gistfile1.txt

#!/bin/bash
set -euo pipefail

echo "=== Detecting current netplan interface ==="

NETPLAN_FILE=$(ls /etc/netplan/*.yaml | head -n 1)

if [[ -z "$NETPLAN_FILE" ]]; then
  echo "ERROR: No netplan YAML file found in /etc/netplan"
  exit 1
fi

echo "Using netplan file: $NETPLAN_FILE"

# Grab the first interface name under 'ethernets:'
IFACE=$(awk '/ethernets:/ {getline; gsub(":", "", $1); print $1; exit}' "$NETPLAN_FILE")

if [[ -z "$IFACE" ]]; then
  echo "ERROR: Could not detect interface name from netplan"
  exit 1
fi

if [[ "$IFACE" == "eth0" ]]; then
  echo "Interface is already eth0. Nothing to do."
  exit 0
fi

echo "Detected netplan interface: $IFACE"

# Get MAC address for that interface
if [[ ! -d "/sys/class/net/$IFACE" ]]; then
  echo "ERROR: Interface $IFACE does not exist in /sys/class/net"
  exit 1
fi

MAC=$(cat /sys/class/net/$IFACE/address)
echo "MAC address: $MAC"

echo "=== Creating udev rule to rename $IFACE → eth0 ==="

sudo tee /etc/udev/rules.d/10-rename-to-eth0.rules >/dev/null <<EOF
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="$MAC", NAME="eth0"
EOF

echo "Udev rule created."

echo "=== Updating netplan configuration to use eth0 ==="

# Replace interface name in netplan
sudo sed -i "s/$IFACE:/eth0:/g" "$NETPLAN_FILE"
sudo sed -i "s/$IFACE/eth0/g" "$NETPLAN_FILE"

# Ensure nameservers block is in correct format if present
if grep -q "nameservers:" "$NETPLAN_FILE" && ! grep -q "addresses:" "$NETPLAN_FILE"; then
  echo "Fixing nameserver structure..."
  # This is conservative; if your file is already correct, this won't hurt
  sudo sed -i 's/nameservers:/nameservers:\n        addresses:/g' "$NETPLAN_FILE"
fi

echo "=== Validating netplan ==="
sudo netplan try --timeout 5 || {
  echo "Netplan validation failed. Check $NETPLAN_FILE"
  exit 1
}

echo "=== Applying netplan ==="
sudo netplan apply

echo "=== Rebooting to apply interface rename to eth0 ==="
sudo reboot