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Use: netstat -tlnp | grep port

Example using netstat:
[root@trioxin2 jhopkins]# netstat -tlnp | grep 80
tcp 0 0 :::80 :::* LISTEN 4246/httpd

The above example reveals that the httpd process with a PID of 4246 is running on port 80.

To verify, you can run the ps command and grep for the application name or PID:
[root@trioxin2 jhopkins]# ps -ef | grep 4246
root 4246 1 0 13:35 ? 00:00:00 /usr/sbin/httpd
apache 4249 4246 0 13:35 ? 00:00:00 /usr/sbin/httpd
apache 4250 4246 0 13:35 ? 00:00:00 /usr/sbin/httpd
apache 4251 4246 0 13:35 ? 00:00:00 /usr/sbin/httpd
apache 4252 4246 0 13:35 ? 00:00:00 /usr/sbin/httpd
apache 4253 4246 0 13:35 ? 00:00:00 /usr/sbin/httpd
apache 4254 4246 0 13:35 ? 00:00:00 /usr/sbin/httpd
apache 4255 4246 0 13:35 ? 00:00:00 /usr/sbin/httpd
apache 4256 4246 0 13:35 ? 00:00:00 /usr/sbin/httpd

Example using fuser:
# fuser 80/tcp
80/tcp: 3130 7057 11956 11957 11958 26771 26801 30170 32433 32434 32766

# ps -ef | grep 3130
root 3130 1 0 Mar02 ? 00:01:19 /usr/sbin/apache2 -k start
www-data 7057 3130 0 Apr01 ? 00:01:18 /usr/sbin/apache2 -k start
www-data 11956 3130 0 Apr04 ? 00:00:23 /usr/sbin/apache2 -k start
www-data 11957 3130 0 Apr04 ? 00:00:38 /usr/sbin/apache2 -k start
www-data 11958 3130 0 Apr04 ? 00:00:42 /usr/sbin/apache2 -k start
www-data 26771 3130 0 Apr03 ? 00:00:54 /usr/sbin/apache2 -k start
www-data 26801 3130 0 Apr03 ? 00:00:50 /usr/sbin/apache2 -k start
…