306 lines
14 KiB
Plaintext
306 lines
14 KiB
Plaintext
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About pdnsd
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pdnsd is a proxy DNS server with permanent caching (the cache contents are
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written to hard disk on exit) that is designed to cope with unreachable or down
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DNS servers (for example in dial-in networking).
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Since version 1.1.0, pdnsd supports negative caching.
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It is licensed under the GNU General Public License (GPL). This, in short,
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means that the sources are distributed togehter with the program, and that you
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are free to modify the sources and redistribute them as long as you also
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license them under the GPL. You do not need to pay anything for pdnsd. It also
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means that there is ABSOLUTELY NO WARRANTY for pdnsd or any part of it. For
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details, please read the GPL.
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pdnsd can be used with applications that do DNS lookups, e.g. on startup, and
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can't be configured to change that behaviour, to prevent the often minute-long
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hangs (or even crashes) that result from stalled DNS queries. Some Netscape
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Navigator versions for Unix, for example, expose this behaviour.
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pdnsd is configurable via a file and supports run-time configuration using the
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program pdnsd-ctl that comes with pdnsd. This allows you to set the status
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flags of servers that pdnsd knows (to influence which servers pdnsd will
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query), and the addition, deletion and invalidation of DNS records in pdnsd's
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cache.
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Parallel name server queries are supported. This is a technique that allows
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querying several servers at the same time so that very slow or unavailable
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servers will not block the answer for one timeout interval.
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Since version 1.0.0, pdnsd has full IPv6 support.
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There is also a limited support for local zone records, intended for defining
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1.0.0.127.in-addr.arpa. and localhost. , since some clients request that
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information and it must be served even if the cached servers are not available
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or do not serve these records. pdnsd may also read your /etc/hosts file (this
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file is normally used by your local resolver and usually contains information
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for localhost as well as for your machines FQDN) and serve its contents.
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pdnsd was started on Linux, and has since been ported to FreeBSD (and Cygwin
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and Darwin). 90% of the source code should be easily portable to POSIX- and
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BSD-compatible systems, provided that those systems support the POSIX threads
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(pthreads). The rest might need OS-specific rewrites.
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Currently, pdnsd is only compileable by gcc. This should be easy to fix, but I
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just do not have documentation for other compilers. If you are not able or do
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not want to use gcc, I would recommend you just try to do the minor changes.
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pdnsd must be started as root in some cases (raw sockets are needed for icmp
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echoes for the option uptest=ping, and the default port is 53, this must be >
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1024 to allow non-root execution). However, pdnsd can be configured to change
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it's user and group id to those of a non-privileged user after opening the
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sockets needed for this.
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The server should support the full standard DNS queries following the rfcs 1034
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and 1035. As of version 1.0.0, the rfc compliance has been improved again, and
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pdnsd is now believed (or hoped?) to be fully rfc-compatible. It completely
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follows rfc 2181 (except for one minor issue in the FreeBSD port, see the
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documentation). It does not support the following features, of which most are
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marked optional, experimental or obsolete in these rfcs:
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* Inverse queries
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* Status queries
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* Completion queries
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* Namespaces other than IN (Internet)
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* AXFR and IXFR queries (whole zone transfers); since pdnsd does not maintain
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zones, that should not violate the standard
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The following record types, that are extensions to the original DNS standard,
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are supported for caching since version 1.2.9 (if you do not need most of them,
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you can disable runtime support for the unneeded ones before compiling pdnsd
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and save a little cache and executable space, see the source file src/
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rr_types.in):
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* RP (responsible person, RFC 1183)
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* AFSDB (AFS database location, RFC 1183)
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* X25 (X25 address, RFC 1183)
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* ISDN (ISDN number/address, RFC 1183)
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* RT (route through, RFC 1183)
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* NSAP (Network Service Access Protocol address , RFC 1348)
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* PX (X.400/RFC822 mapping information, RFC 1995)
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* GPOS (geographic position, deprecated)
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* AAAA (IPv6 address, RFC 1886)
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* LOC (location, RFC 1876)
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* EID (Nimrod EID)
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* NIMLOC (Nimrod locator)
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* SRV (service record, RFC 2782)
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* ATMA (ATM address)
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* NAPTR (URI mapping, RFC 2168)
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* KX (key exchange, RFC 2230)
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* CERT (Certificate record, RFC 4398)
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* DS (Delegation Signer, RFC 4034)
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* RRSIG (Resource Record Signature, RFC 4034)
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* NSEC (Next Secure, RFC 4034)
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* DNSKEY (record containing the public key for a zone, RFC 4034)
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* NSEC3 (Next Secure version 3, RFC 5155)
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* NSEC3PARAM (NSEC3 parameters, RFC 5155)
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Note: This list is incomplete. For the complete list see the source file src/
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rr_types.in.
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There are FreeBSD and OpenBSD ports available for pdnsd (ports/net/pdnsd for
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both). Thanks go to Roman Shterenzon for the FreeBSD port Sebastian Stark for
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the OpenBSD one! Thanks to Kiyo Kelvin Lee now also runs on the Cygwin
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platform! Thanks goes to Rodney Brown for extending portability to the Darwin
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(Apple Mac OS X) platform!
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If you have questions left, you should take a look into the FAQ.
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Bugfixes, patches and compatability fixes for other OSs are very welcome!
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Features in detail
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This section describes some of pdnsds features in detail. Most of the options
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are set in the config file. For more information on the configuration file, see
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the documenation page.
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Uptests
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pdnsd provides several methods to test whether a remote DNS server should be
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regarded as available (so that pdnsd can query it), in addition to the obvious
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"none" test (the server is always regarded as available, or availability is set
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on or off using the pdnsd-ctl utility). These tests are:
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* ping: a given adress is ping'ed in a given interval. If it there is no
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response or the host is unreachable, the server is seen to be not available
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(for those who don't know: pinging is sending a certain Internet packet
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type to a host to which any standard-conformant host is required to reply).
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* if: a given network interface is tested whether it is existent, up and
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running. If it is not, the server is regarded to be not available. This is
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especially useful for ppp and similar interfaces. A special case test for
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Linux isdn (ippp*) interfaces is integrated, so that the uptests should
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also work for these.
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* dev: this is a variant of the if uptest for use with Linux dial-on-demand
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ppp interfaces. In addition to performing an if-style interface uptest, it
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also tests whether a specified program (e.g. pppd) owns a lock to a given
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(modem-) device.
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* exec: a given shell command line is executed and the exit status of the
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whole command line (which is normally the exit status of the last command)
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is evaluated. If it is not zero, the server is regarded to be not
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available. This is a very flexible testing method with which it should be
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able to perform virtually any needed test.
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* query: New in version 1.2: This works like the ping test, except it sends
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an (empty) DNS query to the remote server. If the server sends a
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well-formed response back within the timeout period (except SERVFAIL), it
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will be regarded as available. This test is useful if a remote server does
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not respond to ICMP_ECHO requests at all, which unfortunately is quite
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common these days. In many cases this test will be a more reliable
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indicator of availability than the ones mentioned above.
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Local Records ("Zones")
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As mentioned above, there are only very basic local record types (ie the record
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types that you may use in record declarations in your local configuration for
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records that pdnsd shall serve in addion to the cached ones). They are
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organized roughly in zones but have not complete zone declarations, so I
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generally do not use the term "zone" for them, but rather "local records".
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These are the local record types pdnsd can understand:
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* SOA (information about the name server)
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* A (domain-name-to-address mapping)
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* PTR (pointer, used normally for address-to-domain-name mapping)
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* NS (name server, generated automatically by pdnsd for any local record set)
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* CNAME (canonical host name)
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* MX (mail exchange for the domain)
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* TXT (arbitrary text strings, often used for Sender Policy Framework)
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You can specify these records in the configuration file.
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You may "source" a file in a format like that used in the /etc/hosts file, that
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means that pdnsd reads this file, extracts addresses and domain names from it
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and automatically generates A records for name to address mapping, PTR records
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for address to name mapping and NS records (name server specifiation) for each
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entry in the file.
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Records can also be changed dynamically at run time.
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A script contributed by Marko Stolle makes pdnsd usable in a DHCP setup using
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this feature.
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System requirements
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As mentioned, pdnsd currently runs under Linux, FreeBSD and Cygwin. Other BSD
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flavours may or may not work (feedback is very welcome!). The system and
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software requirements under Linux are:
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* Kernel version >2.2.0
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* glibc version >2.0.1 (aka libc6) with LinuxThreads (normally included) or
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NPTL (Native Posix Thread Library, recommended).
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Due to a bug, pdnsd 0.9.8 does not run with glibc2.1.1. This behaviour was
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fixed in pdnsd 0.9.9.
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* For IPv6: glibc>=2.1
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The system requirements under FreeBSD are:
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* FreeBSD versions >=2.6 (prior ones may or may not work)
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* For IPv6: FreeBSD >=4.0 is recommended (no idea if it runs on prior
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versions)
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The common software requirements for all supported systems are:
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* GCC, preferably egcs-2.* or 3.* (other compilers are currently not
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supported; the needed patch for another compiler should not be difficult,
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however)
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* GNU or BSD make
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* the standard commands install, grep, sed, awk, touch and which (along with
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the REALLY standard ones mv, cp, ln, rm, pwd, test, echo, cat, mkdir,
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chown, chmod, tar). In any standard Unix installation, this should be no
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problem.
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* for hacking and building own packages, you might also need gzip, bzip2,
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perl and rpmbuild
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Download
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If you want to download pdnsd, please visit the download page.
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Authors
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pdnsd was originally written by Thomas Moestl, but is no longer maintained by
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him. Paul A. Rombouts has revised large portions of the code and has added a
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number of new features. See README.par and the ChangeLog in the source
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directory (or /usr/share/doc/pdnsd-<version> if you have installed a binary
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package) for more details. If you have questions about the recent
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modifications, you can find the email address of the current maintainer at the
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end of README.par.
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Daniel Smolik has contributed RedHat RPMs (the most recent RPMs are available
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here).
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Torben Janssen contributed start scripts for Red Hat Linux.
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Soenke J. Peters contributed patches and suggestions for Red Hat compatability.
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Wolfgang Ocker has contributed the code and documentation for the server_ip
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option.
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Markus Mohr contributed a Debian rc script.
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Nikita V. Youschenko contributed extensions to the "if" uptest.
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Lyonel Vincent extended the serve_aliases option to support an arbitrary number
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of aliases.
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Sourav K. Mandal wrote the autoconf scripts and contributed many fixes and
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suggestions.
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Stephan Boettcher contributed the SCHEME= option.
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Ron Yorston contributed the uptest for Linux ppp dial-on-demand devices.
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Alexandre Nunes fixed some bugs in the autoconf files.
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Sverker Wiberg contributed fixes for IPv6.
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Carsten Block contributed configure-able rc scripts.
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Olaf Kirch contributed a security fix for the run_as code.
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Paul Wagland contributed various patches for bind9-compatability and other
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issues.
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Roman Shterenzon contributed patches and lots of helpful hints for FreeBSD
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compatability.
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Bernd Leibing has contributed spec file fixes.
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Michael Wiedmann has contributed the pdnsd-ctl.8 man page.
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Marko Stolle has contributed the contrib/pdnsd_update.pl script that makes
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pdnsd usable in a DHCP setup.
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P.J. Bostley has contributed patches to get pdnsd working on alpha properly.
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Christian Engstler contributed patches for SuSE compatability.
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Bjoern Fischer contributed code to make pdnsd leave the case of names in the
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cache unchanged.
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Marko Stolle contributed the contrib/pdnsd_update.pl script that makes pdnsd
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usable in a DHCP setup.
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Andrew M. Bishop contributed the support for the label server option and the
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pdnsd-ctl interface for using it.
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Frank Elsner contributed rc script fixes.
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Andreas Steinmetz contributed the code for query_port_start and query_port_end
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options.
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Mahesh T. Pai contributed the pdnsd.8 man page.
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Nikola Kotur contributed the Slackware start-up script.
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Kiyo Kelvin Lee contributed a patch for Cygwin support.
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Rodney Brown contributed a patch for Darwin (Apple Mac OS X) support.
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Jan-Marek Glogowski contributed a patch implementing the use_nss option.
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Special thanks to Bert Frederiks for letting me do a late-night debugging run
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on his machine to spot obscure bugs!
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Thanks to the following persons for reporting bugs and being helpful:
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David G. Andersen,
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Dirk Armbrust,
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Daniel Black,
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Kevin A. Burton,
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Juliusz Chroboczek,
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Joachim Dorner,
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Stefan Erhardt,
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Stefan F?rster,
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Mike Hammer,
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Jonathan Hudson,
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Dan Jacobson,
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Byrial Jensen,
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Patrick Loschmidt,
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James MacLean,
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Fraser McCrossan,
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Michael M?ller,
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Erich Reitz,
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Brian Schroeder,
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Milan P. Stanic,
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Michael Steiner,
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Norbert Steinl,
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Markus Storm,
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Michael Str?der,
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Alan Swanson,
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Eelco Vriezekolk.
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-------------------------------------------------------------------------------
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Thomas Moestl and Paul A. Rombouts
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Last revised: 17 March 2012 by Paul A. Rombouts
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