@sgiri - This has already been answered above. If you use un-secure YARN, all your containers and the commands the container runs (such as in shell action) will run as the "yarn" user (i.e. the user your NodeManager daemon runs as).
If you want to run containers in YARN as the actual submitting user, use the LinuxContainerExecutor instead. The caveat of using it is that you need your user accounts available on all NodeManagers so a setuid can be done against them when spawning the container processes.