nmap does not show all open ports

Question

I have a YARN cluster running in EMR. When ssh into the master node and run nmap 10.0.0.254 I get the following result

Starting Nmap 5.51 ( http://nmap.org ) at 2015-06-10 00:17 UTC
Nmap scan report for ip-10-0-0-254.ec2.internal (10.0.0.254)
Host is up (0.00045s latency).
Not shown: 987 closed ports
PORT      STATE SERVICE
22/tcp    open  ssh
80/tcp    open  http
3306/tcp  open  mysql
8443/tcp  open  https-alt
8649/tcp  open  unknown
8651/tcp  open  unknown
8652/tcp  open  unknown
9000/tcp  open  cslistener
9101/tcp  open  jetdirect
9102/tcp  open  jetdirect
9103/tcp  open  jetdirect
9200/tcp  open  wap-wsp
14000/tcp open  scotty-ft

I know the YARN resource manager is running on 10.0.0.254:9026, but I do not see it in the result above, however when I run nmap -p 9026 10.0.0.254 I get

Starting Nmap 5.51 ( http://nmap.org ) at 2015-06-10 00:18 UTC
Nmap scan report for ip-10-0-0-254.ec2.internal (10.0.0.254)
Host is up (0.000055s latency).
PORT     STATE SERVICE
9026/tcp open  unknown

Why does nmap not include the service running on 9026 when I run the first command?

Answer 1

By default, Nmap scans the most common 1,000 ports for each protocol (TCP in your case) 9026 is not one of the most common.

Here's how to specify ports to scan: http://nmap.org/book/man-port-specification.html