How to find listening and open ports in Linux
In many cases I want to check information about the network ports on my system, either to see what is using a specific port, or to see which ports are listening for requests.
Option 1 - lsof
lsof -nP +c 15 | grep LISTEN
The command lsof stands for “list open files”. It provides information about files and processes that are currently open on the system.
The following options to lsof make the command faster by avoiding DNS and service lookups.
-nprevents the conversion of network numbers to hostnames.-Pprevents the conversion of port numbers to service names.
The option +c 15 specifies the number of seconds to wait before giving up on network-related operations.
The | grep LISTEN pipe command filters the output of lsof for lines containing the word LISTEN, which indicates processes that are listening for incoming network connections.
Option 2 - netstat
netstat -tuln
The command netstat stands for “network statistics”. It provides information about network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.
The command netstat -tuln is used to display information about active network connections and listening sockets.
The options -tuln to netstat mean:
-tspecifies that only TCP connections should be displayed. It filters the output to show only information related to TCP protocols.-uspecifies that only UDP connections should be displayed. Similar to the-toption, it filters the output to show only information related to UDP protocols.-lstands for “listening” and instructs netstat to display only listening sockets, which are endpoints for incoming connections.-nprevents the conversion of numeric addresses to symbolic hostnames. It speeds up the command execution by avoiding DNS lookups.
Appending the | grep http pipe command filters the output of netstat for lines containing the word http, which indicates processes that are listening for incoming HTTP connections.
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