How to Use 'vnstat' Command (with Examples)

The vnstat command is a versatile and console-based network traffic monitor that provides detailed network statistics for your system interfaces. It is an invaluable tool for system administrators and anyone interested in monitoring network usage over specific periods, enabling users to keep track of all traffic data without ever having to reboot their machines. vnstat can also be set to gather and store network traffic statistics that span across system reboots, making it a robust solution for long-term monitoring and reporting.

Use Case 1: Display Traffic Summary for All Interfaces

Code:

vnstat

Motivation:

Using vnstat without any additional parameters provides a quick and comprehensive summary of network traffic across all available interfaces on the system. This use case is ideal for getting an overview of general network usage and identifying which interfaces are handling the most traffic. It’s a fast way to get a sense of overall network activity and can help determine if any interface requires closer attention due to unusual patterns or traffic loads.

Explanation:

• vnstat: When run without additional options, the command will automatically detect all network interfaces and provide a summary of their traffic usage. This default behavior exemplifies vnstat’s efficiency in quickly returning useful data with minimal user input.

Example Output:

Database updated: Mon Oct 30 10:00:00 2023

   eth0                     rx      |     tx      |  total
-------------------------------------|---------------|-----------
  today                      234 MiB |   120 MiB   |   354 MiB
  yesterday                  300 MiB |   150 MiB   |   450 MiB
  monthly                 2.3 GiB   |  1.1 GiB   |  3.4 GiB

Use Case 2: Display Traffic Summary for a Specific Network Interface

Code:

vnstat -i eth0

Motivation:

Focusing on a specific network interface is crucial when you need detailed traffic statistics for a particular connection, whether for troubleshooting, performance monitoring, or specialized configuration. This is especially helpful in environments where multiple interfaces are present and monitored differently, such as separating public and private network interfaces in a server setting.

Explanation:

• -i network_interface: The -i option specifies a particular network interface to monitor. Here, eth0 can be replaced with any valid interface identified on the system. This argument narrows down the data to a specific connection, allowing for more targeted analysis.

Example Output:

Database updated: Mon Oct 30 10:10:00 2023

   eth0                     rx      |     tx      |  total
------------------------------------|--------------|-----------
  today                      150 MiB |   70 MiB    |   220 MiB
  yesterday                  180 MiB |   80 MiB    |   260 MiB
  monthly                   1.5 GiB |  750 MiB   |  2.2 GiB

Use Case 3: Display Live Stats for a Specific Network Interface

Code:

vnstat -l -i eth0

Motivation:

Real-time monitoring of network traffic is essential for diagnosing network issues as they occur. Viewing live statistics helps network administrators and IT professionals observe immediate effects of changes, detect traffic spikes, or observe the behavior of a network over time during an event process.

Explanation:

• -l: This option switches vnstat to live tracking mode, providing real-time data about the chosen network interface.
• -i network_interface: Again used to specify the interface to be monitored, focusing live stats on a particular connection point.

Example Output:

Live traffic (Ethernet 0) at Mon Oct 30 10:15:00 2023

 rx: 2 kbit/s   tx: 1 kbit/s   total: 3 kbit/s

Use Case 4: Show Traffic Statistics on an Hourly Basis for the Last 24 Hours Using a Bar Graph

Code:

vnstat -hg

Motivation:

Hourly statistics provide valuable insights for performance tuning, capacity planning, and understanding usage patterns throughout the day. This granular data capture helps identify peak usage times and underutilized periods, thereby enabling better resource allocation and planning.

Explanation:

• -hg: The -hg parameter instructs vnstat to generate a horizontal bar graph through the shell, displaying hourly traffic data over the past 24-hour period. This visualization aids in quickly interpreting data trends across each hour.

Example Output:

 eth0  /  hourly traffic statistics
 
  hour          rx      |    tx     |   total
-------------------------------|---------------|-----------
  0- 1   10 MiB |   5 MiB   |   15 MiB
  1- 2    8 MiB   |   4 MiB   |   12 MiB
  [snip]
 22-23  15 MiB |   7 MiB   |   22 MiB

Use Case 5: Measure and Show Average Traffic for 30 Seconds

Code:

vnstat -tr 30

Motivation:

Measuring the average traffic over a specific, short-duration time window, like 30 seconds, can be invaluable for instantaneous performance checks and brief network assessments to identify short-lived spikes or dips in utilization.

Explanation:

• -tr: This argument tells vnstat to calculate the average traffic rate during a period specified as a number of seconds (30 in this example). It provides quick insight into short-term network load, which can be pivotal during performance testing or troubleshooting.

Example Output:

Test run for 30 seconds, statistics shown below:

   rx:   5 kbit/s    19 packets
   tx:   3 kbit/s    11 packets

Conclusion:

The vnstat command is a powerful tool for obtaining detailed network traffic statistics across multiple time frames and interfaces. Whether for high-level overviews, specific interface scrutiny, real-time monitoring, or detailed hourly breakdowns, vnstat provides the command-line flexibility and detailed data needed to manage and optimize network performance professionally.