[808]There were errors checking the update sites: SSLHandshakeException: sun.secu解決方案
（1）外掛管理頁面提示：There were errors checking the update sites:IOException:Unable to tunnel through proxy.Proxy returins “HTTP/1.1 400”
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（2）外掛管理頁面提示：There were errors checking the update sites: SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
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查到的解決方法是同一個：
解決方案：
進入外掛管理->Advanced,修改Update Site的URL，
預設是透過https://updates.jenkins.io/update-center.json進行更新的。此處，將https改為http，修改完成，submit，然後重啟Jenkins，問題解決。