Let me share some problems that I often encountered when using hadoop many days ago.
The prompt Name node is in safe mode in the middle indicates that NameNode is in safe mode.
We shut down during use, improper operation and other situations can easily enter the safe mode. For example, a blogger's
computer has small memory, and when using multiple nodes, it often gets stuck and has to be restarted. Therefore, this situation often occurs.
So why is the NameNode in safe mode?
1. The NameNode will enter the safe mode when it finds that the loss of DataNodes in the cluster reaches a certain percentage (0.01%). At this time, only the data is allowed to be viewed and no operations on the data are allowed.
2. Even if the HDFS cluster starts normally, it will only enter the safe mode for a period of time. At this time, you can wait a moment.
exit safe Mode:
hadoop dfsadmin -safemode leave