Provided by: dhcpcd_3.2.3-11+deb7u1build0.14.04.1_amd64 
NAME
dhcpcd — an RFC 2131 compliant DHCP client
SYNOPSIS
dhcpcd [-dknpAEGHMLNRSTY] [-c, --script script] [-h, --hostname hostname] [-i, --classid classid]
[-l, --leasetime seconds] [-m, --metric metric] [-r, --request address] [-t, --timeout seconds]
[-u, --userclass class] [-F, --fqdn FQDN] [-I, --clientid clientid] [-P, --pidfile pidfile]
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 will then write DNS information to resolvconf(8), if available, otherwise directly
to /etc/resolv.conf. dhcpcd will also configure /etc/yp.conf and /etc/ntpd.conf with NIS and NTP
information if the DHCP server provided them. If those file contents changed, then dhcpcd will also
attempt to restart the respective services to notify them of the change. If the hostname is currenly
blank, (null) or localhost then dhcpcd will set the hostname to the one supplied by the DHCP server, or
look it up in DNS if none supplied. 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.
Local Link configuration
If dhcpcd failed to obtain a lease, it will probe for a valid IPv4LL address (aka Zeroconf, aka APIPA).
Once obtained it will probe every 10 seconds for a DHCP server to get a proper address.
Even when dhcpcd obtains a proper lease, it will still add a Local Link route (165.254.0.0/16) so that
the host can communicate with clients using these addresses.
When using IPv4LL, dhcpcd will always succeed and return a 0 exit code. To disable this behaviour, you
can use the -L, --noipv4ll option.
Hooking into DHCP events
dhcpcd will run /etc/dhcpcd.sh, or the script specified by the -c, --script option. It will set $1 to a
shell compatible file that holds various configuration settings obtained from the DHCP server and $2 to
either up, down or new depending on the state of dhcpcd. dhcpcd ignores the exist code of the script.
Fine tuning
You can fine tune the behaviour of dhcpcd with the following options :-
-d, --debug
Echo debug and informational messages to the console. Subsequent debug options stop dhcpcd from
daemonising.
-h, --hostname hostname
By default, dhcpcd will send 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, --classid classid
Override the DHCP vendor classid field we send. The default is dhcpcd-<version>.
-k, --release
This causes an existing dhcpcd process running on the interface to release it's lease,
deconfigure the interface and then exit.
-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
Added routes will use the metric on systems where this is supported (presently only Linux).
Route metrics allow the addition of routes to the same destination across different interfaces,
the lower the metric the more it is preferred.
-n, --renew
Notifies an existing dhcpcd process running on the interface to renew it's lease. If dhcpcd is
not running, then it starts up as normal.
-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 Broadcast to find servers to offer an address. dhcpcd will then
request the address used. You can use this option to skip the broadcast step and just request an
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 broadcast again. If no address is given then we use the first address currently
assigned to the interface.
-s, --inform [address [/ cidr]]
Behaves exactly like -r, --request as above, but sends a DHCP inform instead of a request. This
requires the interface to be configured first. This does not get a lease as such, just notifies
the DHCP server of the address we are using.
-t, --timeout seconds
Timeout after seconds, instead of the default 20. 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 memebers of the class
DHCP options other than the default, without having to know things like hardware address or
hostname. ∞Requests that the DHCP server updates DNS using FQDN instead of just a hostname.
Valid values for fqdn are none, ptr and both. dhcpcd dhcpcd itself never does any DNS updates.
-H, ---sethostname
Forces dhcpcd to set the hostname as supplied by the DHCP server. Because some OS's and users
prefer to have just the hostname, or the full FQDN more -H, ---sethostname options change the
behaviour. Below is the list of possible combinations:-
-H set the hostname to the full FQDN.
-HH strip the domain if it matches the dns domain.
-HHH strip the domain regardless.
-HHHH same as -H but force hostname lookup via DNS.
-HHHHH same as above, but strip the domain if it matches the dns domain.
-HHHHHH
same as above, but strip the domain regardless.
-I, --clientid clientid
Send clientid as a client identifier string. If clientid matches a hardware address format, such
as 01:00:01:02:03:04:05 then we encode it as that, otherwise as a string. You need to specify the
hardware type in the first byte. Ethernet is 01, and the hardware address in the example is
00:01:02:03:04:05. If the clientid is a blank string, then we disable DUID support and use a
clientid as shown above.
-S, --mscsr
Microsoft have their own code for Classless Static Routes (RFC 3442). You can use this option to
request this as well as the normal CSR. Another instace of this option only requests the
Microsoft CSR to prevent DHCP message over-running its maximum size. DHCP server administrators
should update their CSR code from the Microsoft specific one to the RFC compliant one as the
content is fully compatible.
-P, --pidfile filename
Write the PID to filename instead of /var/run/dhcpcd-interface.pid.
Restriciting 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 option that
deal with turning these bits off.
-A, --noarp
Don't request or claim the address by ARP.
-G, --nogateway
Don't set any default routes.
-L, --noipv4ll
Don't use IPv4LL at all.
-M, --nomtu
Don't set the MTU of the interface.
-N, --nontp
Don't touch /etc/ntpd.conf or restart the ntp service.
-R, --nodns
Don't send DNS information to resolvconf or touch /etc/resolv.conf.
-T, --test
On receipt of discover messages, simply print the contents of the DHCP message to the console.
dhcpcd will not configure the interface, touch any files or restart any services.
-Y, --nonis
Don't touch /etc/yp.conf or restart the ypbind service.
NOTES
Because dhcpcd supports InfiniBand, we put a Node-specific Client Identifier in the ClientID field. This
is required by RFC 4390. It's also required for DHCP IPv6 which dhcpcd should support one day. However,
some DHCP servers have no idea what this is and reject the message as they do not understand type 255.
This is not conformant with RFC 2132 and the server should be fixed. Also, some DHCP server
configurations require an ethernet hardware address of 6 hexacdecimal numbers in the ClientID which is
the default behaviour of most other DHCP clients. If your DHCP server is as desribed above, you should
fix the server, or if that is not an option you can compile DUID support out of dhcpcd or use the -I,
--clientid clientid option and set clientid to ''.
ISC dhcpd, dnsmasq, udhcpd and Microsoft DHCP server 2003 default configurations work just fine with the
default dhcpcd configuration.
dhcpcd requires a Berkley Packet Filter, or BPF device on BSD based systems and a Linux Socket Filter, or
LPF device on Linux based systems.
FILES
/etc/dhcpcd.sh
Bourne shell script that is run when we configure or deconfigure an interface.
/var/lib/dhcpcd/dhcpcd.duid
Text file that holds the DUID used to identify the host.
/var/lib/dhcpcd/dhcpcd-interface.info
Bourne shell file that holds the DHCP values used in configuring the interface. This path is passed as
the first argument to /etc/dhcpcd.sh.
SEE ALSO
ntp(1), resolv.conf(5), resolvconf(8), yp.conf(5), ypbind(8)
STANDARDS
RFC 2131, RFC 2132, RFC 2855, RFC 3004, RFC 3361, RFC 3397, RFC 3442, RFC 3927, RFC 4361, RFC 4390, RFC
4702.
AUTHORS
Roy Marples <roy@marples.name>
BUGS
Please report them to http://bugs.marples.name
Feb 20, 2008 DHCPCD(8)