How to check the physical status of an ethernet port in Linux?
I want to check if a specified ethX is physically up or down. How do I do that with the command line?
Solution 1:
$ ethtool <eth?>
For example:
$ ethtool eth0
provides:
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised pause frame use: No
Advertised auto-negotiation: Yes
Speed: 1000Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: on
MDI-X: on
Supports Wake-on: pumbg
Wake-on: g
Current message level: 0x00000001 (1)
Link detected: yes
Solution 2:
Check /sys/class/net/eth0/operstate
and other files in this directory.
As far as I know this is specific to Linux 2.6+, but it provides a clean interface to the kernel driver.
Full documentation for this part of the sys
file system can be found here:
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-net
Solution 3:
ethtool [interface]
last line shows what you want:
# ethtool eth0 Settings for eth0: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full Port: Twisted Pair PHYAD: 0 Transceiver: internal Auto-negotiation: on Supports Wake-on: g Wake-on: d Current message level: 0x00000037 (55) Link detected: yes
Solution 4:
ip link show
is another. Good old
ifconfig dev_name
or
ifconfig -a
will also tell you if the interface is up. NOTE: Use caution with these methods since they can show out of date information regarding the link's state.
Solution 5:
dmesg | grep eth
you should see all statuschanges