dhcpd.leases.5

DHCP服务器源码

.\"	dhcpd.leases.5
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.\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
.\" Copyright (c) 1996-2003 by Internet Software Consortium
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.\" This software has been written for Internet Systems Consortium
.\" by Ted Lemon in cooperation with Vixie Enterprises and Nominum, Inc.
.\" To learn more about Internet Systems Consortium, see
.\" ``http://www.isc.org/''.  To learn more about Vixie Enterprises,
.\" see ``http://www.vix.com''.   To learn more about Nominum, Inc., see
.\" ``http://www.nominum.com''.
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.\" $Id: dhcpd.leases.5,v 1.8.2.6 2004/06/10 17:59:53 dhankins Exp $
.\"
.TH dhcpd.leases 5
.SH NAME
dhcpd.leases - DHCP client lease database
.SH DESCRIPTION
The Internet Systems Consortium DHCP Server keeps a persistent
database of leases that it has assigned.  This database is a free-form
ASCII file containing a series of lease declarations.  Every time a
lease is acquired, renewed or released, its new value is recorded at
the end of the lease file.  So if more than one declaration appears
for a given lease, the last one in the file is the current one.
.PP
When dhcpd is first installed, there is no lease database.   However,
dhcpd requires that a lease database be present before it will start.
To make the initial lease database, just create an empty file called
DBDIR/dhcpd.leases.   You can do this with:
.PP
.nf
	touch DBDIR/dhcpd.leases
.fi
.PP
In order to prevent the lease database from growing without bound, the
file is rewritten from time to time.   First, a temporary lease
database is created and all known leases are dumped to it.   Then, the
old lease database is renamed DBDIR/dhcpd.leases~.   Finally, the
newly written lease database is moved into place.
.SH FORMAT
Lease descriptions are stored in a format that is parsed by the same
recursive descent parser used to read the
.B dhcpd.conf(5)
and
.B dhclient.conf(5)
files.  Lease files can contain lease declarations, and also group and
subgroup declarations, host declarations and failover state
declarations.  Group, subgroup and host declarations are used to
record objects created using the OMAPI protocol.
.PP
The lease file is a log-structured file - whenever a lease changes,
the contents of that lease are written to the end of the file.   This
means that it is entirely possible and quite reasonable for there to
be two or more declarations of the same lease in the lease file at the
same time.   In that case, the instance of that particular lease that
appears last in the file is the one that is in effect.
.PP
Group, subgroup and host declarations in the lease file are handled in
the same manner, except that if any of these objects are deleted, a
\fIrubout\fR is written to the lease file.   This is just the same
declaration, with \fB{ deleted; }\fR in the scope of the
declaration.   When the lease file is rewritten, any such rubouts that
can be eliminated are eliminated.   It is possible to delete a
declaration in the \fBdhcpd.conf\fR file; in this case, the rubout
can never be eliminated from the \fBdhcpd.leases\fR file.
.SH THE LEASE DECLARATION
.PP
.B lease \fIip-address\fB { \fIstatements...\fB }
.PP
Each lease declaration includes the single IP address that has been
leased to the client.   The statements within the braces define the
duration of the lease and to whom it is assigned.
.PP
.nf
.B starts \fIdate\fB;\fR
.B ends \fIdate\fB;\fR
.B tstp \fIdate\fB;\fR
.B tsfp \fIdate\fB;\fR
.fi
.PP
The start and end time of a lease are recorded using the \fBstarts\fR
and \fBends\fR statements.   The \fBtstp\fR statement is specified if
the failover protocol is being used, and indicates what time the peer
has been told the lease expires.   The \fBtsfp\fR statement is
also specified if the failover protocol is being used, and indicates
the lease expiry time that the peer has acknowledged.   The \fIdate\fR
is specified as follows:
.PP
.I weekday year\fB/\fImonth\fB/\fIday hour\fB:\fIminute\fB:\fIsecond\fR
.PP
The weekday is present to make it easy for a human to tell when a
lease expires - it's specified as a number from zero to six, with zero
being Sunday.  The day of week is ignored on input.  The year is
specified with the century, so it should generally be four digits
except for really long leases.  The month is specified as a number
starting with 1 for January.  The day of the month is likewise
specified starting with 1.  The hour is a number between 0 and 23, the
minute a number between 0 and 59, and the second also a number between
0 and 59.
.PP
Lease times are specified in Universal Coordinated Time (UTC), not in
the local time zone.  There is probably nowhere in the world where the
times recorded on a lease are always the same as wall clock times.  On
most unix machines, you can display the current time in UTC by typing
\fBdate -u\fR.
.PP
If a lease will never expire, \fIdate\fR is \fBnever\fR instead of an
actual date.
.PP
.B hardware \fIhardware-type mac-address\fB;\fR
.PP
The hardware statement records the MAC address of the network
interface on which the lease will be used.   It is specified as a
series of hexadecimal octets, separated by colons.
.PP
.B uid \fIclient-identifier\fB;\fR
.PP
The \fBuid\fR statement records the client identifier used by the
client to acquire the lease.   Clients are not required to send client
identifiers, and this statement only appears if the client did in fact
send one.   Client identifiers are normally an ARP type (1 for
ethernet) followed by the MAC address, just like in the \fBhardware\fI
statement, but this is not required.
.PP
The client identifier is recorded as a colon-separated hexadecimal
list or as a quoted string.   If it is recorded as a quoted string and
it contains one or more non-printable characters, those characters are
represented as octal escapes - a backslash character followed by three
octal digits.
.PP
.B client-hostname "\fIhostname\fB";\fR
.PP
Most DHCP clients will send their hostname in the \fIhost-name\fR
option.  If a client sends its hostname in this way, the hostname is
recorded on the lease with a \fBclient-hostname\fR statement.   This
is not required by the protocol, however, so many specialized DHCP
clients do not send a host-name option.
.PP
.B abandoned;
.PP
The \fBabandoned\fR statement indicates that the DHCP server has
abandoned the lease.   In that case, the \fBabandoned\fR statement
will be used to indicate that the lease should not be reassigned.
Please see the \fBdhcpd.conf(5)\fR manual page for information about
abandoned leases.
.PP
.B binding state \fIstate\fB;
.B next binding state \fIstate\fB;
.PP
The \fBbinding state\fR statement declares the lease's binding state.
When the DHCP server is not configured to use the failover protocol, a
lease's binding state will be either \fBactive\fR or \fBfree\fR.   The
failover protocol adds some additional transitional states, as well as
the \fBbackup\fR state, which indicates that the lease is available
for allocation by the failover secondary.
.PP
The \fBnext binding state\fR statement indicates what state the lease
will move to when the current state expires.   The time when the
current state expires is specified in the \fIends\fR statement.
.PP
.B option agent.circuit-id \fIstring\fR;
.B option agent.remote-id \fIstring\fR;
.PP
The \fBoption agent.circuit-id\fR and \fBoption agent.remote-id\fR
statements are used to record the circuit ID and remote ID options
send by the relay agent, if the relay agent uses the \fIrelay agent
information option\fR.   This allows these options to be used
consistently in conditional evaluations even when the client is
contacting the server directly rather than through its relay agent.
.PP
.B set \fIvariable\fB = \fIvalue\fB;
.PP
The \fBset\fR statement sets the value of a variable on the lease.
For general information on variables, see the \fBdhcp-eval(5)\fR
manual page.
.PP
.B The \fIddns-text\fB variable
.PP
The \fIddns-text\fR variable is used to record the value of the
client's TXT identification record when the interim ddns update
style has been used to update the DNS for a particular lease.
.PP
.B The \fIddns-fwd-name\fB variable
.PP
The \fIddns-fwd-name\fB variable records the value of the name used in
updating the client's A record if a DDNS update has been successfully
done by the server.   The server may also have used this name to
update the client's PTR record.
.PP
.B The \fIddns-client-fqdn\fB variable
.PP
If the server is configured to use the interim ddns update style, and
is also configured to allow clients to update their own fqdns, and the
client did in fact update its own fqdn, then the
\fIddns-client-fqdn\fR variable records the name that the client has
indicated it is using.   This is the name that the server will have
used to update the client's PTR record in this case.
.PP
.B The \fIddns-rev-name\fB variable
.PP
If the server successfully updates the client's PTR record, this
variable will record the name that the DHCP server used for the PTR
record.   The name to which the PTR record points will be either the
\fIddns-fwd-name\fR or the \fIddns-client-fqdn\fR.
.PP
.B on \fIevents\fB { \fIstatements...\fB }
The \fBon\fI statement records a list of statements to execute if a
certain event occurs.   The possible events that can occur for an
active lease are \fBrelease\fR and \fBexpiry\fR.   More than one event
can be specified - if so, the events are separated by '|' characters.
.SH THE FAILOVER PEER STATE DECLARATION
The state of any failover peering arrangements is also recorded in the
lease file, using the \fBfailover peer\fR statement:
.PP
.nf
.B failover peer "\fIname\fB" state {
.B   my   state \fIstate\fB at \fIdate\fB;
.B   peer state \fIstate\fB at \fIdate\fB;
.B }
.fi
.PP
The states of the peer named \fIname\fR is being recorded.   Both the
state of the running server (\fBmy state\fR) and the other failover
partner (\fIpeer state\fR) are recorded.   The following states are
possible: \fBunknown-state\fR, \fBpartner-down\fR, \fBnormal\fR,
\fBcommunications-interrupted\fR, \fBresolution-interrupted\fR,
\fBpotential-conflict\fR, \fBrecover\fR, \fBrecover-done\fR,
\fBshutdown\fR, \fBpaused\fR, and \fBstartup\fR.
.B DBDIR/dhcpd.leases
.SH SEE ALSO
dhcpd(8), dhcp-options(5), dhcp-eval(5), dhcpd.conf(5), RFC2132, RFC2131.
.SH AUTHOR
.B dhcpd(8)
was written by Ted Lemon
under a contract with Vixie Labs.   Funding
for this project was provided by Internet Systems Consortium.
Information about Internet Systems Consortium can be found at:
.B http://www.isc.org/