Netstat

In computing, codice_1 ("network statistics") is a command-line network utility that displays network connections for Transmission Control Protocol (both incoming and outgoing), routing tables, and a number of network interface (network interface controller or software-defined network interface) and network protocol statistics. It is available on Unix, Plan 9, Inferno, and Unix-like operating systems including macOS, Linux, Solaris and BSD. It is also available on IBM OS/2 and on Microsoft Windows NT-based operating systems including Windows XP, Windows Vista, Windows 7, Windows 8 and Windows 10.
It is used for finding problems in the network and to determine the amount of traffic on the network as a performance measurement. On Linux this program is mostly obsolete, although still included in many distributions.
On Linux, codice_1 (part of "net-tools") is superseded by codice_3 (part of iproute2). The replacement for codice_4 is codice_5, the replacement for codice_6 is codice_7, and the replacement for codice_8 is codice_9, all of which are recommended instead.
Statistics provided.
Netstat provides statistics for the following:
Parameters.
Parameters used with this command must be prefixed with a hyphen (-) rather than a slash (/). Some parameters are not supported on all platforms.
Examples.
Cross platform.
On macOS, BSD systems, Linux distributions, and Microsoft Windows:
To display the statistics for only the TCP or UDP protocols, type one of the following commands:
codice_10
codice_11
Unix-like.
On Unix-like systems:
To display all ports open by a process with id "pid":
codice_12
To continuously display open TCP and UDP connections numerically and also which program is using them on Linux:
codice_13
Windows.
On Microsoft Windows:
To display active TCP connections and the process IDs every 5 seconds, type the following command (works on NT based systems only, or Windows 2000 with hotfix):
codice_14
To display active TCP connections and the process IDs using numerical form, type the following command (works on NT based systems only, or Windows 2000 with hotfix):
codice_15
Wildcards.
Netstat uses a asterisk * as a wildcard which means "any". An example would be
Example output:
...Local Address Foreign Address State
... *:smtp *:* LISTEN
Under "Local Address" *, in codice_16, means the process is listening on all of the network interfaces the machine has for the port mapped as smtp (see /etc/services for service resolution). This can also be shown as 0.0.0.0.
The first *, in codice_17, means connections can come from any IP address, and the second *, in codice_17, means the connection can originate from any port on the remote machine.
Caveats.
Some versions of codice_1 lack explicit field delimiters in their printf-generated output, leading to numeric fields running together and thus corrupting the output data.
Platform specific remarks.
Under Linux, raw data can often be obtained from the /proc/net/dev to work around the printf output corruption arising in netstat's network interface statistics summary, codice_6, until such time as the problem is corrected.
On the Windows platform, netstat information can be retrieved by calling the GetTcpTable and GetUdpTable functions in the IP Helper API, or IPHLPAPI.DLL. Information returned includes local and remote IP addresses, local and remote ports, and (for GetTcpTable) TCP status codes. In addition to the command-line netstat.exe tool that ships with Windows, GUI-based netstat programs are available.
On the Windows platform, this command is available only if the Internet Protocol (TCP/IP) protocol is installed as a component in the properties of a network adapter in Network Connections.
On the Windows platform running Remote Desktop Services (formerly Terminal Services) it will only show connections for the current user, not for the whole computer.
On macOS, the /System/Library/CoreServices/Applications folder (or /Applications/Utilities in OS X Mountain Lion and earlier) contains a network GUI utility called Network Utility, the Netstat tab of which runs the netstat command and displays its output in the tab.