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1 | \versionid $Id: faq.but,v 1.34 2002/09/02 13:04:46 jacob Exp $ |
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2 | |
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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? |
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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 | |
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34 | Public key authentication (both RSA and DSA) in SSH v2 is new in |
35 | version 0.52. |
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36 | |
a1d2976b |
37 | \S{faq-ssh2-keyfmt}{Question} Does PuTTY support reading OpenSSH or |
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38 | \cw{ssh.com} SSHv2 private key files? |
39 | |
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40 | Version 0.52 doesn't, but in the latest development snapshots |
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41 | PuTTYgen can load and save both OpenSSH and \cw{ssh.com} private key |
42 | files. |
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43 | |
a1d2976b |
44 | \S{faq-ssh1}{Question} Does PuTTY support SSH v1? |
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45 | |
46 | Yes. SSH 1 support has always been available in PuTTY. |
47 | |
a1d2976b |
48 | \S{faq-localecho}{Question} Does PuTTY support local echo? |
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49 | |
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50 | Yes. Version 0.52 has proper support for local echo. |
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51 | |
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52 | In version 0.51 and before, local echo could not be separated from |
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53 | local line editing (where you type a line of text locally, and it is |
54 | not sent to the server until you press Return, so you have the |
55 | chance to edit it and correct mistakes \e{before} the server sees |
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56 | it). New in version 0.52, local echo and local line editing are |
57 | separate options, and by default PuTTY will try to determine |
58 | automatically whether to enable them or not, based on which protocol |
59 | you have selected and also based on hints from the server. If you |
60 | have a problem with PuTTY's default choice, you can force each |
61 | option to be enabled or disabled as you choose. The controls are in |
62 | the Terminal panel, in the section marked \q{Line discipline |
63 | options}. |
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64 | |
a1d2976b |
65 | \S{faq-disksettings}{Question} Does PuTTY support storing its |
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66 | settings in a disk file? |
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67 | |
68 | Not at present, although \k{config-file} in the documentation gives |
69 | a method of achieving the same effect. |
70 | |
a1d2976b |
71 | \S{faq-fullscreen}{Question} Does PuTTY support full-screen mode, |
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72 | like a DOS box? |
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73 | |
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74 | Yes; this is a new feature in version 0.52. |
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75 | |
babac7bd |
76 | \S{faq-password-remember}{Question} Does PuTTY have the ability to |
77 | remember my password so I don't have to type it every time? |
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78 | |
79 | No, it doesn't. |
80 | |
81 | Remembering your password is a bad plan for obvious security |
82 | reasons: anyone who gains access to your machine while you're away |
83 | from your desk can find out the remembered password, and use it, |
84 | abuse it or change it. |
85 | |
86 | In addition, it's not even \e{possible} for PuTTY to automatically |
87 | send your password in a Telnet session, because Telnet doesn't give |
88 | the client software any indication of which part of the login |
89 | process is the password prompt. PuTTY would have to guess, by |
90 | looking for words like \q{password} in the session data; and if your |
91 | login program is written in something other than English, this won't |
92 | work. |
93 | |
94 | In SSH, remembering your password would be possible in theory, but |
95 | there doesn't seem to be much point since SSH supports public key |
96 | authentication, which is more flexible and more secure. See |
97 | \k{pubkey} in the documentation for a full discussion of public key |
98 | authentication. |
99 | |
a1d2976b |
100 | \S{faq-hostkeys}{Question} Is there an option to turn off the |
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101 | annoying host key prompts? |
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102 | |
103 | No, there isn't. And there won't be. Even if you write it yourself |
104 | and send us the patch, we won't accept it. |
105 | |
106 | Those annoying host key prompts are the \e{whole point} of SSH. |
107 | Without them, all the cryptographic technology SSH uses to secure |
108 | your session is doing nothing more than making an attacker's job |
109 | slightly harder; instead of sitting between you and the server with |
110 | a packet sniffer, the attacker must actually subvert a router and |
111 | start modifying the packets going back and forth. But that's not all |
112 | that much harder than just sniffing; and without host key checking, |
113 | it will go completely undetected by client or server. |
114 | |
115 | Host key checking is your guarantee that the encryption you put on |
116 | your data at the client end is the \e{same} encryption taken off the |
117 | data at the server end; it's your guarantee that it hasn't been |
118 | removed and replaced somewhere on the way. Host key checking makes |
119 | the attacker's job \e{astronomically} hard, compared to packet |
120 | sniffing, and even compared to subverting a router. Instead of |
121 | applying a little intelligence and keeping an eye on Bugtraq, the |
122 | attacker must now perform a brute-force attack against at least one |
123 | military-strength cipher. That insignificant host key prompt really |
124 | does make \e{that} much difference. |
125 | |
126 | If you're having a specific problem with host key checking - perhaps |
127 | you want an automated batch job to make use of PSCP or Plink, and |
128 | the interactive host key prompt is hanging the batch process - then |
129 | the right way to fix it is to add the correct host key to the |
130 | Registry in advance. That way, you retain the \e{important} feature |
131 | of host key checking: the right key will be accepted and the wrong |
132 | ones will not. Adding an option to turn host key checking off |
133 | completely is the wrong solution and we will not do it. |
134 | |
a1d2976b |
135 | \S{faq-server}{Question} Will you write an SSH server for the PuTTY |
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136 | suite, to go with the client? |
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137 | |
138 | No. The only reason we might want to would be if we could easily |
139 | re-use existing code and significantly cut down the effort. We don't |
140 | believe this is the case; there just isn't enough common ground |
141 | between an SSH client and server to make it worthwhile. |
142 | |
143 | If someone else wants to use bits of PuTTY in the process of writing |
144 | a Windows SSH server, they'd be perfectly welcome to of course, but |
145 | I really can't see it being a lot less effort for us to do that than |
146 | it would be for us to write a server from the ground up. We don't |
147 | have time, and we don't have motivation. The code is available if |
148 | anyone else wants to try it. |
149 | |
67325335 |
150 | \S{faq-pscp-ascii}{Question} Can PSCP or PSFTP transfer files in |
151 | ASCII mode? |
152 | |
153 | Unfortunately not. This is a limitation of the file transfer |
154 | protocols: the SCP and SFTP protocols have no notion of transferring |
155 | a file in anything other than binary mode. |
156 | |
157 | SFTP is designed to be extensible, so it's possible that an |
158 | extension might be proposed at some later date that implements ASCII |
159 | transfer. But the PuTTY team can't do anything about it until that |
160 | happens. |
161 | |
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162 | \H{faq-ports} Ports to other operating systems |
163 | |
164 | The eventual goal is for PuTTY to be a multi-platform program, able |
165 | to run on at least Windows, MacOS and Unix. Whether this will |
166 | actually ever happen I have no idea, but it is the plan. A Mac port |
167 | has been started, but is only half-finished and currently not moving |
168 | very fast. |
169 | |
170 | Porting will become easier once PuTTY has a generalised porting |
171 | layer, drawing a clear line between platform-dependent and |
172 | platform-independent code. The general intention is for this porting |
173 | layer to evolve naturally as part of the process of doing the first |
174 | port. One particularly nasty part of this will be separating the |
175 | many configuration options into platform-dependent and |
176 | platform-independent ones; for example, the options controlling when |
177 | the Windows System menu appears will be pretty much meaningless |
178 | under X11 or perhaps other windowing systems, whereas Telnet Passive |
179 | Mode is universal and shouldn't need to be specified once for each |
180 | platform. |
181 | |
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182 | \S{faq-ports-general}{Question} What ports of PuTTY exist? |
183 | |
184 | Currently, PuTTY only runs on full Win32 systems. This includes |
185 | Windows 95, 98, and ME, and it includes Windows NT, Windows 2000 and |
186 | Windows XP. |
187 | |
188 | It does \e{not} include Windows CE (see \k{faq-wince}), and it does |
189 | not quite include the Win32s environment under Windows 3.1 (see |
190 | \k{faq-win31}). |
191 | |
192 | We do not have ports for any other systems at the present time. If |
193 | anyone told you we had a Unix port, or an iPaq port, or any other |
194 | port of PuTTY, they were mistaken. We don't. |
195 | |
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196 | \S{faq-wince}{Question} Will there be a port to Windows CE or PocketPC? |
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197 | |
198 | Probably not in the particularly near future. Despite sharing large |
199 | parts of the Windows API, in practice WinCE doesn't appear to be |
200 | significantly easier to port to than a totally different operating |
201 | system. |
202 | |
203 | However, PuTTY on portable devices would clearly be a useful thing, |
204 | so in the long term I hope there will be a WinCE port. |
205 | |
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206 | \S{faq-win31}{Question} Is there a port to Windows 3.1? |
207 | |
208 | PuTTY is a 32-bit application from the ground up, so it won't run on |
209 | Windows 3.1 as a native 16-bit program; and it would be \e{very} |
210 | hard to port it to do so, because of Windows 3.1's vile memory |
211 | allocation mechanisms. |
212 | |
213 | However, it is possible in theory to compile the existing PuTTY |
214 | source in such a way that it will run under Win32s (an extension to |
215 | Windows 3.1 to let you run 32-bit programs). In order to do this |
216 | you'll need the right kind of C compiler - modern versions of Visual |
217 | C at least have stopped being backwards compatible to Win32s. Also, |
218 | the last time we tried this it didn't work very well. |
219 | |
220 | If you're interested in running PuTTY under Windows 3.1, help and |
221 | testing in this area would be very welcome! |
222 | |
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223 | \S{faq-mac-port}{Question} Will there be a port to the Mac? |
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224 | |
225 | A Mac port was started once and is half-finished, but development |
226 | has been static for some time and the main PuTTY code has moved on, |
227 | so it's not clear how quickly development would resume even if |
228 | developer effort were available. |
229 | |
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230 | \S{faq-unix}{Question} Will there be a port to Unix? |
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231 | |
232 | I hope so, if only so that I can have an \cw{xterm}-like program |
233 | that supports exactly the same terminal emulation as PuTTY. If and |
234 | when we do do a Unix port, it will have a local-terminal back end so |
235 | it can be used like an \cw{xterm}, rather than only being usable as |
236 | a network utility. |
237 | |
a1d2976b |
238 | \S{faq-epoc}{Question} Will there be a port to EPOC? |
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239 | |
240 | I hope so, but given that ports aren't really progressing very fast |
241 | even on systems the developers \e{do} already know how to program |
242 | for, it might be a long time before any of us get round to learning |
243 | a new system and doing the port for that. |
244 | |
245 | \H{faq-embedding} Embedding PuTTY in other programs |
246 | |
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247 | \S{faq-dll}{Question} Is the SSH or Telnet code available as a DLL? |
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248 | |
249 | No, it isn't. It would take a reasonable amount of rewriting for |
250 | this to be possible, and since the PuTTY project itself doesn't |
251 | believe in DLLs (they make installation more error-prone) none of us |
252 | has taken the time to do it. |
253 | |
254 | Most of the code cleanup work would be a good thing to happen in |
255 | general, so if anyone feels like helping, we wouldn't say no. |
256 | |
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257 | \S{faq-vb}{Question} Is the SSH or Telnet code available as a Visual |
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258 | Basic component? |
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259 | |
260 | No, it isn't. None of the PuTTY team uses Visual Basic, and none of |
261 | us has any particular need to make SSH connections from a Visual |
262 | Basic application. In addition, all the preliminary work to turn it |
263 | into a DLL would be necessary first; and furthermore, we don't even |
264 | know how to write VB components. |
265 | |
266 | If someone offers to do some of this work for us, we might consider |
267 | it, but unless that happens I can't see VB integration being |
268 | anywhere other than the very bottom of our priority list. |
269 | |
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270 | \S{faq-ipc}{Question} How can I use PuTTY to make an SSH connection |
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271 | from within another program? |
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272 | |
273 | Probably your best bet is to use Plink, the command-line connection |
274 | tool. If you can start Plink as a second Windows process, and |
275 | arrange for your primary process to be able to send data to the |
276 | Plink process, and receive data from it, through pipes, then you |
277 | should be able to make SSH connections from your program. |
278 | |
279 | This is what CVS for Windows does, for example. |
280 | |
281 | \H{faq-details} Details of PuTTY's operation |
282 | |
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283 | \S{faq-term}{Question} What terminal type does PuTTY use? |
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284 | |
285 | For most purposes, PuTTY can be considered to be an \cw{xterm} |
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286 | terminal. |
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287 | |
288 | PuTTY also supports some terminal control sequences not supported by |
289 | the real \cw{xterm}: notably the Linux console sequences that |
290 | reconfigure the colour palette, and the title bar control sequences |
291 | used by \cw{DECterm} (which are different from the \cw{xterm} ones; |
292 | PuTTY supports both). |
293 | |
294 | By default, PuTTY announces its terminal type to the server as |
295 | \c{xterm}. If you have a problem with this, you can reconfigure it |
296 | to say something else; \c{vt220} might help if you have trouble. |
297 | |
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298 | \S{faq-settings}{Question} Where does PuTTY store its data? |
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299 | |
300 | PuTTY stores most of its data (saved sessions, SSH host keys) in the |
301 | Registry. The precise location is |
302 | |
303 | \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY |
304 | |
305 | and within that area, saved sessions are stored under \c{Sessions} |
306 | while host keys are stored under \c{SshHostKeys}. |
307 | |
308 | PuTTY also requires a random number seed file, to improve the |
309 | unpredictability of randomly chosen data needed as part of the SSH |
310 | cryptography. This is stored by default in your Windows home |
311 | directory (\c{%HOMEDRIVE%\\%HOMEPATH%}), or in the actual Windows |
312 | directory (such as \c{C:\\WINDOWS}) if the home directory doesn't |
313 | exist, for example if you're using Win95. If you want to change the |
314 | location of the random number seed file, you can put your chosen |
315 | pathname in the Registry, at |
316 | |
317 | \c HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\RandSeedFile |
318 | |
319 | \H{faq-howto} HOWTO questions |
320 | |
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321 | \S{faq-startmax}{Question} How can I make PuTTY start up maximised? |
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322 | |
323 | Create a Windows shortcut to start PuTTY from, and set it as \q{Run |
324 | Maximized}. |
325 | |
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326 | \S{faq-startsess}{Question} How can I create a Windows shortcut to |
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327 | start a particular saved session directly? |
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328 | |
329 | To run a PuTTY session saved under the name \q{\cw{mysession}}, |
330 | create a Windows shortcut that invokes PuTTY with a command line |
331 | like |
332 | |
333 | \c \path\name\to\putty.exe @mysession |
334 | |
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335 | \S{faq-startssh}{Question} How can I start an SSH session straight |
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336 | from the command line? |
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337 | |
338 | Use the command line \c{putty -ssh host.name}. Alternatively, create |
339 | a saved session that specifies the SSH protocol, and start the saved |
340 | session as shown in \k{faq-startsess}. |
341 | |
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342 | \S{faq-cutpaste}{Question} How do I copy and paste between PuTTY and |
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343 | other Windows applications? |
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344 | |
345 | Copy and paste works similarly to the X Window System. You use the |
346 | left mouse button to select text in the PuTTY window. The act of |
347 | selection \e{automatically} copies the text to the clipboard: there |
348 | is no need to press Ctrl-Ins or Ctrl-C or anything else. In fact, |
349 | pressing Ctrl-C will send a Ctrl-C character to the other end of |
350 | your connection (just like it does the rest of the time), which may |
351 | have unpleasant effects. The \e{only} thing you need to do, to copy |
352 | text to the clipboard, is to select it. |
353 | |
354 | To paste the clipboard contents into a PuTTY window, by default you |
355 | click the right mouse button. If you have a three-button mouse and |
356 | are used to X applications, you can configure pasting to be done by |
357 | the middle button instead, but this is not the default because most |
358 | Windows users don't have a middle button at all. |
359 | |
360 | You can also paste by pressing Shift-Ins. |
361 | |
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362 | \S{faq-tunnels}{Question} How do I use X forwarding and port |
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363 | forwarding? I can't find the Tunnels panel. |
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364 | |
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365 | This is a new feature in version 0.52. You should upgrade. |
f2003e32 |
366 | |
a1d2976b |
367 | \S{faq-options}{Question} How do I use all PuTTY's features (public |
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368 | keys, port forwarding, SSH v2, etc.) in PSCP, PSFTP and Plink? |
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369 | |
370 | The command-line tools are currently rather short of command line |
371 | options to enable this sort of thing. However, you can use most of |
372 | PuTTY's features if you create a PuTTY saved session, and then use |
373 | the name of the saved session on the command line in place of a |
374 | hostname. This works for PSCP, PSFTP and Plink (but don't expect |
375 | port forwarding in the file transfer applications!). |
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376 | |
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377 | \S{faq-pscp}{Question} How do I use PSCP.EXE? When I double-click it |
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378 | gives me a command prompt window which then closes instantly. |
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379 | |
380 | PSCP is a command-line application, not a GUI application. If you |
381 | run it without arguments, it will simply print a help message and |
382 | terminate. |
383 | |
384 | To use PSCP properly, run it from a Command Prompt window. See |
385 | \k{pscp} in the documentation for more details. |
386 | |
a1d2976b |
387 | \S{faq-pscp-spaces}{Question} How do I use PSCP to copy a file whose |
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388 | name has spaces in? |
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389 | |
390 | If PSCP is using the traditional SCP protocol, this is confusing. If |
391 | you're specifying a file at the local end, you just use one set of |
392 | quotes as you would normally do: |
393 | |
394 | \c pscp "local filename with spaces" user@host: |
395 | \c pscp user@host:myfile "local filename with spaces" |
396 | |
397 | But if the filename you're specifying is on the \e{remote} side, you |
398 | have to use backslashes and two sets of quotes: |
399 | |
400 | \c pscp user@host:"\"remote filename with spaces\"" local_filename |
401 | \c pscp local_filename user@host:"\"remote filename with spaces\"" |
402 | |
403 | Worse still, in a remote-to-local copy you have to specify the local |
404 | file name explicitly, otherwise PSCP will complain that they don't |
405 | match (unless you specified the \c{-unsafe} option). The following |
406 | command will give an error message: |
407 | |
408 | \c c:\>pscp user@host:"\"oo er\"" . |
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409 | \c warning: remote host tried to write to a file called 'oo er' |
410 | \c when we requested a file called '"oo er"'. |
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411 | |
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412 | Instead, you need to specify the local file name in full: |
413 | |
414 | \c c:\>pscp user@host:"\"oo er\"" "oo er" |
415 | |
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416 | If PSCP is using the newer SFTP protocol, none of this is a problem, |
417 | and all filenames with spaces in are specified using a single pair |
418 | of quotes in the obvious way: |
419 | |
420 | \c pscp "local file" user@host: |
421 | \c pscp user@host:"remote file" . |
422 | |
423 | \H{faq-trouble} Troubleshooting |
424 | |
babac7bd |
425 | \S{faq-incorrect-mac}{Question} Why do I see \q{Incorrect MAC |
426 | received on packet}? |
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427 | |
428 | This is due to a bug in old SSH 2 servers distributed by |
429 | \cw{ssh.com}. Version 2.3.0 and below of their SSH 2 server |
430 | constructs Message Authentication Codes in the wrong way, and |
431 | expects the client to construct them in the same wrong way. PuTTY |
432 | constructs the MACs correctly by default, and hence these old |
433 | servers will fail to work with it. |
434 | |
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435 | If you are using PuTTY version 0.52 or better, this should work |
436 | automatically: PuTTY should detect the buggy servers from their |
437 | version number announcement, and automatically start to construct |
438 | its MACs in the same incorrect manner as they do, so it will be able |
439 | to work with them. |
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440 | |
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441 | If you are using PuTTY version 0.51 or below, you can enable the |
442 | workaround by going to the SSH panel and ticking the box labelled |
443 | \q{Imitate SSH 2 MAC bug}. It's possible that you might have to do |
444 | this with 0.52 as well, if a buggy server exists that PuTTY doesn't |
445 | know about. |
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446 | |
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447 | In this context MAC stands for Message Authentication Code. It's a |
448 | cryptographic term, and it has nothing at all to do with Ethernet |
449 | MAC (Media Access Control) addresses. |
450 | |
67325335 |
451 | \S{faq-pscp-protocol}{Question} Why do I see \q{Fatal: Protocol |
452 | error: Expected control record} in PSCP? |
453 | |
454 | This happens because PSCP was expecting to see data from the server |
455 | that was part of the PSCP protocol exchange, and instead it saw data |
456 | that it couldn't make any sense of at all. |
457 | |
458 | This almost always happens because the startup scripts in your |
459 | account on the server machine are generating output. This is |
460 | impossible for PSCP, or any other SCP client, to work around. You |
461 | should never use startup files (\c{.bashrc}, \c{.cshrc} and so on) |
462 | which generate output in non-interactive sessions. |
463 | |
464 | This is not actually a PuTTY problem. If PSCP fails in this way, |
465 | then all other SCP clients are likely to fail in exactly the same |
466 | way. The problem is at the server end. |
467 | |
a1d2976b |
468 | \S{faq-colours}{Question} I clicked on a colour in the Colours |
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469 | panel, and the colour didn't change in my terminal. |
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470 | |
471 | That isn't how you're supposed to use the Colours panel. |
472 | |
473 | During the course of a session, PuTTY potentially uses \e{all} the |
474 | colours listed in the Colours panel. It's not a question of using |
475 | only one of them and you choosing which one; PuTTY will use them |
476 | \e{all}. The purpose of the Colours panel is to let you adjust the |
477 | appearance of all the colours. So to change the colour of the |
478 | cursor, for example, you would select \q{Cursor Colour}, press the |
479 | \q{Modify} button, and select a new colour from the dialog box that |
480 | appeared. Similarly, if you want your session to appear in green, |
481 | you should select \q{Default Foreground} and press \q{Modify}. |
482 | Clicking on \q{ANSI Green} won't turn your session green; it will |
483 | only allow you to adjust the \e{shade} of green used when PuTTY is |
484 | instructed by the server to display green text. |
485 | |
a1d2976b |
486 | \S{faq-winsock2}{Question} Plink on Windows 95 says it can't find |
70706890 |
487 | \cw{WS2_32.DLL}. |
ee46ef84 |
488 | |
489 | Plink requires the extended Windows network library, WinSock version |
490 | 2. This is installed as standard on Windows 98 and above, and on |
491 | Windows NT, and even on later versions of Windows 95; but early |
492 | Win95 installations don't have it. |
493 | |
494 | In order to use Plink on these systems, you will need to download |
495 | the |
496 | \W{http://www.microsoft.com/windows95/downloads/contents/wuadmintools/s_wunetworkingtools/w95sockets2/}{WinSock 2 upgrade}: |
497 | |
498 | \c http://www.microsoft.com/windows95/downloads/contents/wuadmintools/ |
499 | \c s_wunetworkingtools/w95sockets2/ |
500 | |
a1d2976b |
501 | \S{faq-rekey}{Question} My PuTTY sessions close after an hour and |
70706890 |
502 | tell me \q{Server failed host key check}. |
ee46ef84 |
503 | |
504 | This is a bug in all versions of PuTTY up to and including 0.51. SSH |
505 | v2 servers from \cw{ssh.com} will require the key exchange to be |
506 | repeated one hour after the start of the connection, and PuTTY will |
507 | get this wrong. |
508 | |
32c37ecd |
509 | Upgrade to version 0.52 and the problem should go away. |
ee46ef84 |
510 | |
a1d2976b |
511 | \S{faq-outofmem}{Question} After trying to establish an SSH 2 |
70706890 |
512 | connection, PuTTY says \q{Out of memory} and dies. |
ee46ef84 |
513 | |
514 | If this happens just while the connection is starting up, this often |
515 | indicates that for some reason the client and server have failed to |
516 | establish a session encryption key. Somehow, they have performed |
517 | calculations that should have given each of them the same key, but |
518 | have ended up with different keys; so data encrypted by one and |
519 | decrypted by the other looks like random garbage. |
520 | |
521 | This causes an \q{out of memory} error because the first encrypted |
522 | data PuTTY expects to see is the length of an SSH message. Normally |
523 | this will be something well under 100 bytes. If the decryption has |
524 | failed, PuTTY will see a completely random length in the region of |
525 | two \e{gigabytes}, and will try to allocate enough memory to store |
526 | this non-existent message. This will immediately lead to it thinking |
527 | it doesn't have enough memory, and panicking. |
528 | |
529 | If this happens to you, it is quite likely to still be a PuTTY bug |
530 | and you should report it (although it might be a bug in your SSH |
531 | server instead); but it doesn't necessarily mean you've actually run |
532 | out of memory. |
533 | |
9accb45d |
534 | \S{faq-outofmem2}{Question} When attempting a file transfer, either |
535 | PSCP or PSFTP says \q{Out of memory} and dies. |
536 | |
537 | This is almost always caused by your login scripts on the server |
538 | generating output. PSCP or PSFTP will receive that output when they |
539 | were expecting to see the start of a file transfer protocol, and |
540 | they will attempt to interpret the output as file-transfer protocol. |
541 | This will usually lead to an \q{out of memory} error for much the |
542 | same reasons as given in \k{faq-outofmem}. |
543 | |
544 | This is a setup problem in your account on your server, \e{not} a |
545 | PSCP/PSFTP bug. Your login scripts should \e{never} generate output |
546 | during non-interactive sessions; secure file transfer is not the |
547 | only form of remote access that will break if they do. |
548 | |
549 | On Unix, a simple fix is to ensure that all the parts of your login |
550 | script that might generate output are in \c{.profile} (if you use a |
551 | Bourne shell derivative) or \c{.login} (if you use a C shell). |
552 | Putting them in more general files such as \c{.bashrc} or \c{.cshrc} |
553 | is liable to lead to problems. |
554 | |
555 | \S{faq-psftp-slow} PSFTP transfers files much slower than PSCP. |
556 | |
557 | We believe this is because the SFTP and SSH2 protocols are less |
558 | efficient at bulk data transfer than SCP and SSH1, because every |
559 | block of data transferred requires an acknowledgment from the far |
560 | end. It would in theory be possible to queue several blocks of data |
561 | to get round this speed problem, but as yet we haven't done the |
562 | coding. If you really want this fixed, feel free to offer to help. |
563 | |
a1d2976b |
564 | \S{faq-bce}{Question} When I run full-colour applications, I see |
70706890 |
565 | areas of black space where colour ought to be. |
f1453e5c |
566 | |
567 | You almost certainly need to enable the \q{Use background colour to |
568 | erase screen} setting in the Terminal panel. Note that if you do |
569 | this in mid-session, it won't take effect until you reset the |
570 | terminal (see \k{faq-resetterm}). |
571 | |
a1d2976b |
572 | \S{faq-resetterm}{Question} When I change some terminal settings, |
70706890 |
573 | nothing happens. |
f1453e5c |
574 | |
575 | Some of the terminal options (notably Auto Wrap and |
576 | background-colour screen erase) actually represent the \e{default} |
577 | setting, rather than the currently active setting. The server can |
578 | send sequences that modify these options in mid-session, but when |
579 | the terminal is reset (by server action, or by you choosing \q{Reset |
580 | Terminal} from the System menu) the defaults are restored. |
581 | |
582 | If you want to change one of these options in the middle of a |
583 | session, you will find that the change does not immediately take |
584 | effect. It will only take effect once you reset the terminal. |
585 | |
a1d2976b |
586 | \S{faq-altgr}{Question} I can't type characters that require the |
70706890 |
587 | AltGr key. |
ee46ef84 |
588 | |
32c37ecd |
589 | In PuTTY version 0.51, the AltGr key was broken. Upgrade to version |
590 | 0.52. |
ee46ef84 |
591 | |
a1d2976b |
592 | \S{faq-idleout}{Question} My PuTTY sessions unexpectedly close after |
70706890 |
593 | they are idle for a while. |
ee46ef84 |
594 | |
595 | Some types of firewall, and almost any router doing Network Address |
596 | Translation (NAT, also known as IP masquerading), will forget about |
597 | a connection through them if the connection does nothing for too |
598 | long. This will cause the connection to be rudely cut off when |
599 | contact is resumed. |
600 | |
601 | You can try to combat this by telling PuTTY to send \e{keepalives}: |
602 | packets of data which have no effect on the actual session, but |
603 | which reassure the router or firewall that the network connection is |
604 | still active and worth remembering about. |
605 | |
606 | Keepalives don't solve everything, unfortunately; although they |
607 | cause greater robustness against this sort of router, they can also |
608 | cause a \e{loss} of robustness against network dropouts. See |
609 | \k{config-keepalive} in the documentation for more discussion of |
610 | this. |
611 | |
a1d2976b |
612 | \S{faq-timeout}{Question} PuTTY's network connections time out too |
70706890 |
613 | quickly when network connectivity is temporarily lost. |
ee46ef84 |
614 | |
615 | This is a Windows problem, not a PuTTY problem. The timeout value |
616 | can't be set on per application or per session basis. To increase |
617 | the TCP timeout globally, you need to tinker with the Registry. |
618 | |
619 | On Windows 95, 98 or ME, the registry key you need to change is |
620 | |
621 | \c HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\ |
622 | \c MSTCP\MaxDataRetries |
623 | |
624 | (it must be of type DWORD in Win95, or String in Win98/ME). |
625 | |
626 | On Windows NT or 2000, the registry key is |
627 | |
628 | \c HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\ |
629 | \c Parameters\TcpMaxDataRetransmissions |
630 | |
631 | and it must be of type DWORD. |
632 | |
633 | Set the key's value to something like 10. This will cause Windows to |
634 | try harder to keep connections alive instead of abandoning them. |
635 | |
a1d2976b |
636 | \S{faq-puttyputty}{Question} When I \cw{cat} a binary file, I get |
ee46ef84 |
637 | `PuTTYPuTTYPuTTY' on my command line. |
638 | |
a5a6cb30 |
639 | Don't do that, then. |
ee46ef84 |
640 | |
641 | This is designed behaviour; when PuTTY receives the character |
642 | Control-E from the remote server, it interprets it as a request to |
643 | identify itself, and so it sends back the string \q{\cw{PuTTY}} as |
644 | if that string had been entered at the keyboard. Control-E should |
645 | only be sent by programs that are prepared to deal with the |
646 | response. Writing a binary file to your terminal is likely to output |
647 | many Control-E characters, and cause this behaviour. Don't do it. |
648 | It's a bad plan. |
649 | |
a5a6cb30 |
650 | To mitigate the effects, you could configure the answerback string |
651 | to be empty (see \k{config-answerback}); but writing binary files to |
652 | your terminal is likely to cause various other unpleasant behaviour, |
653 | so this is only a small remedy. |
654 | |
babac7bd |
655 | \S{faq-wintitle}{Question} When I \cw{cat} a binary file, my window |
656 | title changes to a nonsense string. |
ee46ef84 |
657 | |
a5a6cb30 |
658 | Don't do that, then. |
ee46ef84 |
659 | |
660 | It is designed behaviour that PuTTY should have the ability to |
661 | adjust the window title on instructions from the server. Normally |
662 | the control sequence that does this should only be sent |
663 | deliberately, by programs that know what they are doing and intend |
664 | to put meaningful text in the window title. Writing a binary file to |
665 | your terminal runs the risk of sending the same control sequence by |
666 | accident, and cause unexpected changes in the window title. Don't do |
667 | it. |
668 | |
babac7bd |
669 | \S{faq-password-fails}{Question} My keyboard stops working once |
670 | PuTTY displays the password prompt. |
59c1f1f6 |
671 | |
672 | No, it doesn't. PuTTY just doesn't display the password you type, so |
673 | that someone looking at your screen can't see what it is. |
674 | |
675 | Unlike the Windows login prompts, PuTTY doesn't display the password |
676 | as a row of asterisks either. This is so that someone looking at |
677 | your screen can't even tell how \e{long} your password is, which |
678 | might be valuable information. |
679 | |
b5bee048 |
680 | \S{faq-keyboard}{Question} One or more function keys don't do what I |
681 | expected in a server-side application. |
682 | |
683 | If you've already tried all the relevant options in the PuTTY |
684 | Keyboard panel, you may need to mail the PuTTY maintainers and ask. |
685 | |
686 | It is \e{not} usually helpful just to tell us which application, |
687 | which server operating system, and which key isn't working; in order |
688 | to replicate the problem we would need to have a copy of every |
689 | operating system, and every application, that anyone has ever |
690 | complained about. |
691 | |
692 | PuTTY responds to function key presses by sending a sequence of |
693 | control characters to the server. If a function key isn't doing what |
694 | you expect, it's likely that the character sequence your application |
695 | is expecting to receive is not the same as the one PuTTY is sending. |
696 | Therefore what we really need to know is \e{what} sequence the |
697 | application is expecting. |
698 | |
699 | The simplest way to investigate this is to find some other terminal |
700 | environment, in which that function key \e{does} work; and then |
701 | investigate what sequence the function key is sending in that |
702 | situation. One reasonably easy way to do this on a Unix system is to |
703 | type the command \c{cat}, and then press the function key. This is |
704 | likely to produce output of the form \c{^[[11~}. You can also do |
705 | this in PuTTY, to find out what sequence the function key is |
706 | producing in that. Then you can mail the PuTTY maintainers and tell |
707 | us \q{I wanted the F1 key to send \c{^[[11~}, but instead it's |
708 | sending \c{^[OP}, can this be done?}, or something similar. |
709 | |
710 | You should still read the |
711 | \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/feedback.html}{Feedback |
712 | page} on the PuTTY website (also provided as \k{feedback} in the |
713 | manual), and follow the guidelines contained in that. |
714 | |
941d39e2 |
715 | \S{faq-openssh-bad-openssl}{Question} Since my SSH server was upgraded |
716 | to OpenSSH 3.1p1/3.4p1, I can no longer connect with PuTTY. |
1d2a9c9c |
717 | |
718 | There is a known problem when OpenSSH has been built against an |
719 | incorrect version of OpenSSL; the quick workaround is to configure |
720 | PuTTY to use SSH protocol 2 and the Blowfish cipher. |
721 | |
941d39e2 |
722 | For more details and OpenSSH patches, see |
723 | \W{http://bugzilla.mindrot.org/show_bug.cgi?id=138}{bug 138} in the |
724 | OpenSSH BTS. |
725 | |
1d2a9c9c |
726 | This is not a PuTTY-specific problem; if you try to connect with |
941d39e2 |
727 | another client you'll likely have similar problems. (Although PuTTY's |
728 | default cipher differs from many other clients.) |
1d2a9c9c |
729 | |
941d39e2 |
730 | \e{OpenSSH 3.1p1:} configurations known to be broken (and symptoms): |
1d2a9c9c |
731 | |
732 | \b SSH 2 with AES cipher (PuTTY says "Assertion failed! Expression: |
733 | (len & 15) == 0" in sshaes.c, or "Out of memory", or crashes) |
734 | |
9712b085 |
735 | \b SSH 2 with 3DES (PuTTY says "Incorrect MAC received on packet") |
736 | |
1d2a9c9c |
737 | \b SSH 1 with Blowfish (PuTTY says "Incorrect CRC received on |
738 | packet") |
739 | |
740 | \b SSH 1 with 3DES |
741 | |
941d39e2 |
742 | \e{OpenSSH 3.4p1:} as of 3.4p1, only the problem with SSH 1 and |
743 | Blowfish remains. Rebuild your server, apply the patch linked to from |
744 | bug 138 above, or use another cipher (e.g., 3DES) instead. |
59f76022 |
745 | |
1bb76745 |
746 | \S{faq-ssh2key-ssh1conn}{Question} Why do I see "Couldn't load private |
747 | key from ..."? Why can PuTTYgen load my key but not PuTTY? |
748 | |
749 | It's likely that you've generated an SSH protocol 2 key with PuTTYgen, |
750 | but you're trying to use it in an SSH 1 connection. SSH1 and SSH2 keys |
751 | have different formats, and (at least in 0.52) PuTTY's reporting of a |
752 | key in the wrong format isn't optimal. |
753 | |
754 | To connect using SSH 2 to a server that supports both versions, you |
755 | need to change the configuration from the default (see \k{faq-ssh2}). |
756 | |
ee46ef84 |
757 | \H{faq-secure} Security questions |
758 | |
a1d2976b |
759 | \S{faq-publicpc}{Question} Is it safe for me to download PuTTY and |
70706890 |
760 | use it on a public PC? |
ee46ef84 |
761 | |
762 | It depends on whether you trust that PC. If you don't trust the |
763 | public PC, don't use PuTTY on it, and don't use any other software |
764 | you plan to type passwords into either. It might be watching your |
765 | keystrokes, or it might tamper with the PuTTY binary you download. |
766 | There is \e{no} program safe enough that you can run it on an |
767 | actively malicious PC and get away with typing passwords into it. |
768 | |
769 | If you do trust the PC, then it's probably OK to use PuTTY on it |
770 | (but if you don't trust the network, then the PuTTY download might |
771 | be tampered with, so it would be better to carry PuTTY with you on a |
772 | floppy). |
773 | |
a1d2976b |
774 | \S{faq-cleanup}{Question} What does PuTTY leave on a system? How can |
70706890 |
775 | I clean up after it? |
ee46ef84 |
776 | |
777 | PuTTY will leave some Registry entries, and a random seed file, on |
778 | the PC (see \k{faq-settings}). If you are using PuTTY on a public |
779 | PC, or somebody else's PC, you might want to clean these up when you |
780 | leave. You can do that automatically, by running the command |
781 | \c{putty -cleanup}. |
782 | |
a1d2976b |
783 | \S{faq-dsa}{Question} How come PuTTY now supports DSA, when the |
70706890 |
784 | website used to say how insecure it was? |
ee46ef84 |
785 | |
786 | DSA has a major weakness \e{if badly implemented}: it relies on a |
787 | random number generator to far too great an extent. If the random |
788 | number generator produces a number an attacker can predict, the DSA |
789 | private key is exposed - meaning that the attacker can log in as you |
790 | on all systems that accept that key. |
791 | |
792 | The PuTTY policy changed because the developers were informed of |
793 | ways to implement DSA which do not suffer nearly as badly from this |
794 | weakness, and indeed which don't need to rely on random numbers at |
795 | all. For this reason we now believe PuTTY's DSA implementation is |
796 | probably OK. However, if you have the choice, we still recommend you |
797 | use RSA instead. |
798 | |
ee4b471f |
799 | \S{faq-virtuallock}{Question} Couldn't Pageant use |
800 | \cw{VirtualLock()} to stop private keys being written to disk? |
f9908cf7 |
801 | |
ee4b471f |
802 | Unfortunately not. The \cw{VirtualLock()} function in the Windows |
803 | API doesn't do a proper job: it may prevent small pieces of a |
804 | process's memory from being paged to disk while the process is |
805 | running, but it doesn't stop the process's memory as a whole from |
806 | being swapped completely out to disk when the process is long-term |
807 | inactive. And Pageant spends most of its time inactive. |
f9908cf7 |
808 | |
ee46ef84 |
809 | \H{faq-admin} Administrative questions |
810 | |
a1d2976b |
811 | \S{faq-domain}{Question} Would you like me to register you a nicer |
70706890 |
812 | domain name? |
ee46ef84 |
813 | |
814 | No, thank you. Even if you can find one (most of them seem to have |
815 | been registered already, by people who didn't ask whether we |
816 | actually wanted it before they applied), we're happy with the PuTTY |
817 | web site being exactly where it is. It's not hard to find (just type |
818 | \q{putty} into \W{http://www.google.com/}{google.com} and we're the |
819 | first link returned), and we don't believe the administrative hassle |
820 | of moving the site would be worth the benefit. |
821 | |
822 | In addition, if we \e{did} want a custom domain name, we would want |
823 | to run it ourselves, so we knew for certain that it would continue |
824 | to point where we wanted it, and wouldn't suddenly change or do |
825 | strange things. Having it registered for us by a third party who we |
826 | don't even know is not the best way to achieve this. |
827 | |
a1d2976b |
828 | \S{faq-webhosting}{Question} Would you like free web hosting for the |
70706890 |
829 | PuTTY web site? |
ee46ef84 |
830 | |
831 | We already have some, thanks. |
832 | |
a1d2976b |
833 | \S{faq-sourceforge}{Question} Why don't you move PuTTY to |
70706890 |
834 | SourceForge? |
ee46ef84 |
835 | |
836 | Partly, because we don't want to move the web site location (see |
837 | \k{faq-domain}). |
838 | |
839 | Also, security reasons. PuTTY is a security product, and as such it |
840 | is particularly important to guard the code and the web site against |
841 | unauthorised modifications which might introduce subtle security |
842 | flaws. Therefore, we prefer that the CVS repository, web site and |
843 | FTP site remain where they are, under the direct control of system |
844 | administrators we know and trust personally, rather than being run |
845 | by a large organisation full of people we've never met and which is |
846 | known to have had breakins in the past. |
847 | |
848 | No offence to SourceForge; I think they do a wonderful job. But |
849 | they're not ideal for everyone, and in particular they're not ideal |
850 | for us. |
851 | |
a1d2976b |
852 | \S{faq-mailinglist1}{Question} Why can't I subscribe to the |
70706890 |
853 | putty-bugs mailing list? |
ee46ef84 |
854 | |
855 | Because you're not a member of the PuTTY core development team. The |
856 | putty-bugs mailing list is not a general newsgroup-like discussion |
857 | forum; it's a contact address for the core developers, and an |
858 | \e{internal} mailing list for us to discuss things among ourselves. |
859 | If we opened it up for everybody to subscribe to, it would turn into |
860 | something more like a newsgroup and we would be completely |
861 | overwhelmed by the volume of traffic. It's hard enough to keep up |
862 | with the list as it is. |
863 | |
a1d2976b |
864 | \S{faq-mailinglist2}{Question} If putty-bugs isn't a |
70706890 |
865 | general-subscription mailing list, what is? |
ee46ef84 |
866 | |
867 | There isn't one, that we know of. |
868 | |
869 | If someone else wants to set up a mailing list for PuTTY users to |
870 | help each other with common problems, that would be fine with us; |
871 | but the PuTTY team would almost certainly not have the time to read |
872 | it, so any questions the list couldn't answer would have to be |
873 | forwarded on to us by the questioner. In any case, it's probably |
874 | better to use the established newsgroup \cw{comp.security.ssh} for |
875 | this purpose. |
876 | |
a1d2976b |
877 | \S{faq-donations}{Question} How can I donate to PuTTY development? |
ee46ef84 |
878 | |
879 | Please, \e{please} don't feel you have to. PuTTY is completely free |
880 | software, and not shareware. We think it's very important that |
881 | \e{everybody} who wants to use PuTTY should be able to, whether they |
882 | have any money or not; so the last thing we would want is for a |
883 | PuTTY user to feel guilty because they haven't paid us any money. If |
884 | you want to keep your money, please do keep it. We wouldn't dream of |
885 | asking for any. |
886 | |
887 | Having said all that, if you still really \e{want} to give us money, |
888 | we won't argue :-) The easiest way for us to accept donations is if |
889 | you go to \W{http://www.e-gold.com}\cw{www.e-gold.com}, and deposit |
890 | your donation in account number 174769. Then send us e-mail to let |
891 | us know you've done so (otherwise we might not notice for months!). |
9cd3f7b0 |
892 | Alternatively, if e-gold isn't convenient for you, you can donate to |
893 | \cw{<anakin@pobox.com>} using PayPal |
894 | (\W{http://www.paypal.com/}\cw{www.paypal.com}). |
ee46ef84 |
895 | |
896 | Small donations (tens of dollars or tens of euros) will probably be |
897 | spent on beer or curry, which helps motivate our volunteer team to |
898 | continue doing this for the world. Larger donations will be spent on |
899 | something that actually helps development, if we can find anything |
9cd3f7b0 |
900 | (perhaps new hardware, or a copy of Windows XP), but if we can't |
ee46ef84 |
901 | find anything then we'll just distribute the money among the |
902 | developers. If you want to be sure your donation is going towards |
903 | something worthwhile, ask us first. If you don't like these terms, |
904 | feel perfectly free not to donate. We don't mind. |
905 | |
f9908cf7 |
906 | \H{faq-misc} Miscellaneous questions |
907 | |
908 | \S{faq-openssh}{Question} Is PuTTY a port of OpenSSH, or based on |
909 | OpenSSH? |
910 | |
911 | No, it isn't. PuTTY is almost completely composed of code written |
912 | from scratch for PuTTY. The only code we share with OpenSSH is the |
913 | detector for SSH1 CRC compensation attacks, written by CORE SDI S.A. |
914 | |
606398fb |
915 | \S{faq-sillyputty}{Question} Where can I buy silly putty? |
916 | |
917 | You're looking at the wrong web site; the only PuTTY we know about |
918 | here is the name of a computer program. |
919 | |
920 | If you want the kind of putty you can buy as an executive toy, the |
921 | PuTTY team can personally recommend Thinking Putty, which you can |
922 | buy from Crazy Aaron's Putty World, at |
923 | \W{http://www.puttyworld.com}\cw{www.puttyworld.com}. |
924 | |
a1d2976b |
925 | \S{faq-pronounce}{Question} How do I pronounce PuTTY? |
ee46ef84 |
926 | |
927 | Exactly like the normal word \q{putty}. Just like the stuff you put |
928 | on window frames. (One of the reasons it's called PuTTY is because |
929 | it makes Windows usable. :-) |