NAME
dhcpcd —
a DHCP client
SYNOPSIS
dhcpcd |
[-146ABbDdEGgHJKLMNPpqTV]
[-C,
--nohook
hook] [-c,
--script
script]
[-e,
--env
value]
[-F,
--fqdn
FQDN] [-f,
--config
file] [-h,
--hostname
hostname]
[-I,
--clientid
clientid]
[-i,
--vendorclassid
vendorclassid]
[-j,
--logfile
logfile]
[-l,
--leasetime
seconds]
[-m,
--metric
metric]
[-O,
--nooption
option]
[-o,
--option
option]
[-Q,
--require
option]
[-r,
--request
address]
[-S,
--static
value]
[-s,
--inform
address[/cidr[/broadcast_address]]]
[--inform6]
[-t,
--timeout
seconds]
[-u,
--userclass
class]
[-v,
--vendor code,
value]
[-W,
--whitelist
address[/cidr]]
[-w]
[--waitip
[4 | 6]]
[-y,
--reboot
seconds]
[-X,
--blacklist
address[/cidr]]
[-Z,
--denyinterfaces
pattern]
[-z,
--allowinterfaces
pattern]
[- -inactive]
[interface] [...] |
dhcpcd |
-n, --rebind
[interface] |
dhcpcd |
-k, --release
[interface] |
dhcpcd |
-U, --dumplease
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
currently blank, (null) or localhost, or
force_hostname
is YES or TRUE or 1 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. It will then attempt to renew its
lease and reconfigure if the new lease changes when the lease beings to expire
or the DHCP server sends message to renew early.
If any interface reports a working carrier then
dhcpcd will
try and obtain a lease before forking to the background, otherwise it will
fork right away. This behaviour can be modified with the
-b,
--background and
-w,
--waitip options.
dhcpcd is also an implementation of the BOOTP client specified
in
RFC 951
.
dhcpcd is also an implementation of the IPv6 Router Solicitor
as specified in
RFC 4861
and
RFC
6106
.
dhcpcd is also an implementation of the IPv6 Privacy
Extensions to AutoConf as specified in
RFC 4941
. This
feature needs to be enabled in the kernel and
dhcpcd will
start using it.
dhcpcd is also an implementation of the DHCPv6 client as
specified in
RFC 3315
. By default,
dhcpcd only starts DHCPv6 when instructed to do so by an
IPV6 Router Advertisement. If no Identity Association is configured, then a
Non-temporary Address is requested.
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 disable
this behaviour, you can use the
-L,
--noipv4ll option.
Multiple interfaces
If a list of interfaces are given on the command line, then
dhcpcd only works with those interfaces, otherwise
dhcpcd discovers available Ethernet interfaces that can be
configured. When
dhcpcd not limited to one interface on the
command line, it is running in Master mode. The
dhcpcd-ui
project expects dhcpcd to be running this way.
If a single interface is given then
dhcpcd only works for that
interface and runs as a separate instance to other
dhcpcd
processes.
-w,
--waitip
option is enabled in this instance to maintain compatibility with older
versions. Using a single interface also affects the
-k,
-N,
-n and
-x options
where the same interface will need to be specified as a lack of an interafce
will imply Master mode which this is not. To force starting in Master mode
with only one interface, the
-M,
--master option can be used.
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 which interfaces we allow and deny through the use of patterns.
Hooking into 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 supplies the scripts
01-test,
02-dump,
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 currently
ignores the exit code of the script.
More scripts are supplied in
/usr/share/examples/dhcpcd/hooks
and need to be copied to
/libexec/dhcpcd-hooks if you intend
to use them. For example, you could install
10-wpa_supplicant so that
dhcpcd can
ensure that
wpa_supplicant(8) is
always running on a hot-plugged wireless interface.
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,
--duid
- Use a DHCP Unique Identifier. If a system UUID is
available, that will be used to create a DUID-UUID, otheriwse 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 -I,
--clientid. The DUID generated will be
held in /var/db/dhcpcd/duid and should not be copied to
other hosts. This file also takes precedence over the above rules.
-
-
- -d,
--debug
- Echo debug messages to the stderr and syslog.
-
-
- -E,
--lastlease
- If dhcpcd cannot obtain a lease, then try
to use the last lease acquired for the interface.
-
-
- --lastleaseextend
- Same as the above, but he lease will be retained even if it
expires. dhcpcd will give it up if any other host tries
to claim it for their own via ARP. This is does violate RFC2131 section
3.7 which states the lease should be dropped once it has expired.
-
-
- -e,
--env value
- 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
with -e force_hostname=YES.
-
-
- -g,
--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 afterwards.
dhcpcd does not read a new configuration when this
happens - you should rebind if you need that functionality.
-
-
- -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
.
-
-
- -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
- 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.
-
-
- -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.
-
-
- -i,
--vendorclassid
vendorclassid
- Override the DHCPv4 vendorclassid
field sent. The default is
dhcpcd-<version>:<os>:<machine>:<platform>. For
example
dhcpcd-5.5.6:NetBSD-6.99.5:i386:i386
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.
-
-
- -j,
--logfile
logfile
- Writes to the specified logfile
rather than syslog(3). The
logfile is s reopened when dhcpcd
receives the
SIGUSR2
signal.
-
-
- -k,
--release
[interface]
- This causes an existing dhcpcd process
running on the interface to release its lease and
de-configure the interface regardless of the
-p, --persistent
option. If no interface is specified then this
applies to all interfaces in Master mode. If no interfaces are left
running, dhcpcd will exit.
-
-
- -l,
--leasetime
seconds
- Request a specific lease time in
seconds. By default dhcpcd does
not request any lease time and leaves it in the hands of the DHCP
server.
-
-
- -M,
--master
- Start dhcpcd in Master mode even if only
one interface specified on the command line. See the Multiple Interfaces
section above.
-
-
- -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.
-
-
- -n,
--rebind
[interface]
- Notifies dhcpcd to reload its
configuration and rebind the specified interface. If
no interface is specified then this applies to all
interfaces in Master mode. If dhcpcd is not running,
then it starts up as normal. This may also cause
wpa_supplicant(8) to
reload its configuration for each interface as well if the relevant hook
script has been installed.
-
-
- -N,
--renew
[interface]
- Notifies dhcpcd to renew existing
addresses on the specified interface. If no
interface is specified then this applies to all
interfaces in Master mode. If dhcpcd is not running,
then it starts up as normal. Unlike the -n,
--rebind option above, the
configuration for dhcpcd is not reloaded.
-
-
- -o,
--option
option
- Request the DHCP option variable for
use in /libexec/dhcpcd-run-hooks.
-
-
- -p,
--persistent
- 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.
-
-
- -r,
--request
address
- Request the address in the DHCP
DISCOVER message. There is no guarantee this is the address the DHCP
server will actually give. If no address is given
then the first address currently assigned to the
interface is used.
-
-
- -s,
--inform
address[/cidr[/broadcast_address]]
- Behaves like -r,
--request as above, but sends a DHCP
INFORM instead of DISCOVER/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-configure the interface when
it exits. If dhcpcd fails to contact a DHCP server then
it returns a failure instead of falling back on IPv4LL.
-
-
- --inform6
- Performs a DHCPv6 Information Request. No address is
requested or specified, but all other DHCPv6 options are allowed. This is
normally performed automatically when the IPv6 Router Advertises that the
client should perform this operation. This option is only needed when
dhcpcd is not processing IPv6RA messages and the need
for DHCPv6 Information Request exists.
-
-
- -S,
--static
value
- Configures a static DHCP 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
You cannot presently set static DHCPv6 values. Use the -e,
--env option instead.
-
-
- -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. If
dhcpcd is working on a single interface then
dhcpcd will exit when a timeout occurs, otherwise
dhcpcd will fork into the background.
-
-
- -u,
--userclass
class
- Tags the DHCPv4 message with the userclass
class. DHCP servers use this to 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 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.
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
Set the vendor option 03 with an IP address as a string.
dhcpcd -v 03,\"192.168.0.2\" eth0
Set un-encapsulated vendor option to hello world.
dhcpcd -v ,"hello world" eth0
-
-
- --version
- Display both program version and copyright information.
dhcpcd then exits before doing any configuration.
-
-
- -w
- Wait for an address to be assigned before forking to the
background. Does not take an argument, unlike the below option.
-
-
- --waitip
[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 will wait for any address protocol to be
assigned. It is possible to wait for more than one address protocol and
dhcpcd will only fork to the background when all waiting
conditions are satisfied.
-
-
- -x,
--exit
[interface]
- This will signal an existing dhcpcd
process running on the interface to exit. If no
interface is specified, then the above is applied to
all interfaces in Master mode. See the -p,
--persistent option to control
configuration persistence on exit, which is enabled by default in
dhcpcd.conf(5).
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. Allow
reboot seconds before starting fallback states from
the discover phase. IPv4LL is started when the first
reboot timeout is reached. The default is 5 seconds.
A setting of 0 seconds causes dhcpcd to skip the reboot
phase and go straight into discover. This has no effect on DHCPv6 other
than skipping the reboot phase.
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.
Note that when
dhcpcd is restricted to a single interface then
the interface also needs to be specified when asking
dhcpcd
to exit using the commandline. If the protocol is restricted as well then the
protocol needs to be included with the exit instruction.
-
-
- -1,
--oneshot
- Exit after configuring an interface. Use the
-w, --waitip option
to specify which protocol(s) to configure before exiting.
-
-
- -4,
--ipv4only
- Configure IPv4 only.
-
-
- -6,
--ipv6only
- Configure IPv6 only.
-
-
- -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 settings you
would do:-
dhcpcd -C resolv.conf eth0
-
-
- -G,
--nogateway
- Don't set any default routes.
-
-
- -H,
--xidhwaddr
- Use the last four bytes of the hardware address as the DHCP
xid instead of a randomly generated number.
-
-
- -J,
--broadcast
- 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 instances, dhcpcd will
set this automatically.
-
-
- -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
- Removes the option from the DHCP
message before processing.
-
-
- -P,
--printpidfile
- Print the pidfile
dhcpcd will use based on commmand-line arguments to
stdout.
-
-
- -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.
-
-
- -q,
--quiet
- Quiet dhcpcd on the command line, only
warnings and errors will be displayed. The messages are still logged
though.
-
-
- -T,
--test
- On receipt of DHCP messages just call
/libexec/dhcpcd-run-hooks with the reason of TEST which
echos the DHCP variables found in the message to the console. The
interface configuration isn't touched and neither are any configuration
files. The rapid_commit option is not sent in TEST
mode so that the server does not lease an address. To test INFORM the
interface needs to be configured with the desired address before starting
dhcpcd.
-
-
- -U,
--dumplease
interface
- Dumps the last lease for the
interface to stdout. If omitted, standard input is
used to read a DHCP wire formatted message. Use the -4
or -6 flags to specify an address family.
-
-
- -V,
--variables
- Display a list of option codes, the associated variable and
encoding 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.
-
-
- -W,
--whitelist
address[/cidr]
- Only accept packets from
address[/cidr].
-X, --blacklist is
ignored if -W,
--whitelist is set.
-
-
- -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).
-
-
- -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.
-
-
- --inactive
- Don't start any interfaces other than those specified on
the command line. This allows dhcpcd to be started in
Master mode and then wait for subsequent dhcpcd commands
to start each interface as required.
-
-
- --nodev
- Don't load any /dev management
modules.
3RDPARTY LINK MANAGEMENT
Some interfaces require configuration by 3rd parties, such as PPP or VPN. When
an interface configuration in
dhcpcd is marked as STATIC or
INFORM without an address then
dhcpcd will monitor the
interface until an address is added or removed from it and act accordingly.
For point to point interfaces (like PPP), a default route to its destination
is automatically added to the configuration. If the point to point interface
is configured for INFORM, then
dhcpcd unicasts INFORM to the
destination, otherwise it defaults to STATIC.
NOTES
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
for all IPv4 configuration.
If restricting
dhcpcd to a single interface and optionally
address family via the command-line then all further calls to
dhcpcd to rebind, reconfigure or exit need to include the
same restrictive flags so that
dhcpcd knows which process to
signal.
Some DHCP servers implement ClientID filtering. If
dhcpcd is
replacing an in-use DHCP client then you might need to adjust the clientid
option
dhcpcd sends to match. If using a DUID in place of
the ClientID, edit
/var/db/dhcpcd/duid accordingly.
FILES
- /etc/dhcpcd.conf
- Configuration file for dhcpcd. If you always use the same
options, put them here.
- /libexec/dhcpcd-run-hooks
- Bourne shell script that is run to configure or
de-configure an interface.
- /lib/dhcpcd/dev
- /dev management modules.
- /libexec/dhcpcd-hooks
- A directory containing bourne shell scripts that are run
by the above script. Each script can be disabled by using the
-C, --nohook option
described above.
- /var/db/dhcpcd/duid
- Text file that holds the DUID used to identify the
host.
- /var/db/dhcpcd/secret
- Text file that holds a secret key known only to the
host.
- /var/db/dhcpcd/interface-ssid.lease
- The actual DHCP message sent by the server. We use this
when reading the last lease and use the files mtime as when it was
issued.
- /var/db/dhcpcd/interface-ssid.lease6
- The actual DHCPv6 message sent by the server. We use this
when reading the last lease and use the files mtime as when it was
issued.
- /var/db/dhcpcd/rdm_monotonic
- Stores the monotonic counter used in the
replay field in Authentication Options.
- /var/run/dhcpcd.pid
- Stores the PID of dhcpcd running on all
interfaces.
- /var/run/dhcpcd-interface.pid
- Stores the PID of dhcpcd running on the
interface.
- /var/run/dhcpcd.sock
- Control socket to the master daemon.
- /var/run/dhcpcd.unpriv.sock
- Unprivileged socket to the master daemon, only allows
state retrieval.
- /var/run/dhcpcd-interface.sock
- Control socket to per interface daemon.
SEE ALSO
fnmatch(3),
if_nametoindex(3),
dhcpcd.conf(5),
resolv.conf(5),
dhcpcd-run-hooks(8),
resolvconf(8)
STANDARDS
RFC 951, RFC 1534, RFC 2104, RFC 2131, RFC 2132,
RFC 2563, RFC 2855, RFC 3004, RFC 3118, RFC 3203,
RFC 3315, RFC 3361, RFC 3633, RFC 3396, RFC 3397,
RFC 3442, RFC 3495, RFC 3925, RFC 3927, RFC 4039,
RFC 4075, RFC 4242, RFC 4361, RFC 4390, RFC 4702,
RFC 4074, RFC 4861, RFC 4833, RFC 4941, RFC 5227,
RFC 5942, RFC 5969, RFC 6106, RFC 6334, RFC 6355,
RFC 6603, RFC 6704, RFC 7217, RFC 7550.
AUTHORS
Roy Marples
<
roy@marples.name>
BUGS
Please report them to
http://roy.marples.name/projects/dhcpcd