Kerboers认证由于和Master时间不同步导致的错误
刚发现Hbase集群一台RegionServer挂掉了，重启之后仍然不正常，日志中的错误：
Caused by: java.io.IOException: Login failure for hbase/hd0159-sw36.dc.sh-wgq.sdo.com@DC.SH-WGQ.SDO.COM from keytab /home/hdfs/hbase-current/conf/hbase.keytab at org.apache.hadoop.security.UserGroupInformation.loginUserFromKeytab(UserGroupInformation.java:638) at org.apache.hadoop.security.SecurityUtil.login(SecurityUtil.java:234) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.hbase.security.User.call(User.java:394) at org.apache.hadoop.hbase.security.User.access$600(User.java:54) at org.apache.hadoop.hbase.security.User$SecureHadoopUser.login(User.java:359) at org.apache.hadoop.hbase.security.User.login(User.java:141) at org.apache.hadoop.hbase.regionserver.HRegionServer.<init>(HRegionServer.java:352) ... 10 moreCaused by: javax.security.auth.login.LoginException: Clock skew too great (37) - PREAUTH_FAILED at com.sun.security.auth.module.Krb5LoginModule.attemptAuthentication(Krb5LoginModule.java:696) at com.sun.security.auth.module.Krb5LoginModule.login(Krb5LoginModule.java:542) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at javax.security.auth.login.LoginContext.invoke(LoginContext.java:769) at javax.security.auth.login.LoginContext.access$000(LoginContext.java:186) at javax.security.auth.login.LoginContext$4.run(LoginContext.java:683) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.login.LoginContext.invokePriv(LoginContext.java:680) at javax.security.auth.login.LoginContext.login(LoginContext.java:579) at org.apache.hadoop.security.UserGroupInformation.loginUserFromKeytab(UserGroupInformation.java:629) ... 20 more
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主要是这句：
Caused by: javax.security.auth.login.LoginException: Clock skew too great
其实是这台RegionServer的时间和Kerboers服务器的时间偏差太大（大于5分钟），因此kerboers认证失败。
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于是将这台RegionServer上的时间做了同步，从世界标准时间中心获取时间：
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ntpdate 0.pool.ntp.org
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之后重启RegionServer，恢复正常。
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