udhcpc 后台运行的方法【总结】

udhcpc 后台运行的方法【总结】  

最近在做项目的时候卡在了dhcp处，当没有网络的时候，板子一直发送dhcp请求，导致程序不往下执行，解决的办法是把它切换到后台运行，可是如何切换到后台呢，有办法，它自带参数可以实现该功能。如下：

   udhcpc -b -i eth0 -p /var/run/udhcpc.pid

解释一下，-b就是切换到后台指令，-i是指定使用哪个网络接口，双网卡的时候一定要使用它来指定eth0  or  eth1。

业务不熟练害死人啊，所以只要多看看源码，一般问题都能搞定。

下面引用网友的一篇文章：

udhcpc 的配置记录

 

udhcpc scripts

Here's some debian scripts I wrote for udhcpc 0.9.6. I wanted to make it easy to run local scripts for DHCP changes so I created /etc/udhcpc.d. All the /usr/share/udhcpc/default.* scripts have been merged into /etc/udhcpc.d/S50default. S99local is an example script that patches resolv.conf and calls a DNS update script.

/etc/init.d/udhcpc/etc/udhcpc.script/etc/udhcpc.d/S50default/etc/udhcpc.d/S99local

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Last modified: Mon Feb 4 10:23:49 PST 2002

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单调的分割线

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http://udhcp.busybox.net/README.udhcpc

udhcp client (udhcpc)--------------------The udhcp client negotiates a lease with the DHCP server and notifiesa set of scripts when a leases is obtained or lost.command line options-------------------The command line options for the udhcp client are:-c, --clientid=CLIENTID         Client identifier-H, --hostname=HOSTNAME         Client hostname-h,    Alias for -H-f, --foreground                Do not fork after getting lease-b, --background                Fork to background if lease cannot be                                immediately negotiated.-i, --interface=INTERFACE       Interface to use (default: eth0)-n, --now                       Exit with failure if lease cannot be                                immediately negotiated.-p, --pidfile=file              Store process ID of daemon in file-q, --quit                      Quit after obtaining lease-r, --request=IP                IP address to request (default: none)-s, --script=file               Run file at dhcp events (default:                                /usr/share/udhcpc/default.script)-v, --version                   Display versionIf the requested IP address cannot be obtained, the client accepts theaddress that the server offers.udhcp client scripts-------------------When an event occurs, udhcpc calls the action script. The script bydefault is /usr/share/udhcpc/default.script but this can be changed via the command line arguments. The three possible arguments to the script are: deconfig: This argument is used when udhcpc starts, and when a leases is lost. The script should put the interface in an up, but deconfigured state, ie: ifconfig $interface 0.0.0.0.  bound: This argument is used when udhcpc moves from an unbound, to a bound state. All of the paramaters are set in enviromental variables, The script should configure the interface, and set any other relavent parameters (default gateway, dns server,  etc).  renew: This argument is used when a DHCP lease is renewed. All of the paramaters are set in enviromental variables. This argument is used when the interface is already configured, so the IP address, will not change, however, the other DHCP paramaters, such as the default gateway, subnet mask, and dns server may change. nak: This argument is used with udhcpc receives a NAK message. The script with the deconfig argument will be called directly afterwards, so no changes to the network interface are neccessary. This hook is provided for purely informational purposes (the message option may contain a reason for the NAK).The paramaters for enviromental variables are as follows: $HOME  - The set $HOME env or "/" $PATH  - the set $PATH env or "/bin:/usr/bin:/sbin:/usr/sbin" $1  - What action the script should perform interface - The interface this was obtained on ip  - The obtained IP siaddr  - The bootp next server option sname  - The bootp server name option boot_file - The bootp boot file option subnet  - The assigend subnet mask timezone - Offset in seconds from UTC router  - A list of routers timesvr  - A list of time servers namesvr  - A list of IEN 116 name servers dns  - A list of DNS server logsvr  - A list of MIT-LCS UDP log servers cookiesvr - A list of RFC 865 cookie servers lprsvr  - A list of LPR servers hostname - The assigned hostname bootsize - The length in 512 octect blocks of the bootfile domain  - The domain name of the network swapsvr  - The IP address of the client's swap server rootpath - The path name of the client's root disk ipttl  - The TTL to use for this network mtu  - The MTU to use for this network broadcast - The broadcast address for this network ntpsrv  - A list of NTP servers wins  - A list of WINS servers lease  - The lease time, in seconds dhcptype - DHCP message type (safely ignored) serverid - The IP of the server message  - Reason for a DHCPNAK tftp  - The TFTP server name bootfile - The bootfile nameadditional options are easily added in options.c.note on udhcpc's random seed---------------------------udhcpc will seed its random number generator (used for generating xid's)by reading /dev/urandom. If you have a lot of embedded systems on the samenetwork, with no entropy, you can either seed /dev/urandom by a method ofyour own, or doing the following on startup:ifconfig eth0 > /dev/urandomin order to seed /dev/urandom with some data (mac address) unique to yoursystem. If reading /dev/urandom fails, udhcpc will fall back to its oldbehavior of seeding with time(0).signals accepted by udhcpc-------------------------udhcpc also responds to SIGUSR1 and SIGUSR2. SIGUSR1 will force a renew state,and SIGUSR2 will force a release of the current lease, and cause udhcpc togo into an inactive state (until it is killed, or receives a SIGUSR1). You donot need to sleep between sending signals, as signals received are processedsequencially in the order they are received.compile time options-------------------options.c contains a set of dhcp options for the client: name[10]: The name of the option as it will appear in scripts  flags: The type of option, as well as if it will be requested by the client (OPTION_REQ) code: The DHCP code for this option

浅析如何使用busybox的udhcpc实现开发板ip和dns自动获取
busybox中udhcpc的默认script脚本地址为
#define DEFAULT_SCRIPT   CONFIG_UDHCPC_DEFAULT_SCRIPT
#define CONFIG_UDHCPC_DEFAULT_SCRIPT "/usr/share/udhcpc/default.script"
我想之所以以它作为默认地址,肯定有他的道理,所以在这个地址上创建它[luther.gliethttp]

luther@gliethttp:/vobs/initramfs$ mkdir usr/share/udhcpc/ -p
luther@gliethttp:/vobs/initramfs$ cp ~/busybox-1.14.3/examples/udhcp/simple.script usr/share/udhcpc/default.script
luther@gliethttp:/vobs/initramfs$ chmod +x usr/share/udhcpc/default.script
在/etc/inittab中加入下面一行语句:
::once:"/sbin/udhcpc >/dev/null 2>&1" # udhcpc会退出,所以不能使用respawn,必须为once,1次,否则将一直出现udhcpc重启log信息
就这样简单的几行ip和dns就能自动获取了[luther.gliethttp]
其实有些东西就可以放在rcS等启动脚本中,有些可以到init脚本中去完成.
# /sbin/udhcpc
### adapter index 2
### adapter hardware address 00:00:00:00:08:36
udhcpc (v1.14.3) started
### vfork'ing and exec'ing /usr/share/udhcpc/default.script
### entering raw listen mode
### opening raw socket on ifindex 2
### got raw socket fd 5
### attached filter to raw socket fd 5
### bound to raw socket fd 5
### adding option 0x35
### adding option 0x3d
### adding option 0x3c
### adding option 0x39
Sending discover...
### Waiting on select...
### Got valid DHCP packet
### adding option 0x35
### adding option 0x3d
### adding option 0x3c
### adding option 0x32
### adding option 0x36
Sending select for 192.168.1.102...
### Waiting on select...
### Got valid DHCP packet
Lease of 192.168.1.102 obtained, lease time 172800
### vfork'ing and exec'ing /usr/share/udhcpc/default.script
deleting routers
route: SIOCDELRT: No such process
adding dns 211.161.46.84
adding dns 202.106.0.20
### entering none listen mode
#