Shell 腳本自動修改 Linux 網卡 IP/子網遮罩/閘道：sed 就地替換配置檔並重啟網路

批次部署或遷移伺服器時，需快速修改網卡 IP 設定。本文提供一支參數化 Shell 腳本，讀取 /etc/sysconfig/network-scripts/ifcfg-eth0 与 /etc/sysconfig/network 現有值，以 sed -i 就地替換為新 IP/Netmask/Gateway，並自動重啟網路服務生效。附帶參數檢查、備份原檔、錯誤碼回傳、systemd 相容版本，適合納入 Ansible、Kickstart、PXE 自動化流程。

一、腳本完整內容 (ip_change.sh)

#!/bin/bash
# 自動修改網卡 IP/Netmask/Gateway
# 用法：./ip_change.sh NEW_IP NEW_NETMASK NEW_GATEWAY [INTERFACE]
# 範例：./ip_change.sh 192.168.10.50 255.255.255.0 192.168.10.1 eth0

set -euo pipefail

# 參數解析
NEW_IP=${1:-}
NEW_NETMASK=${2:-}
NEW_GATEWAY=${3:-}
IFACE=${4:-eth0}

if [[ -z "$NEW_IP" || -z "$NEW_NETMASK" || -z "$NEW_GATEWAY" ]]; then
    echo "Usage: $0 NEW_IP NEW_NETMASK NEW_GATEWAY [INTERFACE]"
    echo "Example: $0 192.168.10.50 255.255.255.0 192.168.10.1 eth0"
    exit 1
fi

# 配置檔路徑 (CentOS/RHEL 6/7)
IFCFG="/etc/sysconfig/network-scripts/ifcfg-$IFACE"
NETWORK="/etc/sysconfig/network"

# 檢查檔案存在
for f in "$IFCFG" "$NETWORK"; do
    if [[ ! -f "$f" ]]; then
        echo "ERROR: Config file not found: $f"
        exit 2
    fi
done

# 備份原檔 (含時間戳)
TS=$(date +%Y%m%d_%H%M%S)
cp "$IFCFG" "${IFCFG}.bak.$TS"
cp "$NETWORK" "${NETWORK}.bak.$TS"
echo "Backed up: ${IFCFG}.bak.$TS, ${NETWORK}.bak.$TS"

# 讀取舊值
OLD_IP=$(grep -i '^IPADDR=' "$IFCFG" | cut -d= -f2)
OLD_NETMASK=$(grep -i '^NETMASK=' "$IFCFG" | cut -d= -f2)
OLD_GATEWAY=$(grep -i '^GATEWAY=' "$NETWORK" | cut -d= -f2)

echo "Current: IP=$OLD_IP, NETMASK=$OLD_NETMASK, GATEWAY=$OLD_GATEWAY"
echo "New:     IP=$NEW_IP, NETMASK=$NEW_NETMASK, GATEWAY=$NEW_GATEWAY"

# 就地替換 (sed -i)
sed -i "s/^IPADDR=.*/IPADDR=$NEW_IP/" "$IFCFG"
sed -i "s/^NETMASK=.*/NETMASK=$NEW_NETMASK/" "$IFCFG"
# GATEWAY 可能在 ifcfg 或 network 中，兩邊都替換以防萬一
sed -i "s/^GATEWAY=.*/GATEWAY=$NEW_GATEWAY/" "$IFCFG"
sed -i "s/^GATEWAY=.*/GATEWAY=$NEW_GATEWAY/" "$NETWORK"

# 驗證替換結果
echo "=== Updated $IFCFG ==="
grep -E '^(IPADDR|NETMASK|GATEWAY)=' "$IFCFG"
echo "=== Updated $NETWORK ==="
grep -E '^GATEWAY=' "$NETWORK"

# 重啟網路服務
echo "Restarting network..."
if command -v systemctl &>/dev/null && systemctl is-active --quiet NetworkManager; then
    # NetworkManager 管理介面
    nmcli con reload
    nmcli con up "$IFACE"
else
    # 傳統 network service
    systemctl restart network 2>/dev/null || /etc/init.d/network restart
fi

# 等待介面啟動並驗證
sleep 3
CURRENT_IP=$(ip -4 addr show "$IFACE" | grep -oP 'inet \K[\d.]+')
if [[ "$CURRENT_IP" == "$NEW_IP" ]]; then
    echo "SUCCESS: Interface $IFACE now has IP $CURRENT_IP"
    exit 0
else
    echo "WARNING: IP not updated yet (current: $CURRENT_IP). Check logs."
    exit 3
fi

二、關鍵技術細節

三、進階擴充：支援多介面、靜態路由、DNS

# 多介面迴圈版本片段
for IFACE in eth0 eth1; do
    # 為每張卡準備對應參數陣列
    # IP_ARRAY=(192.168.10.50 10.0.0.5)
    # ...
done

# 修改 DNS (resolve.conf 或 ifcfg 中 DNS1/DNS2)
sed -i "/^DNS1=/d;/^DNS2=/d" "$IFCFG"
echo "DNS1=8.8.8.8" >> "$IFCFG"
echo "DNS2=1.1.1.1" >> "$IFCFG"

# 新增靜態路由
echo "192.168.20.0/24 via 192.168.10.1 dev $IFACE" > "/etc/sysconfig/network-scripts/route-$IFACE"

四、systemd 服務化 (開機自動套用)

cat > /etc/systemd/system/ip-change@.service <<'EOF'
[Unit]
Description=Apply IP config for %i
Before=network-online.target
Wants=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/local/sbin/ip_change.sh 192.168.10.50 255.255.255.0 192.168.10.1 %i
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
EOF

systemctl daemon-reload
systemctl enable ip-change@eth0

五、常見問題與排解