When working in data centers or server racks, identifying a specific network interface card (NIC) among dozens can be challenging. The ethtool utility provides the perfect solution with its LED blinking functionality.

sudo ethtool -p|--identify [interface_name] [duration_in_seconds]

Example to blink eth0 for 30 seconds:

sudo ethtool -p eth0 30

This becomes particularly useful when:

• Rack-mounting new servers
• Troubleshooting network connectivity
• Verifying interface mapping in virtualization
• Confirming link status during maintenance

For persistent identification (until manually stopped):

sudo ethtool --identify eth0 0

To stop the blinking:

sudo ethtool --identify eth0 off

While ethtool is Linux-specific, other platforms have similar tools:

• Windows: Device Manager's "Blink LED" option
• Cisco IOS: test interface command
• HP ProCurve: show port led

If the blinking doesn't work:

1. Verify interface is up (ip link show)
2. Check driver support (ethtool -i eth0)
3. Confirm NIC actually has controllable LEDs

When working in server rooms with multiple network interfaces, identifying a specific NIC can be challenging. The ethtool utility provides a simple way to flash the link light on Ethernet adapters for physical identification.

sudo ethtool -p [interface_name] [duration_in_seconds]

Example to blink eth0 for 30 seconds:

sudo ethtool -p eth0 30

For scripting purposes, you might want to combine this with interface discovery:

#!/bin/bash
INTERFACE="eth0"
DURATION=60

if ip link show $INTERFACE > /dev/null 2>&1; then
    sudo ethtool -p $INTERFACE $DURATION
    echo "Blinking $INTERFACE for $DURATION seconds"
else
    echo "Interface $INTERFACE not found"
fi

Some distributions may use different tools:

• mii-tool on older systems
• ip link set dev [interface] flash on some modern kernels

If the command doesn't work:

1. Verify NIC driver supports this feature: ethtool --show-features [interface]
2. Check for firmware updates
3. Try root privileges if not already using sudo

For persistent identification, consider labeling or using unique MAC addresses:

ethtool -P eth0