The main work of JobTracker and TaskTracker in hadoop is given below.
JobTracker is a master which creates and runs the job. JobTracker which can run on the NameNode allocates the job to tasktrackers. It is tracking resource availability and task life cycle management, tracking its progress, fault tolerance etc.
TaskTracker run the tasks and report the status of task to JobTracker. TaskTracker run on DataNodes. It has function of following the orders of the job tracker and updating the job tracker with its progress status periodically.