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 | 119 | </style></head>
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 | 120 | 
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 | 121 | <body>
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 | 122 | <div class="body">
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 | 123 | <p style="text-align: center; background: #ccc; border: 1px solid #2d5588;"><a 
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 | 124 |    style="text-decoration: none;" 
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 | 125 |    href="http://www.la-samhna.de/samhain/">samhain file integrity 
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 | 126 |    scanner</a> | <a style="text-decoration: none;" 
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 | 127 |    href="http://www.la-samhna.de/samhain/s_documentation.html">online 
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 | 128 |    documentation</a></p>
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 | 129 | <br><center>
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 | 130 | <h1>Samhain client/server: What can go wrong, and how can you fix it ?</h1>
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 | 131 | </center>
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 | 132 | <br>
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 | 133 | <hr>
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| [89] | 134 | <div class="warnblock">
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 | 135 | <ul>
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 | 136 |   <li>Almost all problems can only be diagnosed correctly by checking the 
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| [307] | 137 |       <b>server logs</b>.</li>
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 | 138 |   <li>
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 | 139 |     If the server does not write logs, <b>fix this first</b>. For debugging, 
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 | 140 |     stop the server, then run it in the foreground with 
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 | 141 |     <tt>yule -p info --foreground</tt>
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 | 142 |     <ul>
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 | 143 |       <li>
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 | 144 |         By default, the server logs to the file 
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 | 145 |         <tt>/var/log/yule/yule_log</tt>, and since the server drops 
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 | 146 |         root privileges on startup, the directory <tt>/var/log/yule</tt>
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 | 147 |         must be writable for the nonprivileged user the server runs 
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 | 148 |         as (the first existing out of: yule, daemon, nobody).
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 | 149 |       </li>
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 | 150 |       <li>
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 | 151 |         Logging to the logfile must be enabled in the
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 | 152 |         <tt>/etc/yulerc</tt> config file (e.g. LogSeverity=mark, or 
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 | 153 |         LogSeverity=info for enhanced verbosity).
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 | 154 |       </li>
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 | 155 |     </ul>
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 | 156 |   </li>
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| [91] | 157 | </ul>
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| [89] | 158 | </div>
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| [1] | 159 | <p>
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 | 160 | This document aims to explain how to diagnose and fix common problems that
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 | 161 | may result from misunderstanding or misconfiguration when setting up 
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 | 162 | a client/server samhain system. This document is divided in several sections
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 | 163 | more or less corresponding to the different stages when a client
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 | 164 | connects to a server. Each section starts with a brief explanation that
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 | 165 | should provide a basic understanding of what is going on.
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 | 166 | </p>
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 | 167 | <p>
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 | 168 | This document does not discuss <i>how</i> to setup a client/server (for
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 | 169 | this, look into the manual and/or the HOWTO-client+server). 
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 | 170 | </p>
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 | 171 | 
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 | 172 | <h2><a name="sect1">Table of Contents</a></h2>
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 | 173 | <p>
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 | 174 | <a href="#sect1">Connecting to the server</a><br>
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 | 175 | <a href="#sect2">Authentication</a><br>
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 | 176 | <a href="#sect3">Downloading config/database files</a><br>
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 | 177 | <a href="#sect4">Other connection problems</a><br>
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 | 178 | </p>
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 | 179 | 
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 | 180 | <h2><a name="sect1">Connecting to the server</a></h2>
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 | 181 | 
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 | 182 | <p>
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 | 183 | Client/server connections are always initiated from the client. The port
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 | 184 | is compiled in (there is a configure option to change the default).
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 | 185 | The default port is 49777.
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 | 186 | </p>
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 | 187 | 
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 | 188 | <h3>Problem #1</h3>
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 | 189 | <p>
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 | 190 | The client reports: <b>Connection refused</b>. The server reports nothing.
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 | 191 | </p>
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 | 192 | <p>
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 | 193 | The server is down, listens on the wrong port, or network failure.
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 | 194 | </p>
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 | 195 | 
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 | 196 | <h3>Problem #2</h3>
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 | 197 | <p>
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 | 198 | The client reports: <b>Connection error: Connection reset by peer</b>, and
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 | 199 | later also <b>Session key negotiation failed</b>. The server reports:
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 | 200 | <b>msg="Refused connection from ..." subroutine="libwrap"</b>.
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 | 201 | </p>
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 | 202 | <p>
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 | 203 | The server is compiled with libwrap (TCP Wrapper) support, and the
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 | 204 | client is either in <tt>/etc/hosts.deny</tt>, or you have set <i>yule: ALL</i>
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 | 205 | in <tt>/etc/hosts.deny</tt>, and forgot to put the client in 
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 | 206 | <tt>/etc/hosts.allow</tt>.
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 | 207 | </p>
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 | 208 | <p>
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 | 209 | To fix: make proper entries in <tt>/etc/hosts.allow</tt> and/or 
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 | 210 | <tt>/etc/hosts.deny</tt>. There is no need to restart/reload the server.
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 | 211 | </p>
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 | 212 | 
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 | 213 | 
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 | 214 | <h2><a name="sect2">Authentication</a></h2>
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 | 215 | <p>
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 | 216 | The client has a password that is used to authenticate to the server.
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 | 217 | This password is located within the binary, and is set with the
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 | 218 | <tt>samhain_setpwd</tt> helper application, as explained e.g. in the
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 | 219 | manual or in the Client+Server HOWTO.
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 | 220 | </p><p>
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 | 221 | The server has a list of clients that are allowed to connect, and the
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 | 222 | verifiers corresponding to the passwords of these clients.
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 | 223 | </p>
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 | 224 | <p>
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 | 225 | Upon successful authentication, client and server will negotiate
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 | 226 | a <b>session key</b> that is used for signing further messages
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 | 227 | from the client.
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 | 228 | </p>
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 | 229 | 
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 | 230 | <h3>Problem #1</h3>
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 | 231 | 
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 | 232 | <p>
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 | 233 | If the password is wrong, the client will report 
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 | 234 | <b>Session key negotiation failed</b>. The server will
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 | 235 | report: <b>Invalid connection attempt: Session key mismatch</b>
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 | 236 | </p>
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 | 237 | <p>
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 | 238 | To fix: make sure that the password has in fact been set, that you are
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 | 239 | using the correct executable for the client (the one where the password is 
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 | 240 | set), and that the entry in the server config file is the one generated
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 | 241 | for this password (also look out for double entries for this client).
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 | 242 | </p>
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 | 243 | 
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 | 244 | <h3>Problem #2</h3>
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 | 245 | 
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 | 246 | <p>
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 | 247 | If the client name (as resolved on the server) is wrong, the client 
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 | 248 | will report 
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 | 249 | <b>Session key negotiation failed</b>. The server will
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 | 250 | report: <b>Invalid connection attempt: Not in client list</b>,
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 | 251 | <i>and</i> it will tell you in the same error message 
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 | 252 | what name it has inferred for the connecting
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 | 253 | client (example): <b>client="client.mydomain.com"</b>.
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 | 254 | </p>
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 | 255 | <p> 
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 | 256 | The fix depends on the nature of the problem. In principle, it should be
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 | 257 | sufficient to change the name of the client in the config file entry, which
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 | 258 | isn't really a solution if e.g. the server thinks the client is 'localhost'.
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 | 259 | </p>
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 | 260 | <p>
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 | 261 | There are two different ways to determine the client name. 
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 | 262 | Unfortunately, judging 
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 | 263 | from customer feedback as well from common sense, both do not work very well
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 | 264 | with a messed up local DNS (including /etc/hosts files) and/or
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 | 265 | überparanoid or misconfigured firewalls (in case of connections 
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 | 266 | across one).
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 | 267 | </p>
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 | 268 | <ul>
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 | 269 |   <li>
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 | 270 |      <p>
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 | 271 |      <i>First method: Determine client name on client, and 
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 | 272 |      try to cross-check on server</i>
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 | 273 |      <p>
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 | 274 |      <p>
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| [307] | 275 |      This does not work for a number of people because
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 | 276 |      <ol>
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 | 277 |        <li>
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 | 278 |          the
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 | 279 |          <tt>/etc/hosts</tt> file on the client machine has errors 
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 | 280 |          (yes, there are plenty machines with a completely 
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 | 281 |          messed up <tt>/etc/hosts</tt> file),
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 | 282 |        </li>
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 | 283 |        <li>
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 | 284 |          the
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 | 285 |          server cannot resolve the client address because the local DNS is
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 | 286 |          misconfigured, or 
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 | 287 |        </li>
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 | 288 |        <li> 
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 | 289 |          the client machine has multiple network interfaces, and
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 | 290 |          the interface used is not the one the client name resolves to.
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 | 291 |        </li>
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 | 292 |      </ol>
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| [1] | 293 |      </p>
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| [89] | 294 | 
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| [307] | 295 |      <p>
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| [1] | 296 |        If the client uses the wrong interface on a multi-interface machine, 
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 | 297 |        there is a config file option 
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 | 298 |        <tt>SetBindAddress=</tt><i>IP address</i>
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 | 299 |        that allows to choose the interface the client will use for
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 | 300 |        outgoing connections.
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| [307] | 301 |      </p>
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 | 302 |      <p>
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| [1] | 303 |        If you want to download the config file from the server, you
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| [89] | 304 |        should instead use the corresponding command line option
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| [1] | 305 |        <tt>--bind-address=</tt><i>IP address</i>
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 | 306 |        to select the interface.
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| [307] | 307 |      </p>
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| [1] | 308 | 
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 | 309 |      <p>
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| [307] | 310 |        If you encounter problems, you may (1) fix your 
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 | 311 |        <tt>/etc/hosts</tt> file(s), (2) fix your local DNS, or
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 | 312 |        (3) switch to the second method.
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| [1] | 313 |      </p>
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 | 314 |      <p>
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| [307] | 315 |        Error messages related to name resolving/cross-checking can be 
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 | 316 |        suppressed by setting a 
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 | 317 |        very low severity (lower than the logging threshold), e.g.
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| [1] | 318 |      </p>
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 | 319 |      <p>
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| [307] | 320 |        <tt>SeverityLookup=</tt><i>debug</i>
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| [1] | 321 |      </p>
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 | 322 |      <p>
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| [307] | 323 |        in the <i>Misc</i> section of the server configuration,
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 | 324 |        if you prefer running <i>unsafe</i> at any speed 
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 | 325 |        instead of fixing the problem (you have been warned). Doing so will
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 | 326 |        allow an attacker to pose as the client.
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| [1] | 327 |      </p>
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 | 328 |   </li>
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 | 329 |   <li>
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 | 330 |      <p><i>Second method: Use address of connecting entity as 
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 | 331 |      known to the communication layer</i></p>
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 | 332 |      <p>
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 | 333 |      This has been dropped as default 
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 | 334 |      long ago because it may not always be the 
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 | 335 |      address of the client machine. 
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 | 336 |      To enable this method, use
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 | 337 |      </p>
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 | 338 |      <p>
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 | 339 |      <tt>SetClientFromAccept=</tt><i>true</i>
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 | 340 |      </p>
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 | 341 |      <p>
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 | 342 |      in the <i>Misc</i> section of the server configuration
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 | 343 |      file. If the address cannot be resolved, or reverse lookup of the
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 | 344 |      resolved name fails, <i>no</i> error message will be issued,
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 | 345 |      but the numerical address will be used.
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 | 346 |      </p>
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 | 347 |   </li>
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 | 348 | </ul>
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 | 349 | 
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 | 350 | 
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 | 351 | <h2><a name="sect3">Downloading config/database files</a></h2>
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 | 352 | 
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 | 353 | <p>
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 | 354 | The client does <i>not</i> tell the server the path to the requested
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| [307] | 355 | file - it just tells the <em>type</em> of the file, i.e. 
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 | 356 | either a configuration file or a database file. It is entirely the
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| [1] | 357 | responsibility of the server to locate the correct file and send it.
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 | 358 | </p>
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 | 359 | <p>
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 | 360 | The server has a <i>data directory</i>, which by default would be 
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 | 361 | <tt>/var/lib/yule</tt>. Here the config/database files should be placed.
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 | 362 | </p>
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 | 363 | <p>
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 | 364 | Configuration files: <tt>rc.</tt><i>client.mydomain.tld</i> or 
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 | 365 | simply <tt>rc</tt> 
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 | 366 | (this can be used as a catchall file).
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 | 367 | </p>
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 | 368 | <p>
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 | 369 | Database files: <tt>file.</tt><i>client.mydomain.tld</i> or 
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 | 370 | simply <tt>file</tt> 
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 | 371 | (this can be used as a catchall file).
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 | 372 | </p>
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 | 373 | 
 | 
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 | 374 | <h3>Problem #1</h3>
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 | 375 | 
 | 
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 | 376 | <p>
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 | 377 | If the server cannot access the configuration (or database) file, either
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 | 378 | because it does not exist or the server has no read permission, the
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 | 379 | client will report <b>File download failed</b>. The server will
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 | 380 | report: <b>File not accessible</b>, <i>and</i> it will tell you in the
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 | 381 | same report the path where it would have expected the file (example):
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 | 382 | <b>path="/var/lib/yule/rc.client.mydomain.com"</b>
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 | 383 | </p>
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 | 384 | <p>
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 | 385 | To fix: put the file in the correct location, make sure the permissions
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 | 386 | are ok.
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| [307] | 387 | <ul>
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 | 388 |   <li>
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 | 389 |     Note that <em>the server drops root privileges at startup</em> and
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 | 390 |     runs as an unprivileged user (the first existing out of: 
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 | 391 |     yule, daemon, nobody).
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 | 392 |   </li>
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 | 393 |   <li>
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 | 394 |     Also remember that to access a file, at least execute permission is required
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 | 395 |     <em>for every directory in the path</em>.
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 | 396 |   </li>
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 | 397 | </ul>
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| [1] | 398 | </p>
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 | 399 | 
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 | 400 | 
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 | 401 | <h2><a name="sect4">Other connection problems</a></h2>
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 | 402 | 
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 | 403 | <p>
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 | 404 | The server has a table with client names and their session keys. If 
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 | 405 | another client process accesses the server from the same host,
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 | 406 | it will negotiate a fresh session key for that host. As a consequence,
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 | 407 | the session key of the first client process will become <i>invalid</i>.
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 | 408 | </p>
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 | 409 | <p>
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 | 410 | Also, the server keeps track of the status of a client. If a client 
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 | 411 | process does not announce its termination to the server, the server
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 | 412 | will not expect a <i>startup</i> message, and issue a warning for any
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 | 413 | such message.
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 | 414 | </p>
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 | 415 | 
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 | 416 | <h3>Problem #1</h3>
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 | 417 | 
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 | 418 | <p>
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 | 419 | The client reports: <b>Invalid connection state</b>. The server reports:
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 | 420 | <b>Invalid connection attempt: Signature mismatch</b>. This is a sign that
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 | 421 | a client has tried to connect using an invalid session key. Most probably,
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 | 422 | another instance of the client is/was started on the respective host.
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 | 423 | </p>
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 | 424 | <p>
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 | 425 | To fix: if you need to have concurrent access to the server, 
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 | 426 | suspend the first process with SIGUSR2 before starting the second. Use
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 | 427 | SIGUSR2 again to wake up the first process. Give the process a second or two
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 | 428 | to return into the main event loop and go into suspend mode. Do not just use
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 | 429 | SIGSTOP/SIGCONT: it is important that the client tells the server that
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 | 430 | it will go into suspend.
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 | 431 | </p>
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 | 432 | 
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 | 433 | <h3>Problem #2</h3>
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 | 434 | 
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 | 435 | <p>
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 | 436 | The server reports:
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 | 437 | <b>Restart without prior exit</b> for a client.
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 | 438 | This is a sign that
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 | 439 | a client has re-started without informing the server about a previous
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 | 440 | termination.
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 | 441 | </p>
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 | 442 | <p>
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 | 443 | This would happen if the client was killed with SIGKILL, or if it terminated
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 | 444 | within the routine to send a message to the server (the routine is 
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 | 445 | not re-entrant). You may want to investigate messages logged via another
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 | 446 | logging facility (e.g. the client's local logfile). Of course it <i>may</i>
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 | 447 | also be a segfault, which would be reported via syslog.
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 | 448 | </p>
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 | 449 | 
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 | 450 | </div>
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 | 451 | </body>
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 | 452 | </html>
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