dhcpcd configuration file
can do everything from the command
line, there are cases where it's just easier to do it once in a configuration
file. Most of the options found in dhcpcd(8)
be used here. The first word on the line is the option and the rest of the
line is the value. Leading and trailing whitespace for the option and value
are trimmed. You can escape characters in the value using the \ character.
Blank lines and lines starting with # are ignored.
Here's a list of available options:
- 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 denyinterfaces then it is still
- When discovering interfaces, the interface name must not
match pattern which is a space or comma
separated list of patterns passed to
- dhcpcd will arping each
address in order before attempting DHCP. If an address is found, we will
select the replying hardware address as the profile, otherwise the ip
- Authenticate DHCP messages. See the Supported
Authentication Protocols section.
- Define a shared key for use in authentication.
realm can be to for use with the
expire is the date the token expires and
should be formatted "yyy-mm-dd HH:MM". You can use the keyword
0 which means the token never expires.
For the token protocol, secretid needs to
be 0 and realm needs to be "".
If dhcpcd has the error
dhcp_auth_encode: Invalid argument
then it means that dhcpcd could not find the
correct authentication token in your configuration.
- Background immediately. This is useful for startup scripts
which don't disable link messages for carrier status.
- Ignores all packets from
- Only accept packets from
blacklist is ignored if
whitelist is set.
- Be a BOOTP client. Basically, this just doesn't send a DHCP
Message Type option and will only interact with a BOOTP server. All other
DHCP options still work.
- Instructs the DHCP server to broadcast replies back to the
client. Normally this is only set for non Ethernet interfaces, such as
FireWire and InfiniBand. In most cases,
dhcpcd will set this automatically.
- Sets the group ownership of
/var/run/dhcpcd.sock so that users other than
root can connect to dhcpcd.
- Echo debug messages to the stderr and syslog.
- Load the value
/dev management module.
dhcpcd will load the first one found to work,
- Push value to the
environment for use in dhcpcd-run-hooks(8).
For example, you can force the hostname hook to always set the hostname
force_hostname=YES. Or set which driver
wpa_supplicant(8) should use with
If the hostname is set, will be will set to the FQDN if possible as per RFC
4702 section 3.1. If the FQDN option is missing,
dhcpcd will still try and set a FQDN from the
hostname and domain options for consistency. To override this, set
hostname_fqdn=[YES|NO|SERVER]. A value of
server means just what the server says, don't manipulate it. This could
lead to an inconsistent hostname on a DHCPv4 and DHCPv6 network where the
DHCPv4 hostname is short and the DHCPv6 has an FQDN. DHCPv6 has no
- 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
- Generate an
compliant DHCP Unique Identifier. If persistent storage is available then
a DUID-LLT (link local address + time) is generated, otherwise DUID-LL is
generated (link local address). This, plus the IAID will be used as the
clientid. The DUID-LLT generated will be held
in /etc/dhcpcd.duid and should not be copied
to other hosts.
- Set the Interface Association Identifier to
iaid. This option must be used in an
interface block. This defaults to the last 4
bytes of the hardware address assigned to the interface. Each instance of
this should be unique within the scope of the client and
dhcpcd warns if a conflict is detected. If
there is a conflict, it is only a problem if the conflicted IAIDs are used
on the same network.
- Enable DHCP on the interface, on by default.
- Enable DHCPv6 on the interface, on by default.
- Enable IPv4 on the interface, on by default.
- Enable IPv6 on the interface, on by default.
- dhcpcd normally de-configures
the interface and configuration when it exits. Sometimes, this isn't
desirable if, for example, you have root mounted over NFS or SSH clients
connect to this host and they need to be notified of the host shutting
down. You can use this option to stop this from happening.
- Fallback to using this profile if DHCP fails. This allows
you to configure a static profile instead of using ZeroConf.
- Sends hostname to the DHCP
server so it can be registered in DNS. If
hostname is an empty string then the
current system hostname is sent. If
hostname is a FQDN (ie, contains a .)
then it will be encoded as such.
- Sends the short hostname to the DHCP server instead of the
FQDN. This is useful because DHCP servers will not register the FQDN in
their DNS if the domain part does not match theirs.
Also, see the env option above to control how
the hostname is set on the host.
- Request a DHCPv6 Normal Address for
iaid defaults to the
iaid option as described above. You can
request more than one ia_na by specifying a unique
iaid for each one.
- Request a DHCPv6 Temporary Address for
iaid. You can request more than one ia_ta
by specifying a unique iaid for each
- Request a DHCPv6 Delegated Prefix for
iaid. This option must be used in an
interface block. Unless a
sla_id of 0 is assigned, a reject route
is installed for the Delegated Prefix to stop unallocated addresses being
resolved upstream. This reject route is in essence SLA 0, thus you need
space within the prefix to assign a SLA per interface. If no
interface is given then we will assign a
prefix to every other interface with a
sla_id equivalent to the interface index
assigned by the OS. Otherwise addresses are only assigned for each
sla_id. Each assigned address will have a
suffix of 1. You cannot assign a prefix to the requesting interface unless
the DHCPv6 server supports
RFC6603 Prefix Exclude
Option. dhcpcd has to be running for all the
interfaces it is delegating to. A default
prefix_len of 64 is assumed, unless the
maximum sla_id does not fit. In this case
prefix_len is increased to the highest
multiple of 8 that can accommodate the
sla_id is an integer and is added to the
prefix which must fit inside prefix_len
less the length of the delegated prefix. sla_id
can be 0 only if the Delegated Prefix is assigned to one interface.
You can specify multiple interface /
ia_pd, space separated. IPv6RS should be
disabled globally when requesting a Prefix Delegation.
In the following example eth0 is the externally facing interface to be
configured for both IPv4 and IPv6. The DHCPv4 server will provide us with
an IPv4 address and a default route. The DHCPv6 server is going to provide
us with an IPv6 address, a default route and a /64 subnet to be delegated
to the internal interface. The eth1 interface will be automatically
configured for IPv6 using the first address (::1) from the delegated
prefix. A second prefix is requested and assigned to two other interfaces.
rtadvd(8) can be used with an empty
configuration file on eth1, eth2 and eth3, to provide automatic IPv6
address configuration for the internal network.
noipv6rs # disable routing solicitation
denyinterfaces eth2 # Don't touch eth2 at all
ipv6rs # enable routing solicitation get the
# default IPv6 route
ia_na 1 # request an IPv6 address
ia_pd 2 eth1/0 # request a PD and assign it to eth1
ia_pd 3 eth2/1 eth3/2 # req a PD and assign it to eth2 and eth3
# we cannot use SLA 0 above because we are
# assinging the PD to more than one interface
- Only configure IPv4.
- Only confgiure IPv6.
[disable | ptr | both]
- ptr just asks the DHCP server to update the PTR record of
the host in DNS whereas both also updates the A record. disable will
disable the FQDN option. The default is both.
dhcpcd itself never does any DNS updates.
dhcpcd encodes the FQDN hostname as specified
- Subsequent options are only parsed for this
- Generate SLAAC addresses for each Prefix advertised by a
Router Advertisement message with the Auto flag set. On by default.
- Disables the above option.
- By default, when dhcpcd
receives an IPv6 RA, dhcpcd will only fork to
the background if the RA contains at least one unexpired RDNSS option and
a valid prefix or no DHCPv6 instruction. Set this option so to make
dhcpcd always fork on an RA.
- Disables kernel IPv6 Router Advertisement processing so
dhcpcd can manage addresses and routes.
- Each time dhcpcd receives an IPv6 Router Adveristment,
dhcpcd will manage the default route only. This allows dhcpcd to prefer an
interface for outbound traffic based on metric and/or user selection
rather than the kernel.
- Some IPv6 routers advertise themselves as a default router
without any public prefixes or managed addresses. Generally, this is
incorrect behaviour and dhcpcd will ignore
the advertisement unless this option is turned on.
- Enables IPv6 Router Advertisement solicitation. This is on
by default, but is documented here in the case where it is disabled
globally but needs to be enabled for one interface.
- Request a leasetime of
- Writes to the specified
logfile rather than
logfile is truncated when opened and is
reopened when dhcpcd receives the
- Metrics are used to prefer an interface over another one,
lowest wins. dhcpcd will supply a default
metric of 200 + if_nametoindex(3). An extra
100 will be added for wireless interfaces.
- Any pre-existing IPv4 addresses existing address will be
removed from the interface when adding a new IPv4 address.
- Don't send any ARP requests. This also disables
- Don't require authentication even though we requested it.
Also allows FORCERENEW and RECONFIGURE messages without
- Don't delay for an initial randomised time when starting
- Don't load /dev management
- Don't start DHCP or listen to DHCP messages. This is only
useful when allowing IPv4LL.
- Don't start DHCPv6 or listen to DHCPv6 messages. Normally
DHCPv6 is started by a RA instruction or configuration.
- Don't install any default routes.
- Install a default route if available (default).
- 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
settings or starting wpa_supplicant you would do:-
nohook resolv.conf, wpa_supplicant
- Don't attempt to configure an IPv4 address.
- Don't attempt to obtain an IPv4LL address if we failed to
get one via DHCP. See RFC
- Don't attmept to configure an IPv6 address.
- Disable solicitation and receipt of IPv6 Router
- Don't receive link messages about carrier status. You
should only set this for buggy interface drivers.
- Don't bring the interface up when in master mode. If
dhcpcd.conf cannot determine the carrier
state, dhcpcd.conf will enter a tight polling
loop until the interface is marked up and running or a valid carrier state
- Requests the option from
the server. It can be a variable to be used in
dhcpcd-run-hooks(8) or the numerical value.
You can specify more options separated by
commas, spaces or more option lines.
option Prepend dhcp6_ to
option to request a DHCPv6 option. If no
DHCPv6 options are configured, then DHCPv4 options are mapped to
equivalent DHCPv6 options.
Prepend nd_ to option to handle ND options,
but this only works for the nooption,
- Remove the option from the message before it's
- Requires the option to be
present in all messages, otherwise the message is ignored. To enforce that
dhcpcd only responds to DHCP servers and not
BOOTP servers, you can require
dhcp_message_type. This isn't an exact
science though because a BOOTP server can send DHCP like options.
- Reject a message that contains the
option. This is useful when you cannot
use require to select / de-select BOOTP
- If dhcpcd.conf detects an
address added to a point to point interface (PPP, TUN, etc) then it will
set the listed DHCP options to the destination address of the
- Subsequent options are only parsed for this profile
- Suppress any dhcpcd output to the console, except for
- Allow reboot seconds
before moving to the DISCOVER phase if we have an old lease to use and
moving from DISCOVER to IPv4LL if no reply. The default is 5 seconds. A
setting of 0 seconds causes dhcpcd to skip
the REBOOT phase and go straight into DISCOVER. This is desirable for
mobile users because if you change from network A to network B and they
use the same subnet and the address from network A isn't in use on network
B, then the DHCP server will remain silent even if authoritative which
means dhcpcd will timeout before moving back
to the DISCOVER phase.
- dhcpcd will release the lease
prior to stopping the interface.
- Use script instead of the
- Subsequent options are only parsed for this wireless
- Selects the interface identifier used for SLAAC generated
IPv6 addresses. If private is used, a
RFC7217 address is generated.
- 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.
Here is an example for PPP which gives the destination a default route. It
uses the special destination keyword to insert the destination address
into the value.
- Timeout after seconds,
instead of the default 30. A setting of 0
dhcpcd to wait forever to get a lease. If
dhcpcd is working on a single interface then
dhcpcd will exit when a timeout occurs,
otherwise dhcpcd will fork into the
background. If using IPv4LL then dhcpcd start
the IPv4LL process after the timeout and then wait a little longer before
really timing out.
- Tag the DHCPv4 messages with the userclass. You can specify
more than one.
- Add an encapsulated vendor option.
code should be between 1 and 254
inclusive. To add a raw vendor string, omit
code but keep the comma. Examples.
Set the vendor option 01 with an IP address.
Set the vendor option 02 with a hex code.
Set the vendor option 03 with an IP address as a string.
Set un-encapsulated vendor option to hello world.
vendor ,"hello world"
- Set the DHCP Vendor Class. DHCPv6 has it's own option as
shown below. The default is
If not set then none is sent. Some badly configured DHCP servers reject
unknown vendorclassids. To work around it, try and impersonate Windows by
using the MSFT vendorclassid.
- Add the DHCPv6 Vendor Indetifying Vendor Class with the
IANA assigned Enterprise Number en with
the data. This option can be set more
than once to add more data, but the behaviour, as per
RFC(3925) is undefined if the Enterprise
[4 | 6]
- Wait for an address to be assigned before forking to the
background. 4 means wait for an IPv4 address to be assigned. 6 means wait
for an IPv6 address to be assigned. If no argument is given,
dhcpcd.conf will wait for any address
protocol to be assigned. It is possible to wait for more than one address
protocol and dhcpcd.conf will only fork to
the background when all waiting conditions are satisfied.
- Use the last four bytes of the hardware address as the DHCP
xid instead of a randomly generated number.
DHCP, ND and DHCPv6 allow for the use of custom options. Each option needs to be
started with the define
directive. This can optionally be
followed by both embed
options. Both can be specified more than
once and embed
must come before
- Defines the DHCP option
type with a name of
variable exported to
- Defines the ND option code
of type with a name of
variable exported to
dhcpcd-run-hooks(8), with a prefix of
- Defines the DHCPv6 option
type with a name of
variable exported to
dhcpcd-run-hooks(8), with a prefix of
- Defines the Vendor-Identifying Vendor Options. The
code is the IANA Enterprise Number which
will unqiuely describe the encapsulated options.
type is normally
variable names the Vendor option to be
- Defines an embedded variable within the defined option. The
length is determined by the type. If the
variable is not the same as defined in
the parent option, it is prefixed with the parent
variable first with an underscore. If the
variable has the name of
reserved then it is not processed.
- Defines an encapsulated variable within the defined option.
The length is determined by the type. If
the variable is not the same as defined
in the parent option, it is prefixed with the parent
variable first with an underscore.
These keywords come before the type itself, to describe it more fully. You can
use more than one, but they must appear in the order listed below.
- Requests the option by default without having to be
specified in user configuration
- This option cannot be requested, regardless of user
- This option is optional. Only makes sense for embedded
options where like the client FQDN option where the FQDN string itself is
- The option can appear more than once and will be
- The option data is split into a space separated array, each
element being the same type.
The type directly affects the length of data consumed inside the option. Any
remaining data is normally discarded. Lengths can be specified for string and
binhex types, but this is generally with other data embedded afterwards in the
- An IPv4 address, 4 bytes.
- An IPv6 address, 16 bytes.
- A NVT ASCII string of printable characters.
- A byte.
- A byte represented as a string of flags, most significant
bit first. For example, using ABCDEFGH then A would equal 10000000, B
01000000, C 00100000, etc. If the bit is not set, the flag is not printed.
A flag of 0 is not printed even if the bit postition is set. This is to
allow reservation of the first bits while assinging the last bits.
- A signed 16bit integer, 2 bytes.
- An unsigned 16bit integer, 2 bytes.
- A signed 32bit integer, 4 bytes.
- An unsigned 32bit integer, 4 bytes.
- A fixed value (1) to indicate that the option is present, 0
- A RFC 3397 encoded string.
- A RFC 1035 validated string.
- Binary data expressed as hexadecimal.
- Contains embedded options (implies encap as well).
- Contains encapsulated options (implies embed as well).
- References an option from the global definition.
# DHCP option 81, Fully Qualified Domain Name, RFC4702
define 81 embed fqdn
embed byte flags
embed byte rcode1
embed byte rcode2
embed domain fqdn
# DHCP option 125, Vendor Specific Information Option,
define 125 encap vsio
embed uint32 enterprise_number
# Options defined for the enterprise number
encap 1 ipaddress ipaddress
- Sends and expects the token with the secretid 0 and realm
of "" in each message.
- Delayed Authentication. dhcpcd
will send an authentication option with no key or MAC. The server will see
this option, and select a key for
dhcpcd.conf, writing the
secretid in it.
dhcpcd will then look for a non-expired token
with a matching realm and secretid. This token is used to authenicate all
- Same as above, but without a realm.
If none specified, hmac-md5
is the default.
If none specified, monotonic
is the default. If
this is changed from what was previously used, or the means of calculating or
storing it is broken then the DHCP server will probably have to have its
notion of the clients Replay Detection Value reset.
- Read the number in the file
/var/lib/dhcpcd5/dhcpcd-rdm.monotonic and add
one to it.
- Create a NTP timestamp from the system time.
- Same as monotime.
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