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Netstat – Network Statistics

Netstat monitors both incoming and outgoing network connections, displays the routing table, interface statistics, multicast memberships, lists open ports, lists programs listening on any ports and masquerade connections. Applied in troubleshooting network issues and monitoring network performance.

Display all listening sockets using tcp while showing only numerical addresses. This is applied when you are running a program which is using specific socket(s) on tcp protocol and you want to check if the socket(s) is/are opened.

$ netstat -aln --tcp

Display all listening sockets using tcp while showing only resolved names

$ netstat -al --tcp

Other options of netstat

Display network interface statistics and specifically ip connections. Gives similar output to “ifconfig

$ netstat -inet

Display statistics for only tcp protocol

$ netstat -st | less

List all the programs holding socket and their respective PID number

$ netstat -p | less

Display the routing table (Similar to “route -e” command)

$ netstat -r

Nethogs -  Monitor Per Process Network Bandwidth

NetHogs monitors network activity of each process, displaying bandwidth of each process while sorting from the most intensive process to the least intensive. This is applied to view the processes utilizing the most network bandwidth in REAL TIME.  The details of the process shown are PID, process name/path and user running the process.

$ sudo nethogs

Special Note: Incase nethogs is not installed, you can install as follows depending on your linux flavor.

For Centos

$ sudo yum install epel-release
$ sudo yum install -y nethogs

For Ubuntu

$ sudo apt-get install nethogs

Other options of nethogs

Display nethogs output with a refresh rate of 3 seconds

$ sudo nethogs -d 3

Display nethogs output for specific network interface

$ sudo nethogs eth0

Iftop – Monitor Network Bandwidth Utilization

iftop acts similarly to “top” (CPU usage) command but now for network usage. It shows the network bandwidth i.e. transmitted and received packets per network interface in REAL TIME. It also shows the source and destination hosts sending and receiving the packets. It’s applied when system admin needs to know why specific network link is slow.

$ sudo iftop

Special Note: Incase iftop is not installed, you can install as follows depending on your linux flavor.

For Centos

$ sudo yum install epel-release
$ sudo yum install -y iftop

For Ubuntu

$ sudo apt-get install iftop

To show only numerical addresses

$ sudo iftop -n

Other options of iftop

Monitor network bandwidth on specific network interface with resolved names

$ sudo iftop -i eth0

Monitor network bandwidth on specific network interface with numerical addresses

$ sudo iftop -n eth0

Display ports

$ sudo iftop -P

ss  - Socket Statistics

ss  displays socket statistics similarly to netstat.  It displays more TCP and state information than other tools. By-default it shows all open non-listening sockets on TCP/UNIX/UDP that have established connection.

$ ss | less

List all the currently opened network ports

$ ss -l | less

 

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