While lspci | grep Ethernet is a common first approach to detect network interfaces, dedicated servers sometimes need deeper inspection. Here are more robust methods to verify physical NIC installation:

sudo dmidecode -t slot | grep -A10 "Network"

This queries the motherboard's DMI table directly, revealing physical slot information that PCI enumeration might miss.

lsmod | grep -e 'igb\|ixgbe\|e1000\|bnx2'

Different drivers load for different NICs. Common drivers include:

• igb: Intel Gigabit
• ixgbe: Intel 10GbE
• e1000: Older Intel
• bnx2: Broadcom NetXtreme

ls -l /sys/class/net/

Compare physical devices with symbolic links. Physical interfaces typically show under:

ls -l /sys/class/net/*/device

For servers with NICs that don't show as Ethernet controllers:

lspci -nnk | grep -i network -A3

This reveals both classified and unclassified network devices with their kernel drivers.

Combine multiple verification methods:

ip -d link show | grep -B1 'link/ether'
ethtool -i eth0  # Repeat for all interfaces
find /sys/devices -name net -exec ls -l {} \;

For missing NICs:

1. Check dmesg for detection errors: dmesg | grep -i eth
2. Verify kernel module loading: modprobe DRIVER_NAME
3. Inspect BIOS settings for disabled ports

While lspci | grep Ethernet is the standard approach, sometimes it doesn't show all physical NICs due to driver issues or hardware detection problems. Here's how to perform a thorough investigation:

# Check kernel messages for detected hardware
dmesg | grep -i ethernet

# List all network interfaces (including disabled ones)
ip link show

# Detailed PCI device information
lspci -v | grep -A 10 Ethernet

# Check loaded network modules
lsmod | grep eth

For servers with potentially undiscovered hardware, these commands provide low-level access:

# View all PCI devices in tree format
lspci -tv

# Check sysfs for network devices
ls -l /sys/class/net/

# Examine kernel ring buffer
journalctl -k | grep -i eth

On a server where one NIC wasn't showing up, I discovered it through:

# First attempt showed only one NIC
$ lspci | grep Ethernet
02:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)

# Deeper inspection revealed the second NIC
$ dmesg | grep -i eth
[    3.224566] igb 0000:02:00.0: eth0: (PCIe:2.5Gb/s:Width x1)
[    3.224568] igb 0000:02:00.1: eth1: (PCIe:2.5Gb/s:Width x1)

• Check if the NIC requires firmware: dmesg | grep firmware
• Verify kernel module loading: modprobe MODULE_NAME
• Inspect BIOS settings for disabled ports
• Test with alternative Linux live CD to rule out OS configuration

# Install ethtool for detailed NIC information
sudo apt install ethtool

# Get detailed NIC specs
sudo ethtool -i eth0

# Check for link detection
sudo ethtool eth0