Looking at your Linux system’s network interface with ethtool
The ethtool utility on Linux allows you to view and change some of your network-driver and interface-card settings, especially for wired devices. These include their speed, whether the interface uses auto-negotiation, whether it runs in half- or full-duplex mode, and other settings as well. Ethtool also provides an easy way to view or troubleshoot your network interface.
More than likely, ethtool is already available on your Linux system. However, to check, you can use one or both of these commands:
$ which ethtool /usr/sbin/ethtool $ sudo ethtool —version ethtool version 5.13
To get a sense of how this utility can control settings, run a command like the one below. The -h means “help”. You’ll likely find yourself looking at 10 pages or so of syntax like what is shown here.
$ ethtool -h | more ethtool version 5.13 Usage: ethtool [ FLAGS ] DEVNAME Display standard information about device ethtool [ FLAGS ] -s|—change DEVNAME Change generic options [ speed %d ] [ lanes %d ] [ duplex half|full ] [ port tp|aui|bnc|mii|fibre|da ] [ mdix auto|on|off ] [ autoneg on|off ] [ advertise %x[/%x] | mode on|off ... [—] ] [ phyad %d ] [ xcvr internal|external ] [ wol %d[/%d] | p|u|m|b|a|g|s|f|d... ] [ sopass %x:%x:%x:%x:%x:%x ] [ msglvl %d[/%d] | type on|off ... [—] ] [ master-slave preferred-master|preferred-slave|forced-master|forced-slave ] ethtool [ FLAGS ] -a|—show-pause DEVNAME Show pause options ethtool [ FLAGS ] -A|—pause DEVNAME Set pause options [ autoneg on|off ] [ rx on|off ] —More—
View settings
There are clearly many things that the ethtool utility can do for you. However, to simply view the settings on your network interface, type “ethtool” followed by the name of your network interface (e.g. eth0). In the examples below, we’re looking at a network interface named enp0s25.
$ ethtool enp0s25: Settings for enp0s25: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/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 Advertised pause frame use: No Advertised auto-negotiation: Yes Advertised FEC modes: Not reported Speed: 100Mb/s Duplex: Full Auto-negotiation: on Port: Twisted Pair PHYAD: 1 Transceiver: internal MDI-X: on (auto) Current message level: 0x00000007 (7) drv probe link Link detected: yes
Notice the “yes” in the last line telling you that this interface is working. The output also displays the supported link modes and that auto-negotiation is turned on. Notice the speed (100Mbps) and that the interface is running in full duplex.
You can check Ethernet driver settings with a command like this one:
$ ethtool -i enp0s25 driver: e1000e version: 5.13.9-200.fc34.x86_64 firmware-version: 1.1-2 expansion-rom-version: bus-info: 0000:00:19.0 supports-statistics: yes supports-test: yes supports-eeprom-access: yes supports-register-dump: yes supports-priv-flags: yes
Network-interface stats
To view your network-interface stats, you can use a command like the one below. I put the output into two columns to make it a little easier to review the settings.
$ ethtool -S enp0s25 | column NIC statistics: tx_single_coll_ok: 0 rx_packets: 455502 tx_multi_coll_ok: 0 tx_packets: 44344 tx_timeout_count: 0 rx_bytes: 79840149 tx_restart_queue: 0 tx_bytes: 4734660 rx_long_length_errors: 0 rx_broadcast: 261026 rx_short_length_errors: 0 tx_broadcast: 35 rx_align_errors: 0 rx_multicast: 154850 tx_tcp_seg_good: 165 tx_multicast: 3561 tx_tcp_seg_failed: 0 rx_errors: 0 rx_flow_control_xon: 0 tx_errors: 0 rx_flow_control_xoff: 0 tx_dropped: 0 tx_flow_control_xon: 0 multicast: 154850 tx_flow_control_xoff: 0 collisions: 0 rx_csum_offload_good: 289057 rx_length_errors: 0 rx_csum_offload_errors: 0 rx_over_errors: 0 rx_header_split: 0 rx_crc_errors: 0 alloc_rx_buff_failed: 0 rx_frame_errors: 0 tx_smbus: 0 rx_no_buffer_count: 0 rx_smbus: 0 rx_missed_errors: 0 dropped_smbus: 0 tx_aborted_errors: 0 rx_dma_failed: 0 tx_carrier_errors: 0 tx_dma_failed: 0 tx_fifo_errors: 0 rx_hwtstamp_cleared: 0 tx_heartbeat_errors: 0 uncorr_ecc_errors: 0 tx_window_errors: 0 corr_ecc_errors: 0 tx_abort_late_coll: 0 tx_hwtstamp_timeouts: 0 tx_deferred_ok: 0 tx_hwtstamp_skipped: 0
No collisions and no errors. That’s a good sign.
To test a network interface, you need to use sudo and a command like the one below with the -t (test) option. Notice that the interface has passed the test.
$ sudo ethtool -t enp0s25 The test result is PASS <== PASS! The test extra info: Register test (offline) 0 Eeprom test (offline) 0 Interrupt test (offline) 0 Loopback test (offline) 0 Link test (on/offline) 0
Notice that these tests were all run in offline mode. There are two modes, online and offline, and offline is the default. It runs the full set of tests, but can interrupt normal operations. Online tests are limited and will not cause any interruptions. Keep this in mind if you are working on a production system.
Changing settings
Network interface changes will require that you use sudo or run as root. In addition, changes don’t persist through a reboot unless you also modify settings in the configuration file on your particular Linux distribution. For some changes, you also need to bring the interface down with ifdown and back up with ifup so you should be working on the system console.