ethtool

Getting Started with ethtool

Before we jump into specific commands, let’s begin with the basics. To display general information about a network interface, say eth0, you’d use:

ethtool eth0

This provides a summary including driver information, link speed, duplex mode, and auto-negotiation status.

Exploring Network Interface Details

ethtool offers more granular control and information retrieval. For example, to view the driver in use:

ethtool -i eth0

This displays the driver name, version, and other driver-specific details.

Managing Auto-Negotiation

Auto-negotiation allows network devices to automatically determine the best speed and duplex settings. You can disable it using:

sudo ethtool -s eth0 speed 1000 duplex full autoneg off

This forces a 1 Gigabit connection with full duplex mode. Remember to replace eth0 with your interface name. Enabling auto-negotiation again:

sudo ethtool -s eth0 autoneg on

Setting Speed and Duplex

If auto-negotiation is off, you can manually configure the speed and duplex settings:

sudo ethtool -s eth0 speed 100 duplex half

This sets the speed to 100 Mbps and duplex to half. Be mindful of compatibility with connected devices.

Working with Coalescing Parameters

Coalescing affects how often the network card interrupts the CPU. Adjusting these settings can impact performance, particularly under heavy network load. You can view current settings:

ethtool -c eth0

And modify them (requires root privileges):

sudo ethtool -C eth0 rx-usecs 100 rx-frames 100 tx-usecs 100 tx-frames 100

This example sets receive and transmit coalescing parameters. Experiment with different values to find the optimal configuration for your system.

Checking Link Status

A quick way to check the link status is:

ethtool link info eth0

This will indicate whether a link is up or down.

Advanced Features: Offload Settings

Network interfaces often support various offloading features, like checksum offloading. You can see what features are supported and enabled using:

ethtool -k eth0

This reveals a detailed list of offloading capabilities. Enabling or disabling specific offloads usually involves the -K option, but the exact parameters depend on your network card and driver. Consult your driver’s documentation for details.

Troubleshooting with ethtool

ethtool is useful for troubleshooting network issues. For instance, if you experience connection problems, you can quickly check the link status, speed, and duplex settings to identify potential misconfigurations.

Important Note on Permissions

Most ethtool commands requiring changes to network interface settings need root privileges (using sudo). Always run commands with sudo when modifying settings. Remember to replace "eth0" with the actual name of your network interface. Use the ip link show command to list your interfaces.