Debugging Linux Network Drivers: Essential Tools and Techniques

When network interfaces fail or behave unexpectedly, you need to inspect driver details, hardware state, and kernel messages. Here’s the practical toolkit for diagnosing network hardware and driver issues.

Kernel Messages and Logs

Start by checking kernel logs where driver initialization and errors are recorded:

dmesg | grep -i network
dmesg | grep -i driver
dmesg | tail -50

For persistent logs across reboots, use the systemd journal:

journalctl -k | grep -i network
journalctl -k | grep -i eth
journalctl --since "1 hour ago" | grep -i driver
journalctl -u NetworkManager -n 50

On systems still using rsyslog, check traditional log files:

grep -i network /var/log/messages
grep -i driver /var/log/syslog

Hardware Detection and Driver Information

PCI and USB Devices

lspci lists PCI devices including built-in network adapters:

lspci | grep -i network
lspci -v | grep -i network  # verbose output
lspci -k | grep -A 2 -i network  # includes loaded kernel modules

lsusb lists USB devices including USB network adapters:

lsusb
lsusb -v  # verbose output with all details
lsusb -d 0bda:8153  # search by vendor:device ID
lsusb -t  # tree view with hubs

lshw provides comprehensive hardware details with driver information:

lshw -c network
lshw -c network -businfo

Ethernet Driver Details

ethtool queries and modifies Ethernet device settings:

ethtool eth0  # basic interface information
ethtool -i eth0  # driver and firmware information
ethtool -S eth0  # driver statistics
ethtool -k eth0  # show offloads (TSO, GSO, etc.)
ethtool -g eth0  # ring buffer settings
ethtool -c eth0  # coalescing settings

Example output from ethtool -i eth0:

driver: e1000e
version: 3.2.6-k
firmware-version: 0.13-4
bus-info: 0000:00:1f.6
supports-statistics: yes
supports-test: yes
supports-eeprom-access: yes
supports-register-dump: yes
supports-priv-flags: no

Wireless Device Management

For wireless interfaces, check hardware block state:

rfkill list
rfkill unblock all  # unblock WiFi if hardware-blocked
rfkill unblock wifi

Modern systems use iw for wireless configuration:

iw dev
iw dev wlan0 link  # connection status
iw list  # supported capabilities
iw wlan0 station dump  # connected station info

The legacy iwconfig still works on some systems but is deprecated:

iwconfig
iwconfig wlan0

Network Interface Configuration

View active interfaces and their state:

ip link show
ip link show eth0
ip -s link show eth0  # statistics (RX/TX packets, errors, dropped)

Check IP configuration:

ip addr show
ip route show
ip -6 route show  # IPv6 routes

For DNS and DHCP information:

resolvectl status
resolvectl status eth0
nmcli device show eth0  # if using NetworkManager

Finding Driver Module Information

Determine which kernel module drives a device:

ethtool -i eth0 | grep driver
lsmod | grep driver_name
modinfo driver_name  # detailed module information

Check module parameters and current values:

cat /sys/module/driver_name/parameters/*
cat /sys/module/e1000e/parameters/debug

To see what firmware files a driver is trying to load:

journalctl -k | grep firmware
dmesg | grep -i "firmware\|fw_path"

Detailed Hardware State

For USB network devices, check power management and descriptor information:

lsusb -d 0bda:8153 -v
cat /sys/bus/usb/devices/*/power/control  # check autosuspend settings

To disable autosuspend on a USB network device (permanent):

echo "0" | sudo tee /sys/bus/usb/devices/1-1/power/autosuspend_delay_ms

Check USB device tree:

lsusb -t
cat /sys/bus/usb/devices/1-1/speed  # USB 2.0, 3.0, etc.

Practical Debugging Workflow

When a network device isn’t recognized or behaves incorrectly:

Check kernel logs for hardware detection

dmesg | grep -E "eth|wlan|usb|Ethernet" | tail -30
journalctl -k --since "30 minutes ago"

Verify the device appears in hardware lists

lspci | grep -i network
lsusb | grep -i network

Confirm the driver module is loaded

lsmod | grep driver_name
ethtool -i eth0 | grep driver

If the driver isn’t loaded, load it manually

sudo modprobe driver_name
sudo modprobe -v driver_name  # verbose, shows what it's doing

Check for hardware blocks (wireless devices)

rfkill list

Inspect detailed device status

ethtool -i eth0
ip -s link show eth0
journalctl -k --grep="eth0" --all

For USB devices, check power state and firmware

lsusb -d vendor:product -v | grep -A 5 "MaxPower\|bMaxPower"
dmesg | grep -E "firmware|fw" | tail -10

Common Issues and Solutions

Driver not loading automatically: Check if the module exists and isn’t blacklisted:

find /lib/modules/$(uname -r) -name "*driver_name*"
grep -r "blacklist" /etc/modprobe.d/

Driver loads but interface doesn’t appear: Check kernel messages and driver initialization:

sudo modprobe -r driver_name
sudo modprobe driver_name
dmesg | tail -20

Interface shows as DOWN: Check hardware block state and driver state:

ip link show eth0
ethtool eth0 | grep -i "link detected"
rfkill list

Poor network performance: Check for driver issues, offloads, and ring buffers:

ethtool -k eth0  # check if offloads are enabled
ethtool -g eth0  # verify ring buffer sizes
ethtool -S eth0 | grep -i drop  # check for dropped packets

Most modern distributions manage network interfaces through systemd-networkd or NetworkManager. Always verify their status alongside driver information for complete visibility.