Provided by: dhcpcd5_6.10.1-1_amd64 bug


     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]] [--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] [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
     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

     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 is operating on more than one interface, it is called Master mode. and this
     behaviour can be forced with the -M, --master option so that an individual interface can
     start dhcpcd but only one instance is running.  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.  The -w, --waitip option is enabled in this instance to maintain
     compatibility with older versions.

     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

   Hooking into events
     dhcpcd runs /lib/dhcpcd/dhcpcd-run-hooks, or the script specified by the -c, --script
     option.  This script runs each script found in /lib/dhcpcd/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
     /lib/dhcpcd/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 /lib/dhcpcd/dhcpcd-run-hooks.

     -D, --duid
             Generate an RFC 4361 compliant clientid.  This requires persistent storage and not
             all DHCP servers work with it so it is not enabled by default.  dhcpcd generates the
             DUID and stores it in /etc/dhcpcd.duid.  This file should not be copied to other

     -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.  If the -p, --persistent option is not given then the lease is used if it
             hasn't 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
             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

     -j, --logfile logfile
             Writes to the specified logfile rather than syslog(3).  The logfile is truncated
             when opened and 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.  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.  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.  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 /lib/dhcpcd/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]]
             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

             Here is an example which configures a static address, routes and dns.
                   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

     -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, 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.  -fl -waitip 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.  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

   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.

     -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

     -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, -FL -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 /lib/dhcpcd/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.

             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 futher calls to dhcpcd to rebind, reconfigure or exit need to include the same
     restrictive flags so that dhcpcd knows which process to signal.


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

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

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

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

     /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.

     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.

     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.

     Stores the monotonic counter used in the replay field in Authentication Options.

     Stores the PID of dhcpcd running on all interfaces.

     Stores the PID of dhcpcd running on the interface.

     Control socket to the master daemon.

     Unpriviledged socket to the master daemon, only allows state retrieval.

     Control socket to per interface daemon.


     fnmatch(3), if_nametoindex(3), dhcpcd.conf(5), resolv.conf(5), dhcpcd-run-hooks(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 6603, RFC 6704,
     RFC 7217, RFC 7550.


     Roy Marples <>


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