安装DB2后，切换到db2inst1用户后，执行命令"db2cc"，出现以下错误。

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Xlib: connection to ":0.0" refused by server
Xlib: No protocol specified

Exception in thread "main" java.lang.NoClassDefFoundError: sun.awt.X11.XToolkit (initialization failure)
        at java.lang.J9VMInternals.initialize(J9VMInternals.java:130)
        at java.lang.Class.forNameImpl(Native Method)
        at java.lang.Class.forName(Class.java:130)
        at java.awt.Toolkit$2.run(Toolkit.java:864)
        at java.security.AccessController.doPrivileged(AccessController.java:193)
        at java.awt.Toolkit.getDefaultToolkit(Toolkit.java:847)
        at javax.swing.UIManager.initialize(UIManager.java:1296)
        at javax.swing.UIManager.maybeInitialize(UIManager.java:1279)
        at javax.swing.UIManager.getDefaults(UIManager.java:590)
        at javax.swing.UIManager.get(UIManager.java:852)
        at com.ibm.db2.tools.common.CommonUIManager.initialize(Unknown Source)
        at CC.setLookAndFeel(Unknown Source)
        at CC.<init>(Unknown Source)
        at CC.main(Unknown Source)
Caused by: java.lang.InternalError: Can't connect to X11 window server using ':0.0' as the value of the DISPLAY variable.
        at sun.awt.X11GraphicsEnvironment.initDisplay(Native Method)
        at sun.awt.X11GraphicsEnvironment.access$000(X11GraphicsEnvironment.java:95)
        at sun.awt.X11GraphicsEnvironment$1.run(X11GraphicsEnvironment.java:184)
        at java.security.AccessController.doPrivileged(AccessController.java:193)
        at sun.awt.X11GraphicsEnvironment.<clinit>(X11GraphicsEnvironment.java:173)
        at java.lang.J9VMInternals.initializeImpl(Native Method)
        at java.lang.J9VMInternals.initialize(J9VMInternals.java:192)
        at java.lang.Class.forNameImpl(Native Method)
        at java.lang.Class.forName(Class.java:130)
        at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:101)
        at sun.awt.X11.XToolkit.<clinit>(XToolkit.java:127)
        at java.lang.J9VMInternals.initializeImpl(Native Method)
        at java.lang.J9VMInternals.initialize(J9VMInternals.java:192)
        at java.lang.Class.forNameImpl(Native Method)
        at java.lang.Class.forName(Class.java:130)
        at java.awt.Toolkit$2.run(Toolkit.java:864)
        at java.security.AccessController.doPrivileged(AccessController.java:193)
        at java.awt.Toolkit.getDefaultToolkit(Toolkit.java:847)
        at javax.swing.ImageIcon.<init>(ImageIcon.java:149)
        at javax.swing.ImageIcon.<init>(ImageIcon.java:168)
        at com.ibm.db2.tools.common.CommonImageRepository.loadImageFromURL(Unknown Source)
        at com.ibm.db2.tools.common.CommonImageRepository.loadImage(Unknown Source)
        at com.ibm.db2.tools.common.CommonImageRepository.loadImage(Unknown Source)
        at com.ibm.db2.tools.common.CommonImageRepository.getCommonIcon(Unknown Source)
        at com.ibm.db2.tools.hc.gui.HealthCenterLegendAction.<init>(Unknown Source)
        at CC.getViewMenuActions(Unknown Source)
        at CC.getRegisteredToolsActions(Unknown Source)
        ... 2 more
DB2JAVIT : RC = 1

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开始百度，有的说jdk版本不对，还怀疑没有安装控制中心。

在CSDN上有人问同样的问题，说啥的都有，最后有人给出答案。。超级简单啊。

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1. 以root 执行 xhost + 
2. 以root 执行 env, 看一下DISPLAY 值是什么, 如 :1
3. su - db2inst1
4. export DISPLAY= 同root 下的变量
5. xhost +
6. db2cc

?查看后我的DISPLAY都是：0.0，分别执行xhost +后，一切正常了。

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