I just installed a new gigabit network interface card (NIC) in Linux. How do I tell if it is really set to gigabit speeds? I see ethtool has an option to set the speed, but I can't seem to figure out how to report its current speed.

  • 1
    ethtool -h says: ethtool DEVNAME Display standard information about device Oct 17, 2015 at 23:12

10 Answers 10


Just use a command like: ethtool eth0 to get the needed info. Ex:

$ sudo ethtool eth0 | grep Speed

Speed: 1000Mb/s
  • 7
    If you want to have the full list of all your interfaces with theyr speed, you can use this command: for i in $(netstat -i | cut -f1 -d" " | tail -n+3) ; do echo "$i: $(ethtool "$i" | grep Speed | sed 's/Speed://g')" ; done Nov 11, 2017 at 20:13
  • 1
    If you get "Speed: Unknown!" you may be using the wrong ethXX name, worth a double check :)
    – rogerdpack
    Sep 24, 2018 at 16:00
  • 2
    This only gives you the negotiated speed of your current network configuration (hence your ethernet port must be connected). The speed indicated also depends on the cable and the other end of the connection. This does NOT give the max supported speed of the NIC on your PC. For that, you need to look under Supported link modes also shown in ethtool. 1000baseT means gigabit ethernet, etc.
    – Rufus
    Nov 5, 2020 at 2:19
  • 1
    apt install ethtool on debian.
    – Timo
    May 8, 2021 at 9:25
  • 1
    No sudo required!
    – Raymo111
    Nov 9, 2021 at 22:47

It is possible to use the information from the kernel when ethtool is missing:

cat /sys/class/net/<interface>/speed

Example for interface named eth0:

cat /sys/class/net/eth0/speed
  • 7
    Note: Only available since 2.6.33 version
    – zhaorufei
    May 5, 2016 at 5:55
  • 17
    Getting "Invalid argument"
    – wi1
    Sep 20, 2017 at 15:28
  • 1
    @Christian Yes it is thanks, but only on some of my interfaces which I've read is expected so I'm all good
    – wi1
    Sep 25, 2017 at 15:10
  • 2
    What does it mean if cat /sys/class/net/eth1/speed shows 10000 but "ip a" does only show 1000. Can someone clarify?
    – jsterr
    Feb 6, 2019 at 16:14
  • 1
    It seems /sys/class interface was right. Dmesg also lists 100Mbit/s # dmesg|grep duplex [ 5.417536] smsc95xx 1-1.1:1.0 eth0: link up, 100Mbps, full-duplex, lpa 0xC5E1. I am running on a special purpose OS build without ethtool.
    – user643011
    Dec 31, 2019 at 15:48

NOTE: the man page for mii-tool has this disclaimer:

This program is obsolete. For replacement check ethtool.

Use mii-tool to watch the negotiated network speed.


eth0: no link
eth1: negotiated 100baseTx-FD, link ok
  • 15
    For Debian based systems, ethtool is not installed by default. But mii-tool is, as part of the essential "net-tools" package. So this was the best solution for me.
    – mivk
    Jul 6, 2014 at 13:20
  • 2
    I see this in the man page for mii-tool "This program is obsolete. Valid media are only 100baseT4, 100baseTx-FD,100baseTx-HD, 10baseT-FD and 10baseT-HD ethernet cards. For replace-ment check ethtool." :|
    – rogerdpack
    Jun 28, 2017 at 16:13
  • 1
    While mii-tool reports 'negotiated 100baseTx-FD flow-control, link ok', both ethtool and cat /sys/class/net/eth…/speed agree on '1000Mb/s Full duplex'. This is for a USB 3.0 controller, namely ASIX AX88179 ('ax88179_178a' driver for Linux). Sep 24, 2018 at 10:11

There are some great answers here, I just wanted to add a few more options.

1. I know this is not quite what you asked (read on for other ways). But if you want to know the real world performance of your NIC, rather than what your computer says it should be, you can use iperf. I usually do this - because you never know. I bought a 1Gb NIC recently that that only transferred at 672Mbps but it's uplink was 1Gb. Good thing I checked.

You'll need two computers.

On computer one, run iperf in server mode:

iperf -s

On the other, run iperf in client mode:

iperf -c

If you want to see the full duplex speed, try this instead:

iperf -d -c

Substitute for the servers IP address

2. On Ubuntu systems, /var/log/kern.log has limited logging of kernel events. It will record link speed and status of a NIC when it changes. I'm sure other distributions probably do something similar or can be setup to do so.

$ tail -n 300 /var/log/kern.log.1 | grep slave0
Aug 28 12:54:04 haze kernel: [ 9452.766248] e1000e: slave0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: Rx/Tx
Aug 28 12:54:41 haze NetworkManager[921]: <info>  [1472403281.8486] device (slave0): link disconnected
Aug 28 12:54:41 haze kernel: [ 9489.898476] e1000e: slave0 NIC Link is Down

3. You'll probably never, ever need to go this far, but you can write c code that to get the speed. Tested working and root is not required.


#include <stdio.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <linux/sockios.h>
#include <linux/if.h>
#include <linux/ethtool.h>
#include <string.h>
#include <stdlib.h>
int main (int argc, char **argv)
    int sock;
    struct ifreq ifr;
    struct ethtool_cmd edata;
    int rc;
    sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
    if (sock < 0) {
    strncpy(ifr.ifr_name, "eth0", sizeof(ifr.ifr_name));
    ifr.ifr_data = &edata;
    edata.cmd = ETHTOOL_GSET;
    rc = ioctl(sock, SIOCETHTOOL, &ifr);
    if (rc < 0) {
    switch (ethtool_cmd_speed(&edata)) {
        case SPEED_10: printf("10Mbps\n"); break;
        case SPEED_100: printf("100Mbps\n"); break;
        case SPEED_1000: printf("1Gbps\n"); break;
        case SPEED_2500: printf("2.5Gbps\n"); break;
        case SPEED_10000: printf("10Gbps\n"); break;
        default: printf("Speed returned is %d\n", edata.speed);
    return (0);
  • 2
    What was your eventual resolution to the non expected performance?
    – rogerdpack
    Jan 22, 2019 at 0:39
  • 2
    Using iperf as you stated is the answer if one wants to get current speed and not simply the nic potential speed. Feb 23, 2019 at 2:50

As Khaled mentioned, you should be able to run ethtool with just the interface as an argument. This will list the supported speeds, the advertised speeds, the current speed, and a bunch of other things too:

Settings for eth0:
    Supported ports: [ TP ]
    Supported link modes:   10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
    Advertised auto-negotiation: Yes
    Speed: 1000Mb/s
    Duplex: Full
    Port: Twisted Pair
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    Supports Wake-on: d
    Wake-on: d
    Current message level: 0x00000007 (7)
    Link detected: yes

You can also run dmesg, and grep for your interface, but this might not work if your system has been running for a long time and the current buffer no longer has that information (in that case, you'll have to grep the older /var/log/dmesg.* files):

dmesg |grep eth0
[    2.867481] e1000: eth0: e1000_probe: Intel(R) PRO/1000 Network Connection
[   19.429444] ADDRCONF(NETDEV_UP): eth0: link is not ready
[   19.431555] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
[   19.449341] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[   26.972379] e1000: eth0: e1000_set_tso: TSO is Enabled
[   29.920458] eth0: no IPv6 routers present

Use below command

 dmesg | grep -i duplex
 Output: eth0: link up, 100Mbps, full-duplex, lpa 0x45E1

refer this

  • 1
    Useful when you don't have root access.
    – mehdix
    Apr 11, 2016 at 8:24
  • useful when the log is not overwritten. I'm in the unfortunate situation.
    – zhaorufei
    May 5, 2016 at 6:01
  • this came in handy when I didn't have superuser privs on the box. thanks!
    – Sankalp
    Aug 24, 2017 at 8:07
  • If you don't know the name of your network adapter, you can run: /sbin/ifconfig. Then: dmesg | grep -F $nicname
    – kevinarpe
    Apr 12, 2022 at 13:14

Also for future reference I've noticed that the speed field in ethtool gives the maximum speed supported by the NIC and mii-tool give the actual speed on which the NIC is running.

[ root @  ]# mii-tool
eth0: negotiated 100baseTx-FD, link ok
[ root @  ]# ethtool eth0
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Supported pause frame use: No
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 2
        Transceiver: internal
        Auto-negotiation: on
        MDI-X: off (auto)
        Supports Wake-on: pumbg
        Wake-on: g
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes

UPDATE: After a while a found out the mii-tool wasn't returning the right speed as it was outdated and deprecated and ethtool was returning the negotiated speed.


If you are using network manager:

nmcli -f CAPABILITIES.SPEED dev show <interface>

For example:

$ nmcli -f CAPABILITIES.SPEED dev show enp0s31f6 
CAPABILITIES.SPEED:                     100 Mb/s

With systemd-networkd, you can use the networkctl command:

$ networkctl status enp37s0
● 2: enp37s0                                                                   
                     Link File: /usr/lib/systemd/network/99-default.link
                  Network File: /etc/systemd/network/enp37s0.network
                         State: routable (configured)
                  Online state: online                                         
                          Type: ether
                         Speed: 1Gbps

ethtool eth0 worked for me. Example:

$ethtool eth0 |grep -i speed
Speed: 1000Mb/s
  • 4
    Please read other answers before answering. This has alread been said six years ago and is the accepted answer with 66 upvotes.
    – Sven
    Jul 11, 2016 at 12:15
  • one can still post his answer regardless. Given answers might not work for someone, so just wanted to add another option that suited me in my situation.
    – dragon
    Jul 19, 2016 at 16:00
  • 3
    Your answer is the exact same as the accepted one and does not add value.
    – Sven
    Jul 19, 2016 at 16:28
  • where is the ethtool command mentioned in previous options?
    – dragon
    Aug 12, 2016 at 10:46
  • 2
    look at the very top answer with the green tick beside it. This is the accepted answer and it very clearly uses ethtool.
    – Sven
    Aug 12, 2016 at 11:17

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