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dhcpd.leases(5) dhcpd.leases(5)

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[править] NAME

      dhcpd.leases - DHCP client lease database

[править] 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.
      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:
           touch DBDIR/dhcpd.leases
      In  order to prevent the lease database from growing without bound, the
      file is rewritten from time to time.   First, a temporary  lease  data-
      base  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.

[править] FORMAT

      Lease  descriptions  are  stored in a format that is parsed by the same
      recursive  descent  parser  used  to   read   the   dhcpd.conf(5)   and
      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.
      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.
      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
      rubout  is  written to the lease file.   This is just the same declara-
      tion, with { deleted; } 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  dhcpd.conf
      file;  in  this  case,  the  rubout  can  never  be eliminated from the
      dhcpd.leases file.

[править] THE LEASE DECLARATION

      lease ip-address { statements... }
      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.
      starts date;
      ends date;
      tstp date;
      tsfp date;
      atsfp date;
      cltt date;
      The start and end time of a lease are recorded  using  the  starts  and
      ends statements.   The tstp statement is specified if the failover pro-
      tocol is being used, and indicates what time the peer has been told the
      lease  expires.    The tsfp statement is also specified if the failover
      protocol is being used, and indicates the lease expiry  time  that  the
      peer  has  acknowledged.   The  atsfp statement is the actual time sent
      from the failover partner.  The cltt statement  is  the  client's  last
      transaction time.
      The date is specified in two ways, depending on the configuration value
      for the db-time-format parameter.  If it was set to default,  then  the
      date fields appear as follows:
      weekday year/month/day hour:minute:second
      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.
      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
      date -u.
      If the db-time-format was configured to local,  then  the  date  fields
      appear as follows:
       epoch  <seconds-since-epoch>;  #  <day-name> <month-name> <day-number>
      <hours>:<minutes>:<seconds> <year>
      The seconds-since-epoch is as according to  the  system's  local  clock
      (often  referred  to  as "unix time").  The # symbol supplies a comment
      that describes what actual time this is as according  to  the  system's
      configured timezone, at the time the value was written.  It is provided
      only for human inspection.
      If a lease will never expire, date is never instead of an actual  date.
      hardware hardware-type mac-address;
      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 hexa-
      decimal octets, separated by colons.
      uid client-identifier;
      The  uid  statement records the client identifier used by the client to
      acquire the lease.   Clients are not required to  send  client  identi-
      fiers,  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 hardware statement, but
      this is not required.
      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.
      client-hostname hostname ;
      Most DHCP clients will send their hostname in the host-name option.  If
      a  client  sends  its hostname in this way, the hostname is recorded on
      the lease with a client-hostname statement.   This is not  required  by
      the  protocol,  however, so many specialized DHCP clients do not send a
      host-name option.
      abandoned;
      The abandoned statement indicates that the DHCP  server  has  abandoned
      the  lease.    In  that  case,  the abandoned statement will be used to
      indicate that the lease should  not  be  reassigned.   Please  see  the
      dhcpd.conf(5) manual page for information about abandoned leases.
      binding state state; next binding state state;
      The  binding  state 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 active or free.   The failover
      protocol adds some additional  transitional  states,  as  well  as  the
      backup  state,  which indicates that the lease is available for alloca-
      tion by the failover secondary.
      The next binding state 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 ends statement.
      option agent.circuit-id string; option agent.remote-id string;
      The option agent.circuit-id and option agent.remote-id  statements  are
      used  to  record the circuit ID and remote ID options send by the relay
      agent, if the relay agent uses  the  relay  agent  information  option.
      This allows these options to be used consistently in conditional evalu-
      ations even when the client is contacting the  server  directly  rather
      than through its relay agent.
      set variable = value;
      The  set statement sets the value of a variable on the lease.  For gen-
      eral information on variables, see the dhcp-eval(5) manual page.
      The ddns-text variable
      The ddns-text 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.
      The ddns-fwd-name variable
      The ddns-fwd-name variable records the value of the name used in updat-
      ing  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.
      The ddns-client-fqdn variable
      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 ddns-client-fqdn vari-
      able 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.
      The ddns-rev-name variable
      If the server successfully updates the client's PTR record, this  vari-
      able 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  ddns-fwd-
      name or the ddns-client-fqdn.
      The vendor-class-identifier variable
      The  server  retains the client-supplied Vendor Class Identifier option
      for informational  purposes,  and  to  render  them  in  DHCPLEASEQUERY
      responses.
      on  events  { statements... } The on statement records a list of state-
      ments to execute if a certain event occurs.   The possible events  that
      can  occur  for an active lease are release and expiry.   More than one
      event can be specified - if so, the events are separated by '|' charac-
      ters.
      bootp;  reserved;  These  two  statements  are  effectively  flags.  If
      present, they indicate that the  BOOTP  and  RESERVED  failover  flags,
      respectively,  should  be  set.   BOOTP and RESERVED dynamic leases are
      treated differently than normal dynamic leases, as  they  may  only  be
      used by the client to which they are currently allocated.

[править] THE FAILOVER PEER STATE DECLARATION

      The  state of any failover peering arrangements is also recorded in the
      lease file, using the failover peer statement:
      failover peer name state {
      my state state at date;
      peer state state at date;
      }
      The states of the peer named name is being recorded.   Both  the  state
      of  the  running server (my state) and the other failover partner (peer
      state) are recorded.   The  following  states  are  possible:  unknown-
      state,  partner-down,  normal,  communications-interrupted, resolution-
      interrupted,  potential-conflict,  recover,   recover-done,   shutdown,
      paused, and startup.

[править] FILES

      DBDIR/dhcpd.leases DBDIR/dhcpd.leases~

[править] SEE ALSO

dhcpd(8) • dhcp-options(5) • dhcp-eval(5) • dhcpd.conf(5) • RFC2132 • RFC2131.

[править] AUTHOR

      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:
      https://www.isc.org/
                                                              dhcpd.leases(5)