ifconfigは誰でも知ってるけど、こっちは意外と覚えてない事が多い。

# ethtool eth0
【出力例】
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: umbg
        Wake-on: g
        Current message level: 0x00000003 (3)
        Link detected: yes

あれ？そもそもこのNICってgigabitイーサだっけ？どうだっけ？なんて基本的な事がすっぽりもれてたりしないように。。。
ifconfigとかnetwork-scripts/ifcfg-eth0とかでは確認できない詳細を見る必要がたまーにあるときに覚えてると便利。