How to get the process listening on certain port

At times we are asked: "what program is listening on port XX?"

In Redhat, we can easily get this using lsof. let's say if we want to know which program is listening on port 80.
[root@localhost ~]# lsof -i :80
COMMAND  PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
httpd   2047   root    4u  IPv6  12636      0t0  TCP *:http (LISTEN)
httpd   2049 apache    4u  IPv6  12636      0t0  TCP *:http (LISTEN)
httpd   2050 apache    4u  IPv6  12636      0t0  TCP *:http (LISTEN)
httpd   2051 apache    4u  IPv6  12636      0t0  TCP *:http (LISTEN)
httpd   2052 apache    4u  IPv6  12636      0t0  TCP *:http (LISTEN)
httpd   2053 apache    4u  IPv6  12636      0t0  TCP *:http (LISTEN)
httpd   2054 apache    4u  IPv6  12636      0t0  TCP *:http (LISTEN)
httpd   2055 apache    4u  IPv6  12636      0t0  TCP *:http (LISTEN)
httpd   2056 apache    4u  IPv6  12636      0t0  TCP *:http (LISTEN)

From the output, we know that httpd is listening on port 80.

Another way to get the process listening on certain port is using netstat.
[root@localhost ~]# netstat -anp | grep 80
tcp        0      0 :::80     :::*            LISTEN      2009/httpd
 
[root@localhost ~]# ps -ef | awk '$2 == 2009'
root      2009     1  0 23:21 ?        00:00:00 /usr/sbin/httpd
 
[root@localhost ~]#
In AIX, most of the time it has no lsof installed, and the netstat is also different from Redhat, but we still can get our question answered.
$ netstat -Aan | grep '.22 ' | grep LISTEN
f1000e0001382bb8 tcp4   0  0  *.22          *.*        LISTEN

$ rmsock f1000e0001382bb8 tcpcb
The socket 0xf1000e0001382808 is being held by proccess 3670142 (sshd).
 
$ ps -ef | grep 3670142
root 3670142 3014676   0   Sep 06      -  0:00 /usr/sbin/sshd

Please note rmsock will not remove the socket, you can confirm this by checking the content of /var/adm/ras/rmsock.log.

reference: http://unix.ittoolbox.com/groups/technical-functional/ibm-aix-l/determine-which-process-is-listening-on-a-port-without-using-lsof-on-aix-1468555