Final answer:
A JobTracker in Hadoop is responsible for assigning tasks to nodes in a cluster and managing MapReduce jobs. There is only one instance of JobTracker that runs on a Hadoop cluster.
Step-by-step explanation:
In Hadoop, a JobTracker is responsible for assigning tasks to the various nodes in a Hadoop cluster. It manages the execution and monitoring of MapReduce jobs.
There is only one instance of JobTracker that runs on a Hadoop cluster. The JobTracker is a single point of failure, so it is typically run on a highly available machine.
JobTracker keeps track of the progress of each job, handles job scheduling, and ensures fault tolerance by reassigning tasks if a node fails. It also coordinates the distributed processing of input data and the aggregation of output data.