SYNOPSIS

     dhcpcd [-bdeknpqABDEGKLTV] [-c, --script script] [-f, --config file]             [-h, --hostname hostname] [-i, --vendorclassid vendorclassid]             [-l, --leasetime seconds] [-m, --metric metric]             [-o, --option option] [-r, --request address]             [-s, --inform address[/cidr]] [-t, --timeout seconds]             [-u, --userclass class] [-v, --vendor code, value]             [-y, --reboot seconds] [-z, --allowinterfaces pattern]             [-C, --nohook hook] [-F, --fqdn FQDN] [-I, --clientid clientid]             [-O, --nooption option] [-Q, --require option]             [-S, --static value] [-X, --blacklist address[/cidr]]             [-Z, --denyinterfaces pattern] [interface] [...]      dhcpcd -k, --release [interface]      dhcpcd -x, --exit [interface] DESCRIPTION      dhcpcd is an implementation of the DHCP client specified in RFC 2131.      dhcpcd gets the host information (IP address, routes, etc) from a DHCP      server and configures the network interface of the machine on which it is      running.  dhcpcd then runs the configuration script which writes DNS      information to resolvconf(8), if available, otherwise directly to      /etc/resolv.conf.  If the hostname is currenly blank, (null) or localhost      then dhcpcd sets the hostname to the one supplied by the DHCP server.      dhcpcd then daemonises and waits for the lease renewal time to lapse.      Then it attempts to renew its lease and reconfigure if the new lease      changes.      dhcpcd is also an implementation of the BOOTP client specified in RFC      951.    Local Link configuration      If dhcpcd failed to obtain a lease, it probes for a valid IPv4LL address      (aka ZeroConf, aka APIPA).  Once obtained it restarts the process of      looking for a DHCP server to get a proper address.      When using IPv4LL, dhcpcd nearly always succeeds and returns an exit code      of 0.  In the rare case it fails, it normally means that there is a      reverse ARP proxy installed which always defeats IPv4LL probing.  To dis-      able this behaviour, you can use the -L, --noipv4ll option.    Multiple interfaces      dhcpcd can be run per interface or as a single instance to manage all      interfaces.  If a list of interfaces are given on the command line, then      dhcpcd only works with those interfaces, otherwise dhcpcd discovers      available interfaces.  If link management is enabled and no interfaces      are given on the command line, dhcpcd forks to the background right away.      Interfaces are preferred by carrier, DHCP lease/IPv4LL and then lowest      metric.  For systems that support route metrics, each route will be      tagged with the metric, otherwise dhcpcd changes the routes to use the      interface with the same route and the lowest metric.  See options below      for controlling what interfaces we allow and deny through the use of pat-      terns. Also, see the BUGS section if dhcpcd runs on a BSD system.    Hooking into DHCP events      dhcpcd runs /libexec/dhcpcd-run-hooks, or the script specified by the -c,      --script option.  This script runs each script found in      /libexec/dhcpcd-hooks in a lexical order.  The default installation sup-      plies the scripts 01-test, 10-mtu, 20-resolv.conf and 30-hostname.  You      can disable each script by using the -C, --nohook option.  See      dhcpcd-run-hooks(8) for details on how these scripts work.  dhcpcd cur-      rently ignores the exit code of the script.    Fine tuning      You can fine tune the behaviour of dhcpcd with the following options:      -b, --background              Background immediately.  This is useful for startup scripts which              don't disable link messages for carrier status.      -c, --script script              Use this script instead of the default /libexec/dhcpcd-run-hooks.      -d, --debug              Echo debug and informational messages to the console.  Subsequent              debug options stop dhcpcd from daemonising.      -e, --reconfigure              dhcpcd will re-apply IP address, routing and run              dhcpcd-run-hooks(8) for each interface.  This is useful so that a              3rd party such as PPP or VPN can change the routing table and /              or DNS, etc and then instruct dhcpcd to put things back after-              wards.  dhcpcd does not read a new configuration when this hap-              pens - you should rebind if you need that functionality.      -f, --config file              Specify a config to load instead of /etc/dhcpcd.conf.  dhcpcd              always processes the config file before any command line options.      -h, --hostname hostname              By default, dhcpcd sends the current hostname to the DHCP server              so it can register in DNS.  You can use this option to specify              the hostname sent, or an empty string to stop any hostname from              being sent.      -i, --vendorclassid vendorclassid              Override the vendorclassid field sent. The default is dhcpcd              <version>.  If not set then none is sent.      -k, --release              This causes an existing dhcpcd process running on the interface              to release its lease, deconfigure the interface and then exit.              dhcpcd then waits until this process has exited.      -l, --leasetime seconds              Request a specific lease time in seconds.  By default dhcpcd does              not request any lease time and leaves the it in the hands of the              DHCP server.      -m, --metric metric              Metrics are used to prefer an interface over another one, lowest              wins.  dhcpcd will supply a default metic of 200 +              if_nametoindex(3).  An extra 100 will be added for wireless              interfaces.      -o, --option option              Request the DHCP option variable for use in              /libexec/dhcpcd-run-hooks.      -n, --rebind              Notifies an existing dhcpcd process running on the interface to              rebind it's lease.  dhcpcd will not re-configure itself or use              any other command line arguments.  dhcpcd will timeout the rebind              after 30 seconds at which point the lease will be expired and              dhcpcd will enter the discovery state to obtain a new lease.  Use              the -t, --timeout option to change this.  If dhcpcd is not run-              ning, then it starts up as normal.  This option used to be renew,              but rebind is more accurate as we need to broadcast the request              instead of unicasting.      -p, --persistent              dhcpcd normally deconfigures the interface and configuration when              it exits.  Sometimes, this isn't desirable if for example you              have root mounted over NFS.  You can use this option to stop this              from happening.      -r, --request [address]              dhcpcd normally sends a DHCP DISCOVER to find servers to offer an              address.  dhcpcd then requests the address used.  You can use              this option to skip the BROADCAST step and just request the              address.  The downside is if you request an address the DHCP              server does not know about or the DHCP server is not authorative,              it will remain silent.  In this situation, we go back to the init              state and DISCOVER again.  If no address is given then the first              address currently assigned to the interface is used.      -s, --inform [address[/cidr]]              Behaves like -r, --request as above, but sends a DHCP INFORM              instead of a REQUEST.  This does not get a lease as such, just              notifies the DHCP server of the address in use.  You should also              include the optional cidr network number in-case the address is              not already configured on the interface.  dhcpcd remains running              and pretends it has an infinite lease.  dhcpcd will not de-con-              figure the interface when it exits.  If dhcpcd fails to contact a              DHCP server then it returns a failure instead of falling back on              IPv4LL.      -t, --timeout seconds              Timeout after seconds, instead of the default 30.  A setting of 0              seconds causes dhcpcd to wait forever to get a lease.      -u, --userclass class              Tags the DHCP message with the userclass class.  DHCP servers use              this give members of the class DHCP options other than the              default, without having to know things like hardware address or              hostname.      -v, --vendor code,value              Add an enscapulated vendor option.  code should be between 1 and              254 inclusive.  Examples.              Set the vendor option 01 with an IP address.                    dhcpcd -v 01,192.168.0.2 eth0              Set the vendor option 02 with a hex code.                    dhcpcd -v 02,01:02:03:04:05 eth0              Do the above and set a third option with a string and not an IP              address.                    dhcpcd -v 01,192.168.0.2 -v 02,01:02:03:04:05 -v                    03,"192.168.0.2" eth0      -x, --exit              This will signal an existing dhcpcd process running on the              interface to deconfigure the interface and exit.  dhcpcd then              waits until this process has exited.      -y, --reboot seconds              Allow reboot seconds before moving to the discover phase if we              have an old lease to use.  The default is 10 seconds.  A setting              if 0 seconds causes dhcpcd to skip the reboot phase and go              straight into discover.      -D, --duid              Generate an RFC 4361 compliant clientid.  This requires persis-              tent storage and not all DHCP servers work with it so it's not              enabled by default.  dhcpcd generates the DUID and stores in it              /etc/dhcpcd.duid This file should not be copied to other hosts.      -E, --lastlease              If dhcpcd cannot obtain a lease, then try to use the last lease              acquired for the interface.  If the -p, --persistent option is              not given then the lease is used if it hasn't expired.      -F, --fqdn fqdn              Requests that the DHCP server updates DNS using FQDN instead of              just a hostname.  Valid values for fqdn are disable, none, ptr              and both.  dhcpcd itself never does any DNS updates.  dhcpcd              encodes the FQDN hostname as specified in RFC1035.      -I, --clientid clientid              Send the clientid.  If the string is of the format 01:02:03 then              it is encoded as hex.  For interfaces whose hardware address is              longer than 8 bytes, or if the clientid is an empty string then              dhcpcd sends a default clientid of the hardware family and the              hardware address.    Restricting behaviour      dhcpcd will try to do as much as it can by default.  However, there are      sometimes situations where you don't want the things to be configured      exactly how the the DHCP server wants.  Here are some options that deal      with turning these bits off.      -q, --quiet              Quiet dhcpcd on the command line, only warnings and errors will              be displayed.  The messages are still logged though.      -z, --allowinterfaces pattern              When discovering interfaces, the interface name must match              pattern which is a space or comma separated list of patterns              passed to fnmatch(3).  If the same interface is matched in -Z,              --denyinterfaces then it is still denied.      -A, --noarp              Don't request or claim the address by ARP.  This also disables              IPv4LL.      -B, --nobackground              Don't run in the background when we acquire a lease.  This is              mainly useful for running under the control of another process,              such as a debugger or a network manager.      -C, --nohook script              Don't run this hook script.  Matches full name, or prefixed with              2 numbers optionally ending with .sh.              So to stop dhcpcd from touching your DNS or MTU settings you              would do:-                    dhcpcd -C resolv.conf -C mtu eth0      -G, --nogateway              Don't set any default routes.      -K, --nolink              Don't receive link messages for carrier status.  You should only              have to use this with buggy device drivers or running dhcpcd              through a network manager.      -L, --noipv4ll              Don't use IPv4LL (aka APIPA, aka Bonjour, aka ZeroConf).      -O, --nooption option              Don't request the specified option.  If no option given, then              don't request any options other than those to configure the              interface and routing.      -Q, --require option              Requires the option to be present in all DHCP messages, otherwise              the message is ignored.  To enforce that dhcpcd only responds to              DHCP servers and not BOOTP servers, you can -Q dhcp_message_type.      -S, --static value              Configures a static value.  If you set ip_address then dhcpcd              will not attempt to obtain a lease and just use the value for the              address with an infinite lease time.              Here is an example which configures a static address, routes and              dns.                    dhcpcd -S ip_address=192.168.0.10/24                     -S routers=192.168.0.1                     -S domain_name_servers=192.168.0.1                     eth0      -T, --test              On receipt of OFFER messages just call /libexec/dhcpcd-run-hooks              with the reason of TEST which echo's the DHCP variables found in              the message to the console.  The interface configuration isn't              touched and neither are any configuration files.      -V, --variables              Display a list of option codes and the associated variable for              use in dhcpcd-run-hooks(8).  Variables are prefixed with new_ and              old_ unless the option number is -.  Variables without an option              are part of the DHCP message and cannot be directly requested.      -X, --blacklist address[/cidr]              Ignore all packets from address[/cidr].      -Z, --denyinterfaces pattern              When discovering interfaces, the interface name must not match              pattern which is a space or comma separated list of patterns              passed to fnmatch(3). You should read the  dhcpcd.conf man page and put your options into /etc/dhcpcd.conf. The default configuration file should work for most people just fine. Here it is, in case you lose it. # A sample configuration for dhcpcd. # See dhcpcd.conf(5) for details. # We normally want to inform the DHCP server of our hostname for DDNS. hostname # A list of options we should request from the DHCP server. option domain_name_servers, domain_name, domain_search, host_name # Most distros have ntp support. option ntp_servers # We should behave nicely on networks and respect their MTU. # However, a lot of buggy DHCP servers set invalid MTUs so this is not # enabled by default. #option interface_mtu # We provide a hook script to lookup the hostname if not set by the DHCP # server, but we should not run it by default. nohook lookup-hostname

一些总结：

1.dhcpcd配置静态ip。

编写配置文件dhcpcd.conf，此文件安卓环境下默认在/system/etc/dhcpcd/目录下，也可使用-f参数指定配置文件路径。配置静态ip，内容可如下所示：

2.dhcp对接完毕后，在setting里面点设置（动态获取或静态配置）的时候会出现失败的情况，失败后再次点设置就会成功。

此问题是是由于对于一个网络接口（eth0），只能有一个dhcpcd的实例运行，开机的时候dhcpcd就运行在后台了，会在/data/misc/dhcp/目录下生成一个.pid文件，如果再次点设置，会通过libnetutiles.so重新启动dhcpcd，检测到/data/misc/dhcp/下的pid文件，就会失败返回，返回前会把.pid文件删除，下次再调用，就会成功了。一种解决办法就是在调用前把pid文件删除就好了

3.dhcp添加option 60字段

dhcpcd可配置发送option 60 字段，添加“-i vendor_class_id”参数就可以，但是加完后，需要在源码中加入验证的代码，不含有相同option 60字段的offer以及ACK，扔掉，这样就只响应特定的dhcp服务器了。