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initramfs-tools自带的dhcp有时不能获取到ip，修改使用udhcpc配置dhcp，先禁用自带的网络配置：

sed -i -e '/configure_networking\(\)/{n; a\' -e 'return 0' -e '}' /usr/share/initramfs-tools/scripts/functions

初始化时启动udhcpc：

cat << EOF > /usr/share/initramfs-tools/scripts/init-premount/00-network
#!/bin/sh
PREREQ=""

prereqs() {
  echo "$PREREQ"
}

case "$1" in
  prereqs)
    prereqs
    exit 0
    ;;
esac

interface=eth0
ip link set dev $interface up
udhcpc -i $interface -t 5 -T 5 -A 30 -b -s /scripts/udhcpc.script

exit 0
EOF
chmod +x /usr/share/initramfs-tools/scripts/init-premount/00-network

udhcpc调用的ip配置脚本：

cat << EOF > /etc/initramfs-tools/scripts/udhcpc.script 
#!/bin/sh

case "$1" in
  BOUND|bound|RENEW|renew)
        # 配置网卡
        ip addr flush dev $interface
        ip addr add $ip/$mask dev $interface
        ip link set dev $interface up

        # 配置默认路由
        ip route del default 2>/dev/null
        if [ -n "$router" ]; then
          for gw in $router; do
            ip route add default via $gw dev $interface
          done
        fi

        # 配置 DNS
        if [ -n "$dns" ]; then
          for ns in $dns; do
            echo "nameserver $ns" >> /etc/resolv.conf
          done
        fi

        ;;
esac

exit 0
EOF
chmod +x /etc/initramfs-tools/scripts/udhcpc.script