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1 | \define{versioniderrors} \versionid $Id$ |
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2 | |
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3 | \C{errors} Common \i{error messages} |
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4 | |
5 | This chapter lists a number of common error messages which PuTTY and |
6 | its associated tools can produce, and explains what they mean in |
7 | more detail. |
8 | |
9 | We do not attempt to list \e{all} error messages here: there are |
10 | many which should never occur, and some which should be |
11 | self-explanatory. If you get an error message which is not listed in |
12 | this chapter and which you don't understand, report it to us as a |
13 | bug (see \k{feedback}) and we will add documentation for it. |
14 | |
15 | \H{errors-hostkey-absent} \q{The server's host key is not cached in |
16 | the registry} |
17 | |
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18 | \cfg{winhelp-topic}{errors.hostkey.absent} |
19 | |
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20 | This error message occurs when PuTTY connects to a new SSH server. |
21 | Every server identifies itself by means of a host key; once PuTTY |
22 | knows the host key for a server, it will be able to detect if a |
23 | malicious attacker redirects your connection to another machine. |
24 | |
25 | If you see this message, it means that PuTTY has not seen this host |
26 | key before, and has no way of knowing whether it is correct or not. |
27 | You should attempt to verify the host key by other means, such as |
28 | asking the machine's administrator. |
29 | |
30 | If you see this message and you know that your installation of PuTTY |
31 | \e{has} connected to the same server before, it may have been |
32 | recently upgraded to SSH protocol version 2. SSH protocols 1 and 2 |
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33 | use separate host keys, so when you first use \i{SSH-2} with a server |
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34 | you have only used SSH-1 with before, you will see this message |
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35 | again. You should verify the correctness of the key as before. |
36 | |
37 | See \k{gs-hostkey} for more information on host keys. |
38 | |
39 | \H{errors-hostkey-wrong} \q{WARNING - POTENTIAL SECURITY BREACH!} |
40 | |
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41 | \cfg{winhelp-topic}{errors.hostkey.changed} |
42 | |
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43 | This message, followed by \q{The server's host key does not match |
44 | the one PuTTY has cached in the registry}, means that PuTTY has |
45 | connected to the SSH server before, knows what its host key |
46 | \e{should} be, but has found a different one. |
47 | |
48 | This may mean that a malicious attacker has replaced your server |
49 | with a different one, or has redirected your network connection to |
50 | their own machine. On the other hand, it may simply mean that the |
51 | administrator of your server has accidentally changed the key while |
52 | upgrading the SSH software; this \e{shouldn't} happen but it is |
53 | unfortunately possible. |
54 | |
55 | You should contact your server's administrator and see whether they |
56 | expect the host key to have changed. If so, verify the new host key |
57 | in the same way as you would if it was new. |
58 | |
59 | See \k{gs-hostkey} for more information on host keys. |
60 | |
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61 | \H{errors-cipher-warning} \q{The first cipher supported by the server is |
62 | ... below the configured warning threshold} |
63 | |
64 | This occurs when the SSH server does not offer any ciphers which you |
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65 | have configured PuTTY to consider strong enough. By default, PuTTY |
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66 | puts up this warning only for \ii{single-DES} and \i{Arcfour} encryption. |
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67 | |
68 | See \k{config-ssh-encryption} for more information on this message. |
69 | |
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70 | \H{errors-toomanyauth} \q{Server sent disconnect message type 2 |
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71 | (protocol error): "Too many authentication failures for root"} |
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72 | |
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73 | This message is produced by an \i{OpenSSH} (or \i{Sun SSH}) server if it |
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74 | receives more failed authentication attempts than it is willing to |
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75 | tolerate. |
76 | |
77 | This can easily happen if you are using Pageant and have a |
78 | large number of keys loaded into it, since these servers count each |
79 | offer of a public key as an authentication attempt. This can be worked |
80 | around by specifying the key that's required for the authentication in |
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81 | the PuTTY configuration (see \k{config-ssh-privkey}); PuTTY will ignore |
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82 | any other keys Pageant may have, but will ask Pageant to do the |
83 | authentication, so that you don't have to type your passphrase. |
84 | |
85 | On the server, this can be worked around by disabling public-key |
86 | authentication or (for Sun SSH only) by increasing \c{MaxAuthTries} in |
87 | \c{sshd_config}. |
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88 | |
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89 | \H{errors-memory} \q{\ii{Out of memory}} |
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90 | |
91 | This occurs when PuTTY tries to allocate more memory than the system |
92 | can give it. This \e{may} happen for genuine reasons: if the |
93 | computer really has run out of memory, or if you have configured an |
94 | extremely large number of lines of scrollback in your terminal. |
95 | PuTTY is not able to recover from running out of memory; it will |
96 | terminate immediately after giving this error. |
97 | |
98 | However, this error can also occur when memory is not running out at |
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99 | all, because PuTTY receives data in the wrong format. In SSH-2 and |
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100 | also in SFTP, the server sends the length of each message before the |
101 | message itself; so PuTTY will receive the length, try to allocate |
102 | space for the message, and then receive the rest of the message. If |
103 | the length PuTTY receives is garbage, it will try to allocate a |
104 | ridiculous amount of memory, and will terminate with an \q{Out of |
105 | memory} error. |
106 | |
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107 | This can happen in SSH-2, if PuTTY and the server have not enabled |
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108 | encryption in the same way (see \k{faq-outofmem} in the FAQ). Some |
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109 | versions of \i{OpenSSH} have a known problem with this: see |
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110 | \k{faq-openssh-bad-openssl}. |
111 | |
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112 | This can also happen in PSCP or PSFTP, if your \i{login scripts} on the |
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113 | server generate output: the client program will be expecting an SFTP |
114 | message starting with a length, and if it receives some text from |
115 | your login scripts instead it will try to interpret them as a |
116 | message length. See \k{faq-outofmem2} for details of this. |
117 | |
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118 | \H{errors-internal} \q{\ii{Internal error}}, \q{\ii{Internal fault}}, |
119 | \q{\ii{Assertion failed}} |
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120 | |
121 | Any error beginning with the word \q{Internal} should \e{never} |
122 | occur. If it does, there is a bug in PuTTY by definition; please see |
123 | \k{feedback} and report it to us. |
124 | |
125 | Similarly, any error message starting with \q{Assertion failed} is a |
126 | bug in PuTTY. Please report it to us, and include the exact text |
127 | from the error message box. |
128 | |
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129 | \H{errors-cant-load-key} \q{Unable to use this private key file}, |
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130 | \q{Couldn't load private key}, \q{Key is of wrong type} |
131 | |
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132 | \cfg{winhelp-topic}{errors.cantloadkey} |
133 | |
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134 | Various forms of this error are printed in the PuTTY window, or |
135 | written to the PuTTY Event Log (see \k{using-eventlog}) when trying |
136 | public-key authentication, or given by Pageant when trying to load a |
137 | private key. |
138 | |
139 | If you see one of these messages, it often indicates that you've tried |
140 | to load a key of an inappropriate type into PuTTY, Plink, PSCP, PSFTP, |
141 | or Pageant. |
142 | |
143 | You may have specified a key that's inappropriate for the connection |
144 | you're making. The SSH-1 and SSH-2 protocols require different private |
145 | key formats, and a SSH-1 key can't be used for a SSH-2 connection (or |
146 | vice versa). |
147 | |
148 | Alternatively, you may have tried to load an SSH-2 key in a \q{foreign} |
149 | format (OpenSSH or \cw{ssh.com}) directly into one of the PuTTY tools, |
150 | in which case you need to import it into PuTTY's native format |
151 | (\c{*.PPK}) using PuTTYgen - see \k{puttygen-conversions}. |
152 | |
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153 | \H{errors-refused} \q{Server refused our public key} or \q{Key |
154 | refused} |
155 | |
156 | Various forms of this error are printed in the PuTTY window, or |
157 | written to the PuTTY Event Log (see \k{using-eventlog}) when trying |
158 | public-key authentication. |
159 | |
160 | If you see one of these messages, it means that PuTTY has sent a |
161 | public key to the server and offered to authenticate with it, and |
162 | the server has refused to accept authentication. This usually means |
163 | that the server is not configured to accept this key to authenticate |
164 | this user. |
165 | |
166 | This is almost certainly not a problem with PuTTY. If you see this |
167 | type of message, the first thing you should do is check your |
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168 | \e{server} configuration carefully. Common errors include having |
169 | the wrong permissions or ownership set on the public key or the |
170 | user's home directory on the server. Also, read the PuTTY Event Log; |
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171 | the server may have sent diagnostic messages explaining exactly what |
172 | problem it had with your setup. |
173 | |
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174 | \K{pubkey-gettingready} has some hints on server-side public key |
175 | setup. |
176 | |
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177 | \H{errors-access-denied} \q{Access denied}, \q{Authentication refused} |
178 | |
179 | Various forms of this error are printed in the PuTTY window, or |
180 | written to the PuTTY Event Log (see \k{using-eventlog}) during |
181 | authentication. |
182 | |
183 | If you see one of these messages, it means that the server has refused |
184 | all the forms of authentication PuTTY has tried and it has no further |
185 | ideas. |
186 | |
187 | It may be worth checking the Event Log for diagnostic messages from |
188 | the server giving more detail. |
189 | |
190 | This error can be caused by buggy SSH-1 servers that fail to cope with |
191 | the various strategies we use for camouflaging passwords in transit. |
192 | Upgrade your server, or use the workarounds described in |
193 | \k{config-ssh-bug-ignore1} and possibly \k{config-ssh-bug-plainpw1}. |
194 | |
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195 | \H{errors-no-auth} \q{No supported authentication methods available} |
196 | |
197 | This error indicates that PuTTY has run out of ways to authenticate |
198 | you to an SSH server. This may be because PuTTY has TIS or |
199 | keyboard-interactive authentication disabled, in which case |
200 | \k{config-ssh-tis} and \k{config-ssh-ki}. |
201 | |
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202 | \H{errors-crc} \q{Incorrect \i{CRC} received on packet} or \q{Incorrect |
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203 | \i{MAC} received on packet} |
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204 | |
205 | This error occurs when PuTTY decrypts an SSH packet and its checksum |
206 | is not correct. This probably means something has gone wrong in the |
207 | encryption or decryption process. It's difficult to tell from this |
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208 | error message whether the problem is in the client, in the server, |
209 | or in between. |
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210 | |
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211 | In particular, if the network is corrupting data at the TCP level, it |
212 | may only be obvious with cryptographic protocols such as SSH, which |
213 | explicitly check the integrity of the transferred data and complain |
214 | loudly if the checks fail. Corruption of protocols without integrity |
215 | protection (such as HTTP) will manifest in more subtle failures (such |
216 | as misdisplayed text or images in a web browser) which may not be |
217 | noticed. |
218 | |
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219 | A known server problem which can cause this error is described in |
220 | \k{faq-openssh-bad-openssl} in the FAQ. |
221 | |
222 | \H{errors-garbled} \q{Incoming packet was garbled on decryption} |
223 | |
224 | This error occurs when PuTTY decrypts an SSH packet and the |
225 | decrypted data makes no sense. This probably means something has |
226 | gone wrong in the encryption or decryption process. It's difficult |
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227 | to tell from this error message whether the problem is in the client, |
228 | in the server, or in between. |
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229 | |
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230 | If you get this error, one thing you could try would be to fiddle with |
231 | the setting of \q{Miscomputes SSH-2 encryption keys} (see |
232 | \k{config-ssh-bug-derivekey2}) or \q{Ignores SSH-2 maximum packet |
233 | size} (see \k{config-ssh-bug-maxpkt2}) on the Bugs panel . |
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234 | |
235 | Another known server problem which can cause this error is described |
236 | in \k{faq-openssh-bad-openssl} in the FAQ. |
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237 | |
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238 | \H{errors-x11-proxy} \q{PuTTY X11 proxy: \e{various errors}} |
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239 | |
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240 | This family of errors are reported when PuTTY is doing X forwarding. |
241 | They are sent back to the X application running on the SSH server, |
242 | which will usually report the error to the user. |
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243 | |
244 | When PuTTY enables X forwarding (see \k{using-x-forwarding}) it |
245 | creates a virtual X display running on the SSH server. This display |
246 | requires authentication to connect to it (this is how PuTTY prevents |
247 | other users on your server machine from connecting through the PuTTY |
248 | proxy to your real X display). PuTTY also sends the server the |
249 | details it needs to enable clients to connect, and the server should |
250 | put this mechanism in place automatically, so your X applications |
251 | should just work. |
252 | |
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253 | A common reason why people see one of these messages is because they |
254 | used SSH to log in as one user (let's say \q{fred}), and then used |
255 | the Unix \c{su} command to become another user (typically \q{root}). |
256 | The original user, \q{fred}, has access to the X authentication data |
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257 | provided by the SSH server, and can run X applications which are |
258 | forwarded over the SSH connection. However, the second user |
259 | (\q{root}) does not automatically have the authentication data |
260 | passed on to it, so attempting to run an X application as that user |
261 | often fails with this error. |
262 | |
263 | If this happens, \e{it is not a problem with PuTTY}. You need to |
264 | arrange for your X authentication data to be passed from the user |
265 | you logged in as to the user you used \c{su} to become. How you do |
266 | this depends on your particular system; in fact many modern versions |
267 | of \c{su} do it automatically. |
268 | |
269 | \H{errors-connaborted} \q{Network error: Software caused connection |
270 | abort} |
271 | |
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272 | This is a generic error produced by the Windows network code when it |
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273 | kills an established connection for some reason. For example, it might |
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274 | happen if you pull the network cable out of the back of an |
275 | Ethernet-connected computer, or if Windows has any other similar |
276 | reason to believe the entire network has become unreachable. |
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277 | |
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278 | Windows also generates this error if it has given up on the machine |
279 | at the other end of the connection ever responding to it. If the |
280 | network between your client and server goes down and your client |
281 | then tries to send some data, Windows will make several attempts to |
282 | send the data and will then give up and kill the connection. In |
283 | particular, this can occur even if you didn't type anything, if you |
284 | are using SSH-2 and PuTTY attempts a key re-exchange. (See |
285 | \k{config-ssh-kex-rekey} for more about key re-exchange.) |
286 | |
287 | (It can also occur if you are using keepalives in your connection. |
288 | Other people have reported that keepalives \e{fix} this error for |
289 | them. See \k{config-keepalive} for a discussion of the pros and cons |
290 | of keepalives.) |
291 | |
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292 | We are not aware of any reason why this error might occur that would |
293 | represent a bug in PuTTY. The problem is between you, your Windows |
294 | system, your network and the remote system. |
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295 | |
296 | \H{errors-connreset} \q{Network error: Connection reset by peer} |
297 | |
298 | This error occurs when the machines at each end of a network |
299 | connection lose track of the state of the connection between them. |
300 | For example, you might see it if your SSH server crashes, and |
301 | manages to reboot fully before you next attempt to send data to it. |
302 | |
303 | However, the most common reason to see this message is if you are |
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304 | connecting through a \i{firewall} or a \i{NAT router} which has timed the |
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305 | connection out. See \k{faq-idleout} in the FAQ for more details. You |
306 | may be able to improve the situation by using keepalives; see |
307 | \k{config-keepalive} for details on this. |
308 | |
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309 | Note that Windows can produce this error in some circumstances without |
310 | seeing a connection reset from the server, for instance if the |
311 | connection to the network is lost. |
312 | |
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313 | \H{errors-connrefused} \q{Network error: Connection refused} |
314 | |
315 | This error means that the network connection PuTTY tried to make to |
316 | your server was rejected by the server. Usually this happens because |
317 | the server does not provide the service which PuTTY is trying to |
318 | access. |
319 | |
320 | Check that you are connecting with the correct protocol (SSH, Telnet |
321 | or Rlogin), and check that the port number is correct. If that |
322 | fails, consult the administrator of your server. |
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323 | |
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324 | \H{errors-conntimedout} \q{Network error: Connection timed out} |
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325 | |
326 | This error means that the network connection PuTTY tried to make to |
327 | your server received no response at all from the server. Usually |
328 | this happens because the server machine is completely isolated from |
329 | the network, or because it is turned off. |
330 | |
331 | Check that you have correctly entered the host name or IP address of |
332 | your server machine. If that fails, consult the administrator of |
333 | your server. |
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334 | |
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335 | \i{Unix} also generates this error when it tries to send data down a |
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336 | connection and contact with the server has been completely lost |
337 | during a connection. (There is a delay of minutes before Unix gives |
338 | up on receiving a reply from the server.) This can occur if you type |
339 | things into PuTTY while the network is down, but it can also occur |
340 | if PuTTY decides of its own accord to send data: due to a repeat key |
341 | exchange in SSH-2 (see \k{config-ssh-kex-rekey}) or due to |
342 | keepalives (\k{config-keepalive}). |