dhclient(8) - Remove NOTES section.
[dragonfly.git] / sbin / dhclient / dhclient.8
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6695d9cf 1.\" $OpenBSD: src/sbin/dhclient/dhclient.8,v 1.8 2011/03/02 07:44:42 jmc Exp $
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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
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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
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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
51The
52.Nm
53utility provides a means for configuring network interfaces using DHCP, BOOTP,
54or if these protocols fail, by statically assigning an address.
55.Pp
56The name of the network interface that
57.Nm
58should attempt to
59configure must be specified on the command line.
60.Pp
61The options are as follows:
62.Bl -tag -width "-p port"
63.It Fl c Ar file
64Specify an alternate location,
65.Ar file ,
66for the configuration file.
67.It Fl d
68Forces
69.Nm
70to always run as a foreground process.
71By default,
72.Nm
73runs in the foreground until it has configured the interface, and then
74will revert to running in the background.
75.It Fl l Ar file
76Specify an alternate location,
77.Ar file ,
78for the leases file.
79.It Fl q
80Forces
81.Nm
82to be less verbose on startup.
83.It Fl u
84Forces
85.Nm
86to reject leases with unknown options in them.
87The default behaviour is to accept such lease offers.
88.El
89.Pp
90The DHCP protocol allows a host to contact a central server which
91maintains a list of IP addresses which may be assigned on one or more
92subnets.
93A DHCP client may request an address from this pool, and
94then use it on a temporary basis for communication on the network.
95The DHCP protocol also provides a mechanism whereby a client can learn
96important details about the network to which it is attached, such as
97the location of a default router, the location of a name server, and
98so on.
99.Pp
100On startup,
101.Nm
102reads
103.Pa /etc/dhclient.conf
104for configuration instructions.
105It then gets a list of all the
106network interfaces that are configured in the current system.
107It then attempts to configure each interface with DHCP.
108.Pp
109In order to keep track of leases across system reboots and server
110restarts,
111.Nm
112keeps a list of leases it has been assigned in the
113.Pa /var/db/dhclient.leases.IFNAME
114file.
115.Qq IFNAME
116represents the network interface of the DHCP client
117.Pq e.g. em0 ,
118one for each interface.
119On startup, after reading the
120.Xr dhclient.conf 5
121file,
122.Nm
123reads the leases file to refresh its memory about what leases it has been
124assigned.
125.Pp
126Old leases are kept around in case the DHCP server is unavailable when
127.Nm
128is first invoked (generally during the initial system boot
129process).
130In that event, old leases from the
131.Pa dhclient.leases.IFNAME
132file which have not yet expired are tested, and if they are determined to
133be valid, they are used until either they expire or the DHCP server
134becomes available.
135.Pp
136A mobile host which may sometimes need to access a network on which no
137DHCP server exists may be preloaded with a lease for a fixed
138address on that network.
139When all attempts to contact a DHCP server have failed,
140.Nm
141will try to validate the static lease, and if it
142succeeds, it will use that lease until it is restarted.
143.Pp
144A mobile host may also travel to some networks on which DHCP is not
145available but BOOTP is.
146In that case, it may be advantageous to
147arrange with the network administrator for an entry on the BOOTP
148database, so that the host can boot quickly on that network rather
149than cycling through the list of old leases.
6695d9cf 150.Pp
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151.Nm
152requires at least one
153.Pa /dev/bpf*
6695d9cf 154file for each broadcast network interface.
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155See
156.Xr bpf 4
157for more information.
158.Sh FILES
159.Bl -tag -width /var/db/dhclient.leases.IFNAME~ -compact
160.It Pa /etc/dhclient.conf
161DHCP client configuration file
162.It Pa /var/db/dhclient.leases.IFNAME
163database 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 ,
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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
176was written by
177.An Ted Lemon Aq mellon@fugue.com
178and
179.An Elliot Poger Aq elliot@poger.com .
180.Pp
181The current implementation was reworked by
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182.An Henning Brauer Aq henning@openbsd.org
183and was imported into
184.Dx 2.1 .