The Job Browser application lets you examine
jobs running on your cluster.

A MapReduce job, as presented by the Job Browser,
has many layers. You start with a list of jobs,
then dig down into that job's tasks. Each
task may have multiple task attempts.
It is often useful, if a job has failed, to examine
the "logs" tab of one of the attempts.

If you are the user who submitted the job, you can kill the job by hitting the "Stop" icon.
Job Metadata (like where the inputs and outputs are) and counters are available using the Job Browser.