For working with YARN, one resourcemanager and one node manager have to be started as the user yarn:

$  su - yarn
$ cd /opt/yarn/hadoop-2.7.3/sbin
$ ./yarn-daemon.sh start resourcemanager

You should receive the following message on your terminal if the preceding commands succeed:

starting resourcemanager, logging to /opt/yarn/hadoop-2.7.3/logs/yarn-yarn-resourcemanager-limulus.out

Tehn execute the following command to start the node manager:

$ ./yarn-daemon.sh start nodemanager

You should receive the following message on your terminal if the preceding commands succeed:

starting nodemanager, logging to /opt/yarn/hadoop-2.7.3/logs/yarn-yarn-nodemanager-limulus.out

If you want to make sure that every services in those nodes are running, you should use the $jsp command. Moreover, if you want to stop your resource manager or nodemanager, use the following g commands:

$ ./yarn-daemon.sh stop nodemanager
$ ./yarn-daemon.sh stop resourcemanager