vnstat Command Linux: Complete Network Traffic Monitoring Guide

Network traffic monitoring is a crucial aspect of system administration, and the vnstat command in Linux provides an elegant solution for tracking network usage statistics. This lightweight, console-based tool offers comprehensive insights into your network interface traffic patterns without consuming significant system resources.

What is vnstat Command?

The vnstat command is a network traffic monitor that keeps track of network usage for selected network interfaces. Unlike other monitoring tools that require constant running processes, vnstat works by reading kernel-provided network statistics and storing them in a database for historical analysis. This approach makes it extremely efficient and suitable for long-term monitoring.

Key Features of vnstat

• Low resource consumption – Minimal CPU and memory usage
• Historical data – Maintains long-term statistics
• Multiple time periods – Hourly, daily, weekly, and monthly views
• Multiple interfaces – Monitor several network interfaces simultaneously
• Database storage – Persistent data across reboots
• JSON output – Machine-readable format for integration

Installing vnstat on Linux

The installation process varies depending on your Linux distribution. Here are the most common methods:

Ubuntu/Debian Systems

sudo apt update
sudo apt install vnstat

CentOS/RHEL/Fedora Systems

# For CentOS/RHEL
sudo yum install vnstat

# For Fedora
sudo dnf install vnstat

Arch Linux

sudo pacman -S vnstat

Initial Setup and Configuration

After installation, you need to initialize the database and start the vnstat daemon:

Initialize Database

# Initialize database for default interface (usually eth0 or ens33)
sudo vnstat -i eth0 --create

# Start and enable the vnstat service
sudo systemctl start vnstat
sudo systemctl enable vnstat

Configuration File

The main configuration file is located at /etc/vnstat.conf. Key configuration options include:

# Database directory
DatabaseDir "/var/lib/vnstat"

# Update interval (seconds)
UpdateInterval 30

# Save interval (minutes)
SaveInterval 5

# Interface monitoring
Interface "eth0"

Basic vnstat Command Usage

Let’s explore the fundamental usage of vnstat with practical examples:

Display Current Statistics

vnstat

Sample Output:

Database updated: 2025-08-26 04:30:01

   eth0 since 2025-08-01

          rx:  2.45 GiB      tx:  1.23 GiB      total:  3.68 GiB

                     rx      |     tx      |    total    |   avg. rate
     ------------------------+-------------+-------------+---------------
       yesterday     45.2 MiB |   23.1 MiB |   68.3 MiB |    0.79 kbit/s
           today    123.4 MiB |   67.8 MiB |  191.2 MiB |    1.42 kbit/s
     ------------------------+-------------+-------------+---------------
     estimated       156 MiB |    85 MiB |   241 MiB |

Specify Network Interface

vnstat -i wlan0

Display Hourly Statistics

vnstat -h

Sample Output:

 eth0                                                                     04:30
  ^                                                                           
  |                                                                           
  |    r                                                                      
  |    x   r                                                                  
  |    |   x                                                                  
  | t  |t  |                                                                  
  | x  |x  |                                                                  
  | |  ||  |  r                                                               
  | |  ||  |  x                                                               
  +-+--++--+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23

 h  rx (MiB)   tx (MiB)      h  rx (MiB)   tx (MiB)      h  rx (MiB)   tx (MiB)
00      12.4       6.7     08       0.0       0.0     16       0.0       0.0
01      15.2       8.1     09       0.0       0.0     17       0.0       0.0
02      18.7       9.3     10       0.0       0.0     18       0.0       0.0
03      21.1      11.2     11       0.0       0.0     19       0.0       0.0

Advanced vnstat Command Options

Daily Statistics

vnstat -d

This displays daily network usage for the current month with a calendar-like view.

Weekly Statistics

vnstat -w

Monthly Statistics

vnstat -m

Sample Monthly Output:

 eth0  /  monthly

       month        rx      |     tx      |    total    |   avg. rate
     ------------------------+-------------+-------------+---------------
      2025-06      1.25 GiB |  642.3 MiB |    1.87 GiB |   0.73 kbit/s
      2025-07      2.14 GiB |    1.12 GiB |    3.26 GiB |   1.28 kbit/s
      2025-08      3.45 GiB |    1.78 GiB |    5.23 GiB |   2.05 kbit/s
     ------------------------+-------------+-------------+---------------
     estimated      4.12 GiB |    2.13 GiB |    6.25 GiB |

Top 10 Traffic Days

vnstat -t

Live Traffic Monitoring

vnstat -l

This provides real-time traffic monitoring. Press Ctrl+C to stop.

Sample Live Output:

Monitoring eth0...    (press CTRL-C to stop)

   rx:        2.34 kbit/s     8 p/s          tx:        1.67 kbit/s     6 p/s
   rx:        3.45 kbit/s    12 p/s          tx:        2.12 kbit/s     8 p/s
   rx:        1.89 kbit/s     5 p/s          tx:        1.23 kbit/s     4 p/s

JSON Output Format

For automation and integration purposes, vnstat supports JSON output:

vnstat --json

Sample JSON Output:

{
    "vnstatversion": "2.6",
    "jsonversion": "1",
    "interfaces": [
        {
            "name": "eth0",
            "alias": "",
            "created": {
                "date": {
                    "year": 2025,
                    "month": 8,
                    "day": 1
                }
            },
            "updated": {
                "date": {
                    "year": 2025,
                    "month": 8,
                    "day": 26
                },
                "time": {
                    "hour": 4,
                    "minute": 30
                }
            },
            "traffic": {
                "total": {
                    "rx": 2636046336,
                    "tx": 1320157184
                },
                "days": [
                    {
                        "date": {
                            "year": 2025,
                            "month": 8,
                            "day": 25
                        },
                        "rx": 47472640,
                        "tx": 24235008
                    }
                ]
            }
        }
    ]
}

Managing Multiple Network Interfaces

Add New Interface to Monitoring

sudo vnstat -i wlan0 --create

List All Monitored Interfaces

vnstat --iflist

Remove Interface from Monitoring

sudo vnstat -i wlan0 --delete

Customizing Output

Specify Date Range

# Show data for specific date
vnstat -i eth0 -d --begin 2025-08-01 --end 2025-08-25

Change Units

# Display in different units
vnstat --style 0  # Adaptive units
vnstat --style 1  # Bytes
vnstat --style 2  # Bits

Limit Output Lines

# Show only last 5 days
vnstat -d -l 5

Database Management

Database Information

vnstat --dbdir

Export Database

vnstat --exportdb > network_stats_backup.db

Import Database

vnstat --importdb < network_stats_backup.db

Practical Use Cases

Bandwidth Usage Monitoring

Create a script to monitor daily bandwidth usage and send alerts:

#!/bin/bash
# Check if daily usage exceeds 1GB
USAGE=$(vnstat --json -d | jq '.interfaces[0].traffic.days[-1].rx + .interfaces[0].traffic.days[-1].tx')
LIMIT=1073741824  # 1GB in bytes

if [ $USAGE -gt $LIMIT ]; then
    echo "Daily bandwidth limit exceeded: $(($USAGE / 1024 / 1024)) MB used"
fi

Monthly Report Generation

# Generate monthly HTML report
vnstat -i eth0 -m --xml > monthly_report.xml

Troubleshooting Common Issues

Interface Not Found Error

If you encounter “interface not found” errors:

# List available interfaces
ip link show

# Verify interface name and create database
sudo vnstat -i correct_interface_name --create

Permission Issues

For permission-related problems:

# Check database permissions
ls -la /var/lib/vnstat/

# Fix permissions if needed
sudo chown vnstat:vnstat /var/lib/vnstat/*

Service Not Running

# Check service status
systemctl status vnstat

# Restart if needed
sudo systemctl restart vnstat

Integration with Other Tools

Combining with awk for Custom Reports

# Extract total monthly usage
vnstat -m | awk '/total/ {print $5, $7, $9}'

Creating Graphs with vnstati

Install vnstati for graphical output:

sudo apt install vnstati

# Generate hourly graph
vnstati -h -i eth0 -o hourly_traffic.png

Best Practices

• Regular backups – Export database regularly for data protection
• Monitor multiple interfaces – Include all active network interfaces
• Set up alerts – Create scripts to notify about unusual traffic patterns
• Use JSON output – For automated processing and integration
• Regular maintenance – Clean old data if disk space is limited

Performance Considerations

vnstat is designed to be lightweight, but consider these optimization tips:

• Adjust UpdateInterval in configuration for less frequent updates if needed
• Use SaveInterval to control how often data is written to disk
• Monitor database size and implement rotation if necessary
• Consider using --limit options to reduce output size for scripting

Conclusion

The vnstat command is an indispensable tool for Linux system administrators and users who need to monitor network traffic efficiently. Its lightweight design, comprehensive features, and flexible output formats make it perfect for both real-time monitoring and historical analysis. Whether you’re tracking bandwidth usage, generating reports, or integrating with automated systems, vnstat provides the reliability and functionality needed for effective network monitoring.

By mastering vnstat’s various options and features, you can gain valuable insights into your network usage patterns, helping you make informed decisions about bandwidth management, capacity planning, and network optimization. The tool’s simplicity combined with its powerful capabilities makes it a must-have utility in any Linux administrator’s toolkit.