Why does netstat not show the process PID/Program Name in RHEL

Issue

• Some applications that are bound to a specific port suddenly cannot start due to the port reservation conflict.
• A telnet command against the port shows that the socket is open but no process can be identified either.
• A dash(-) is seen in the column "PID/Program Name", as shown below:

[user@localhost ~]$ netstat -plnt | head -5
(No info could be read for "-p": geteuid()=500 but you should be root.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name   
tcp        0      0 0.0.0.0:111                 0.0.0.0:*                   LISTEN      -                   
tcp        0      0 0.0.0.0:49234               0.0.0.0:*                   LISTEN      -                   
tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN      -