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。