hadoop-hdfs-safemode

在启动过程中，NAMENODE从FSIMAGE和编辑日志文件加载文件系统状态。然后，它等待数据块报告它们的块，以便即使在集群中已经存在足够的副本，也不会过早地开始复制这些块。在此期间，NAMENODE停留在Safemode。NAMENODE的安全模式本质上是HDFS集群的只读模式，它不允许对文件系统或块进行任何修改。通常，NAMENODE在数据报已经报告大多数文件系统块可用之后自动离开SaveMode。如果需要，HDFS可以使用bin/hdfs dfsadmin -safemode命令显式地放置在SaaMaMeDE中。NAMENODE首页显示Safemode是否打开或关闭。更详细的描述和配置被保持为JavaDoc用于setSafeMode().

相关操作

public interface SafeMode {
  /**
   * Check safe mode conditions.
   * If the corresponding conditions are satisfied,
   * trigger the system to enter/leave safe mode.
   */
  public void checkSafeMode();

  /** Is the system in safe mode? */
  public boolean isInSafeMode();

  /**
   * Is the system in startup safe mode, i.e. the system is starting up with
   * safe mode turned on automatically?
   */
  public boolean isInStartupSafeMode();

  /** Check whether replication queues are being populated. */
  public boolean isPopulatingReplQueues();

  /**
   * Increment number of blocks that reached minimal replication.
   * @param replication current replication 
   */
  public void incrementSafeBlockCount(int replication);

  /** Decrement number of blocks that reached minimal replication. */
  public void decrementSafeBlockCount(Block b);
}