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DHCPCD(8)                   System Manager's Manual                  DHCPCD(8)

     dhcpcd - a DHCP client

     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] [--configure]
            [--noconfigure] [interface] [...]
     dhcpcd -n, --rebind [interface]
     dhcpcd -k, --release [interface]
     dhcpcd -U, --dumplease [interface]
     dhcpcd --version
     dhcpcd -x, --exit [interface]

     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
     begins to expire or the DHCP server sends a message to renew early.

     If any interface reports a working carrier then dhcpcd will try to 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

     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 Manager 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 interface will imply Manager mode which this is not.  To force
     starting in Manager mode with only one interface, the -M, --manager
     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

     Non-ethernet interfaces and some virtual ethernet interfaces such as TAP
     and bridge are ignored by default, as is the FireWire interface.  To work
     with these devices they either need to be specified on the command line,
     be listed in --allowinterfaces or have an interface directive in

   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/dhcpcd/hooks and need to be
     copied to /libexec/dhcpcd-hooks if you intend to use them.  For example,
     you could install 29-lookup-hostname so that dhcpcd can lookup the
     hostname of the IP address in DNS if no hostname is given by the lease
     and one is not already set.

   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 [ll | lt | uuid | value]
             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).  The DUID type can be hinted as an optional parameter
             if the file /var/db/dhcpcd/duid does not exist.  If not ll, lt or
             uuid then value will be converted from 00:11:22:33 format.  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 except for setting a value.

     -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.

             Same as the above, but the 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 violates RFC 2131, 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 RFC 1035.

     -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 (i.e., 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
             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.  dhcpcd still writes to
             syslog(3).  The logfile is 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 Manager mode.  If no interfaces
             are left running, dhcpcd will exit.

     -l, --leasetime seconds
             Request a lease time of seconds.  -1 represents an infinite lease
             time.  By default dhcpcd does not request any lease time and
             leaves it in the hands of the DHCP server.

     -M, --manager
             Start dhcpcd in Manager 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 metric of 1000 +
             if_nametoindex(3).  This will be offset by 2000 for wireless
             interfaces, with additional offsets of 1000000 for IPv4LL and
             2000000 for roaming 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 Manager mode.  If dhcpcd is not
             running, then it starts up as normal.

     -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 Manager 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

     -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.

             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
                   dhcpcd -S ip_address= \
                   -S routers= \
                   -S domain_name_servers= \

             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

     -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, 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,\"\" eth0
             Set un-encapsulated vendor option to hello world.
                   dhcpcd -v ,"hello world" eth0

             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 Manager 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 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

     -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.  If this option is used another time then all
             console output is disabled.  These messages are still logged via

     -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 current lease for the interface to stdout.  If no
             interface is given then all interfaces are dumped.  Use the -4 or
             -6 flags to specify an address family.  If a lease is piped in
             via standard input then that is dumped.  In this case, specifying
             an address family is mandatory.

     -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.

             Don't start any interfaces other than those specified on the
             command line.  This allows dhcpcd to be started in Manager mode
             and then wait for subsequent dhcpcd commands to start each
             interface as required.

             Allows dhcpcd to configure the system.  This is the default
             behaviour and sets if_configured=true.

             dhcpcd will not configure the system at all.  This is only of use
             if the --script that dhcpcd calls at each network event
             configures the system instead.  This is different from -T, --test
             mode in that it's not one shot and the only change to the
             environment is the addition of if_configured=false.

             Don't load any /dev management modules.

     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.

     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.

     Configuration file for dhcpcd.  If you always use the same options, put
     them here.

     Bourne shell script that is run to configure or de-configure an

     Linux /dev management modules.

     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.

     Text file that holds the DUID used to identify the host.

     Text file that holds a secret key known only to the host.

     The actual DHCP message sent by the server.  We use this when reading the
     last lease and use the file's mtime as when it was issued.

     The actual DHCPv6 message sent by the server.  We use this when reading
     the last lease and use the file's mtime as when it was issued.

     Stores the monotonic counter used in the replay field in Authentication

     Stores the PID of dhcpcd running on all interfaces.

     Stores the PID of dhcpcd running on the interface.

     Control socket to the manager daemon.

     Unprivileged socket to the manager daemon, only allows state retrieval.

     Control socket to per interface daemon.

     Unprivileged socket to per interface daemon, only allows state retrieval.

     fnmatch(3), if_nametoindex(3), dhcpcd.conf(5), resolv.conf(5),
     dhcpcd-run-hooks(8), resolvconf(8)

     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, RFC 7844.

     Roy Marples <roy@marples.name>

     Please report them to http://roy.marples.name/projects/dhcpcd

NetBSD 9.99                     August 23, 2021                    NetBSD 9.99