976e100378
The main dhclient process is Capsicumized but also chroots to restrict filesystem access. With r322369, pidfile(3) maintains a directory descriptor for the pidfile, which can cause the chroot to fail in certain cases. To minimize the problem, only chroot if we fail to enter capability mode, and store dhclient pidfiles in a subdirectory of /var/run, thus restricting access via pidfile(3)'s directory descriptor. PR: 223327 Reviewed by: cem, oshogbo Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D16584
210 lines
6.5 KiB
Groff
210 lines
6.5 KiB
Groff
.\" $OpenBSD: dhclient.8,v 1.3 2004/04/09 18:30:15 jmc Exp $
|
|
.\"
|
|
.\" Copyright (c) 1997 The Internet Software Consortium.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\"
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. Neither the name of The Internet Software Consortium nor the names
|
|
.\" of its contributors may be used to endorse or promote products derived
|
|
.\" from this software without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
|
|
.\" CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
|
|
.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
|
|
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
|
|
.\" DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
|
|
.\" CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
|
|
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
|
|
.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
|
|
.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
|
|
.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
|
|
.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
|
|
.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" This software has been written for the Internet Software Consortium
|
|
.\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
|
|
.\" Enterprises. To learn more about the Internet Software Consortium,
|
|
.\" see ``http://www.isc.org/isc''. To learn more about Vixie
|
|
.\" Enterprises, see ``http://www.vix.com''.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd August 4, 2018
|
|
.Dt DHCLIENT 8
|
|
.Os
|
|
.Sh NAME
|
|
.Nm dhclient
|
|
.Nd "Dynamic Host Configuration Protocol (DHCP) client"
|
|
.Sh SYNOPSIS
|
|
.Nm
|
|
.Op Fl bdqu
|
|
.Op Fl c Ar file
|
|
.Op Fl l Ar file
|
|
.Op Fl p Ar file
|
|
.Ar interface
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
utility provides a means for configuring network interfaces using DHCP, BOOTP,
|
|
or if these protocols fail, by statically assigning an address.
|
|
.Pp
|
|
The name of the network interface that
|
|
.Nm
|
|
should attempt to
|
|
configure must be specified on the command line.
|
|
.Pp
|
|
The options are as follows:
|
|
.Bl -tag -width ".Fl c Ar file"
|
|
.It Fl b
|
|
Forces
|
|
.Nm
|
|
to immediately move to the background.
|
|
.It Fl c Ar file
|
|
Specify an alternate location,
|
|
.Ar file ,
|
|
for the configuration file.
|
|
.It Fl d
|
|
Forces
|
|
.Nm
|
|
to always run as a foreground process.
|
|
By default,
|
|
.Nm
|
|
runs in the foreground until it has configured the interface, and then
|
|
will revert to running in the background.
|
|
.It Fl l Ar file
|
|
Specify an alternate location,
|
|
.Ar file ,
|
|
for the leases file.
|
|
.It Fl p Ar file
|
|
Specify an alternate location for the PID file.
|
|
The default is
|
|
.Pa /var/run/dhclient/dhclient. Ns Ar interface Ns Pa .pid .
|
|
.It Fl q
|
|
Forces
|
|
.Nm
|
|
to be less verbose on startup.
|
|
.It Fl u
|
|
Forces
|
|
.Nm
|
|
to reject leases with unknown options in them.
|
|
The default behaviour is to accept such lease offers.
|
|
.El
|
|
.Pp
|
|
The DHCP protocol allows a host to contact a central server which
|
|
maintains a list of IP addresses which may be assigned on one or more
|
|
subnets.
|
|
A DHCP client may request an address from this pool, and
|
|
then use it on a temporary basis for communication on the network.
|
|
The DHCP protocol also provides a mechanism whereby a client can learn
|
|
important details about the network to which it is attached, such as
|
|
the location of a default router, the location of a name server, and
|
|
so on.
|
|
.Pp
|
|
On startup,
|
|
.Nm
|
|
reads
|
|
.Pa /etc/dhclient.conf
|
|
for configuration instructions.
|
|
It then gets a list of all the
|
|
network interfaces that are configured in the current system.
|
|
It then attempts to configure each interface with DHCP.
|
|
.Pp
|
|
In order to keep track of leases across system reboots and server
|
|
restarts,
|
|
.Nm
|
|
keeps a list of leases it has been assigned in the
|
|
.Pa /var/db/dhclient.leases. Ns Ar IFNAME
|
|
file.
|
|
.Ar IFNAME
|
|
represents the network interface of the DHCP client
|
|
(e.g.,
|
|
.Li em0 ) ,
|
|
one for each interface.
|
|
On startup, after reading the
|
|
.Xr dhclient.conf 5
|
|
file,
|
|
.Nm
|
|
reads the leases file to refresh its memory about what leases it has been
|
|
assigned.
|
|
.Pp
|
|
Old leases are kept around in case the DHCP server is unavailable when
|
|
.Nm
|
|
is first invoked (generally during the initial system boot
|
|
process).
|
|
In that event, old leases from the
|
|
.Pa dhclient.leases. Ns Ar IFNAME
|
|
file which have not yet expired are tested, and if they are determined to
|
|
be valid, they are used until either they expire or the DHCP server
|
|
becomes available.
|
|
.Pp
|
|
A mobile host which may sometimes need to access a network on which no
|
|
DHCP server exists may be preloaded with a lease for a fixed
|
|
address on that network.
|
|
When all attempts to contact a DHCP server have failed,
|
|
.Nm
|
|
will try to validate the static lease, and if it
|
|
succeeds, it will use that lease until it is restarted.
|
|
.Pp
|
|
A mobile host may also travel to some networks on which DHCP is not
|
|
available but BOOTP is.
|
|
In that case, it may be advantageous to
|
|
arrange with the network administrator for an entry on the BOOTP
|
|
database, so that the host can boot quickly on that network rather
|
|
than cycling through the list of old leases.
|
|
.Sh NOTES
|
|
You must have the Berkeley Packet Filter (BPF) configured in your kernel.
|
|
The
|
|
.Nm
|
|
utility
|
|
requires at least one
|
|
.Pa /dev/bpf*
|
|
device for each broadcast network interface that is attached to your system.
|
|
See
|
|
.Xr bpf 4
|
|
for more information.
|
|
.Sh FILES
|
|
.Bl -tag -width ".Pa /var/db/dhclient.leases. Ns Ar IFNAME" -compact
|
|
.It Pa /etc/dhclient.conf
|
|
DHCP client configuration file
|
|
.It Pa /var/db/dhclient.leases. Ns Ar IFNAME
|
|
database of acquired leases
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr dhclient.conf 5 ,
|
|
.Xr dhclient.leases 5 ,
|
|
.Xr dhclient-script 8
|
|
.Sh AUTHORS
|
|
.An -nosplit
|
|
The
|
|
.Nm
|
|
utility
|
|
was written by
|
|
.An Ted Lemon Aq Mt mellon@fugue.com
|
|
and
|
|
.An Elliot Poger Aq Mt elliot@poger.com .
|
|
.Pp
|
|
The current implementation was reworked by
|
|
.An Henning Brauer Aq Mt henning@openbsd.org .
|
|
.Sh BUGS
|
|
The
|
|
.Nm
|
|
utility uses
|
|
.Xr capsicum 4
|
|
to sandbox the main process.
|
|
If the requisite kernel support is not available, the main process will
|
|
attempt to run in a
|
|
.Xr chroot 2
|
|
sandbox instead.
|
|
This will fail if the process is jailed or the
|
|
.Va kern.chroot_allow_open_directories
|
|
sysctl is set to 0.
|