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1 | \versionid $Id: errors.but,v 1.3 2003/01/30 10:19:05 simon Exp $ |
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2 | |
3 | \C{errors} Common error messages |
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 | |
18 | This error message occurs when PuTTY connects to a new SSH server. |
19 | Every server identifies itself by means of a host key; once PuTTY |
20 | knows the host key for a server, it will be able to detect if a |
21 | malicious attacker redirects your connection to another machine. |
22 | |
23 | If you see this message, it means that PuTTY has not seen this host |
24 | key before, and has no way of knowing whether it is correct or not. |
25 | You should attempt to verify the host key by other means, such as |
26 | asking the machine's administrator. |
27 | |
28 | If you see this message and you know that your installation of PuTTY |
29 | \e{has} connected to the same server before, it may have been |
30 | recently upgraded to SSH protocol version 2. SSH protocols 1 and 2 |
31 | use separate host keys, so when you first use SSH 2 with a server |
32 | you have only used SSH 1 with before, you will see this message |
33 | again. You should verify the correctness of the key as before. |
34 | |
35 | See \k{gs-hostkey} for more information on host keys. |
36 | |
37 | \H{errors-hostkey-wrong} \q{WARNING - POTENTIAL SECURITY BREACH!} |
38 | |
39 | This message, followed by \q{The server's host key does not match |
40 | the one PuTTY has cached in the registry}, means that PuTTY has |
41 | connected to the SSH server before, knows what its host key |
42 | \e{should} be, but has found a different one. |
43 | |
44 | This may mean that a malicious attacker has replaced your server |
45 | with a different one, or has redirected your network connection to |
46 | their own machine. On the other hand, it may simply mean that the |
47 | administrator of your server has accidentally changed the key while |
48 | upgrading the SSH software; this \e{shouldn't} happen but it is |
49 | unfortunately possible. |
50 | |
51 | You should contact your server's administrator and see whether they |
52 | expect the host key to have changed. If so, verify the new host key |
53 | in the same way as you would if it was new. |
54 | |
55 | See \k{gs-hostkey} for more information on host keys. |
56 | |
57 | \H{errors-portfwd-space} \q{Out of space for port forwardings} |
58 | |
59 | PuTTY has a fixed-size buffer which it uses to store the details of |
60 | all port forwardings you have set up in an SSH session. If you |
61 | specify too many port forwardings on the PuTTY or Plink command line |
62 | and this buffer becomes full, you will see this error message. |
63 | |
64 | We need to fix this (fixed-size buffers are almost always a mistake) |
65 | but we haven't got round to it. If you actually have trouble with |
66 | this, let us know and we'll move it up our priority list. |
67 | |
68 | \H{errors-cipher-warning} \q{The first cipher supported by the server is |
69 | ... below the configured warning threshold} |
70 | |
71 | This occurs when the SSH server does not offer any ciphers which you |
72 | have configured PuTTY to consider strong enough. |
73 | |
74 | See \k{config-ssh-encryption} for more information on this message. |
75 | |
76 | \H{errors-memory} \q{Out of memory} |
77 | |
78 | This occurs when PuTTY tries to allocate more memory than the system |
79 | can give it. This \e{may} happen for genuine reasons: if the |
80 | computer really has run out of memory, or if you have configured an |
81 | extremely large number of lines of scrollback in your terminal. |
82 | PuTTY is not able to recover from running out of memory; it will |
83 | terminate immediately after giving this error. |
84 | |
85 | However, this error can also occur when memory is not running out at |
86 | all, because PuTTY receives data in the wrong format. In SSH 2 and |
87 | also in SFTP, the server sends the length of each message before the |
88 | message itself; so PuTTY will receive the length, try to allocate |
89 | space for the message, and then receive the rest of the message. If |
90 | the length PuTTY receives is garbage, it will try to allocate a |
91 | ridiculous amount of memory, and will terminate with an \q{Out of |
92 | memory} error. |
93 | |
94 | This can happen in SSH 2, if PuTTY and the server have not enabled |
95 | encryption in the same way (see \k{faq-outofmem} in the FAQ). Some |
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96 | versions of OpenSSH have a known problem with this: see |
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97 | \k{faq-openssh-bad-openssl}. |
98 | |
99 | This can also happen in PSCP or PSFTP, if your login scripts on the |
100 | server generate output: the client program will be expecting an SFTP |
101 | message starting with a length, and if it receives some text from |
102 | your login scripts instead it will try to interpret them as a |
103 | message length. See \k{faq-outofmem2} for details of this. |
104 | |
105 | \H{errors-internal} \q{Internal error}, \q{Internal fault}, |
106 | \q{Assertion failed} |
107 | |
108 | Any error beginning with the word \q{Internal} should \e{never} |
109 | occur. If it does, there is a bug in PuTTY by definition; please see |
110 | \k{feedback} and report it to us. |
111 | |
112 | Similarly, any error message starting with \q{Assertion failed} is a |
113 | bug in PuTTY. Please report it to us, and include the exact text |
114 | from the error message box. |
115 | |
116 | \H{errors-refused} \q{Server refused our public key} or \q{Key |
117 | refused} |
118 | |
119 | Various forms of this error are printed in the PuTTY window, or |
120 | written to the PuTTY Event Log (see \k{using-eventlog}) when trying |
121 | public-key authentication. |
122 | |
123 | If you see one of these messages, it means that PuTTY has sent a |
124 | public key to the server and offered to authenticate with it, and |
125 | the server has refused to accept authentication. This usually means |
126 | that the server is not configured to accept this key to authenticate |
127 | this user. |
128 | |
129 | This is almost certainly not a problem with PuTTY. If you see this |
130 | type of message, the first thing you should do is check your |
131 | \e{server} configuration carefully. Also, read the PuTTY Event Log; |
132 | the server may have sent diagnostic messages explaining exactly what |
133 | problem it had with your setup. |
134 | |
135 | \H{errors-crc} \q{Incorrect CRC received on packet} or \q{Incorrect |
136 | MAC received on packet} |
137 | |
138 | This error occurs when PuTTY decrypts an SSH packet and its checksum |
139 | is not correct. This probably means something has gone wrong in the |
140 | encryption or decryption process. It's difficult to tell from this |
141 | error message whether the problem is in the client or in the server. |
142 | |
143 | A known server problem which can cause this error is described in |
144 | \k{faq-openssh-bad-openssl} in the FAQ. |
145 | |
146 | \H{errors-garbled} \q{Incoming packet was garbled on decryption} |
147 | |
148 | This error occurs when PuTTY decrypts an SSH packet and the |
149 | decrypted data makes no sense. This probably means something has |
150 | gone wrong in the encryption or decryption process. It's difficult |
151 | to tell from this error message whether the problem is in the client |
152 | or in the server. |
153 | |
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154 | If you get this error, one thing you could try would be to fiddle |
155 | with the setting of \q{Miscomputes SSH2 encryption keys} on the Bugs |
156 | panel (see \k{config-ssh-bug-derivekey2}). |
157 | |
158 | Another known server problem which can cause this error is described |
159 | in \k{faq-openssh-bad-openssl} in the FAQ. |
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160 | |
161 | \H{errors-x11-proxy} \q{Authentication failed at PuTTY X11 proxy} |
162 | |
163 | This error is reported when PuTTY is doing X forwarding. It is sent |
164 | back to the X application running on the SSH server, which will |
165 | usually report the error to the user. |
166 | |
167 | When PuTTY enables X forwarding (see \k{using-x-forwarding}) it |
168 | creates a virtual X display running on the SSH server. This display |
169 | requires authentication to connect to it (this is how PuTTY prevents |
170 | other users on your server machine from connecting through the PuTTY |
171 | proxy to your real X display). PuTTY also sends the server the |
172 | details it needs to enable clients to connect, and the server should |
173 | put this mechanism in place automatically, so your X applications |
174 | should just work. |
175 | |
176 | A common reason why people see this message is because they used SSH |
177 | to log in as one user (let's say \q{fred}), and then used the Unix |
178 | \c{su} command to become another user (typically \q{root}). The |
179 | original user, \q{fred}, has access to the X authentication data |
180 | provided by the SSH server, and can run X applications which are |
181 | forwarded over the SSH connection. However, the second user |
182 | (\q{root}) does not automatically have the authentication data |
183 | passed on to it, so attempting to run an X application as that user |
184 | often fails with this error. |
185 | |
186 | If this happens, \e{it is not a problem with PuTTY}. You need to |
187 | arrange for your X authentication data to be passed from the user |
188 | you logged in as to the user you used \c{su} to become. How you do |
189 | this depends on your particular system; in fact many modern versions |
190 | of \c{su} do it automatically. |
191 | |
192 | \H{errors-connaborted} \q{Network error: Software caused connection |
193 | abort} |
194 | |
195 | In modern versions of PuTTY, you should not see this error. |
196 | |
197 | Windows's documentation about this error condition is not very good, |
198 | but as far as we can tell, this error occurs when PuTTY is listening |
199 | on a port, another program makes a connection to that port, but |
200 | closes the connection so fast that PuTTY has no time to answer it. |
201 | |
202 | PuTTY only ever listens on a port when it is doing local-to-remote |
203 | port forwarding (see \k{using-port-forwarding}); and if an incoming |
204 | connection on that port receives this error, PuTTY should simply |
205 | close the connection and continue without error. |
206 | |
207 | If you see this error in PuTTY 0.53 or above, we would welcome a |
208 | report of the circumstances. |
209 | |
210 | \H{errors-connreset} \q{Network error: Connection reset by peer} |
211 | |
212 | This error occurs when the machines at each end of a network |
213 | connection lose track of the state of the connection between them. |
214 | For example, you might see it if your SSH server crashes, and |
215 | manages to reboot fully before you next attempt to send data to it. |
216 | |
217 | However, the most common reason to see this message is if you are |
218 | connecting through a firewall or a NAT router which has timed the |
219 | connection out. See \k{faq-idleout} in the FAQ for more details. You |
220 | may be able to improve the situation by using keepalives; see |
221 | \k{config-keepalive} for details on this. |
222 | |
223 | \H{errors-connrefused} \q{Network error: Connection refused} |
224 | |
225 | This error means that the network connection PuTTY tried to make to |
226 | your server was rejected by the server. Usually this happens because |
227 | the server does not provide the service which PuTTY is trying to |
228 | access. |
229 | |
230 | Check that you are connecting with the correct protocol (SSH, Telnet |
231 | or Rlogin), and check that the port number is correct. If that |
232 | fails, consult the administrator of your server. |