1DHCPCD(8) BSD System Manager's Manual DHCPCD(8)
2
4 dhcpcd — a DHCP client
5
7 dhcpcd [-146ABbDdEGgHJKLMNPpqTV] [-C, --nohook hook]
8 [-c, --script script] [-e, --env value] [-F, --fqdn FQDN]
9 [-f, --config file] [-h, --hostname hostname]
10 [-I, --clientid clientid] [-i, --vendorclassid vendorclassid]
11 [-j, --logfile logfile] [-l, --leasetime seconds]
12 [-m, --metric metric] [-O, --nooption option]
13 [-o, --option option] [-Q, --require option]
14 [-r, --request address] [-S, --static value]
15 [-s, --inform address[/cidr]] [--inform6] [-t, --timeout seconds]
16 [-u, --userclass class] [-v, --vendor code, value]
17 [-W, --whitelist address[/cidr]] [-w] [--waitip [4 | 6]]
18 [-y, --reboot seconds] [-X, --blacklist address[/cidr]]
19 [-Z, --denyinterfaces pattern] [-z, --allowinterfaces pattern]
20 [--inactive] [interface] [...]
21 dhcpcd -n, --rebind [interface]
22 dhcpcd -k, --release [interface]
23 dhcpcd -U, --dumplease interface
24 dhcpcd --version
25 dhcpcd -x, --exit [interface]
26
28 dhcpcd is an implementation of the DHCP client specified in RFC 2131.
29 dhcpcd gets the host information (IP address, routes, etc) from a DHCP
30 server and configures the network interface of the machine on which it is
31 running. dhcpcd then runs the configuration script which writes DNS
32 information to resolvconf(8), if available, otherwise directly to
33 /etc/resolv.conf. If the hostname is currently blank, (null) or local‐
34 host, or force_hostname is YES or TRUE or 1 then dhcpcd sets the hostname
35 to the one supplied by the DHCP server. dhcpcd then daemonises and waits
36 for the lease renewal time to lapse. It will then attempt to renew its
37 lease and reconfigure if the new lease changes when the lease beings to
38 expire or the DHCP server sends message to renew early.
39 If any interface reports a working carrier then dhcpcd will try and
41 obtain a lease before forking to the background, otherwise it will fork
42 right away. This behaviour can be modified with the -b, --background and
43 -w, --waitip options.
44 dhcpcd is also an implementation of the BOOTP client specified in RFC
46 951.
47 dhcpcd is also an implementation of the IPv6 Router Solicitor as speci‐
49 fied in RFC 4861 and RFC 6106.
50 dhcpcd is also an implementation of the IPv6 Privacy Extensions to Auto‐
52 Conf as specified in RFC 4941. This feature needs to be enabled in the
53 kernel and dhcpcd will start using it.
54 dhcpcd is also an implementation of the DHCPv6 client as specified in RFC
56 3315. By default, dhcpcd only starts DHCPv6 when instructed to do so by
57 an IPV6 Router Advertisement. If no Identity Association is configured,
58 then a Non-temporary Address is requested.
59 Local Link configuration
61 If dhcpcd failed to obtain a lease, it probes for a valid IPv4LL address
62 (aka ZeroConf, aka APIPA). Once obtained it restarts the process of
63 looking for a DHCP server to get a proper address.
64 When using IPv4LL, dhcpcd nearly always succeeds and returns an exit code
66 of 0. In the rare case it fails, it normally means that there is a
67 reverse ARP proxy installed which always defeats IPv4LL probing. To dis‐
68 able this behaviour, you can use the -L, --noipv4ll option.
69 Multiple interfaces
71 If a list of interfaces are given on the command line, then dhcpcd only
72 works with those interfaces, otherwise dhcpcd discovers available Ether‐
73 net interfaces that can be configured. When dhcpcd not limited to one
74 interface on the command line, it is running in Master mode. The
75 dhcpcd-ui project expects dhcpcd to be running this way.
76 If a single interface is given then dhcpcd only works for that interface
78 and runs as a separate instance to other dhcpcd processes. -w, --waitip
79 option is enabled in this instance to maintain compatibility with older
80 versions. Using a single interface also affects the -k, -N, -n and -x
81 options where the same interface will need to be specified as a lack of
82 an interafce will imply Master mode which this is not. To force starting
83 in Master mode with only one interface, the -M, --master option can be
84 used.
85 Interfaces are preferred by carrier, DHCP lease/IPv4LL and then lowest
87 metric. For systems that support route metrics, each route will be
88 tagged with the metric, otherwise dhcpcd changes the routes to use the
89 interface with the same route and the lowest metric. See options below
90 for controlling which interfaces we allow and deny through the use of
91 patterns.
92 Hooking into events
94 dhcpcd runs /usr/libexec/dhcpcd-run-hooks, or the script specified by the
95 -c, --script option. This script runs each script found in
96 /usr/libexec/dhcpcd-hooks in a lexical order. The default installation
97 supplies the scripts 01-test, 02-dump, 20-resolv.conf and 30-hostname.
98 You can disable each script by using the -C, --nohook option. See
99 dhcpcd-run-hooks(8) for details on how these scripts work. dhcpcd cur‐
100 rently ignores the exit code of the script.
101 More scripts are supplied in /usr/share/dhcpcd/hooks and need to be
103 copied to /usr/libexec/dhcpcd-hooks if you intend to use them. For exam‐
104 ple, you could install 10-wpa_supplicant so that dhcpcd can ensure that
105 wpa_supplicant(8) is always running on a hot-plugged wireless interface.
106 Fine tuning
108 You can fine-tune the behaviour of dhcpcd with the following options:
109 -b, --background
111 Background immediately. This is useful for startup scripts which
112 don't disable link messages for carrier status.
113 -c, --script script
115 Use this script instead of the default
116 /usr/libexec/dhcpcd-run-hooks.
117 -D, --duid
119 Generate an RFC 4361 compliant clientid. This requires persis‐
120 tent storage and not all DHCP servers work with it so it is not
121 enabled by default. dhcpcd generates the DUID and stores it in
122 /etc/dhcpcd.duid. This file should not be copied to other hosts.
123 -d, --debug
125 Echo debug messages to the stderr and syslog.
126 -E, --lastlease
128 If dhcpcd cannot obtain a lease, then try to use the last lease
129 acquired for the interface.
130 --lastleaseextend
132 Same as the above, but he lease will be retained even if it
133 expires. dhcpcd will give it up if any other host tries to claim
134 it for their own via ARP. This is does violate RFC2131 section
135 3.7 which states the lease should be dropped once it has expired.
136 -e, --env value
138 Push value to the environment for use in dhcpcd-run-hooks(8).
139 For example, you can force the hostname hook to always set the
140 hostname with -e force_hostname=YES.
141 -g, --reconfigure
143 dhcpcd will re-apply IP address, routing and run
144 dhcpcd-run-hooks(8) for each interface. This is useful so that a
145 3rd party such as PPP or VPN can change the routing table and /
146 or DNS, etc and then instruct dhcpcd to put things back after‐
147 wards. dhcpcd does not read a new configuration when this hap‐
148 pens - you should rebind if you need that functionality.
149 -F, --fqdn fqdn
151 Requests that the DHCP server updates DNS using FQDN instead of
152 just a hostname. Valid values for fqdn are disable, none, ptr
153 and both. dhcpcd itself never does any DNS updates. dhcpcd
154 encodes the FQDN hostname as specified in RFC1035.
155 -f, --config file
157 Specify a config to load instead of /etc/dhcpcd.conf. dhcpcd
158 always processes the config file before any command line options.
159 -h, --hostname hostname
161 Sends hostname to the DHCP server so it can be registered in DNS.
162 If hostname is an empty string then the current system hostname
163 is sent. If hostname is a FQDN (ie, contains a .) then it will
164 be encoded as such.
165 -I, --clientid clientid
167 Send the clientid. If the string is of the format 01:02:03 then
168 it is encoded as hex. For interfaces whose hardware address is
169 longer than 8 bytes, or if the clientid is an empty string then
170 dhcpcd sends a default clientid of the hardware family and the
171 hardware address.
172 -i, --vendorclassid vendorclassid
174 Override the DHCPv4 vendorclassid field sent. The default is
175 dhcpcd-<version>:<os>:<machine>:<platform>. For example
176 dhcpcd-5.5.6:NetBSD-6.99.5:i386:i386
177 If not set then none is sent. Some badly configured DHCP servers
178 reject unknown vendorclassids. To work around it, try and imper‐
179 sonate Windows by using the MSFT vendorclassid.
180 -j, --logfile logfile
182 Writes to the specified logfile rather than syslog(3). The
183 logfile is truncated when opened and is reopened when dhcpcd
184 receives the SIGUSR2 signal.
185 -k, --release [interface]
187 This causes an existing dhcpcd process running on the interface
188 to release its lease and de-configure the interface regardless of
189 the -p, --persistent option. If no interface is specified then
190 this applies to all interfaces in Master mode. If no interfaces
191 are left running, dhcpcd will exit.
192 -l, --leasetime seconds
194 Request a specific lease time in seconds. By default dhcpcd does
195 not request any lease time and leaves it in the hands of the DHCP
196 server.
197 -M, --master
199 Start dhcpcd in Master mode even if only one interface specified
200 on the command line. See the Multiple Interfaces section above.
201 -m, --metric metric
203 Metrics are used to prefer an interface over another one, lowest
204 wins. dhcpcd will supply a default metic of 200 +
205 if_nametoindex(3). An extra 100 will be added for wireless
206 interfaces.
207 -n, --rebind [interface]
209 Notifies dhcpcd to reload its configuration and rebind the speci‐
210 fied interface. If no interface is specified then this applies
211 to all interfaces in Master mode. If dhcpcd is not running, then
212 it starts up as normal. This may also cause wpa_supplicant(8) to
213 reload its configuration for each interface as well if the rele‐
214 vant hook script has been installed.
215 -N, --renew [interface]
217 Notifies dhcpcd to renew existing addresses on the specified
218 interface. If no interface is specified then this applies to all
219 interfaces in Master mode. If dhcpcd is not running, then it
220 starts up as normal. Unlike the -n, --rebind option above, the
221 configuration for dhcpcd is not reloaded.
222 -o, --option option
224 Request the DHCP option variable for use in
225 /usr/libexec/dhcpcd-run-hooks.
226 -p, --persistent
228 dhcpcd normally de-configures the interface and configuration
229 when it exits. Sometimes, this isn't desirable if, for example,
230 you have root mounted over NFS or SSH clients connect to this
231 host and they need to be notified of the host shutting down. You
232 can use this option to stop this from happening.
233 -r, --request [address]
235 Request the address in the DHCP DISCOVER message. There is no
236 guarantee this is the address the DHCP server will actually give.
237 If no address is given then the first address currently assigned
238 to the interface is used.
239 -s, --inform [address[/cidr]]
241 Behaves like -r, --request as above, but sends a DHCP INFORM
242 instead of DISCOVER/REQUEST. This does not get a lease as such,
243 just notifies the DHCP server of the address in use. You should
244 also include the optional cidr network number in case the address
245 is not already configured on the interface. dhcpcd remains run‐
246 ning and pretends it has an infinite lease. dhcpcd will not de-
247 configure the interface when it exits. If dhcpcd fails to con‐
248 tact a DHCP server then it returns a failure instead of falling
249 back on IPv4LL.
250 --inform6
252 Performs a DHCPv6 Information Request. No address is requested
253 or specified, but all other DHCPv6 options are allowed. This is
254 normally performed automatically when the IPv6 Router Advertises
255 that the client should perform this operation. This option is
256 only needed when dhcpcd is not processing IPv6RA messages and the
257 need for DHCPv6 Information Request exists.
258 -S, --static value
260 Configures a static DHCP value. If you set ip_address then
261 dhcpcd will not attempt to obtain a lease and just use the value
262 for the address with an infinite lease time.
263 Here is an example which configures a static address, routes and
265 dns.
266 dhcpcd -S ip_address=192.168.0.10/24 \
267 -S routers=192.168.0.1 \
268 -S domain_name_servers=192.168.0.1 \
269 eth0
270 You cannot presently set static DHCPv6 values. Use the -e, --env
272 option instead.
273 -t, --timeout seconds
275 Timeout after seconds, instead of the default 30. A setting of 0
276 seconds causes dhcpcd to wait forever to get a lease. If dhcpcd
277 is working on a single interface then dhcpcd will exit when a
278 timeout occurs, otherwise dhcpcd will fork into the background.
279 -u, --userclass class
281 Tags the DHCPv4 message with the userclass class. DHCP servers
282 use this to give members of the class DHCP options other than the
283 default, without having to know things like hardware address or
284 hostname.
285 -v, --vendor code,value
287 Add an encapsulated vendor option. code should be between 1 and
288 254 inclusive. To add a raw vendor string, omit code but keep
289 the comma. Examples.
290 Set the vendor option 01 with an IP address.
292 dhcpcd -v 01,192.168.0.2 eth0
293 Set the vendor option 02 with a hex code.
294 dhcpcd -v 02,01:02:03:04:05 eth0
295 Set the vendor option 03 with an IP address as a string.
296 dhcpcd -v 03,\"192.168.0.2\" eth0
297 Set un-encapsulated vendor option to hello world.
298 dhcpcd -v ,"hello world" eth0
299 --version
301 Display both program version and copyright information. dhcpcd
302 then exits before doing any configuration.
303 -w Wait for an address to be assigned before forking to the back‐
305 ground. Does not take an argument, unlike the below option. -fl
306 -waitip option.
307 --waitip [4 | 6]
309 Wait for an address to be assigned before forking to the back‐
310 ground. 4 means wait for an IPv4 address to be assigned. 6
311 means wait for an IPv6 address to be assigned. If no argument is
312 given, dhcpcd will wait for any address protocol to be assigned.
313 It is possible to wait for more than one address protocol and
314 dhcpcd will only fork to the background when all waiting condi‐
315 tions are satisfied.
316 -x, --exit [interface]
318 This will signal an existing dhcpcd process running on the
319 interface to exit. If no interface is specified, then the above
320 is applied to all interfaces in Master mode. See the -p,
321 --persistent option to control configuration persistence on exit,
322 which is enabled by default in dhcpcd.conf(5). dhcpcd then waits
323 until this process has exited.
324 -y, --reboot seconds
326 Allow reboot seconds before moving to the discover phase if we
327 have an old lease to use. Allow reboot seconds before starting
328 fallback states from the discover phase. IPv4LL is started when
329 the first reboot timeout is reached. The default is 5 seconds.
330 A setting of 0 seconds causes dhcpcd to skip the reboot phase and
331 go straight into discover. This has no effect on DHCPv6 other
332 than skipping the reboot phase.
333 Restricting behaviour
335 dhcpcd will try to do as much as it can by default. However, there are
336 sometimes situations where you don't want the things to be configured
337 exactly how the the DHCP server wants. Here are some options that deal
338 with turning these bits off.
339 -1, --oneshot
341 Exit after configuring an interface. Use the -w, --waitip option
342 to specify which protocol(s) to configure before exiting.
343 -4, --ipv4only
345 Configure IPv4 only.
346 -6, --ipv6only
348 Configure IPv6 only.
349 -A, --noarp
351 Don't request or claim the address by ARP. This also disables
352 IPv4LL.
353 -B, --nobackground
355 Don't run in the background when we acquire a lease. This is
356 mainly useful for running under the control of another process,
357 such as a debugger or a network manager.
358 -C, --nohook script
360 Don't run this hook script. Matches full name, or prefixed with
361 2 numbers optionally ending with .sh.
362 So to stop dhcpcd from touching your DNS settings you would do:-
364 dhcpcd -C resolv.conf eth0
365 -G, --nogateway
367 Don't set any default routes.
368 -H, --xidhwaddr
370 Use the last four bytes of the hardware address as the DHCP xid
371 instead of a randomly generated number.
372 -J, --broadcast
374 Instructs the DHCP server to broadcast replies back to the
375 client. Normally this is only set for non Ethernet interfaces,
376 such as FireWire and InfiniBand. In most instances, dhcpcd will
377 set this automatically.
378 -K, --nolink
380 Don't receive link messages for carrier status. You should only
381 have to use this with buggy device drivers or running dhcpcd
382 through a network manager.
383 -L, --noipv4ll
385 Don't use IPv4LL (aka APIPA, aka Bonjour, aka ZeroConf).
386 -O, --nooption option
388 Removes the option from the DHCP message before processing.
389 -P, --printpidfile
391 Print the pidfile dhcpcd will use based on commmand-line argu‐
392 ments to stdout.
393 -Q, --require option
395 Requires the option to be present in all DHCP messages, otherwise
396 the message is ignored. To enforce that dhcpcd only responds to
397 DHCP servers and not BOOTP servers, you can -Q dhcp_message_type.
398 -q, --quiet
400 Quiet dhcpcd on the command line, only warnings and errors will
401 be displayed. The messages are still logged though.
402 -T, --test
404 On receipt of DHCP messages just call
405 /usr/libexec/dhcpcd-run-hooks with the reason of TEST which echos
406 the DHCP variables found in the message to the console. The
407 interface configuration isn't touched and neither are any config‐
408 uration files. The rapid_commit option is not sent in TEST mode
409 so that the server does not lease an address. To test INFORM the
410 interface needs to be configured with the desired address before
411 starting dhcpcd.
412 -U, --dumplease interface
414 Dumps the last lease for the interface to stdout. If omitted,
415 standard input is used to read a DHCP wire formatted message.
416 Use the -4 or -6 flags to specify an address family.
417 -V, --variables
419 Display a list of option codes, the associated variable and
420 encoding for use in dhcpcd-run-hooks(8). Variables are prefixed
421 with new_ and old_ unless the option number is -. Variables
422 without an option are part of the DHCP message and cannot be
423 directly requested.
424 -W, --whitelist address[/cidr]
426 Only accept packets from address[/cidr]. -X, --blacklist is
427 ignored if -W, --whitelist is set.
428 -X, --blacklist address[/cidr]
430 Ignore all packets from address[/cidr].
431 -Z, --denyinterfaces pattern
433 When discovering interfaces, the interface name must not match
434 pattern which is a space or comma separated list of patterns
435 passed to fnmatch(3).
436 -z, --allowinterfaces pattern
438 When discovering interfaces, the interface name must match
439 pattern which is a space or comma separated list of patterns
440 passed to fnmatch(3). If the same interface is matched in -Z,
441 --denyinterfaces then it is still denied.
442 --inactive
444 Don't start any interfaces other than those specified on the com‐
445 mand line. This allows dhcpcd to be started in Master mode and
446 then wait for subsequent dhcpcd commands to start each interface
447 as required.
448 --nodev
450 Don't load any /dev management modules.
451
453 Some interfaces require configuration by 3rd parties, such as PPP or VPN.
454 When an interface configuration in dhcpcd is marked as STATIC or INFORM
455 without an address then dhcpcd will monitor the interface until an
456 address is added or removed from it and act accordingly. For point to
457 point interfaces (like PPP), a default route to its destination is auto‐
458 matically added to the configuration. If the point to point interface is
459 configured for INFORM, then dhcpcd unicasts INFORM to the destination,
460 otherwise it defaults to STATIC.
461
463 dhcpcd requires a Berkley Packet Filter, or BPF device on BSD based sys‐
464 tems and a Linux Socket Filter, or LPF device on Linux based systems for
465 all IPv4 configuration.
466 If restricting dhcpcd to a single interface and optionally address family
468 via the command-line then all further calls to dhcpcd to rebind, recon‐
469 figure or exit need to include the same restrictive flags so that dhcpcd
470 knows which process to signal.
471
473 /etc/dhcpcd.conf
474 Configuration file for dhcpcd. If you always use the same options, put
475 them here.
476 /etc/dhcpcd.duid
478 Text file that holds the DUID used to identify the host.
479 /etc/dhcpcd.secret
481 Text file that holds a secret key known only to the host.
482 /usr/libexec/dhcpcd-run-hooks
484 Bourne shell script that is run to configure or de-configure an inter‐
485 face.
486 /usr/lib64/dhcpcd/dev
488 /dev management modules.
489 /usr/libexec/dhcpcd-hooks
491 A directory containing bourne shell scripts that are run by the above
492 script. Each script can be disabled by using the -C, --nohook option
493 described above.
494 /var/lib/dhcpcd/dhcpcd-interface-ssid.lease
496 The actual DHCP message sent by the server. We use this when reading the
497 last lease and use the files mtime as when it was issued.
498 /var/lib/dhcpcd/dhcpcd-interface-ssid.lease6
500 The actual DHCPv6 message sent by the server. We use this when reading
501 the last lease and use the files mtime as when it was issued.
502 /var/lib/dhcpcd/dhcpcd-rdm.monotonic
504 Stores the monotonic counter used in the replay field in Authentication
505 Options.
506 /var/run/dhcpcd.pid
508 Stores the PID of dhcpcd running on all interfaces.
509 /var/run/dhcpcd-interface.pid
511 Stores the PID of dhcpcd running on the interface.
512 /var/run/dhcpcd.sock
514 Control socket to the master daemon.
515 /var/run/dhcpcd.unpriv.sock
517 Unpriviledged socket to the master daemon, only allows state retrieval.
518 /var/run/dhcpcd-interface.sock
520 Control socket to per interface daemon.
521
523 fnmatch(3), if_nametoindex(3), dhcpcd.conf(5), resolv.conf(5),
524 dhcpcd-run-hooks(8), resolvconf(8)
525
527 RFC 951, RFC 1534, RFC 2104, RFC 2131, RFC 2132, RFC 2563, RFC 2855,
528 RFC 3004, RFC 3118, RFC 3203, RFC 3315, RFC 3361, RFC 3633, RFC 3396,
529 RFC 3397, RFC 3442, RFC 3495, RFC 3925, RFC 3927, RFC 4039, RFC 4075,
530 RFC 4242, RFC 4361, RFC 4390, RFC 4702, RFC 4074, RFC 4861, RFC 4833,
531 RFC 4941, RFC 5227, RFC 5942, RFC 5969, RFC 6106, RFC 6334, RFC 6603,
532 RFC 6704, RFC 7217, RFC 7550.
533
535 Roy Marples <roy@marples.name>
536
538 Please report them to
539 http://roy.marples.name/projects/dhcpcd
540BSD August 15, 2016 BSD