Entering and exiting from the safe mode in a Hadoop cluster
Sometimes, due to an unclear filesystem image state, the Hadoop cluster goes into safemode. In this recipe, we will see how to enter and exit from safemode.
How to do it...
Safemode is an HDFS state that does not allow any new writes to the filesystem. It also does not replicate or delete any blocks from the filesystem. In case you want to make any configuration changes to your cluster, you can put the system into safemode. Here is a command to enter the system into safemode:
hdfs dfsadmin -safemode enter
Now, if you try to make any writes to HDFS, it will not allow you do so. You can perform cluster maintenance and once this is done, you can switch off safemode:
hdfs dfsadmin -safemode leave ...Get Hadoop: Data Processing and Modelling now with the O’Reilly learning platform.
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