最近 打算配开发板的socket通讯，打印环境变量发现却没有 127.0.0.1
/ # ifconfig -a
eth0 Link encap:Ethernet HWaddr 86:43:C9:A1:DF:C8
inet addr:192.168.1.140 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:21 Base address:0x4000 lo Link encap:Local Loopback
LOOPBACK MTU:16436 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
查阅资料得知 需要手动配置本地回环路由lo 【 ifconfig lo up 】
http://blog.csdn.net/liwentao1091/article/details/8276532
/ # ifconfig lo up / # ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:0C:29:7D:85:2C
inet addr:192.168.1.101 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Interrupt:17 Base address:0x2024 lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:10070 errors:0 dropped:0 overruns:0 frame:0
TX packets:10070 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:87913017 (83.8 MiB) TX bytes:87913017 (83.8 MiB)
本地回环路由lo作用：
一是测试本机的网络配置，能PING通127.0.0.1说明本机的网卡和IP协议安装都没有问题；
另一个作用是某些SERVER/CLIENT的应用程序在运行时需调用服务器上的资源，一般要指定SERVER的IP地址，但当该程序要在同一台机器上运行而没有别的SERVER时就可以把SERVER的资源装在本机，SERVER的IP地址设为127.0.0.1也同样可以运行。