606398fb |
1 | \versionid $Id: faq.but,v 1.17 2002/01/02 15:44:06 simon Exp $ |
8f1529bc |
2 | |
ee46ef84 |
3 | \A{faq} PuTTY FAQ |
4 | |
5 | This FAQ is published on the PuTTY web site, and also provided as an |
6 | appendix in the manual. |
7 | |
8 | \H{faq-support} Features supported in PuTTY |
9 | |
10 | In general, if you want to know if PuTTY supports a particular |
11 | feature, you should look for it on the |
12 | \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/}{PuTTY web site}. |
13 | In particular: |
14 | |
15 | \b try the |
16 | \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html}{changes |
17 | page}, and see if you can find the feature on there. If a feature is |
18 | listed there, it's been implemented. If it's listed as a change made |
19 | \e{since} the latest version, it should be available in the |
20 | development snapshots, in which case testing will be very welcome. |
21 | |
22 | \b try the |
23 | \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist.html}{Wishlist |
24 | page}, and see if you can find the feature there. If it's on there, |
25 | it probably \e{hasn't} been implemented. |
26 | |
a1d2976b |
27 | \S{faq-ssh2}{Question} Does PuTTY support SSH v2? |
ee46ef84 |
28 | |
29 | Yes. SSH v2 support has been available in PuTTY since version 0.50. |
30 | However, currently the \e{default} SSH protocol is v1; to select SSH |
31 | v2 if your server supports both, go to the SSH panel and change the |
32 | \e{Preferred SSH protocol version} option. |
33 | |
34 | Public key authentication (both RSA and DSA) in SSH v2 has been |
35 | added since version 0.51. |
36 | |
a1d2976b |
37 | \S{faq-ssh2-keyfmt}{Question} Does PuTTY support reading OpenSSH or |
ee46ef84 |
38 | \cw{ssh.com} SSHv2 private key files? |
39 | |
40 | Not at present. OpenSSH and \cw{ssh.com} have totally different |
41 | formats for private key files, and neither one is particularly |
42 | pleasant, so PuTTY has its own. We do plan to write a converter at |
43 | some stage. |
44 | |
a1d2976b |
45 | \S{faq-ssh1}{Question} Does PuTTY support SSH v1? |
ee46ef84 |
46 | |
47 | Yes. SSH 1 support has always been available in PuTTY. |
48 | |
a1d2976b |
49 | \S{faq-localecho}{Question} Does PuTTY support local echo? |
ee46ef84 |
50 | |
51 | Yes. |
52 | |
53 | In version 0.51 and before, local echo cannot be separated from |
54 | local line editing (where you type a line of text locally, and it is |
55 | not sent to the server until you press Return, so you have the |
56 | chance to edit it and correct mistakes \e{before} the server sees |
57 | it). The two features can be enabled and disabled from the Terminal |
58 | panel, using the checkbox marked \q{Use local terminal line |
59 | discipline}. Note that due to a bug in those versions of PuTTY, |
60 | changing this feature in mid-session will have no effect; you have |
61 | to enable it \e{before} you open the connection. |
62 | |
63 | In later versions, local echo and local line editing are separate |
64 | options, and by default PuTTY will try to determine automatically |
65 | whether to enable them or not, based on which protocol you have |
66 | selected and also based on hints from the server. If you have a |
67 | problem with PuTTY's default choice, you can force each option to be |
68 | enabled or disabled as you choose. The controls are in the Terminal |
69 | panel, in the section marked \q{Line discipline options}. |
70 | |
a1d2976b |
71 | \S{faq-disksettings}{Question} Does PuTTY support storing its |
70706890 |
72 | settings in a disk file? |
ee46ef84 |
73 | |
74 | Not at present, although \k{config-file} in the documentation gives |
75 | a method of achieving the same effect. |
76 | |
a1d2976b |
77 | \S{faq-fullscreen}{Question} Does PuTTY support full-screen mode, |
70706890 |
78 | like a DOS box? |
ee46ef84 |
79 | |
80 | Not in the 0.51 release, but it has been added since then. |
81 | |
babac7bd |
82 | \S{faq-password-remember}{Question} Does PuTTY have the ability to |
83 | remember my password so I don't have to type it every time? |
ee46ef84 |
84 | |
85 | No, it doesn't. |
86 | |
87 | Remembering your password is a bad plan for obvious security |
88 | reasons: anyone who gains access to your machine while you're away |
89 | from your desk can find out the remembered password, and use it, |
90 | abuse it or change it. |
91 | |
92 | In addition, it's not even \e{possible} for PuTTY to automatically |
93 | send your password in a Telnet session, because Telnet doesn't give |
94 | the client software any indication of which part of the login |
95 | process is the password prompt. PuTTY would have to guess, by |
96 | looking for words like \q{password} in the session data; and if your |
97 | login program is written in something other than English, this won't |
98 | work. |
99 | |
100 | In SSH, remembering your password would be possible in theory, but |
101 | there doesn't seem to be much point since SSH supports public key |
102 | authentication, which is more flexible and more secure. See |
103 | \k{pubkey} in the documentation for a full discussion of public key |
104 | authentication. |
105 | |
a1d2976b |
106 | \S{faq-hostkeys}{Question} Is there an option to turn off the |
70706890 |
107 | annoying host key prompts? |
cad566a9 |
108 | |
109 | No, there isn't. And there won't be. Even if you write it yourself |
110 | and send us the patch, we won't accept it. |
111 | |
112 | Those annoying host key prompts are the \e{whole point} of SSH. |
113 | Without them, all the cryptographic technology SSH uses to secure |
114 | your session is doing nothing more than making an attacker's job |
115 | slightly harder; instead of sitting between you and the server with |
116 | a packet sniffer, the attacker must actually subvert a router and |
117 | start modifying the packets going back and forth. But that's not all |
118 | that much harder than just sniffing; and without host key checking, |
119 | it will go completely undetected by client or server. |
120 | |
121 | Host key checking is your guarantee that the encryption you put on |
122 | your data at the client end is the \e{same} encryption taken off the |
123 | data at the server end; it's your guarantee that it hasn't been |
124 | removed and replaced somewhere on the way. Host key checking makes |
125 | the attacker's job \e{astronomically} hard, compared to packet |
126 | sniffing, and even compared to subverting a router. Instead of |
127 | applying a little intelligence and keeping an eye on Bugtraq, the |
128 | attacker must now perform a brute-force attack against at least one |
129 | military-strength cipher. That insignificant host key prompt really |
130 | does make \e{that} much difference. |
131 | |
132 | If you're having a specific problem with host key checking - perhaps |
133 | you want an automated batch job to make use of PSCP or Plink, and |
134 | the interactive host key prompt is hanging the batch process - then |
135 | the right way to fix it is to add the correct host key to the |
136 | Registry in advance. That way, you retain the \e{important} feature |
137 | of host key checking: the right key will be accepted and the wrong |
138 | ones will not. Adding an option to turn host key checking off |
139 | completely is the wrong solution and we will not do it. |
140 | |
a1d2976b |
141 | \S{faq-server}{Question} Will you write an SSH server for the PuTTY |
70706890 |
142 | suite, to go with the client? |
ae915483 |
143 | |
144 | No. The only reason we might want to would be if we could easily |
145 | re-use existing code and significantly cut down the effort. We don't |
146 | believe this is the case; there just isn't enough common ground |
147 | between an SSH client and server to make it worthwhile. |
148 | |
149 | If someone else wants to use bits of PuTTY in the process of writing |
150 | a Windows SSH server, they'd be perfectly welcome to of course, but |
151 | I really can't see it being a lot less effort for us to do that than |
152 | it would be for us to write a server from the ground up. We don't |
153 | have time, and we don't have motivation. The code is available if |
154 | anyone else wants to try it. |
155 | |
ee46ef84 |
156 | \H{faq-ports} Ports to other operating systems |
157 | |
158 | The eventual goal is for PuTTY to be a multi-platform program, able |
159 | to run on at least Windows, MacOS and Unix. Whether this will |
160 | actually ever happen I have no idea, but it is the plan. A Mac port |
161 | has been started, but is only half-finished and currently not moving |
162 | very fast. |
163 | |
164 | Porting will become easier once PuTTY has a generalised porting |
165 | layer, drawing a clear line between platform-dependent and |
166 | platform-independent code. The general intention is for this porting |
167 | layer to evolve naturally as part of the process of doing the first |
168 | port. One particularly nasty part of this will be separating the |
169 | many configuration options into platform-dependent and |
170 | platform-independent ones; for example, the options controlling when |
171 | the Windows System menu appears will be pretty much meaningless |
172 | under X11 or perhaps other windowing systems, whereas Telnet Passive |
173 | Mode is universal and shouldn't need to be specified once for each |
174 | platform. |
175 | |
a1d2976b |
176 | \S{faq-wince}{Question} Will there be a port to Windows CE? |
ee46ef84 |
177 | |
178 | Probably not in the particularly near future. Despite sharing large |
179 | parts of the Windows API, in practice WinCE doesn't appear to be |
180 | significantly easier to port to than a totally different operating |
181 | system. |
182 | |
183 | However, PuTTY on portable devices would clearly be a useful thing, |
184 | so in the long term I hope there will be a WinCE port. |
185 | |
f82f00d0 |
186 | \S{faq-win31}{Question} Is there a port to Windows 3.1? |
187 | |
188 | PuTTY is a 32-bit application from the ground up, so it won't run on |
189 | Windows 3.1 as a native 16-bit program; and it would be \e{very} |
190 | hard to port it to do so, because of Windows 3.1's vile memory |
191 | allocation mechanisms. |
192 | |
193 | However, it is possible in theory to compile the existing PuTTY |
194 | source in such a way that it will run under Win32s (an extension to |
195 | Windows 3.1 to let you run 32-bit programs). In order to do this |
196 | you'll need the right kind of C compiler - modern versions of Visual |
197 | C at least have stopped being backwards compatible to Win32s. Also, |
198 | the last time we tried this it didn't work very well. |
199 | |
200 | If you're interested in running PuTTY under Windows 3.1, help and |
201 | testing in this area would be very welcome! |
202 | |
babac7bd |
203 | \S{faq-mac-port}{Question} Will there be a port to the Mac? |
ee46ef84 |
204 | |
205 | A Mac port was started once and is half-finished, but development |
206 | has been static for some time and the main PuTTY code has moved on, |
207 | so it's not clear how quickly development would resume even if |
208 | developer effort were available. |
209 | |
a1d2976b |
210 | \S{faq-unix}{Question} Will there be a port to Unix? |
ee46ef84 |
211 | |
212 | I hope so, if only so that I can have an \cw{xterm}-like program |
213 | that supports exactly the same terminal emulation as PuTTY. If and |
214 | when we do do a Unix port, it will have a local-terminal back end so |
215 | it can be used like an \cw{xterm}, rather than only being usable as |
216 | a network utility. |
217 | |
a1d2976b |
218 | \S{faq-epoc}{Question} Will there be a port to EPOC? |
ee46ef84 |
219 | |
220 | I hope so, but given that ports aren't really progressing very fast |
221 | even on systems the developers \e{do} already know how to program |
222 | for, it might be a long time before any of us get round to learning |
223 | a new system and doing the port for that. |
224 | |
225 | \H{faq-embedding} Embedding PuTTY in other programs |
226 | |
a1d2976b |
227 | \S{faq-dll}{Question} Is the SSH or Telnet code available as a DLL? |
ee46ef84 |
228 | |
229 | No, it isn't. It would take a reasonable amount of rewriting for |
230 | this to be possible, and since the PuTTY project itself doesn't |
231 | believe in DLLs (they make installation more error-prone) none of us |
232 | has taken the time to do it. |
233 | |
234 | Most of the code cleanup work would be a good thing to happen in |
235 | general, so if anyone feels like helping, we wouldn't say no. |
236 | |
a1d2976b |
237 | \S{faq-vb}{Question} Is the SSH or Telnet code available as a Visual |
70706890 |
238 | Basic component? |
ee46ef84 |
239 | |
240 | No, it isn't. None of the PuTTY team uses Visual Basic, and none of |
241 | us has any particular need to make SSH connections from a Visual |
242 | Basic application. In addition, all the preliminary work to turn it |
243 | into a DLL would be necessary first; and furthermore, we don't even |
244 | know how to write VB components. |
245 | |
246 | If someone offers to do some of this work for us, we might consider |
247 | it, but unless that happens I can't see VB integration being |
248 | anywhere other than the very bottom of our priority list. |
249 | |
a1d2976b |
250 | \S{faq-ipc}{Question} How can I use PuTTY to make an SSH connection |
70706890 |
251 | from within another program? |
ee46ef84 |
252 | |
253 | Probably your best bet is to use Plink, the command-line connection |
254 | tool. If you can start Plink as a second Windows process, and |
255 | arrange for your primary process to be able to send data to the |
256 | Plink process, and receive data from it, through pipes, then you |
257 | should be able to make SSH connections from your program. |
258 | |
259 | This is what CVS for Windows does, for example. |
260 | |
261 | \H{faq-details} Details of PuTTY's operation |
262 | |
a1d2976b |
263 | \S{faq-term}{Question} What terminal type does PuTTY use? |
ee46ef84 |
264 | |
265 | For most purposes, PuTTY can be considered to be an \cw{xterm} |
266 | terminal, although full support for some of \cw{xterm}'s features, |
267 | such as passing mouse actions to the server-side program, is not |
268 | present in the 0.51 release (but has been added since). |
269 | |
270 | PuTTY also supports some terminal control sequences not supported by |
271 | the real \cw{xterm}: notably the Linux console sequences that |
272 | reconfigure the colour palette, and the title bar control sequences |
273 | used by \cw{DECterm} (which are different from the \cw{xterm} ones; |
274 | PuTTY supports both). |
275 | |
276 | By default, PuTTY announces its terminal type to the server as |
277 | \c{xterm}. If you have a problem with this, you can reconfigure it |
278 | to say something else; \c{vt220} might help if you have trouble. |
279 | |
a1d2976b |
280 | \S{faq-settings}{Question} Where does PuTTY store its data? |
ee46ef84 |
281 | |
282 | PuTTY stores most of its data (saved sessions, SSH host keys) in the |
283 | Registry. The precise location is |
284 | |
285 | \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY |
286 | |
287 | and within that area, saved sessions are stored under \c{Sessions} |
288 | while host keys are stored under \c{SshHostKeys}. |
289 | |
290 | PuTTY also requires a random number seed file, to improve the |
291 | unpredictability of randomly chosen data needed as part of the SSH |
292 | cryptography. This is stored by default in your Windows home |
293 | directory (\c{%HOMEDRIVE%\\%HOMEPATH%}), or in the actual Windows |
294 | directory (such as \c{C:\\WINDOWS}) if the home directory doesn't |
295 | exist, for example if you're using Win95. If you want to change the |
296 | location of the random number seed file, you can put your chosen |
297 | pathname in the Registry, at |
298 | |
299 | \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\RandSeedFile |
300 | |
301 | \H{faq-howto} HOWTO questions |
302 | |
a1d2976b |
303 | \S{faq-startmax}{Question} How can I make PuTTY start up maximised? |
ee46ef84 |
304 | |
305 | Create a Windows shortcut to start PuTTY from, and set it as \q{Run |
306 | Maximized}. |
307 | |
a1d2976b |
308 | \S{faq-startsess}{Question} How can I create a Windows shortcut to |
70706890 |
309 | start a particular saved session directly? |
ee46ef84 |
310 | |
311 | To run a PuTTY session saved under the name \q{\cw{mysession}}, |
312 | create a Windows shortcut that invokes PuTTY with a command line |
313 | like |
314 | |
315 | \c \path\name\to\putty.exe @mysession |
316 | |
a1d2976b |
317 | \S{faq-startssh}{Question} How can I start an SSH session straight |
70706890 |
318 | from the command line? |
ee46ef84 |
319 | |
320 | Use the command line \c{putty -ssh host.name}. Alternatively, create |
321 | a saved session that specifies the SSH protocol, and start the saved |
322 | session as shown in \k{faq-startsess}. |
323 | |
a1d2976b |
324 | \S{faq-cutpaste}{Question} How do I copy and paste between PuTTY and |
70706890 |
325 | other Windows applications? |
ee46ef84 |
326 | |
327 | Copy and paste works similarly to the X Window System. You use the |
328 | left mouse button to select text in the PuTTY window. The act of |
329 | selection \e{automatically} copies the text to the clipboard: there |
330 | is no need to press Ctrl-Ins or Ctrl-C or anything else. In fact, |
331 | pressing Ctrl-C will send a Ctrl-C character to the other end of |
332 | your connection (just like it does the rest of the time), which may |
333 | have unpleasant effects. The \e{only} thing you need to do, to copy |
334 | text to the clipboard, is to select it. |
335 | |
336 | To paste the clipboard contents into a PuTTY window, by default you |
337 | click the right mouse button. If you have a three-button mouse and |
338 | are used to X applications, you can configure pasting to be done by |
339 | the middle button instead, but this is not the default because most |
340 | Windows users don't have a middle button at all. |
341 | |
342 | You can also paste by pressing Shift-Ins. |
343 | |
a1d2976b |
344 | \S{faq-tunnels}{Question} How do I use X forwarding and port |
70706890 |
345 | forwarding? I can't find the Tunnels panel. |
f2003e32 |
346 | |
347 | If you're looking in the 0.51 release or earlier, the Tunnels panel |
348 | isn't there. It was added in the development snapshots after 0.51, |
349 | and releases 0.52 and onwards will contain it. |
350 | |
a1d2976b |
351 | \S{faq-options}{Question} How do I use all PuTTY's features (public |
70706890 |
352 | keys, port forwarding, SSH v2, etc.) in PSCP, PSFTP and Plink? |
72be5b5e |
353 | |
354 | The command-line tools are currently rather short of command line |
355 | options to enable this sort of thing. However, you can use most of |
356 | PuTTY's features if you create a PuTTY saved session, and then use |
357 | the name of the saved session on the command line in place of a |
358 | hostname. This works for PSCP, PSFTP and Plink (but don't expect |
359 | port forwarding in the file transfer applications!). |
f2003e32 |
360 | |
a1d2976b |
361 | \S{faq-pscp}{Question} How do I use PSCP.EXE? When I double-click it |
70706890 |
362 | gives me a command prompt window which then closes instantly. |
ee46ef84 |
363 | |
364 | PSCP is a command-line application, not a GUI application. If you |
365 | run it without arguments, it will simply print a help message and |
366 | terminate. |
367 | |
368 | To use PSCP properly, run it from a Command Prompt window. See |
369 | \k{pscp} in the documentation for more details. |
370 | |
a1d2976b |
371 | \S{faq-pscp-spaces}{Question} How do I use PSCP to copy a file whose |
70706890 |
372 | name has spaces in? |
ee46ef84 |
373 | |
374 | If PSCP is using the traditional SCP protocol, this is confusing. If |
375 | you're specifying a file at the local end, you just use one set of |
376 | quotes as you would normally do: |
377 | |
378 | \c pscp "local filename with spaces" user@host: |
379 | \c pscp user@host:myfile "local filename with spaces" |
380 | |
381 | But if the filename you're specifying is on the \e{remote} side, you |
382 | have to use backslashes and two sets of quotes: |
383 | |
384 | \c pscp user@host:"\"remote filename with spaces\"" local_filename |
385 | \c pscp local_filename user@host:"\"remote filename with spaces\"" |
386 | |
387 | Worse still, in a remote-to-local copy you have to specify the local |
388 | file name explicitly, otherwise PSCP will complain that they don't |
389 | match (unless you specified the \c{-unsafe} option). The following |
390 | command will give an error message: |
391 | |
392 | \c c:\>pscp user@host:"\"oo er\"" . |
e9cee352 |
393 | \c warning: remote host tried to write to a file called 'oo er' |
394 | \c when we requested a file called '"oo er"'. |
ee46ef84 |
395 | |
e9cee352 |
396 | Instead, you need to specify the local file name in full: |
397 | |
398 | \c c:\>pscp user@host:"\"oo er\"" "oo er" |
399 | |
ee46ef84 |
400 | If PSCP is using the newer SFTP protocol, none of this is a problem, |
401 | and all filenames with spaces in are specified using a single pair |
402 | of quotes in the obvious way: |
403 | |
404 | \c pscp "local file" user@host: |
405 | \c pscp user@host:"remote file" . |
406 | |
407 | \H{faq-trouble} Troubleshooting |
408 | |
babac7bd |
409 | \S{faq-incorrect-mac}{Question} Why do I see \q{Incorrect MAC |
410 | received on packet}? |
ee46ef84 |
411 | |
412 | This is due to a bug in old SSH 2 servers distributed by |
413 | \cw{ssh.com}. Version 2.3.0 and below of their SSH 2 server |
414 | constructs Message Authentication Codes in the wrong way, and |
415 | expects the client to construct them in the same wrong way. PuTTY |
416 | constructs the MACs correctly by default, and hence these old |
417 | servers will fail to work with it. |
418 | |
419 | If you are using PuTTY version 0.51 or below, go to the SSH panel |
420 | and check the box labelled \q{Imitate SSH 2 MAC bug}. This will |
421 | cause PuTTY to construct its MACs in the same incorrect manner as |
422 | the buggy servers, so it will be able to work with them. |
423 | |
424 | Since version 0.51, PuTTY has been enhanced to detect buggy servers |
425 | automatically (when they announce their version) and enable the |
426 | workaround without the user needing to ask. Therefore you \e{should} |
427 | never have to use this option again after 0.52, but it is still |
428 | provided just in case another buggy server shows up. |
429 | |
b7e2c163 |
430 | In this context MAC stands for Message Authentication Code. It's a |
431 | cryptographic term, and it has nothing at all to do with Ethernet |
432 | MAC (Media Access Control) addresses. |
433 | |
a1d2976b |
434 | \S{faq-colours}{Question} I clicked on a colour in the Colours |
70706890 |
435 | panel, and the colour didn't change in my terminal. |
ee46ef84 |
436 | |
437 | That isn't how you're supposed to use the Colours panel. |
438 | |
439 | During the course of a session, PuTTY potentially uses \e{all} the |
440 | colours listed in the Colours panel. It's not a question of using |
441 | only one of them and you choosing which one; PuTTY will use them |
442 | \e{all}. The purpose of the Colours panel is to let you adjust the |
443 | appearance of all the colours. So to change the colour of the |
444 | cursor, for example, you would select \q{Cursor Colour}, press the |
445 | \q{Modify} button, and select a new colour from the dialog box that |
446 | appeared. Similarly, if you want your session to appear in green, |
447 | you should select \q{Default Foreground} and press \q{Modify}. |
448 | Clicking on \q{ANSI Green} won't turn your session green; it will |
449 | only allow you to adjust the \e{shade} of green used when PuTTY is |
450 | instructed by the server to display green text. |
451 | |
a1d2976b |
452 | \S{faq-winsock2}{Question} Plink on Windows 95 says it can't find |
70706890 |
453 | \cw{WS2_32.DLL}. |
ee46ef84 |
454 | |
455 | Plink requires the extended Windows network library, WinSock version |
456 | 2. This is installed as standard on Windows 98 and above, and on |
457 | Windows NT, and even on later versions of Windows 95; but early |
458 | Win95 installations don't have it. |
459 | |
460 | In order to use Plink on these systems, you will need to download |
461 | the |
462 | \W{http://www.microsoft.com/windows95/downloads/contents/wuadmintools/s_wunetworkingtools/w95sockets2/}{WinSock 2 upgrade}: |
463 | |
464 | \c http://www.microsoft.com/windows95/downloads/contents/wuadmintools/ |
465 | \c s_wunetworkingtools/w95sockets2/ |
466 | |
a1d2976b |
467 | \S{faq-rekey}{Question} My PuTTY sessions close after an hour and |
70706890 |
468 | tell me \q{Server failed host key check}. |
ee46ef84 |
469 | |
470 | This is a bug in all versions of PuTTY up to and including 0.51. SSH |
471 | v2 servers from \cw{ssh.com} will require the key exchange to be |
472 | repeated one hour after the start of the connection, and PuTTY will |
473 | get this wrong. |
474 | |
475 | The bug has been fixed since version 0.51, so upgrading to a later |
476 | version or snapshot should solve the problem. |
477 | |
a1d2976b |
478 | \S{faq-outofmem}{Question} After trying to establish an SSH 2 |
70706890 |
479 | connection, PuTTY says \q{Out of memory} and dies. |
ee46ef84 |
480 | |
481 | If this happens just while the connection is starting up, this often |
482 | indicates that for some reason the client and server have failed to |
483 | establish a session encryption key. Somehow, they have performed |
484 | calculations that should have given each of them the same key, but |
485 | have ended up with different keys; so data encrypted by one and |
486 | decrypted by the other looks like random garbage. |
487 | |
488 | This causes an \q{out of memory} error because the first encrypted |
489 | data PuTTY expects to see is the length of an SSH message. Normally |
490 | this will be something well under 100 bytes. If the decryption has |
491 | failed, PuTTY will see a completely random length in the region of |
492 | two \e{gigabytes}, and will try to allocate enough memory to store |
493 | this non-existent message. This will immediately lead to it thinking |
494 | it doesn't have enough memory, and panicking. |
495 | |
496 | If this happens to you, it is quite likely to still be a PuTTY bug |
497 | and you should report it (although it might be a bug in your SSH |
498 | server instead); but it doesn't necessarily mean you've actually run |
499 | out of memory. |
500 | |
a1d2976b |
501 | \S{faq-bce}{Question} When I run full-colour applications, I see |
70706890 |
502 | areas of black space where colour ought to be. |
f1453e5c |
503 | |
504 | You almost certainly need to enable the \q{Use background colour to |
505 | erase screen} setting in the Terminal panel. Note that if you do |
506 | this in mid-session, it won't take effect until you reset the |
507 | terminal (see \k{faq-resetterm}). |
508 | |
a1d2976b |
509 | \S{faq-resetterm}{Question} When I change some terminal settings, |
70706890 |
510 | nothing happens. |
f1453e5c |
511 | |
512 | Some of the terminal options (notably Auto Wrap and |
513 | background-colour screen erase) actually represent the \e{default} |
514 | setting, rather than the currently active setting. The server can |
515 | send sequences that modify these options in mid-session, but when |
516 | the terminal is reset (by server action, or by you choosing \q{Reset |
517 | Terminal} from the System menu) the defaults are restored. |
518 | |
519 | If you want to change one of these options in the middle of a |
520 | session, you will find that the change does not immediately take |
521 | effect. It will only take effect once you reset the terminal. |
522 | |
a1d2976b |
523 | \S{faq-altgr}{Question} I can't type characters that require the |
70706890 |
524 | AltGr key. |
ee46ef84 |
525 | |
526 | In PuTTY version 0.51, the AltGr key was broken. The bug has been |
527 | fixed since then. |
528 | |
a1d2976b |
529 | \S{faq-idleout}{Question} My PuTTY sessions unexpectedly close after |
70706890 |
530 | they are idle for a while. |
ee46ef84 |
531 | |
532 | Some types of firewall, and almost any router doing Network Address |
533 | Translation (NAT, also known as IP masquerading), will forget about |
534 | a connection through them if the connection does nothing for too |
535 | long. This will cause the connection to be rudely cut off when |
536 | contact is resumed. |
537 | |
538 | You can try to combat this by telling PuTTY to send \e{keepalives}: |
539 | packets of data which have no effect on the actual session, but |
540 | which reassure the router or firewall that the network connection is |
541 | still active and worth remembering about. |
542 | |
543 | Keepalives don't solve everything, unfortunately; although they |
544 | cause greater robustness against this sort of router, they can also |
545 | cause a \e{loss} of robustness against network dropouts. See |
546 | \k{config-keepalive} in the documentation for more discussion of |
547 | this. |
548 | |
a1d2976b |
549 | \S{faq-timeout}{Question} PuTTY's network connections time out too |
70706890 |
550 | quickly when network connectivity is temporarily lost. |
ee46ef84 |
551 | |
552 | This is a Windows problem, not a PuTTY problem. The timeout value |
553 | can't be set on per application or per session basis. To increase |
554 | the TCP timeout globally, you need to tinker with the Registry. |
555 | |
556 | On Windows 95, 98 or ME, the registry key you need to change is |
557 | |
558 | \c HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\ |
559 | \c MSTCP\MaxDataRetries |
560 | |
561 | (it must be of type DWORD in Win95, or String in Win98/ME). |
562 | |
563 | On Windows NT or 2000, the registry key is |
564 | |
565 | \c HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\ |
566 | \c Parameters\TcpMaxDataRetransmissions |
567 | |
568 | and it must be of type DWORD. |
569 | |
570 | Set the key's value to something like 10. This will cause Windows to |
571 | try harder to keep connections alive instead of abandoning them. |
572 | |
a1d2976b |
573 | \S{faq-puttyputty}{Question} When I \cw{cat} a binary file, I get |
ee46ef84 |
574 | `PuTTYPuTTYPuTTY' on my command line. |
575 | |
a5a6cb30 |
576 | Don't do that, then. |
ee46ef84 |
577 | |
578 | This is designed behaviour; when PuTTY receives the character |
579 | Control-E from the remote server, it interprets it as a request to |
580 | identify itself, and so it sends back the string \q{\cw{PuTTY}} as |
581 | if that string had been entered at the keyboard. Control-E should |
582 | only be sent by programs that are prepared to deal with the |
583 | response. Writing a binary file to your terminal is likely to output |
584 | many Control-E characters, and cause this behaviour. Don't do it. |
585 | It's a bad plan. |
586 | |
a5a6cb30 |
587 | To mitigate the effects, you could configure the answerback string |
588 | to be empty (see \k{config-answerback}); but writing binary files to |
589 | your terminal is likely to cause various other unpleasant behaviour, |
590 | so this is only a small remedy. |
591 | |
babac7bd |
592 | \S{faq-wintitle}{Question} When I \cw{cat} a binary file, my window |
593 | title changes to a nonsense string. |
ee46ef84 |
594 | |
a5a6cb30 |
595 | Don't do that, then. |
ee46ef84 |
596 | |
597 | It is designed behaviour that PuTTY should have the ability to |
598 | adjust the window title on instructions from the server. Normally |
599 | the control sequence that does this should only be sent |
600 | deliberately, by programs that know what they are doing and intend |
601 | to put meaningful text in the window title. Writing a binary file to |
602 | your terminal runs the risk of sending the same control sequence by |
603 | accident, and cause unexpected changes in the window title. Don't do |
604 | it. |
605 | |
babac7bd |
606 | \S{faq-password-fails}{Question} My keyboard stops working once |
607 | PuTTY displays the password prompt. |
59c1f1f6 |
608 | |
609 | No, it doesn't. PuTTY just doesn't display the password you type, so |
610 | that someone looking at your screen can't see what it is. |
611 | |
612 | Unlike the Windows login prompts, PuTTY doesn't display the password |
613 | as a row of asterisks either. This is so that someone looking at |
614 | your screen can't even tell how \e{long} your password is, which |
615 | might be valuable information. |
616 | |
b5bee048 |
617 | \S{faq-keyboard}{Question} One or more function keys don't do what I |
618 | expected in a server-side application. |
619 | |
620 | If you've already tried all the relevant options in the PuTTY |
621 | Keyboard panel, you may need to mail the PuTTY maintainers and ask. |
622 | |
623 | It is \e{not} usually helpful just to tell us which application, |
624 | which server operating system, and which key isn't working; in order |
625 | to replicate the problem we would need to have a copy of every |
626 | operating system, and every application, that anyone has ever |
627 | complained about. |
628 | |
629 | PuTTY responds to function key presses by sending a sequence of |
630 | control characters to the server. If a function key isn't doing what |
631 | you expect, it's likely that the character sequence your application |
632 | is expecting to receive is not the same as the one PuTTY is sending. |
633 | Therefore what we really need to know is \e{what} sequence the |
634 | application is expecting. |
635 | |
636 | The simplest way to investigate this is to find some other terminal |
637 | environment, in which that function key \e{does} work; and then |
638 | investigate what sequence the function key is sending in that |
639 | situation. One reasonably easy way to do this on a Unix system is to |
640 | type the command \c{cat}, and then press the function key. This is |
641 | likely to produce output of the form \c{^[[11~}. You can also do |
642 | this in PuTTY, to find out what sequence the function key is |
643 | producing in that. Then you can mail the PuTTY maintainers and tell |
644 | us \q{I wanted the F1 key to send \c{^[[11~}, but instead it's |
645 | sending \c{^[OP}, can this be done?}, or something similar. |
646 | |
647 | You should still read the |
648 | \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/feedback.html}{Feedback |
649 | page} on the PuTTY website (also provided as \k{feedback} in the |
650 | manual), and follow the guidelines contained in that. |
651 | |
ee46ef84 |
652 | \H{faq-secure} Security questions |
653 | |
a1d2976b |
654 | \S{faq-publicpc}{Question} Is it safe for me to download PuTTY and |
70706890 |
655 | use it on a public PC? |
ee46ef84 |
656 | |
657 | It depends on whether you trust that PC. If you don't trust the |
658 | public PC, don't use PuTTY on it, and don't use any other software |
659 | you plan to type passwords into either. It might be watching your |
660 | keystrokes, or it might tamper with the PuTTY binary you download. |
661 | There is \e{no} program safe enough that you can run it on an |
662 | actively malicious PC and get away with typing passwords into it. |
663 | |
664 | If you do trust the PC, then it's probably OK to use PuTTY on it |
665 | (but if you don't trust the network, then the PuTTY download might |
666 | be tampered with, so it would be better to carry PuTTY with you on a |
667 | floppy). |
668 | |
a1d2976b |
669 | \S{faq-cleanup}{Question} What does PuTTY leave on a system? How can |
70706890 |
670 | I clean up after it? |
ee46ef84 |
671 | |
672 | PuTTY will leave some Registry entries, and a random seed file, on |
673 | the PC (see \k{faq-settings}). If you are using PuTTY on a public |
674 | PC, or somebody else's PC, you might want to clean these up when you |
675 | leave. You can do that automatically, by running the command |
676 | \c{putty -cleanup}. |
677 | |
a1d2976b |
678 | \S{faq-dsa}{Question} How come PuTTY now supports DSA, when the |
70706890 |
679 | website used to say how insecure it was? |
ee46ef84 |
680 | |
681 | DSA has a major weakness \e{if badly implemented}: it relies on a |
682 | random number generator to far too great an extent. If the random |
683 | number generator produces a number an attacker can predict, the DSA |
684 | private key is exposed - meaning that the attacker can log in as you |
685 | on all systems that accept that key. |
686 | |
687 | The PuTTY policy changed because the developers were informed of |
688 | ways to implement DSA which do not suffer nearly as badly from this |
689 | weakness, and indeed which don't need to rely on random numbers at |
690 | all. For this reason we now believe PuTTY's DSA implementation is |
691 | probably OK. However, if you have the choice, we still recommend you |
692 | use RSA instead. |
693 | |
694 | \H{faq-admin} Administrative questions |
695 | |
a1d2976b |
696 | \S{faq-domain}{Question} Would you like me to register you a nicer |
70706890 |
697 | domain name? |
ee46ef84 |
698 | |
699 | No, thank you. Even if you can find one (most of them seem to have |
700 | been registered already, by people who didn't ask whether we |
701 | actually wanted it before they applied), we're happy with the PuTTY |
702 | web site being exactly where it is. It's not hard to find (just type |
703 | \q{putty} into \W{http://www.google.com/}{google.com} and we're the |
704 | first link returned), and we don't believe the administrative hassle |
705 | of moving the site would be worth the benefit. |
706 | |
707 | In addition, if we \e{did} want a custom domain name, we would want |
708 | to run it ourselves, so we knew for certain that it would continue |
709 | to point where we wanted it, and wouldn't suddenly change or do |
710 | strange things. Having it registered for us by a third party who we |
711 | don't even know is not the best way to achieve this. |
712 | |
a1d2976b |
713 | \S{faq-webhosting}{Question} Would you like free web hosting for the |
70706890 |
714 | PuTTY web site? |
ee46ef84 |
715 | |
716 | We already have some, thanks. |
717 | |
a1d2976b |
718 | \S{faq-sourceforge}{Question} Why don't you move PuTTY to |
70706890 |
719 | SourceForge? |
ee46ef84 |
720 | |
721 | Partly, because we don't want to move the web site location (see |
722 | \k{faq-domain}). |
723 | |
724 | Also, security reasons. PuTTY is a security product, and as such it |
725 | is particularly important to guard the code and the web site against |
726 | unauthorised modifications which might introduce subtle security |
727 | flaws. Therefore, we prefer that the CVS repository, web site and |
728 | FTP site remain where they are, under the direct control of system |
729 | administrators we know and trust personally, rather than being run |
730 | by a large organisation full of people we've never met and which is |
731 | known to have had breakins in the past. |
732 | |
733 | No offence to SourceForge; I think they do a wonderful job. But |
734 | they're not ideal for everyone, and in particular they're not ideal |
735 | for us. |
736 | |
a1d2976b |
737 | \S{faq-mailinglist1}{Question} Why can't I subscribe to the |
70706890 |
738 | putty-bugs mailing list? |
ee46ef84 |
739 | |
740 | Because you're not a member of the PuTTY core development team. The |
741 | putty-bugs mailing list is not a general newsgroup-like discussion |
742 | forum; it's a contact address for the core developers, and an |
743 | \e{internal} mailing list for us to discuss things among ourselves. |
744 | If we opened it up for everybody to subscribe to, it would turn into |
745 | something more like a newsgroup and we would be completely |
746 | overwhelmed by the volume of traffic. It's hard enough to keep up |
747 | with the list as it is. |
748 | |
a1d2976b |
749 | \S{faq-mailinglist2}{Question} If putty-bugs isn't a |
70706890 |
750 | general-subscription mailing list, what is? |
ee46ef84 |
751 | |
752 | There isn't one, that we know of. |
753 | |
754 | If someone else wants to set up a mailing list for PuTTY users to |
755 | help each other with common problems, that would be fine with us; |
756 | but the PuTTY team would almost certainly not have the time to read |
757 | it, so any questions the list couldn't answer would have to be |
758 | forwarded on to us by the questioner. In any case, it's probably |
759 | better to use the established newsgroup \cw{comp.security.ssh} for |
760 | this purpose. |
761 | |
a1d2976b |
762 | \S{faq-donations}{Question} How can I donate to PuTTY development? |
ee46ef84 |
763 | |
764 | Please, \e{please} don't feel you have to. PuTTY is completely free |
765 | software, and not shareware. We think it's very important that |
766 | \e{everybody} who wants to use PuTTY should be able to, whether they |
767 | have any money or not; so the last thing we would want is for a |
768 | PuTTY user to feel guilty because they haven't paid us any money. If |
769 | you want to keep your money, please do keep it. We wouldn't dream of |
770 | asking for any. |
771 | |
772 | Having said all that, if you still really \e{want} to give us money, |
773 | we won't argue :-) The easiest way for us to accept donations is if |
774 | you go to \W{http://www.e-gold.com}\cw{www.e-gold.com}, and deposit |
775 | your donation in account number 174769. Then send us e-mail to let |
776 | us know you've done so (otherwise we might not notice for months!). |
777 | |
778 | Small donations (tens of dollars or tens of euros) will probably be |
779 | spent on beer or curry, which helps motivate our volunteer team to |
780 | continue doing this for the world. Larger donations will be spent on |
781 | something that actually helps development, if we can find anything |
782 | (perhaps new hardware, or a copy of Windows 2000), but if we can't |
783 | find anything then we'll just distribute the money among the |
784 | developers. If you want to be sure your donation is going towards |
785 | something worthwhile, ask us first. If you don't like these terms, |
786 | feel perfectly free not to donate. We don't mind. |
787 | |
606398fb |
788 | \S{faq-sillyputty}{Question} Where can I buy silly putty? |
789 | |
790 | You're looking at the wrong web site; the only PuTTY we know about |
791 | here is the name of a computer program. |
792 | |
793 | If you want the kind of putty you can buy as an executive toy, the |
794 | PuTTY team can personally recommend Thinking Putty, which you can |
795 | buy from Crazy Aaron's Putty World, at |
796 | \W{http://www.puttyworld.com}\cw{www.puttyworld.com}. |
797 | |
a1d2976b |
798 | \S{faq-pronounce}{Question} How do I pronounce PuTTY? |
ee46ef84 |
799 | |
800 | Exactly like the normal word \q{putty}. Just like the stuff you put |
801 | on window frames. (One of the reasons it's called PuTTY is because |
802 | it makes Windows usable. :-) |