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DHCLIENT(8) FreeBSD System Manager's Manual DHCLIENT(8)
NAME
dhclient - Dynamic Host Configuration Protocol (DHCP) client
SYNOPSIS
dhclient [-bdqu] [-c file] [-l file] [-p file] interface
DESCRIPTION
The dhclient utility provides a means for configuring network interfaces
using DHCP, BOOTP, or if these protocols fail, by statically assigning an
address.
The name of the network interface that dhclient should attempt to
configure must be specified on the command line.
The options are as follows:
-b Forces dhclient to immediately move to the background.
-c file Specify an alternate location, file, for the configuration
file.
-d Forces dhclient to always run as a foreground process. By
default, dhclient runs in the foreground until it has
configured the interface, and then will revert to running in
the background.
-l file Specify an alternate location, file, for the leases file.
-p file Specify an alternate location for the PID file. The default
is /var/run/dhclient/dhclient.interface.pid.
-q Forces dhclient to be less verbose on startup.
-u Forces dhclient to reject leases with unknown options in them.
The default behaviour is to accept such lease offers.
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.
On startup, dhclient reads /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.
In order to keep track of leases across system reboots and server
restarts, dhclient keeps a list of leases it has been assigned in the
/var/db/dhclient.leases.IFNAME file. IFNAME represents the network
interface of the DHCP client (e.g., em0), one for each interface. On
startup, after reading the dhclient.conf(5) file, dhclient reads the
leases file to refresh its memory about what leases it has been assigned.
Old leases are kept around in case the DHCP server is unavailable when
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,
dhclient will try to validate the static lease, and if it succeeds, it
will use that lease until it is restarted.
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.
NOTES
You must have the Berkeley Packet Filter (BPF) configured in your kernel.
The dhclient utility requires at least one /dev/bpf* device for each
broadcast network interface that is attached to your system. See bpf(4)
for more information.
FILES
/etc/dhclient.conf DHCP client configuration file
/var/db/dhclient.leases.IFNAME database of acquired leases
SEE ALSO
dhclient.conf(5), dhclient.leases(5), dhclient-script(8)
AUTHORS
The dhclient utility was written by Ted Lemon <mellon@fugue.com> and
Elliot Poger <elliot@poger.com>.
The current implementation was reworked by Henning Brauer
<henning@openbsd.org>.
BUGS
The dhclient utility uses capsicum(4) to sandbox the main process. If
the requisite kernel support is not available, the main process will
attempt to run in a chroot(2) sandbox instead. This will fail if the
process is jailed or the kern.chroot_allow_open_directories sysctl is set
to 0.
FreeBSD 14.0-RELEASE-p11 August 4, 2018 FreeBSD 14.0-RELEASE-p11