List all used ports on a unix machine

netstat -a -t --numeric-ports -p

How to manage the hadoop services with CDH4

Show HDFS Service status

for x in `cd /etc/init.d ; ls hadoop-hdfs-*` ; do sudo service $x status ; done
 * Hadoop datanode is running
 * Hadoop namenode is running
 * Hadoop secondarynamenode is running

Show Mapreduce service status

for x in `cd /etc/init.d ; ls hadoop-0.20-mapreduce-*` ; do sudo service $x status ; done
hadoop-0.20-jobtracker is running
hadoop-0.20-tasktracker is running