166 lines
3.8 KiB
Groff
166 lines
3.8 KiB
Groff
.Dd January 15, 2023
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.Dt DHCLIENT 8
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.Os
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.Sh NAME
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.Nm dhclient
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.Nd dynamic host configuration protocol client
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.Sh SYNOPSIS
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.Nm
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.Op Fl f Ar config
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.Op Fl t
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.Ar interface
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.Sh DESCRIPTION
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.Nm
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dynamically configures the specified network
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.Ar interface
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.Xr ( if 4 )
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and the Domain Name System (DNS) server list
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via the Dynamic Host Configuration Protocol (DHCP) with settings obtained from
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the local network's DHCP server.
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.Pp
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.Nm
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is configured in
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.Xr dhclient.conf 5 .
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Each network setting can be configured to be automatically obtained from the
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network (default), set manually, or not set at all.
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If the interface is fully manually configured,
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.Nm
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sets the configuration and exits immediately.
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.Pp
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.Nm
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broadcasts a request and selects a DHCP server to obtain the network
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configuration from.
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.Nm
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leases an internet address as needed and remains running to occasionally renew
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the release.
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.Pp
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The options are as follows:
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.Bl -tag -width "12345678"
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.It Fl f Ar config
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Load the configuration from the
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.Ar config
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file instead as a shared configuration file instead of searching for it.
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.It Fl t
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Test the configuration is valid without configuring the network interface.
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The
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.Ar interface
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can optionally be specified to search for its configuration file.
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Exit 0 if the configuration is valid and non-zero otherwise.
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.El
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.Pp
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Port 68 on the network interface is bound to send and receive DHCP messages.
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.Nm
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exits 0 immediately if the port is already bound to avoid interfering with other
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.Nm
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processes.
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.Pp
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.Nm
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supports the Ethernet link layer
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.Xr ether 4
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with the Internet Protocol network layer
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.Xr ip 4 .
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The loopback interface
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.Xr lo 4
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does not need to be configured and
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.Nm
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immediately exits successfully.
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.Pp
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Network interfaces can be manually configured using
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.Xr ifconfig 8
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and the DNS servers using
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.Xr dnsconfig 8 .
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.Nm
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will occasionally reset the configuration when the internet address lease is
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renewed unless disabled.
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.Pp
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.Nm
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is typically automatically started as the
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.Sy dhclient
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daemon, which is depended on by the
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.Sy network
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daemon per the
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.Xr init 5
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configuration.
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.Sh IMPLEMENTATION NOTES
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.Nm
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signals readiness when it has attempted to configure the network interface and
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continues retrying afterwards.
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The first attempt fails if the network interface's link doesn't come up within
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10 seconds.
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Packets are transmitted 6 times with an exponential backoff before giving up
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and the configuration restarts.
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.Sh FILES
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.Bl -tag -width "/etc/dhclient.${mac}.conf" -compact
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.It Pa /etc/dhclient.${mac}.conf
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The preferred
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.Xr dhclient.conf 5
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file for the interface with the hardware address
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.Ar mac .
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.It Pa /etc/dhclient.${if}.conf
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The second priority
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.Xr dhclient.conf 5
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file for the interface with the device name
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.Ar if .
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.It Pa /etc/dhclient.conf
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The lowest priority
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.Xr dhclient.conf 5
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file shared across all network interfaces.
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.El
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.Sh ASYNCHRONOUS EVENTS
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.Bl -tag -width "SIGUSR1"
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.It Dv SIGTERM
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Request daemon termination.
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.El
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.Sh EXIT STATUS
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.Nm
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runs as a
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.Xr daemon 7
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until stopped by
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.Dv SIGTERM .
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.Nm
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signals readiness on the
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.Ev READYFD
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file descriptor when the interface is configured, when waiting for the link to
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come up times out, or when the DHCP server doesn't respond in time or
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configuration fails.
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.Nm
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will exit 0 if the network interface doesn't need to be configured or is fully
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manually configured and will exit non-zero on any fatal startup error.
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.Sh EXAMPLES
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See
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.Xr dhclient.conf 5
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for example configurations.
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.Pp
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See
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.Xr init 5
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for an example disabling the
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.Sy dhclient
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daemon by removing the
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.Sy network
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daemon's dependency on it.
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.Sh SEE ALSO
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.Xr ether 4 ,
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.Xr if 4 ,
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.Xr inet 4 ,
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.Xr ip 4 ,
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.Xr dnsconfig 8 ,
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.Xr ifconfig 8 ,
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.Xr init 8
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.Sh STANDARDS
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.Rs
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.%A R. Droms
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.%D March 1997
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.%R RFC 2131
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.%T Dynamic Host Configuration Protocol
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.%Q Network Working Group
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.Re
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.Pp
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.Rs
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.%A S. Alexander
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.%A R. Droms
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.%D March 1997
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.%R RFC 2132
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.%T DHCP Options and BOOTP Vendor Extensions
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.%Q Network Working Group
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.Re
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