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6695d9cf | 1 | .\" $OpenBSD: src/sbin/dhclient/dhclient.8,v 1.8 2011/03/02 07:44:42 jmc Exp $ |
846204b6 HT |
2 | .\" |
3 | .\" Copyright (c) 1997 The Internet Software Consortium. | |
4 | .\" All rights reserved. | |
5 | .\" | |
6 | .\" Redistribution and use in source and binary forms, with or without | |
7 | .\" modification, are permitted provided that the following conditions | |
8 | .\" are met: | |
9 | .\" | |
10 | .\" 1. Redistributions of source code must retain the above copyright | |
11 | .\" notice, this list of conditions and the following disclaimer. | |
12 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
13 | .\" notice, this list of conditions and the following disclaimer in the | |
14 | .\" documentation and/or other materials provided with the distribution. | |
15 | .\" 3. Neither the name of The Internet Software Consortium nor the names | |
16 | .\" of its contributors may be used to endorse or promote products derived | |
17 | .\" from this software without specific prior written permission. | |
18 | .\" | |
19 | .\" THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND | |
20 | .\" CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, | |
21 | .\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF | |
22 | .\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE | |
23 | .\" DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR | |
24 | .\" CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | |
25 | .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT | |
26 | .\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF | |
27 | .\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND | |
28 | .\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, | |
29 | .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT | |
30 | .\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
31 | .\" SUCH DAMAGE. | |
32 | .\" | |
33 | .\" This software has been written for the Internet Software Consortium | |
34 | .\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie | |
35 | .\" Enterprises. To learn more about the Internet Software Consortium, | |
36 | .\" see ``http://www.isc.org/isc''. To learn more about Vixie | |
37 | .\" Enterprises, see ``http://www.vix.com''. | |
68021bf1 | 38 | .Dd September 3, 2008 |
846204b6 HT |
39 | .Dt DHCLIENT 8 |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm dhclient | |
43 | .Nd Dynamic Host Configuration Protocol (DHCP) Client | |
44 | .Sh SYNOPSIS | |
45 | .Nm | |
46 | .Op Fl dqu | |
47 | .Op Fl c Ar file | |
48 | .Op Fl l Ar file | |
49 | .Ar interface | |
50 | .Sh DESCRIPTION | |
51 | The | |
52 | .Nm | |
53 | utility provides a means for configuring network interfaces using DHCP, BOOTP, | |
54 | or if these protocols fail, by statically assigning an address. | |
55 | .Pp | |
56 | The name of the network interface that | |
57 | .Nm | |
58 | should attempt to | |
59 | configure must be specified on the command line. | |
60 | .Pp | |
61 | The options are as follows: | |
62 | .Bl -tag -width "-p port" | |
63 | .It Fl c Ar file | |
64 | Specify an alternate location, | |
65 | .Ar file , | |
66 | for the configuration file. | |
67 | .It Fl d | |
68 | Forces | |
69 | .Nm | |
70 | to always run as a foreground process. | |
71 | By default, | |
72 | .Nm | |
73 | runs in the foreground until it has configured the interface, and then | |
74 | will revert to running in the background. | |
75 | .It Fl l Ar file | |
76 | Specify an alternate location, | |
77 | .Ar file , | |
78 | for the leases file. | |
79 | .It Fl q | |
80 | Forces | |
81 | .Nm | |
82 | to be less verbose on startup. | |
83 | .It Fl u | |
84 | Forces | |
85 | .Nm | |
86 | to reject leases with unknown options in them. | |
87 | The default behaviour is to accept such lease offers. | |
88 | .El | |
89 | .Pp | |
90 | The DHCP protocol allows a host to contact a central server which | |
91 | maintains a list of IP addresses which may be assigned on one or more | |
92 | subnets. | |
93 | A DHCP client may request an address from this pool, and | |
94 | then use it on a temporary basis for communication on the network. | |
95 | The DHCP protocol also provides a mechanism whereby a client can learn | |
96 | important details about the network to which it is attached, such as | |
97 | the location of a default router, the location of a name server, and | |
98 | so on. | |
99 | .Pp | |
100 | On startup, | |
101 | .Nm | |
102 | reads | |
103 | .Pa /etc/dhclient.conf | |
104 | for configuration instructions. | |
105 | It then gets a list of all the | |
106 | network interfaces that are configured in the current system. | |
107 | It then attempts to configure each interface with DHCP. | |
108 | .Pp | |
109 | In order to keep track of leases across system reboots and server | |
110 | restarts, | |
111 | .Nm | |
112 | keeps a list of leases it has been assigned in the | |
113 | .Pa /var/db/dhclient.leases.IFNAME | |
114 | file. | |
115 | .Qq IFNAME | |
116 | represents the network interface of the DHCP client | |
117 | .Pq e.g. em0 , | |
118 | one for each interface. | |
119 | On startup, after reading the | |
120 | .Xr dhclient.conf 5 | |
121 | file, | |
122 | .Nm | |
123 | reads the leases file to refresh its memory about what leases it has been | |
124 | assigned. | |
125 | .Pp | |
126 | Old leases are kept around in case the DHCP server is unavailable when | |
127 | .Nm | |
128 | is first invoked (generally during the initial system boot | |
129 | process). | |
130 | In that event, old leases from the | |
131 | .Pa dhclient.leases.IFNAME | |
132 | file which have not yet expired are tested, and if they are determined to | |
133 | be valid, they are used until either they expire or the DHCP server | |
134 | becomes available. | |
135 | .Pp | |
136 | A mobile host which may sometimes need to access a network on which no | |
137 | DHCP server exists may be preloaded with a lease for a fixed | |
138 | address on that network. | |
139 | When all attempts to contact a DHCP server have failed, | |
140 | .Nm | |
141 | will try to validate the static lease, and if it | |
142 | succeeds, it will use that lease until it is restarted. | |
143 | .Pp | |
144 | A mobile host may also travel to some networks on which DHCP is not | |
145 | available but BOOTP is. | |
146 | In that case, it may be advantageous to | |
147 | arrange with the network administrator for an entry on the BOOTP | |
148 | database, so that the host can boot quickly on that network rather | |
149 | than cycling through the list of old leases. | |
6695d9cf | 150 | .Pp |
846204b6 HT |
151 | .Nm |
152 | requires at least one | |
153 | .Pa /dev/bpf* | |
6695d9cf | 154 | file for each broadcast network interface. |
846204b6 HT |
155 | See |
156 | .Xr bpf 4 | |
157 | for more information. | |
158 | .Sh FILES | |
159 | .Bl -tag -width /var/db/dhclient.leases.IFNAME~ -compact | |
160 | .It Pa /etc/dhclient.conf | |
161 | DHCP client configuration file | |
162 | .It Pa /var/db/dhclient.leases.IFNAME | |
163 | database of acquired leases | |
164 | .El | |
165 | .Sh SEE ALSO | |
166 | .Xr bpf 4 , | |
167 | .Xr dhclient.conf 5 , | |
168 | .Xr dhclient.leases 5 , | |
169 | .Xr dhclient-script 8 , | |
170 | .Xr dhcp 8 , | |
aa4e0df8 SW |
171 | .Xr dhcpd 8 Pq Pa pkgsrc/net/isc-dhcpd4 , |
172 | .Xr dhcrelay 8 Pq Pa pkgsrc/net/isc-dhcrelay4 | |
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173 | .Sh AUTHORS |
174 | .An -nosplit | |
175 | .Nm | |
176 | was written by | |
177 | .An Ted Lemon Aq mellon@fugue.com | |
178 | and | |
179 | .An Elliot Poger Aq elliot@poger.com . | |
180 | .Pp | |
181 | The current implementation was reworked by | |
68021bf1 MS |
182 | .An Henning Brauer Aq henning@openbsd.org |
183 | and was imported into | |
184 | .Dx 2.1 . |