由于ifconfig命令没法看到网卡的一些状态， 以下有5种方法查看网卡状态，是否连通网线
How to check physical Network Link Status on Linux (RHEL/Centos)
原文：http://linuxsupporttips.wordpress.com/2011/08/01/how-to-check-physical-network-link-status-on-linux-rhelcentos/
There are several ways to check Link status on RHEL,
As far i used to check by 5- ways. Refer Below
1)
# dmesg | grep eth
.....
e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
e1000: eth1 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
2)
# mii-tool
eth0: negotiated 100baseTx-FD, link ok
eth1: negotiated 100baseTx-FD, link ok
3)
# ethtool eth0 | grep Link
Link detected: yes
4)
# cat /sys/class/net/eth0/operstate
up
5)
# ip link show
2: eth0: mtu 1500 qdisc pfifo_fast qlen 1000 link/ether 00:0c:29:b0:ef:e4 brd ff:ff:ff:ff:ff:ff
3: eth1: mtu 1500 qdisc pfifo_fast qlen 1000 link/ether 00:0c:29:b0:ef:ee brd ff:ff:ff:ff:ff:ff