dhcpd - Dynamic Host Configuration Protocol Server


   dhcpd  [  -p  port  ] [ -f ] [ -d ] [ -q ] [ -t | -T ] [ -4 | -6 ] [ -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 Internet Systems Consortium  DHCP  Server,  dhcpd,  implements  the
   Dynamic  Host  Configuration Protocol (DHCP) and the Internet Bootstrap
   Protocol (BOOTP).  DHCP allows hosts on a TCP/IP network to request and
   be  assigned  IP  addresses, and also to discover information about the
   network  to  which  they  are   attached.    BOOTP   provides   similar
   functionality, with certain restrictions.


   The  DHCP  protocol  allows  a  host  which  is  unknown to the network
   administrator 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
   available 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
   permitted 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

   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
   possible  to  dynamically  assign  addresses to BOOTP clients, but some
   administrative  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
   interfaces  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.

   -p port
          The   udp   port  number  on  which  dhcpd  should  listen.   If
          unspecified 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  (
          This option is only supported in IPv4.

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

   -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
          configuration file automatically before installing it.

   -T     Test  the  lease  file.   The  server  tests  the lease file for
          correct syntax, but will not  attempt  to  perform  any  network
          operations.   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
          available  if  the  code  was  compiled  with the PARANOIA patch
          (./configure --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-

   -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
          existing  lease  file  with its test data.  The DHCP server will
          refuse to  operate  in  playback  mode  unless  you  specify  an
          alternate lease file.

          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
   importance  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.

          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
   provide different functions.  Which ports are opened  depends  on  both
   the  way  you compiled your code and the configuration you supply.  The
   following 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 configuartion file there
   will be a TCP socket listening for connections on the ports  specififed
   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
   reference 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
   dynamically 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 netmask {

   Multiple address ranges may be specified like this:

        subnet netmask {

   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.

Lease Lengths

   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

   For example, in an office environment where systems are added from time
   to   time   and   removed  from  time  to  time,  but  move  relatively
   infrequently, 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 packaging 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 netmask {
          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
   environment  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.

BOOTP Support

   Each  BOOTP  client must be explicitly declared in the dhcpd.conf file.
   A very  basic  client  declaration  will  specify  the  client  network
   interface'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;
          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
   something like this:

        subnet netmask {
          default-lease-time 600 max-lease-time 7200;
          option subnet-mask;
          option broadcast-address;
          option routers;
          option domain-name-servers,;
          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;
          filename "/tftpboot/haagen.boot";
          option domain-name-servers;
          option domain-name "vix.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
   configuration 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

   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

   tstp time examine
        the time when the lease's current state ends, as understood by the
   tsfp time examine
        the  adjusted  time  when  the  lease's  current  state  ends,  as
        understood 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
        retransmission 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

   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

   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
   modified.  If a group declaration is created or  deleted  using  OMAPI,
   that  information  will  be  recorded  in the dhcpd.leases file.  It is
   permissible 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

   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
        declaration 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
   resynchronize 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
        unacknowledged at any given time, in this failover relationship.

   mclt integer examine
        Indicates  the  maximum  client  lead  time   in   this   failover

   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

   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

        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
        service  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
        communication 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.


   /etc/dhcp/dhcpd.conf,  /var/lib/dhcp/dhcpd.leases,  /var/run/dhcpd.pid,


   dhclient(8), dhcrelay(8), dhcpd.conf(5), dhcpd.leases(5)


   dhcpd(8) was originally written by Ted  Lemon  under  a  contract  with
   Vixie  Labs.  Funding for this project was provided by Internet Systems
   Consortium.  Version 3 of the DHCP server was funded by  Nominum,  Inc.
   Information   about   Internet   Systems  Consortium  is  available  at



Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.