#完整报错如下：
#java.lang.ClassNotFoundException: hudson.tasks.Mailer
at jenkins.util.AntClassLoader.findClassInComponents(AntClassLoader.java:1374)
at jenkins.util.AntClassLoader.findClass(AntClassLoader.java:1327)
at jenkins.util.AntClassLoader.loadClass(AntClassLoader.java:1080)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
Caused: java.lang.NoClassDefFoundError: hudson/tasks/Mailer
at hudson.plugins.emailext.plugins.content.BuildLogContent.(BuildLogContent.java:25)
at hudson.plugins.emailext.EmailExtensionPlugin.start(EmailExtensionPlugin.java:53)
at hudson.ClassicPluginStrategy.startPlugin(ClassicPluginStrategy.java:539)
at hudson.ClassicPluginStrategy.load(ClassicPluginStrategy.java:528)
Caused: java.io.IOException: Failed to initialize
at hudson.ClassicPluginStrategy.load(ClassicPluginStrategy.java:531)
at hudson.PluginManager.dynamicLoad(PluginManager.java:877)
Caused: java.io.IOException: Failed to install email-ext plugin
at hudson.PluginManager.dynamicLoad(PluginManager.java:886)
at hudson.PluginManager.dynamicLoad(PluginManager.java:822)
at hudson.model.UpdateCenter$InstallationJob._run(UpdateCenter.java:1889)
Caused: java.io.IOException: Failed to dynamically deploy this plugin
at hudson.model.UpdateCenter$InstallationJob._run(UpdateCenter.java:1893)
at hudson.model.UpdateCenter$DownloadJob.run(UpdateCenter.java:1651)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at hudson.remoting.AtmostOneThreadExecutor$Worker.run(AtmostOneThreadExecutor.java:112)
at java.lang.Thread.run(Thread.java:748)
安装步骤不正确，具体是虚拟机还是真机里面？
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