信號質(zhì)量指標 (SQI) 特性并非在所有 PHY 中都實現(xiàn)，它用于檢查信號質(zhì)量（0 表示無鏈路，7 表示最佳）。用于調(diào)試錯誤源頭，例如：鏈路穩(wěn)定但系統(tǒng)發(fā)現(xiàn)丟包。SQI 值較低，表示問題可能出在 MDI 接口（連接器側(cè)）內(nèi)部。如果器件的驅(qū)動程序中實現(xiàn)了 SQI，可以在 ethtool 命令中找到 SQI。如果只想顯示 SQI，可以使用 ethtool ethx | grep SQI。

ethtool eth3
Settings for eth3:
        Supported ports: [ TP    MII ]
        Supported link modes:   100baseT/Full
        Supported pause frame use: Symmetric
        Supports auto-negotiation: No
        Supported FEC modes: Not reported
        Advertised link modes:  Not reported
        Advertised pause frame use: Symmetric
        Advertised auto-negotiation: No
        Advertised FEC modes: Not reported
        Speed: 100Mb/s
        Duplex: Full
        Auto-negotiation: off
        master-slave cfg: forced master
        master-slave status: master
        Port: Twisted Pair
        PHYAD: 5
        Transceiver: external
        MDI-X: Unknown
        Supports Wake-on: d
        Wake-on: d
        Current message level: 0x000020f7 (8439)
                               drv probe link ifdown ifup rx_err tx_err hw
        Link detected: yes
        SQI: 4/7
ethtool eth3 | grep SQI
        SQI: 4/7