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Unveiling the Power of `ethtool`: Your Gateway to Network Driver and Hardware Control

In the realm of networking, having precise control over network drivers and hardware is crucial. Whether you're a system administrator troubleshooting connectivity issues, a network engineer optimizing performance, or a developer working on network-related applications, understanding the tools at your disposal is essential. One such powerful tool is ethtool. This blog post will delve deep into ethtool, exploring its functionality, common use cases, best practices, and example usage.

Table of Contents#

What is ethtool?#

ethtool is a command-line utility in Linux systems that allows users to query and configure network interface controllers (NICs) and their associated drivers. It provides a wide range of capabilities, from retrieving basic information about a network interface (such as its speed, duplex mode, and driver version) to adjusting advanced settings like offloading features (e.g., TCP segmentation offloading, large receive offloading) and even performing hardware diagnostics.

Installation#

On most Linux distributions, ethtool is already installed by default. However, if it's missing on your system, you can install it using the package manager. For example:

  • Debian/Ubuntu:
sudo apt-get install ethtool
  • CentOS/RHEL:
sudo yum install ethtool

Basic Usage#

Querying Network Interface Information#

One of the most common uses of ethtool is to gather information about a network interface. Let's say you want to check details about the interface eth0.

Example:

ethtool eth0

This will display output like:

Settings for eth0:
	Supported ports: [ TP ]
	Supported link modes:   10baseT/Half 10baseT/Full 
	                        100baseT/Half 100baseT/Full 
	                        1000baseT/Full 
	Supported pause frame use: No
	Supports auto-negotiation: Yes
	Supported FEC modes: Not reported
	Advertised link modes:  10baseT/Half 10baseT/Full 
	                        100baseT/Half 100baseT/Full 
	                        1000baseT/Full 
	Advertised pause frame use: Symmetric Receive-only
	Advertised auto-negotiation: Yes
	Advertised FEC modes: Not reported
	Speed: 1000Mb/s
	Duplex: Full
	Port: Twisted Pair
	PHYAD: 0
	Transceiver: internal
	Auto-negotiation: on
	MDI-X: off (auto)
	Supports Wake-on: pumbg
	Wake-on: d
	Current message level: 0x00000007 (7)
			       drv probe link
	Link detected: yes

Here, you can see details like the supported link modes, current speed (in this case, 1000Mb/s), duplex mode (Full), and whether auto-negotiation is enabled.

Suppose you want to force the interface eth0 to operate at a specific speed and duplex mode (let's say 100Mb/s full duplex).

Example:

sudo ethtool -s eth0 speed 100 duplex full autoneg off

Explanation:

  • -s: This option is used to set the parameters.
  • speed 100: Sets the speed to 100Mb/s.
  • duplex full: Sets the duplex mode to full.
  • autoneg off: Disables auto-negotiation.

Configuring Offloading Features#

Offloading features offload certain network processing tasks from the CPU to the NIC hardware. For example, to enable TCP segmentation offloading (TSO) on eth0:

Example:

sudo ethtool -K eth0 tso on

Explanation:

  • -K: This option is used to modify the offloading features.
  • tso on: Enables TCP segmentation offloading.

You can also check the current status of offloading features:

ethtool -k eth0

Which will show output like:

Features for eth0:
rx-checksumming: on
tx-checksumming: on
	tx-checksum-ipv4: on (fixed)
	tx-checksum-ip-generic: off 
	tx-checksum-ipv6: on (fixed)
	tx-checksum-fcoe-crc: off 
	tx-checksum-sctp: off 
scatter-gather: on
	tx-scatter-gather: on
	tx-scatter-gather-fraglist: off 
tcp-segmentation-offload: on
	tx-tcp-segmentation: on
	tx-tcp-ecn-segmentation: off 
	tx-tcp-mangleid-segmentation: off 
	tx-tcp6-segmentation: on
udp-fragmentation-offload: off 
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off 
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off 
receive-hashing: on
highdma: on
rx-vlan-filter: off 
vlan-challenged: off 
tx-lockless: off 
netns-local: off 
tx-gso-robust: off 
tx-fcoe-segmentation: off 
tx-gre-segmentation: off 
tx-gre-csum-segmentation: off 
tx-ipxip4-segmentation: off 
tx-ipxip6-segmentation: off 
tx-udp_tnl-segmentation: off 
tx-udp_tnl-csum-segmentation: off 
tx-gso-partial: off 
tx-sctp-segmentation: off 
tx-esp-segmentation: off 
tx-udp-segmentation: off 
fcoe-mtu: off 
tx-nocache-copy: off 
loopback: off 
rx-fcs: off 
rx-all: off 
tx-vlan-stag-hw-insert: off 
rx-vlan-stag-hw-parse: off 
rx-vlan-stag-filter: off 
l2-fwd-offload: off 
hw-tc-offload: off 
esp-hw-offload: off 
esp-tx-csum-hw-offload: off 
rx-udp_tunnel-port-offload: off 
tls-hw-tx-offload: off 
tls-hw-rx-offload: off

Advanced Usage#

Monitoring Network Statistics#

ethtool can be used to monitor network statistics. For example, to get the statistics related to the number of packets received, transmitted, errors, etc., on eth0:

Example:

ethtool -S eth0

This will display a long list of statistics like:

NIC statistics:
     rx_packets: 123456
     tx_packets: 789012
     rx_bytes: 123456789
     tx_bytes: 987654321
     rx_errors: 0
     tx_errors: 0
     rx_dropped: 0
     tx_dropped: 0
     collisions: 0
     rx_length_errors: 0
     rx_over_errors: 0
     rx_crc_errors: 0
     rx_frame_errors: 0
     rx_fifo_errors: 0
     rx_missed_errors: 0
     tx_aborted_errors: 0
     tx_carrier_errors: 0
     tx_fifo_errors: 0
     tx_heartbeat_errors: 0
     tx_window_errors: 0
     rx_compressed: 0
     tx_compressed: 0

Debugging and Diagnostics#

Some NICs support hardware diagnostics. For instance, to perform a basic link test on eth0 (if supported by the NIC):

Example:

sudo ethtool -t eth0

This may output something like:

Testing ...
  1. Link test: OK

Best Practices#

  • Backup and Test: Before making any significant changes to network interface settings (especially in a production environment), always backup the current configuration (you can use ethtool commands to record the current settings). Also, test the changes in a non-production or isolated environment if possible.
  • Understand the NIC Capabilities: Different NICs support different features. Check the documentation of your specific NIC to know which offloading features, link settings, etc., are truly supported.
  • Regular Monitoring: Use the statistics querying feature (ethtool -S) regularly to keep an eye on network performance. Sudden spikes in error counts or drops in packet counts can indicate issues.

Common Pitfalls and Troubleshooting#

  • Permissions: Many ethtool operations (like changing settings) require root privileges. If you get a "permission denied" error, try using sudo.
  • NIC Compatibility: Some older or less common NICs may not support all the features that ethtool tries to configure. If a setting change doesn't seem to take effect or causes issues (like a loss of network connectivity), check the NIC's documentation and revert the change.
  • Auto-negotiation Conflicts: If you force specific link settings (like speed and duplex) and auto-negotiation is still enabled (even if you thought you disabled it), there can be conflicts. Double-check the autoneg setting.

References#

  • The official ethtool man page
  • Linux networking documentation resources (e.g., the Linux Kernel documentation for network drivers if you want to dig deeper into how ethtool interacts with them).

By mastering ethtool, you gain a powerful tool in your networking arsenal to manage, optimize, and troubleshoot your network interfaces effectively. Whether it's fine-tuning performance or diagnosing issues, ethtool is a go-to utility for any Linux user dealing with network drivers and hardware.

2026-03