DHCPでもらっていたIPをそのまま固定するシェルスクリプト

dhcp-static.sh

#!/bin/bash
set -e

echo "[*] Detecting interface (IPv4 default)..."
IFACE=$(ip -4 route show default | awk '{print $5}' | head -n1)

echo "[*] Detecting current IPv4 (non-secondary)..."
ADDR=$(ip -4 addr show "$IFACE" \
  | awk '/inet / && $0 !~ /secondary/ {print $2}' \
  | head -n1)

echo "[*] Detecting gateway..."
GATEWAY=$(ip -4 route show default | awk '{print $3}' | head -n1)

echo "[*] Detecting DNS (IPv4 only)..."
DNS=$(resolvectl dns "$IFACE" 2>/dev/null \
  | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}' \
  | head -n1)

NETPLAN_FILE="/etc/netplan/01-static-${IFACE}.yaml"

echo "[*] Backing up other netplan configs..."
for f in /etc/netplan/*.yaml; do
  if [[ "$f" != "$NETPLAN_FILE" ]]; then
    mv "$f" "$f.bak"
  fi
done

echo "[*] Writing static netplan config..."
cat <<EOF | tee "$NETPLAN_FILE" >/dev/null
network:
  version: 2
  renderer: networkd
  ethernets:
    $IFACE:
      dhcp4: no
      dhcp6: no
      accept-ra: no
      addresses:
        - $ADDR
      routes:
        - to: default
          via: $GATEWAY
      nameservers:
        addresses:
          - $DNS
EOF

chmod 600 "$NETPLAN_FILE"

echo "[*] Disabling cloud-init network config..."
mkdir -p /etc/cloud/cloud.cfg.d
cat <<EOF | tee /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg >/dev/null
network: {config: disabled}
EOF

echo "[*] Cleaning cloud-init..."
cloud-init clean || true

echo "[*] Removing DHCP leases..."
rm -f /run/systemd/netif/leases/*
rm -f /var/lib/dhcp/dhclient*.lease* || true

echo "[*] Restarting network stack..."
systemctl restart systemd-networkd

echo "[*] Applying netplan..."
netplan apply

echo
echo "[✓] Finished. Verify with:"
echo "    ip addr show $IFACE"