对于运维人员来说备份数据是非常重要的，不管理数据库还是配置文件。在每次变更的操作最好做一个文件备份。这里仅记录一下jenkins的配置文件错误导致无法启动服务的问题。

修改配置文件前切记先备份，以防错误导致数据的丢失。

首先找到jenkins的安装目录，如果使用rpm安装的可以这样找到。

rpm -ql jenkins-2.89.4-1.1.noarch

默认rpm安装目录在：/usr/lib/jenkins，而配置文件config.xml就是此目录下；

cp config.xml{,.bak}   #备份配置文件

其它的安装目录可根据错误信息找到。

错误信息提示如下：

org.xmlpull.v1.XmlPullParserException: only 1.0 is supported as <?xml version not '1.1' (position: START_DOCUMENT seen <?xml version=\'1.1\'... @1:19)  
    at org.xmlpull.mxp1.MXParser.parseXmlDeclWithVersion(MXParser.java:2608) 
    at org.xmlpull.mxp1.MXParser.parseXmlDecl(MXParser.java:2592) 
    at org.xmlpull.mxp1.MXParser.parsePI(MXParser.java:2466) 
    at org.xmlpull.mxp1.MXParser.parseProlog(MXParser.java:1447) 
    at org.xmlpull.mxp1.MXParser.nextImpl(MXParser.java:1395) 
    at org.xmlpull.mxp1.MXParser.next(MXParser.java:1093) 
    at com.thoughtworks.xstream.io.xml.XppReader.pullNextEvent(XppReader.java:109) 
Caused: com.thoughtworks.xstream.io.StreamException:  : only 1.0 is supported as <?xml version not '1.1' (position: START_DOCUMENT seen <?xml version=\'1.1\'... @1:19)  
    at com.thoughtworks.xstream.io.xml.XppReader.pullNextEvent(XppReader.java:124) 
    at com.thoughtworks.xstream.io.xml.AbstractPullReader.readRealEvent(AbstractPullReader.java:148) 
    at com.thoughtworks.xstream.io.xml.AbstractPullReader.readEvent(AbstractPullReader.java:141) 
    at com.thoughtworks.xstream.io.xml.AbstractPullReader.move(AbstractPullReader.java:118) 
    at com.thoughtworks.xstream.io.xml.AbstractPullReader.moveDown(AbstractPullReader.java:103) 
    at com.thoughtworks.xstream.io.xml.XppReader.<init>(XppReader.java:63) 
    at com.thoughtworks.xstream.io.xml.AbstractXppDriver.createReader(AbstractXppDriver.java:54) 
    at com.thoughtworks.xstream.io.xml.AbstractXppDriver.createReader(AbstractXppDriver.java:65) 
    at hudson.XmlFile.unmarshal(XmlFile.java:167) 
Caused: java.io.IOException: Unable to read /var/lib/jenkins/config.xml 
    at hudson.XmlFile.unmarshal(XmlFile.java:169) 
    at jenkins.model.Jenkins.loadConfig(Jenkins.java:3067) 
    at jenkins.model.Jenkins.access$1200(Jenkins.java:304) 
    at jenkins.model.Jenkins$14.run(Jenkins.java:3085) 
    at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169) 
    at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:282) 
    at jenkins.model.Jenkins$5.runTask(Jenkins.java:1068) 
    at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:210) 
    at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117) 
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) 
    at java.lang.Thread.run(Thread.java:745) 
Caused: org.jvnet.hudson.reactor.ReactorException 
    at org.jvnet.hudson.reactor.Reactor.execute(Reactor.java:269) 
    at jenkins.InitReactorRunner.run(InitReactorRunner.java:47) 
    at jenkins.model.Jenkins.executeReactor(Jenkins.java:1102) 
    at jenkins.model.Jenkins.<init>(Jenkins.java:904) 
    at hudson.model.Hudson.<init>(Hudson.java:86) 
    at hudson.model.Hudson.<init>(Hudson.java:82) 
    at hudson.WebAppMain$3.run(WebAppMain.java:233) 
Caused: hudson.util.HudsonFailedToLoad 
    at hudson.WebAppMain$3.run(WebAppMain.java:250)

这里注意红字的部分，提示配置文件中只支持1.0，而不是1.1。然后查看配置文件config.xml发现第一行中果然是1.1，把它改回1.0试下。

sed -i 's/1.1/1.0/' config.xml

重新启动Jenkins服务即可以成功看到界面了。

说明，可能其它的升级版本原因也可能会导致类似的问题，但是最重要的是查看错误日志，提示信息，找解决方法。