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+# Debian网络异常和日志查看命令记录
+## 1. 手动协商命令
+```bash
+ethtool -r lan2
+```
+
+## 2. WatchDog日志查看。
+
+看最近运行日志
+```bash
+journalctl -u lan2-link-watchdog.service -n 100 --no-pager
+```
+
+实时看：
+```bash
+journalctl -u lan2-link-watchdog.service -f
+```
+只看有没有触发过重新协商
+
+这个最有用：
+```bash
+journalctl -u lan2-link-watchdog.service --no-pager | grep -E 'BAD|ACTION|VERIFY|cooldown'
+```
+如果没输出，说明从启动到现在没有触发过异常处理。
+
+如果触发过，会看到类似：
+```bash
+BAD round 1/2: received 92/100, loss=8
+BAD round 2/2: received 90/100, loss=10
+ACTION: renegotiate lan2 because link quality is bad
+VERIFY after renegotiate: received 100/100
+cooldown 300s
+```
+其中关键是这行：
+```bash
+ACTION: renegotiate lan2 because link quality is bad
+```
+看到它就说明 watchdog 执行过：
+```bash
+ethtool -r lan2
+```
+看今天触发过几次
+```bash
+journalctl -u lan2-link-watchdog.service --since today --no-pager | grep -c 'ACTION: renegotiate'
+```
+输出 0 就是今天没触发。
+
+看当前这次开机以来有没有触发
+```bash
+journalctl -b -u lan2-link-watchdog.service --no-pager | grep -E 'BAD|ACTION|VERIFY|cooldown'
+```
+看当前状态
+```bash
+systemctl status lan2-link-watchdog.service --no-pager
+```
+另外，因为脚本里有这句：
+```bash
+logger -t lan2-watchdog "$*"
+```
+所以你也可以按 tag 查：
+```bash
+journalctl -t lan2-watchdog --no-pager
+```
+不过平时用这个就够了：
+```bash
+journalctl -u lan2-link-watchdog.service --no-pager | grep -E 'BAD|ACTION|VERIFY|cooldown'
+```
+如果以后重启后想保留更久的日志，可以确认一下 journald 是否持久化：
+```bash
+journalctl --list-boots
+```
+如果能看到多次 boot 记录，说明日志是保留的。否则以后我再帮你改成单独写 /var/log/lan2-link-watchdog.log 也行。
+
+## 3. 创建 lan3 watchdog 脚本
+```bash
+sudo tee /usr/local/sbin/lan3-link-watchdog.sh >/dev/null <<'EOF'
+#!/bin/bash
+
+IFACE="lan3"
+CHECK_IFACE="lan3"
+GW="192.168.3.1"
+
+COUNT=100
+MIN_RECV=99             # RECV < 99 才算异常；也就是 98/100 或更低
+BAD_ROUNDS_LIMIT=2      # 连续 2 轮异常才执行 ethtool -r
+SLEEP_OK=60             # 正常时，每轮结束后休息 60 秒
+COOLDOWN=300            # 重协商后冷却 300 秒
+ARPING_TIMEOUT=130      # arping 100 次大约 100 秒，给 130 秒超时
+
+BAD_ROUNDS=0
+
+log() {
+    logger -t lan3-watchdog "$*"
+    echo "$(date '+%F %T') $*"
+}
+
+ARPING_BIN="$(command -v arping || true)"
+ETHTOOL_BIN="$(command -v ethtool || true)"
+
+if [ -z "$ARPING_BIN" ]; then
+    log "ERROR: arping not found"
+    exit 1
+fi
+
+if [ -z "$ETHTOOL_BIN" ]; then
+    log "ERROR: ethtool not found"
+    exit 1
+fi
+
+log "started: IFACE=$IFACE CHECK_IFACE=$CHECK_IFACE GW=$GW COUNT=$COUNT MIN_RECV=$MIN_RECV BAD_ROUNDS_LIMIT=$BAD_ROUNDS_LIMIT"
+
+while true; do
+    if [ ! -d "/sys/class/net/$IFACE" ]; then
+        log "WARN: interface $IFACE not found, sleep ${SLEEP_OK}s"
+        sleep "$SLEEP_OK"
+        continue
+    fi
+
+    if [ ! -d "/sys/class/net/$CHECK_IFACE" ]; then
+        log "WARN: check interface $CHECK_IFACE not found, sleep ${SLEEP_OK}s"
+        sleep "$SLEEP_OK"
+        continue
+    fi
+
+    OUT=$(LANG=C timeout "$ARPING_TIMEOUT" "$ARPING_BIN" -I "$CHECK_IFACE" -c "$COUNT" "$GW" 2>&1)
+
+    SENT=$(echo "$OUT" | awk '/^Sent / {print $2}')
+    RECV=$(echo "$OUT" | awk '/^Received / {print $2}')
+
+    if [ -z "$RECV" ]; then
+        BAD_ROUNDS=$((BAD_ROUNDS + 1))
+        log "WARN: could not parse arping result, bad round $BAD_ROUNDS/$BAD_ROUNDS_LIMIT"
+        log "$OUT"
+
+        if [ "$BAD_ROUNDS" -ge "$BAD_ROUNDS_LIMIT" ]; then
+            log "ACTION: renegotiate $IFACE because arping result could not be parsed repeatedly"
+            "$ETHTOOL_BIN" -r "$IFACE"
+
+            BAD_ROUNDS=0
+            log "cooldown ${COOLDOWN}s"
+            sleep "$COOLDOWN"
+        else
+            sleep "$SLEEP_OK"
+        fi
+
+        continue
+    fi
+
+    LOSS=$((COUNT - RECV))
+
+    if [ "$RECV" -gt "$COUNT" ]; then
+        log "OK with extra replies: received $RECV/$COUNT, likely another arping is running"
+        BAD_ROUNDS=0
+        sleep "$SLEEP_OK"
+        continue
+    fi
+
+    if [ "$RECV" -lt "$MIN_RECV" ]; then
+        BAD_ROUNDS=$((BAD_ROUNDS + 1))
+        log "BAD round $BAD_ROUNDS/$BAD_ROUNDS_LIMIT: received $RECV/$COUNT, loss=$LOSS"
+
+        if [ "$BAD_ROUNDS" -ge "$BAD_ROUNDS_LIMIT" ]; then
+            log "ACTION: renegotiate $IFACE because link quality is bad"
+            "$ETHTOOL_BIN" -r "$IFACE"
+
+            sleep 5
+
+            VERIFY=$(LANG=C timeout "$ARPING_TIMEOUT" "$ARPING_BIN" -I "$CHECK_IFACE" -c "$COUNT" "$GW" 2>&1)
+            VERIFY_RECV=$(echo "$VERIFY" | awk '/^Received / {print $2}')
+
+            log "VERIFY after renegotiate: received ${VERIFY_RECV:-unknown}/$COUNT"
+
+            BAD_ROUNDS=0
+            log "cooldown ${COOLDOWN}s"
+            sleep "$COOLDOWN"
+        else
+            sleep "$SLEEP_OK"
+        fi
+    else
+        if [ "$BAD_ROUNDS" -ne 0 ]; then
+            log "RECOVERED without action: received $RECV/$COUNT"
+        fi
+
+        log "OK: received $RECV/$COUNT"
+        BAD_ROUNDS=0
+        sleep "$SLEEP_OK"
+    fi
+done
+EOF
+```
+给脚本赋权限
+```bash
+sudo chmod +x /usr/local/sbin/lan3-link-watchdog.sh
+```
+
+## 4. 创建 lan3 systemd 服务
+```bash
+sudo tee /etc/systemd/system/lan3-link-watchdog.service >/dev/null <<'EOF'
+[Unit]
+Description=Watch lan3 link quality and renegotiate on packet loss
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+ExecStart=/usr/local/sbin/lan3-link-watchdog.sh
+Restart=always
+RestartSec=10
+
+[Install]
+WantedBy=multi-user.target
+EOF
+```
+然后加载一下：
+```bash
+sudo systemctl daemon-reload
+```
+确认 lan3 通了之后，再启用：
+```bash
+sudo systemctl enable lan3-link-watchdog.service
+sudo systemctl start lan3-link-watchdog.service
+```