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.Dd August 20, 2008 .Dt DHCPCD 8 SMM .Sh NAME .Nm dhcpcd .Nd an RFC 2131 compliant DHCP client .Sh SYNOPSIS .Nm .Op Fl bdknpqABDEGKLSTV .Op Fl c , -script Ar script .Op Fl f , -config Ar file .Op Fl h , -hostname Ar hostname .Op Fl i , -vendorclassid Ar vendorclassid .Op Fl l , -leasetime Ar seconds .Op Fl m , -metric Ar metric .Op Fl o , -option Ar option .Op Fl r , -request Ar address .Op Fl s , -inform Ar address Ns Op Ar /cidr .Op Fl t , -timeout Ar seconds .Op Fl u , -userclass Ar class .Op Fl v , -vendor Ar code , Ar value .Op Fl C , -nohook Ar hook .Op Fl F , -fqdn Ar FQDN .Op Fl I , -clientid Ar clientid .Op Fl O , -nooption Ar option .Op Fl Q , -require Ar option .Op Fl X , -blacklist Ar address .Ar interface .Nm .Fl k , -release .Ar interface .Nm .Fl x , -exit .Ar interface .Sh DESCRIPTION .Nm is an implementation of the DHCP client specified in .Li RFC 2131 . .Nm gets the host information
o IP address, routes, etc
c from a DHCP server and configures the network .Ar interface of the machine on which it is running. .Nm then runs the configuration script which writes DNS information to .Xr resolvconf 8 , if available, otherwise directly to
a /etc/resolv.conf . If the hostname is currenly blank, (null) or localhost then .Nm sets the hostname to the one supplied by the DHCP server. .Nm 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. .Ss Local Link configuration If .Nm failed to obtain a lease, it probes for a valid IPv4LL address
o aka ZeroConf, aka APIPA
c . Once obtained it restarts the process of looking for a DHCP server to get a proper address.
p When using IPv4LL, .Nm 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 disable this behaviour, you can use the .Fl L , -noipv4ll option. .Ss Hooking into DHCP events .Nm runs
a /system/etc/dhcpcd/dhcpcd-run-hooks , or the script specified by the .Fl c , -script option. This script runs each script found in
a /system/etc/dhcpcd/dhcpcd-hooks in a lexical order. The default installation supplies the scripts
a 01-test ,
a 10-mtu ,
a 20-resolv.conf and
a 30-hostname . You can disable each script by using the .Fl C , -nohook option. See .Xr dhcpcd-run-hooks 8 for details on how these scripts work. .Nm currently ignores the exit code of the script. .Ss Fine tuning You can fine tune the behaviour of .Nm with the following options: l -tag -width indent t Fl b , -background Background immediately. This is useful for startup scripts which don't disable link messages for carrier status. t Fl c , -script Ar script Use this .Ar script instead of the default
a /system/etc/dhcpcd/dhcpcd-run-hooks . t Fl d , -debug Echo debug and informational messages to the console. Subsequent debug options stop .Nm from daemonising. t Fl f , -config Ar file Specify a config to load instead of
a /system/etc/dhcpcd/dhcpcd.conf . .Nm always processes the config file before any command line options. t Fl h , -hostname Ar hostname By default, .Nm sends the current hostname to the DHCP server so it can register in DNS. You can use this option to specify the .Ar hostname sent, or an empty string to stop any .Ar hostname from being sent. t Fl i , -vendorclassid Ar vendorclassid Override the .Ar vendorclassid field sent. The default is dhcpcd <version>. If not set then none is sent. t Fl k , -release This causes an existing .Nm process running on the .Ar interface to release its lease, deconfigure the .Ar interface and then exit. .Nm then waits until this process has exited. t Fl l , -leasetime Ar seconds Request a specific lease time in .Ar seconds . By default .Nm does not request any lease time and leaves the it in the hands of the DHCP server. t Fl m , -metric Ar metric Added routes will use the .Ar metric on systems where this is supported
o presently only Linux
c . Route metrics allow the addition of routes to the same destination across different interfaces, the lower the metric the more it is preferred. t Fl o , -option Ar option Request the DHCP .Ar option variable for use in
a /system/etc/dhcpcd/dhcpcd-run-hooks . t Fl n , -rebind Notifies an existing .Nm process running on the .Ar interface to rebind it's lease. .Nm will not re-configure itself or use any other command line arguments. .Nm will timeout the rebind after 30 seconds at which point the lease will be expired and .Nm will enter the discovery state to obtain a new lease. Use the .Fl t , -timeout option to change this. If .Nm is not running, 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. t Fl p , -persistent .Nm normally deconfigures the .Ar 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. t Fl r , -request Op Ar address .Nm normally sends a DHCP DISCOVER to find servers to offer an address. .Nm then requests the address used. You can use this option to skip the BROADCAST step and just request the .Ar address . The downside is if you request an .Ar 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 .Ar address is given then the first address currently assigned to the .Ar interface is used. t Fl s , -inform Op Ar address Ns Op Ar /cidr Behaves like .Fl 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 .Ar address in use. You should also include the optional .Ar cidr network number in-case the address is not already configured on the interface. .Nm remains running and pretends it has an infinite lease. .Nm will not de-configure the interface when it exits. If .Nm fails to contact a DHCP server then it returns a failure instead of falling back on IPv4LL. t Fl t , -timeout Ar seconds Timeout after .Ar seconds , instead of the default 30. A setting of 0 .Ar seconds causes .Nm to wait forever to get a lease. t Fl u , -userclass Ar class Tags the DHCP message with the userclass .Ar 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. t Fl v , -vendor Ar code , Ns Ar value Add an enscapulated vendor option. .Ar code should be between 1 and 254 inclusive. Examples.
p Set the vendor option 01 with an IP address. .D1 dhcpcd -v 01,192.168.0.2 eth0 Set the vendor option 02 with a hex code. .D1 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. .D1 dhcpcd -v 01,192.168.0.2 -v 02,01:02:03:04:05 -v 03,\e"192.168.0.2\e" eth0 t Fl x , -exit This will signal an existing .Nm process running on the .Ar interface to deconfigure the .Ar interface and exit. .Nm then waits until this process has exited. t Fl D , -duid Generate an .Li RFC 4361 compliant clientid. This requires persistent storage and not all DHCP servers work with it so it's not enabled by default. .Nm generates the DUID and stores in it
a /system/etc/dhcpcd/dhcpcd.duid This file should not be copied to other hosts. t Fl E , -lastlease If .Nm cannot obtain a lease, then try to use the last lease acquired for the interface. If the .Fl p, -persistent option is not given then the lease is used if it hasn't expired. t Fl F , -fqdn Ar fqdn Requests that the DHCP server updates DNS using FQDN instead of just a hostname. Valid values for .Ar fqdn are disable, none, ptr and both. The current hostname or the hostname specified using the .Fl h , -hostname option must be a FQDN. .Nm itself never does any DNS updates. .Nm encodes the FQDN hostname as specified in .Li RFC1035 . t Fl I , -clientid Ar clientid Change the default clientid sent from the interface hardware address. If the string is of the format 01:02:03 then it is encoded as hex. If not set then none is sent. .El .Ss Restriciting behaviour .Nm 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. l -tag -width indent t Fl q , -quiet Quiet .Nm on the command line, only warnings and errors will be displayed. The messages are still logged though. t Fl A , -noarp Don't request or claim the address by ARP. This also disables IPv4LL. t Fl 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. t Fl C , -nohook Ar script Don't run this hook script. Matches full name, or prefixed with 2 numbers optionally ending with
a .sh .
p So to stop dhcpcd from touching your DNS or MTU settings you would do:- .D1 dhcpcd -C resolv.conf -C mtu eth0 t Fl G , -nogateway Don't set any default routes. t Fl K , -nolink Don't receive link messages for carrier status. You should only have to use this with buggy device drivers or running .Nm through a network manager. t Fl L , -noipv4ll Don't use IPv4LL (aka APIPA, aka Bonjour, aka ZeroConf). t Fl O , -nooption Ar 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. t Fl Q , -require Ar option Requires the .Ar option to be present in all DHCP messages, otherwise the message is ignored. t Fl T, -test On receipt of OFFER messages just call
a /system/etc/dhcpcd/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. t Fl V, -variables Display a list of option codes and the associated variable for use in .Xr dhcpcd-run-hooks 8 . t Fl X, -blacklist Ar address Ignores all DHCP messages which have this .Ar address as the server ID. This may be expanded in future releases to ignore all packets matching either the IP or hardware .Ar address . .El .Sh NOTES .Nm requires a Berkley Packet Filter, or BPF device on BSD based systems and a Linux Socket Filter, or LPF device on Linux based systems. .Sh FILES l -ohang t Pa /system/etc/dhcpcd/dhcpcd.conf Configuration file for dhcpcd. If you always use the same options, put them here. t Pa /system/etc/dhcpcd/dhcpcd.duid Text file that holds the DUID used to identify the host. t Pa /system/etc/dhcpcd/dhcpcd-run-hooks Bourne shell script that is run to configure or deconfigure an interface. t Pa /system/etc/dhcpcd/dhcpcd-hooks A directory containing bourne shell scripts that are run by the above script. Each script can be disabled by using the .Fl C , -nohook option described above. t Pa /data/misc/dhcp/dhcpcd- Ns Ar interface Ns .lease The actual DHCP message send by the server. We use this when reading the last lease and use the files mtime as when it was issued. t Pa /var/run/dhcpcd- Ns Ar interface Ns .pid Stores the PID of .Nm running on the .Ar interface . .El .Sh SEE ALSO .Xr dhcpcd.conf 5 , .Xr dhcpcd-run-hooks 8 , .Xr resolv.conf 5 , .Xr resolvconf 8 , .Sh STANDARDS RFC 2131, RFC 2132, RFC 2855, RFC 3004, RFC 3361, RFC 3396, RFC 3397, RFC 3442, RFC 3927, RFC 4361, RFC 4390, RFC 4702. .Sh AUTHORS .An Roy Marples <roy (at] marples.name> .Sh BUGS Please report them to http://bugs.marples.name
