为了检测固定网线口的拔插消息，在busybox里配置了ifplugd
ptions:
-n Don't daemonize
-s Don't log to syslog
-i IFACE Interface
-f/-F Treat link detection error as link down/link up
(otherwise exit on error)
-a Don't up interface at each link probe
-M Monitor creation/destruction of interface
(otherwise it must exist)
-r PROG Script to run
-x ARG Extra argument for script
-I Don't exit on nonzero exit code from script
-p Don't run script on daemon startup
-q Don't run script on daemon quit
-l Run script on startup even if no cable is detected
-t SECS Poll time in seconds
-u SECS Delay before running script after link up
-d SECS Delay after link down
-m MODE API mode (mii, priv, ethtool, wlan, iff, auto)
-k Kill running daemon
系统起来后运行ifplugd -nI -i eth0 -r /etc/network/if.sh会在当前shell启动ifplugd并检测网口状态
# ifplugd -nI -i eth0 -r /etc/network/if.sh
ifplugd(eth0): started: BusyBox v1.16.1 (2011-01-28 11:42:48 HKT)
ifplugd(eth0): using SIOCETHTOOL detection mode
ifplugd(eth0): link is up
ifplugd(eth0): executing '/etc/network/if.sh eth0 up'
ifplugd(eth0): exit code: 0
GMAC:eth0: Link is down
ifplugd(eth0): link is down
ifplugd(eth0): executing '/etc/network/if.sh eth0 down'
ifplugd(eth0): exit code: 0
GMAC:eth0 : Link is Up
ifplugd(eth0): link is up
ifplugd(eth0): executing '/etc/network/if.sh eth0 up'
ifplugd(eth0): exit code: 0
去掉-n会以daemon方式后台运行。