Hadoop JobTracker & TaskTracker Web Interface
The JobTracker web interface provides a wealth of information on jobs and tasks that are running on the cluster as well as historical information on completed jobs (including ones that failed).
There are no running jobs in the screenshot above but if there were you would be able to view the current status of such jobs (including counters for input / output records read, locality of task execution etc).
At the bottom of this page is a link to the Job Tracker History viewer which allows you to view statistics on completed jobs.
After selecting a job you can drill down into the statistics for the job.
Clicking the analyse job history link on job details history page, displays a summary of task performance statistics.
Details of individual task attempts:
The TaskTracker web interface provides information on the tasks that are running on the tasktracker and allows you to browse the logs for the tasktracker.
The logs directory shows the logs generated for map and reduce tasks that were run on the TaskTracker.
The URL http://<tasktracker-host>:50060/jmx displays the metrics and their values exposed via JMX for the TaskTracker.