netstat

Netstat is a command-line networking utility that reports on current network connections, routing tables, and various network interface statistics. It is available on most Unix-like systems and Windows and is commonly used by system administrators and developers to diagnose connectivity problems, monitor network activity, and verify service bindings. The name stands for network statistics.

Core capabilities include displaying active TCP and UDP connections, listening ports, and the routing table. Typical options vary by platform but common ones include -a to show all connections and listening ports, -t and -u to limit output to TCP or UDP, -l to show only listening sockets, -n to present numeric addresses and ports, -p to show the associated process ID and program name, -r to print the routing table, -i for interface statistics, and -s for per-protocol statistics. Some implementations require elevated privileges to reveal program names or to access certain sockets.

Originating in early Unix as part of the net-tools suite, netstat has long been a standard tool for network inspection. On many Linux distributions its functionality has been superseded in practice by the iproute2 tools and the ss utility, while netstat remains available for compatibility. Windows also includes netstat as a built-in command and it supports similar options with its own syntax.

In practical use, netstat helps verify which services are listening on which ports, identify established versus waiting connections, and inspect routing decisions. For instance, netstat -tuln shows listening TCP/UDP ports with numeric addresses on Linux, while netstat -p shows the owning process. For modern Linux environments, ss is often recommended as a faster alternative, with netstat retained mainly for compatibility.