{Software
922 caused connection abort}?
924 In the documentation for PuTTY 0.53 and 0.53b, we mentioned that we'd
925 like to hear about any occurrences of this error. Since the release
926 of PuTTY 0.54, however, we've been convinced that this error doesn't
927 indicate that PuTTY's doing anything wrong, and we don't need to hear
928 about further occurrences. See \k{errors-connaborted} for our current
929 documentation of this error.
931 \H{faq-secure} Security questions
933 \S{faq-publicpc}{Question} Is it safe for me to download PuTTY and
934 use it on a public PC?
936 It depends on whether you trust that PC. If you don't trust the
937 public PC, don't use PuTTY on it, and don't use any other software
938 you plan to type passwords into either. It might be watching your
939 keystrokes, or it might tamper with the PuTTY binary you download.
940 There is \e{no} program safe enough that you can run it on an
941 actively malicious PC and get away with typing passwords into it.
943 If you do trust the PC, then it's probably OK to use PuTTY on it
944 (but if you don't trust the network, then the PuTTY download might
945 be tampered with, so it would be better to carry PuTTY with you on a
948 \S{faq-cleanup}{Question} What does PuTTY leave on a system? How can
951 PuTTY will leave some Registry entries, and a random seed file, on
952 the PC (see \k{faq-settings}). If you are using PuTTY on a public
953 PC, or somebody else's PC, you might want to clean these up when you
954 leave. You can do that automatically, by running the command
955 \c{putty -cleanup}. (Note that this only removes settings for
956 the currently logged-in user on \i{multi-user systems}.)
958 If PuTTY was installed from the installer package, it will also
959 appear in \q{Add/Remove Programs}. Uninstallation does not currently
960 remove the above-mentioned registry entries and file.
962 \S{faq-dsa}{Question} How come PuTTY now supports DSA, when the
963 website used to say how insecure it was?
965 DSA has a major weakness \e{if badly implemented}: it relies on a
966 random number generator to far too great an extent. If the random
967 number generator produces a number an attacker can predict, the DSA
968 private key is exposed - meaning that the attacker can log in as you
969 on all systems that accept that key.
971 The PuTTY policy changed because the developers were informed of
972 ways to implement DSA which do not suffer nearly as badly from this
973 weakness, and indeed which don't need to rely on random numbers at
974 all. For this reason we now believe PuTTY's DSA implementation is
975 probably OK. However, if you have the choice, we still recommend you
978 \S{faq-virtuallock}{Question} Couldn't Pageant use
979 \cw{VirtualLock()} to stop private keys being written to disk?
981 Unfortunately not. The \cw{VirtualLock()} function in the Windows
982 API doesn't do a proper job: it may prevent small pieces of a
983 process's memory from being paged to disk while the process is
984 running, but it doesn't stop the process's memory as a whole from
985 being swapped completely out to disk when the process is long-term
986 inactive. And Pageant spends most of its time inactive.
988 \H{faq-admin} Administrative questions
990 \S{faq-domain}{Question} Would you like me to register you a nicer
993 No, thank you. Even if you can find one (most of them seem to have
994 been registered already, by people who didn't ask whether we
995 actually wanted it before they applied), we're happy with the PuTTY
996 web site being exactly where it is. It's not hard to find (just type
997 \q{putty} into \W{http://www.google.com/}{google.com} and we're the
998 first link returned), and we don't believe the administrative hassle
999 of moving the site would be worth the benefit.
1001 In addition, if we \e{did} want a custom domain name, we would want
1002 to run it ourselves, so we knew for certain that it would continue
1003 to point where we wanted it, and wouldn't suddenly change or do
1004 strange things. Having it registered for us by a third party who we
1005 don't even know is not the best way to achieve this.
1007 \S{faq-webhosting}{Question} Would you like free web hosting for the
1010 We already have some, thanks.
1012 \S{faq-link}{Question} Would you link to my web site from the PuTTY
1015 Only if the content of your web page is of definite direct interest
1016 to PuTTY users. If your content is unrelated, or only tangentially
1017 related, to PuTTY, then the link would simply be advertising for
1020 One very nice effect of the Google ranking mechanism is that by and
1021 large, the most popular web sites get the highest rankings. This
1022 means that when an ordinary person does a search, the top item in
1023 the search is very likely to be a high-quality site or the site they
1024 actually wanted, rather than the site which paid the most money for
1027 The PuTTY web site is held in high esteem by Google, for precisely
1028 this reason: lots of people have linked to it simply because they
1029 like PuTTY, without us ever having to ask anyone to link to us. We
1030 feel that it would be an abuse of this esteem to use it to boost the
1031 ranking of random advertisers' web sites. If you want your web site
1032 to have a high Google ranking, we'd prefer that you achieve this the
1033 way we did - by being good enough at what you do that people will
1034 link to you simply because they like you.
1036 In particular, we aren't interested in trading links for money (see
1037 above), and we \e{certainly} aren't interested in trading links for
1038 other links (since we have no advertising on our web site, our
1039 Google ranking is not even directly worth anything to us). If we
1040 don't want to link to you for free, then we probably won't want to
1043 If you have software based on PuTTY, or specifically designed to
1044 interoperate with PuTTY, or in some other way of genuine interest to
1045 PuTTY users, then we will probably be happy to add a link to you on
1046 our Links page. And if you're running a mirror of the PuTTY web
1047 site, we're \e{definitely} interested.
1049 \S{faq-sourceforge}{Question} Why don't you move PuTTY to
1052 Partly, because we don't want to move the web site location (see
1055 Also, security reasons. PuTTY is a security product, and as such it
1056 is particularly important to guard the code and the web site against
1057 unauthorised modifications which might introduce subtle security
1058 flaws. Therefore, we prefer that the Subversion repository, web site and
1059 FTP site remain where they are, under the direct control of system
1060 administrators we know and trust personally, rather than being run
1061 by a large organisation full of people we've never met and which is
1062 known to have had breakins in the past.
1064 No offence to SourceForge; I think they do a wonderful job. But
1065 they're not ideal for everyone, and in particular they're not ideal
1068 \S{faq-mailinglist1}{Question} Why can't I subscribe to the
1069 putty-bugs mailing list?
1071 Because you're not a member of the PuTTY core development team. The
1072 putty-bugs mailing list is not a general newsgroup-like discussion
1073 forum; it's a contact address for the core developers, and an
1074 \e{internal} mailing list for us to discuss things among ourselves.
1075 If we opened it up for everybody to subscribe to, it would turn into
1076 something more like a newsgroup and we would be completely
1077 overwhelmed by the volume of traffic. It's hard enough to keep up
1078 with the list as it is.
1080 \S{faq-mailinglist2}{Question} If putty-bugs isn't a
1081 general-subscription mailing list, what is?
1083 There isn't one, that we know of.
1085 If someone else wants to set up a mailing list or other forum for
1086 PuTTY users to help each other with common problems, that would be
1087 fine with us, though the PuTTY team would almost certainly not have the
1088 time to read it. It's probably better to use one of the established
1089 newsgroups for this purpose (see \k{feedback-other-fora}).
1091 \S{faq-donations}{Question} How can I donate to PuTTY development?
1093 Please, \e{please} don't feel you have to. PuTTY is completely free
1094 software, and not shareware. We think it's very important that
1095 \e{everybody} who wants to use PuTTY should be able to, whether they
1096 have any money or not; so the last thing we would want is for a
1097 PuTTY user to feel guilty because they haven't paid us any money. If
1098 you want to keep your money, please do keep it. We wouldn't dream of
1101 Having said all that, if you still really \e{want} to give us money,
1102 we won't argue :-) The easiest way for us to accept donations is if
1103 you send money to \cw{<anakin@pobox.com>} using PayPal
1104 (\W{http://www.paypal.com/}\cw{www.paypal.com}). Alternatively, if
1105 you don't trust PayPal, you could donate through e-gold
1106 (\W{http://www.e-gold.com}\cw{www.e-gold.com}): deposit your
1107 donation in account number 174769, then send us e-mail to let us
1108 know you've done so (otherwise we might not notice for months!).
1110 Small donations (tens of dollars or tens of euros) will probably be
1111 spent on beer or curry, which helps motivate our volunteer team to
1112 continue doing this for the world. Larger donations will be spent on
1113 something that actually helps development, if we can find anything
1114 (perhaps new hardware, or a copy of Windows XP), but if we can't
1115 find anything then we'll just distribute the money among the
1116 developers. If you want to be sure your donation is going towards
1117 something worthwhile, ask us first. If you don't like these terms,
1118 feel perfectly free not to donate. We don't mind.
1120 \S{faq-permission}{Question} Can I have permission to put PuTTY on a
1121 cover disk / distribute it with other software / etc?
1123 Yes. You need not bother asking us explicitly for permission. You
1124 already have permission. Redistribution of the unmodified PuTTY
1125 binary in this way is entirely permitted by our licence (see
1126 \k{licence}), and you are welcome to do it as much as you like.
1128 If you are distributing PuTTY within your own organisation, or for
1129 use with your own product, then we recommend (but do not insist)
1130 that you offer your own first-line technical support, to answer
1131 questions directly relating to the interaction of PuTTY with your
1132 particular environment. If your users mail us directly, we won't be
1133 able to give them very much help about things specific to your own
1136 \H{faq-misc} Miscellaneous questions
1138 \S{faq-openssh}{Question} Is PuTTY a port of OpenSSH, or based on
1141 No, it isn't. PuTTY is almost completely composed of code written
1142 from scratch for PuTTY. The only code we share with OpenSSH is the
1143 detector for SSH1 CRC compensation attacks, written by CORE SDI S.A.
1145 \S{faq-sillyputty}{Question} Where can I buy silly putty?
1147 You're looking at the wrong web site; the only PuTTY we know about
1148 here is the name of a computer program.
1150 If you want the kind of putty you can buy as an executive toy, the
1151 PuTTY team can personally recommend Thinking Putty, which you can
1152 buy from Crazy Aaron's Putty World, at
1153 \W{http://www.puttyworld.com}\cw{www.puttyworld.com}.
1155 \S{faq-meaning}{Question} What does \q{PuTTY} mean?
1157 It's the name of a popular SSH and Telnet client. Any other meaning
1158 is in the eye of the beholder. It's been rumoured that \q{PuTTY}
1159 is the antonym of \q{\cw{getty}}, or that it's the stuff that makes your
1160 Windows useful, or that it's a kind of plutonium Teletype. We
1161 couldn't possibly comment on such allegations.
1163 \S{faq-pronounce}{Question} How do I pronounce \q{PuTTY}?
1165 Exactly like the English word \q{putty}, which we pronounce
1166 /\u02C8{'}p\u028C{V}t\u026A{I}/.