Weekly Linux Command (netstat)

Weekly Linux Command (netstat)

Command Overview (netstat)

netstat (network statistics) is a command-line tool used to display network connections (incoming and outgoing), routing tables, and various network interface (network interface controllers or software-defined network interfaces) and network protocol statistics. It can also be used to diagnose network issues, print status information about the network system in Linux, and view the overall network status of the Linux system.

The netstat tool is widely used across platforms, including Linux, Solaris, and Kylin, as well as Windows NT-based operating systems, including Windows XP, Windows Vista, Windows 7/8/10.

# Syntax

netstat without syntax output, as shown:

root@valwell:~# netstat
-------------------------------------------------------------------------
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0postgres:58288          postgres:amqp           ESTABLISHED
tcp        0      0postgres:45566          postgres:6379           ESTABLISHED
tcp        0      0postgres:58312          postgres:amqp           ESTABLISHED
tcp        0      0postgres:36178          postgres:postgresql     TIME_WAIT
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ]         DGRAM                    23733    /var/lib/haproxy/dev/log
unix  2      [ ]         DGRAM                    1594464  /run/user/1000/systemd/notify
unix  2      [ ]         DGRAM                    40530    /run/user/0/systemd/notify

As shown above:<span>netstat</span> directly outputs two parts (for understanding only):

• <span>Active Internet connections (w/o servers):</span> displays the established network connections on the host

• Active UNIX domain sockets (w/o servers): displays all active “Unix Domain” open sockets

# Practical Command Examples

1. List all ports and connections; the output will list established connections and services that are opening or listening

netstat -a

2. List all TCP ports

netstat -at

3. List all UDP ports

netstat -au

4. List listening ports

netstat -L

5. List kernel IP routing

netstat -r

6. Find the service process for a specific port

(1) Find by port

netstat -ano | grep ‘:[port_number]’

(2) Find by service name

netstat -ap | grep ‘:[service_name]’END