lpic2

   dhcpd  [  -p port ] [ -f ] [ -d ] [ -q ] [ -t | -T ] [ -4 | -6 ] [ -4o6
   port ] [ -s server ] [ -cf config-file ] [ -lf lease-file ] [ -pf  pid-
   file  ]  [ --no-pid ] [ -user user ] [ -group group ] [ -chroot dir ] [
   -tf trace-output-file ] [ -play trace-playback-file ] [ if0 [ ...ifN  ]
   ]

   dhcpd --version

   The DHCP protocol allows a host which is unknown to the network  admin‐
   istrator to be automatically assigned a new IP address out of a pool of
   IP addresses for its network.  In order for this to work,  the  network
   administrator  allocates  address  pools in each subnet and enters them
   into the dhcpd.conf(5) file.

   There are two versions of the DHCP  protocol  DHCPv4  and  DHCPv6.   At
   startup  the  server  may be started for one or the other via the -4 or
   -6 arguments.

   On startup, dhcpd reads the dhcpd.conf file and stores a list of avail‐
   able  addresses  on  each  subnet in memory.  When a client requests an
   address using the DHCP protocol, dhcpd allocates  an  address  for  it.
   Each  client is assigned a lease, which expires after an amount of time
   chosen by the administrator  (by  default,  one  day).   Before  leases
   expire,  the clients to which leases are assigned are expected to renew
   them in order to continue to use  the  addresses.   Once  a  lease  has
   expired,  the client to which that lease was assigned is no longer per‐
   mitted to use the leased IP address.

   In order to keep track of  leases  across  system  reboots  and  server
   restarts,  dhcpd  keeps  a  list  of  leases  it  has  assigned  in the
   dhcpd.leases(5) file.  Before dhcpd  grants  a  lease  to  a  host,  it
   records  the lease in this file and makes sure that the contents of the
   file are flushed to disk.  This ensures that even in  the  event  of  a
   system crash, dhcpd will not forget about a lease that it has assigned.
   On  startup,  after  reading  the  dhcpd.conf  file,  dhcpd  reads  the
   dhcpd.leases  file  to  refresh  its memory about what leases have been
   assigned.

   New leases are appended to the end of the dhcpd.leases file.  In  order
   to  prevent the file from becoming arbitrarily large, from time to time
   dhcpd creates a new dhcpd.leases file from its in-core lease  database.
   Once  this  file  has  been  written  to  disk, the old file is renamed
   dhcpd.leases~, and the new file is renamed dhcpd.leases.  If the system
   crashes  in  the  middle  of  this process, whichever dhcpd.leases file
   remains will contain all the lease information, so there is no need for
   a special crash recovery process.

   BOOTP  support is also provided by this server.  Unlike DHCP, the BOOTP
   protocol does  not  provide  a  protocol  for  recovering  dynamically-
   assigned  addresses once they are no longer needed.  It is still possi‐
   ble to dynamically assign addresses to BOOTP clients, but some adminis‐
   trative  process  for  reclaiming  addresses  is required.  By default,
   leases are granted to BOOTP clients in perpetuity, although the network
   administrator  may set an earlier cutoff date or a shorter lease length
   for BOOTP leases if that makes sense.

   BOOTP clients may also be served in the old standard way, which  is  to
   simply  provide  a  declaration  in  the dhcpd.conf file for each BOOTP
   client, permanently assigning an address to each client.

   Whenever changes are  made  to  the  dhcpd.conf  file,  dhcpd  must  be
   restarted.  To restart dhcpd, send a SIGTERM (signal 15) to the process
   ID contained in /var/run/dhcpd.pid, and then re-invoke dhcpd.   Because
   the  DHCP  server  database  is not as lightweight as a BOOTP database,
   dhcpd does not automatically restart itself when it sees  a  change  to
   the dhcpd.conf file.

   Note:  We get a lot of complaints about this.  We realize that it would
   be nice if one could send a SIGHUP to the server and have it reload the
   database.   This  is not technically impossible, but it would require a
   great deal of work, our resources are extremely limited, and  they  can
   be  better spent elsewhere.  So please don't complain about this on the
   mailing list unless you're prepared to fund a project to implement this
   feature, or prepared to do it yourself.

   The  names  of  the network interfaces on which dhcpd should listen for
   broadcasts may be specified on the command line.  This should  be  done
   on  systems where dhcpd is unable to identify non-broadcast interfaces,
   but should not be required on other systems.  If no interface names are
   specified  on  the  command line dhcpd will identify all network inter‐
   faces which are up, eliminating non-broadcast interfaces  if  possible,
   and listen for DHCP broadcasts on each interface.

   -4     Run as a DHCP server. This is the default and cannot be combined
          with -6.

   -6     Run as a DHCPv6 server. This cannot be combined with -4.

   -4o6 port
          Participate in the DHCPv4 over DHCPv6 protocol specified by  RFC
          7341.  This associates a DHCPv4 and a DHCPv6 server to allow the
          v4 server to receive v4 requests that were encapsulated in a  v6
          packet.  Communication between the two servers is done on a pair
          of UDP sockets bound to ::1 port and port + 1. Both servers must
          be launched using the same port argument.

   -p port
          The  UDP  port number on which dhcpd should listen.  If unspeci‐
          fied dhcpd uses the default port of 67.  This is  mostly  useful
          for debugging purposes.

   -s address
          Specify  an  address  or  host  name  to which dhcpd should send
          replies rather than  the  broadcast  address  (255.255.255.255).
          This option is only supported in IPv4.

   -f     Force  dhcpd to run as a foreground process instead of as a dae‐
          mon in the background.  This is useful when running dhcpd  under
          a  debugger,  or when running it out of inittab on System V sys‐
          tems.

   -d     Send log messages to the standard error descriptor.  This can be
          useful  for debugging, and also at sites where a complete log of
          all dhcp activity must be kept but syslogd is  not  reliable  or
          otherwise  cannot  be used.  Normally, dhcpd will log all output
          using the syslog(3)  function  with  the  log  facility  set  to
          LOG_DAEMON.   Note  that -d implies -f (the daemon will not fork
          itself into the background).

   -q     Be quiet at startup.  This suppresses the printing of the entire
          copyright  message during startup.  This might be desirable when
          starting dhcpd from a system startup script (e.g., /etc/rc).

   -t     Test the configuration file.  The server tests the configuration
          file  for  correct  syntax,  but will not attempt to perform any
          network operations.  This can be used to test a  new  configura‐
          tion file automatically before installing it.

   -T     Test  the  lease file.  The server tests the lease file for cor‐
          rect syntax, but will not attempt to perform any network  opera‐
          tions.   This can be used to test a new lease file automatically
          before installing it.

   -user user
          Setuid to user after completing privileged operations,  such  as
          creating  sockets  that  listen  on privileged ports.  This also
          causes the lease file to be owned by user.  This option is  only
          available  if  the  code  was  compiled  with the PARANOIA patch
          (./configure --enable-paranoia).

   -group group
          Setgid to group after completing privileged operations, such  as
          creating  sockets  that  listen  on privileged ports.  This also
          causes the lease file to use group.  This option is only  avail‐
          able if the code was compiled with the PARANOIA patch (./config‐
          ure --enable-paranoia).

   -chroot dir
          Chroot to directory.  This may occur before or after reading the
          configuration  files  depending on whether the code was compiled
          with the  EARLY_CHROOT  option  enabled  (./configure  --enable-
          early-chroot).   This  option  is only available if the code was
          compiled with the  PARANOIA  patch  (./configure  --enable-para‐
          noia).

   -tf tracefile
          Specify a file into which the entire startup state of the server
          and all the transactions it processes are logged.  This  can  be
          useful  in  submitting  bug  reports - if you are getting a core
          dump every so often, you can  start  the  server  with  the  -tf
          option and then, when the server dumps core, the trace file will
          contain all the transactions that led up to it dumping core,  so
          that the problem can be easily debugged with -play.

   -play playfile
          Specify a file from which the entire startup state of the server
          and all the transactions  it  processed  are  read.   The  -play
          option must be specified with an alternate lease file, using the
          -lf switch, so that the DHCP server doesn't wipe out your exist‐
          ing  lease file with its test data.  The DHCP server will refuse
          to operate in playback mode  unless  you  specify  an  alternate
          lease file.

   --version
          Print version number and exit.

   Modifying  default file locations: The following options can be used to
   modify the locations dhcpd uses for its files.  Because of  the  impor‐
   tance  of using the same lease database at all times when running dhcpd
   in production, these options should be  used  only  for  testing  lease
   files or database files in a non-production environment.

   -cf config-file
          Path to alternate configuration file.

   -lf lease-file
          Path to alternate lease file.

   -pf pid-file
          Path to alternate pid file.

   --no-pid
          Option  to  disable  writing  pid files.  By default the program
          will write a pid file.  If the  program  is  invoked  with  this
          option it will not check for an existing server process.

   During operations the server may use multiple UDP and TCP ports to pro‐
   vide different functions.  Which ports are opened depends on  both  the
   way  you compiled your code and the configuration you supply.  The fol‐
   lowing should provide you an idea of what ports may be in use.

   Normally a DHCPv4 server will open a raw UDP socket to receive and send
   most  DHCPv4  packets.   It also opens a fallback UDP socket for use in
   sending unicast packets.  Normally these will both use the  well  known
   port number for BOOTPS.

   For  each DHCPv4 failover peer you list in the configuration file there
   will be a TCP socket listening for connections on the  ports  specified
   in  the  configuration  file.   When  the  peer  connects there will be
   another socket for the established  connection.   For  the  established
   connection  the side (primary or secondary) opening the connection will
   use a random port.

   For  DHCPv6  the  server  opens  a  UDP  socket  on  the   well   known
   dhcpv6-server port.

   The  server  opens  an  icmp socket for doing ping requests to check if
   addresses are in use.

   If you have included an omapi-port statement in your configuration file
   then the server will open a TCP socket on that port to listen for OMPAI
   connections.  When something connects another port will be used for the
   established connection.

   When  DDNS  is enabled at compile time (see includes/site.h) the server
   will open both a v4 and a v6 UDP socket on random ports.   These  ports
   are opened even if DDNS is disabled in the configuration file.

   The  syntax  of  the  dhcpd.conf(5) file is discussed separately.  This
   section should be used as an overview of the configuration process, and
   the dhcpd.conf(5) documentation should be consulted for detailed refer‐
   ence information.

   dhcpd needs to know the subnet numbers and netmasks of all subnets  for
   which  it  will be providing service.  In addition, in order to dynami‐
   cally allocate addresses, it must be assigned one  or  more  ranges  of
   addresses on each subnet which it can in turn assign to client hosts as
   they boot.  Thus, a very simple configuration  providing  DHCP  support
   might look like this:

        subnet 239.252.197.0 netmask 255.255.255.0 {
          range 239.252.197.10 239.252.197.250;
        }

   Multiple address ranges may be specified like this:

        subnet 239.252.197.0 netmask 255.255.255.0 {
          range 239.252.197.10 239.252.197.107;
          range 239.252.197.113 239.252.197.250;
        }

   If  a  subnet  will  only be provided with BOOTP service and no dynamic
   address assignment, the range clause can be left out entirely, but  the
   subnet statement must appear.

   DHCP  leases  can  be  assigned  almost any length from zero seconds to
   infinity.  What lease length makes sense for any given subnet,  or  for
   any given installation, will vary depending on the kinds of hosts being
   served.

   For example, in an office environment where systems are added from time
   to  time  and  removed  from  time  to time, but move relatively infre‐
   quently, it might make sense to allow lease times of a month  or  more.
   In  a final test environment on a manufacturing floor, it may make more
   sense to assign a maximum lease length of 30 minutes - enough  time  to
   go  through a simple test procedure on a network appliance before pack‐
   aging it up for delivery.

   It is possible to specify two lease lengths: the  default  length  that
   will  be  assigned  if  a  client  doesn't ask for any particular lease
   length, and a maximum lease length.  These are specified as clauses  to
   the subnet command:

        subnet 239.252.197.0 netmask 255.255.255.0 {
          range 239.252.197.10 239.252.197.107;
          default-lease-time 600;
          max-lease-time 7200;
        }

   This  particular  subnet  declaration specifies a default lease time of
   600 seconds (ten minutes), and a maximum lease  time  of  7200  seconds
   (two hours).  Other common values would be 86400 (one day), 604800 (one
   week) and 2592000 (30 days).

   Each subnet need not have the same lease—in the case of an office envi‐
   ronment and a manufacturing environment served by the same DHCP server,
   it might make sense to have widely disparate  values  for  default  and
   maximum lease times on each subnet.

   Each  BOOTP  client must be explicitly declared in the dhcpd.conf file.
   A very basic client declaration will specify the client network  inter‐
   face's  hardware  address  and the IP address to assign to that client.
   If the client needs to be able to load a boot  file  from  the  server,
   that  file's name must be specified.  A simple bootp client declaration
   might look like this:

        host haagen {
          hardware ethernet 08:00:2b:4c:59:23;
          fixed-address 239.252.197.9;
          filename "/tftpboot/haagen.boot";
        }

   DHCP (and also  BOOTP  with  Vendor  Extensions)  provide  a  mechanism
   whereby the server can provide the client with information about how to
   configure its network interface (e.g., subnet mask), and also  how  the
   client  can access various network services (e.g., DNS, IP routers, and
   so on).

   These options can be specified on a per-subnet basis,  and,  for  BOOTP
   clients,  also on a per-client basis.  In the event that a BOOTP client
   declaration specifies options that are also  specified  in  its  subnet
   declaration,  the  options  specified  in  the  client declaration take
   precedence.  A reasonably complete DHCP configuration might look  some‐
   thing like this:

        subnet 239.252.197.0 netmask 255.255.255.0 {
          range 239.252.197.10 239.252.197.250;
          default-lease-time 600 max-lease-time 7200;
          option subnet-mask 255.255.255.0;
          option broadcast-address 239.252.197.255;
          option routers 239.252.197.1;
          option domain-name-servers 239.252.197.2, 239.252.197.3;
          option domain-name "isc.org";
        }

   A  bootp host on that subnet that needs to be in a different domain and
   use a different name server might be declared as follows:

        host haagen {
          hardware ethernet 08:00:2b:4c:59:23;
          fixed-address 239.252.197.9;
          filename "/tftpboot/haagen.boot";
          option domain-name-servers 192.5.5.1;
          option domain-name "example.com";
        }

   A more complete description of the dhcpd.conf file syntax  is  provided
   in dhcpd.conf(5).

   The  DHCP server provides the capability to modify some of its configu‐
   ration while it is running, without stopping it, modifying its database
   files,  and restarting it.  This capability is currently provided using
   OMAPI - an API for manipulating remote objects.  OMAPI clients  connect
   to  the  server  using  TCP/IP,  authenticate, and can then examine the
   server's current status and make changes to it.

   Rather than implementing the underlying OMAPI protocol  directly,  user
   programs  should  use  the  dhcpctl  API or OMAPI itself.  Dhcpctl is a
   wrapper that handles some of the housekeeping chores  that  OMAPI  does
   not  do  automatically.  Dhcpctl and OMAPI are documented in dhcpctl(3)
   and omapi(3).

   OMAPI exports objects, which can then be examined  and  modified.   The
   DHCP  server exports the following objects: lease, host, failover-state
   and group.  Each object has a number  of  methods  that  are  provided:
   lookup,  create,  and  destroy.  In addition, it is possible to look at
   attributes that are stored on objects, and  in  some  cases  to  modify
   those attributes.

   Leases  can't currently be created or destroyed, but they can be looked
   up to examine and modify their state.

   Leases have the following attributes:

   state integer lookup, examine
        1 = free
        2 = active
        3 = expired
        4 = released
        5 = abandoned
        6 = reset
        7 = backup
        8 = reserved
        9 = bootp

   ip-address data lookup, examine
        The IP address of the lease.

   dhcp-client-identifier data lookup, examine, update
        The client identifier that the client used when  it  acquired  the
        lease.   Not  all  clients send client identifiers, so this may be
        empty.

   client-hostname data examine, update
        The value the client sent in the host-name option.

   host handle examine
        the host declaration associated with this lease, if any.

   subnet handle examine
        the subnet object associated with this lease (the subnet object is
        not currently supported).

   pool handle examine
        the pool object associated with this lease (the pool object is not
        currently supported).

   billing-class handle examine
        the handle to the class to which this lease is  currently  billed,
        if any (the class object is not currently supported).

   hardware-address data examine, update
        the  hardware  address  (chaddr)  field sent by the client when it
        acquired its lease.

   hardware-type integer examine, update
        the type of the network interface that the client reported when it
        acquired its lease.

   ends time examine
        the time when the lease's current state ends, as understood by the
        client.

   tstp time examine
        the time when the lease's current state ends, as understood by the
        server.
   tsfp time examine
        the  adjusted  time when the lease's current state ends, as under‐
        stood by the failover peer (if there is  no  failover  peer,  this
        value  is  undefined).   Generally this value is only adjusted for
        expired, released, or reset leases while the server  is  operating
        in  partner-down state, and otherwise is simply the value supplied
        by the peer.
   atsfp time examine
        the actual tsfp value sent from the peer.  This value is forgotten
        when  a lease binding state change is made, to facilitate retrans‐
        mission logic.

   cltt time examine
        The time of the last transaction with the client on this lease.

   Hosts can be created, destroyed, looked up, examined and modified.   If
   a  host declaration is created or deleted using OMAPI, that information
   will be recorded in the dhcpd.leases file.  It is permissible to delete
   host declarations that are declared in the dhcpd.conf file.

   Hosts have the following attributes:

   name data lookup, examine, modify
        the  name of the host declaration.  This name must be unique among
        all host declarations.

   group handle examine, modify
        the named group associated with the host declaration, if there  is
        one.

   hardware-address data lookup, examine, modify
        the  link-layer  address that will be used to match the client, if
        any.  Only valid if hardware-type is also present.

   hardware-type integer lookup, examine, modify
        the type of the network interface that will be used to  match  the
        client, if any.  Only valid if hardware-address is also present.

   dhcp-client-identifier data lookup, examine, modify
        the  dhcp-client-identifier  option that will be used to match the
        client, if any.

   ip-address data examine, modify
        a fixed IP address which  is  reserved  for  a  DHCP  client  that
        matches  this  host  declaration.   The  IP  address  will only be
        assigned to the client if it is valid for the network  segment  to
        which the client is connected.

   statements data modify
        a  list  of  statements  in the format of the dhcpd.conf file that
        will be executed whenever a message from the client is being  pro‐
        cessed.

   known integer examine, modify
        if nonzero, indicates that a client matching this host declaration
        will be treated as known in  pool  permit  lists.   If  zero,  the
        client will not be treated as known.

   Named  groups  can be created, destroyed, looked up, examined and modi‐
   fied.  If a group declaration is created or deleted using  OMAPI,  that
   information will be recorded in the dhcpd.leases file.  It is permissi‐
   ble to delete group declarations that are declared  in  the  dhcpd.conf
   file.

   Named  groups currently can only be associated with hosts - this allows
   one set of statements to be efficiently attached to more than one  host
   declaration.

   Groups have the following attributes:

   name data
        the  name  of  the group.  All groups that are created using OMAPI
        must have names, and the names must be unique among all groups.

   statements data
        a list of statements in the format of  the  dhcpd.conf  file  that
        will  be executed whenever a message from a client whose host dec‐
        laration references this group is processed.

   The control object allows you to shut the server down.  If  the  server
   is  doing  failover  with another peer, it will make a clean transition
   into the shutdown state and notify its peer, so that the  peer  can  go
   into  partner  down,  and  then record the "recover" state in the lease
   file so that when the server is restarted, it will automatically resyn‐
   chronize with its peer.

   On shutdown the server will also attempt to cleanly shut down all OMAPI
   connections.  If these connections do not go down  cleanly  after  five
   seconds,  they  are  shut down preemptively.  It can take as much as 25
   seconds from the beginning of the shutdown process to the time that the
   server actually exits.

   To  shut  the  server  down,  open its control object and set the state
   attribute to 2.

   The failover-state object is the object that tracks the  state  of  the
   failover  protocol  as  it  is being managed for a given failover peer.
   The failover object has the following attributes (please see dhcpd.conf
   (5) for explanations about what these attributes mean):

   name data examine
        Indicates the name of the failover peer relationship, as described
        in the server's dhcpd.conf file.

   partner-address data examine
        Indicates the failover partner's IP address.

   local-address data examine
        Indicates the IP address that is being used by the DHCP server for
        this failover pair.

   partner-port data examine
        Indicates  the TCP port on which the failover partner is listening
        for failover protocol connections.

   local-port data examine
        Indicates the TCP port on which the DHCP server is  listening  for
        failover protocol connections for this failover pair.

   max-outstanding-updates integer examine
        Indicates  the number of updates that can be outstanding and unac‐
        knowledged at any given time, in this failover relationship.

   mclt integer examine
        Indicates the maximum client lead time in this failover  relation‐
        ship.

   load-balance-max-secs integer examine
        Indicates the maximum value for the secs field in a client request
        before load balancing is bypassed.

   load-balance-hba data examine
        Indicates the load balancing hash bucket array for  this  failover
        relationship.

   local-state integer examine, modify
        Indicates  the  present  state of the DHCP server in this failover
        relationship.  Possible values for state are:

             1   - startup
             2   - normal
             3   - communications interrupted
             4   - partner down
             5   - potential conflict
             6   - recover
             7   - paused
             8   - shutdown
             9   - recover done
             10  - resolution interrupted
             11  - conflict done
             254 - recover wait

        (Note that some of  the  above  values  have  changed  since  DHCP
        3.0.x.)

        In  general  it  is not a good idea to make changes to this state.
        However, in the case that the failover  partner  is  known  to  be
        down,  it can be useful to set the DHCP server's failover state to
        partner down.  At this point the DHCP server will take  over  ser‐
        vice  of  the  failover  partner's leases as soon as possible, and
        will give out normal leases, not leases  that  are  restricted  by
        MCLT.   If  you  do put the DHCP server into the partner-down when
        the other DHCP server is not in the partner-down state, but is not
        reachable,  IP  address  assignment  conflicts  are possible, even
        likely.  Once a server has been put into  partner-down  mode,  its
        failover  partner must not be brought back online until communica‐
        tion is possible between the two servers.

   partner-state integer examine
        Indicates the present state of the failover partner.

   local-stos integer examine
        Indicates the time at which the DHCP server  entered  its  present
        state in this failover relationship.

   partner-stos integer examine
        Indicates  the  time  at  which  the  failover partner entered its
        present state.

   hierarchy integer examine
        Indicates whether the DHCP server is primary (0) or secondary  (1)
        in this failover relationship.

   last-packet-sent integer examine
        Indicates  the  time  at which the most recent failover packet was
        sent by this DHCP server to its failover partner.

   last-timestamp-received integer examine
        Indicates the timestamp that was  on  the  failover  message  most
        recently received from the failover partner.

   skew integer examine
        Indicates  the  skew between the failover partner's clock and this
        DHCP server's clock

   max-response-delay integer examine
        Indicates the time in  seconds  after  which,  if  no  message  is
        received  from  the failover partner, the partner is assumed to be
        out of communication.

   cur-unacked-updates integer examine
        Indicates the number of update messages that  have  been  received
        from the failover partner but not yet processed.

                                                           dhcpd(8)