is an implementation of the DHCP client specified in
"RFC 2131"
gets the host information
Po IP address, routes, etc
Pc from a DHCP server and configures the network
interface
of the
machine on which it is running.
will then write DNS information to
resolvconf(8),
if available, otherwise directly to
/etc/resolv.conf
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
will also attempt to restart the respective services to notify them of the
change.
If the hostname is currenly blank, (null) or localhost then
will set the hostname to the one supplied by the DHCP server, or look it up
in DNS if none supplied.
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
failed to obtain a lease, it will probe for a valid IPv4LL address
Po aka Zeroconf, aka APIPA
Pc .
Once obtained it will probe every 10 seconds for a DHCP server to get a
proper address.
Even when
obtains a proper lease, it will still add a Local Link route
Po 165.254.0.0/16
Pc so that the host can communicate with clients using these addresses.
When using IPv4LL,
will always succeed and return a 0 exit code. To disable this behaviour, you
can use the
-L , -noipv4ll
option.
Hooking into DHCP events
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
.
ignores the exist code of the script.
Fine tuning
You can fine tune the behaviour of
with the following options :-
-d , -debug
Echo debug and informational messages to the console.
Subsequent debug options stop
from daemonising.
-h , -hostname hostname
By default,
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
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
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
Po presently only Linux
Pc .
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
process running on the
interface
to renew it's lease. If
is not running, then it starts up as normal.
-p , -persistent
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
]
normally sends a DHCP Broadcast to find servers to offer an address.
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
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.
If Fl F , -fqdn Ar fqdn
Requests that the DHCP server updates DNS using FQDN instead of just a
hostname. Valid values for
fqdn
are none, ptr and both.
dhcpcd itself never does any DNS updates.
-H , --sethostname
Forces
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
Po RFC 3442
Pc .
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.
Restriciting behaviour
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.
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
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
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
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
configuration.
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