Ubuntu Manpage: dictd - a dictionary database server

NAME

       dictd - a dictionary database server

SYNOPSIS

       dictd [options]

DESCRIPTION

       dictd  is  a  server  for  the  Dictionary Server Protocol (DICT), a TCP transaction based
       query/response protocol that allows a client to access dictionary definitions from  a  set
       of natural language dictionary databases.

       For security reasons, dictd drops root permissions after startup.  If user dictd exists on
       the system, the daemon will run as that user, group dictd, otherwise it will run  as  user
       nobody, group nobody or nogroup (depending on the operating system distribution).

       Since  startup time is significant, the server is designed to run continuously, and should
       not be run from inetd(8).  (However, with a fast processor, it is feasible to do so.)

       Databases are distributed separately from the server.

       By default, dictd assumes that  the  index  files  are  sorted  alphabetically,  and  only
       alphanumeric  characters  from  the  7-bit  ASCII character set are used for search.  This
       default may be overridden  by  a  header  in  the  data  file.   The  only  such  features
       implemented  at  this  time  are the headers "00-database-allchars" which tells dictd that
       non-alphanumeric characters may also be used for  search,  the  header  "00-database-utf8"
       which indicates that the database uses utf8 encoding, and the "00-database-8bit-new" which
       indicates that the database is encoded and sorted according to a locale that uses an 8-bit
       encoding.

BACKGROUND

For many years, the Internet community has relied on the "webster" protocol for access to
natural language definitions. The webster protocol supports access to a single dictionary
and (optionally) to a single thesaurus. In recent years, the number of publicly available
webster servers on the Internet has dramatically decreased.

Fortunately, several freely-distributable dictionaries and lexicons have recently become
available on the Internet. However, these freely-distributable databases are not
accessible via a uniform interface, and are not accessible from a single site. They are
often small and incomplete individually, but would collectively provide an interesting and
useful database of English words. Examples include the Jargon file, the WordNet database,
MICRA's version of the 1913 Webster's Revised Unabridged Dictionary, and the Free Online
Dictionary of Computing. (See the DICT protocol specification (RFC) for references.)
Translating and non-English dictionaries are also becoming available (for example, the
FOLDOC dictionary is being translated into Spanish).

The webster protocol is not suitable for providing access to a large number of separate
dictionary databases, and extensions to the current webster protocol were not felt to be a
clean solution to the dictionary database problem.

The DICT protocol is designed to provide access to multiple databases. Word definitions
can be requested, the word index can be searched (using an easily extended set of
algorithms), information about the server can be provided (e.g., which index search
strategies are supported, or which databases are available), and information about a
database can be provided (e.g., copyright, citation, or distribution information).
Further, the DICT protocol has hooks that can be used to restrict access to some or all of
the databases.

dictd(8) is a server that implements the DICT protocol. Bret Martin implemented another
server, and several people (including Bret and myself) have implemented clients in a
variety of languages.

OPTIONS

-V or --version
Display version information.

--license
Display copyright and license information.

-h or --help
Display help information.

-v or --verbose or -dverbose
Be verbose.

-c file or --config file
Specify configuration file. The default is /etc/dictd/dictd.conf , but may be
changed in the defs.h file at compile time (DICTD_CONFIG_FILE).

-p port or --port port
Overrides the keyword port in Global Settings Specification section of
configuration file.

-i or --inetd
Communicate on standard input/output, suitable for use from inetd. Although, due
to its rather large startup time, this daemon was not intended to run from inetd,
with a fast processor it is feasible to do so. This option also implies --fast-
start.

--pp prog
Sets a preprocessor for configuration file. like m4 or cpp . See
examples/dictd_complex.conf file from distribution. By default configuration file
is parsed without preprocessor.

--depth length
Overrides the keyword depth in Global Settings Specification section of
configuration file.

--delay seconds
Overrides the keyword delay in Global Settings Specification section of
configuration file.

--facility facility
The same as syslog_facility keyword in Global Settings Specification of
configuration files.

-f or --force
Force the daemon to start even if an instance of the daemon is already running.
(This is of little value unless a non-default port is specified with -p, since, if
one instance is bound to a port, the second one fails when it can not bind to the
port.)

--limit children
Overrides the keyword limit in Global Settings Specification section of
configuration file.

--listen-to address
Overrides the keyword listen_to in Global Settings Specification section of
configuration file.

--locale locale
Overrides the keyword locale in Global Settings Specification section of
configuration file.

-s The same as syslog keyword in Global Settings Specification of configuration files.

-L file or --logfile file
The same as log_file keyword in Global Settings Specification of configuration
files.

--pid-file file
The same as pid_file keyword in Global Settings Specification of configuration
files.

-m minutes or --mark minutes
Overrides the keyword timestamp in Global Settings Specification section of
configuration file.

--default-strategy strategy
Overrides the keyword default_strategy in Global Settings Specification section of
configuration file.

--without-strategy strat1,strat2,...
The same as without_strategy keyword in Global Settings Specification of
configuration files.

--add-strategy strategy_name:description
The same as add_strategy keyword in Global Settings Specification of configuration
files.

--fast-start
The same as fast_start keyword in Global Settings Specification of configuration
files.

--without-mmap
The same as without_mmap keyword in Global Settings Specification of configuration
files.

--stdin2stdout
When applied with --inetd, each command obtained from stdin is output to stdout.
This option is useful for debugging.

-l option or --log option
The same as log_option keyword in Global Settings Specification of configuration
files.

-d option
The same as debug_option keyword in Global Settings Specification of configuration
files.

CONFIGURATION FILE

Introduction
The configuration file defaults to /etc/dictd/dictd.conf but can be specified on
the command line with the -c option (see above).

The configuration file is read into memory at startup, and is not referenced again
by dictd unless a signal 1 (SIGHUP) is received, which will cause dictd to reread
the configuration file.

The file is divided into sections. The Access Section should come first, followed
by the Database Section, and the User Section. The Database Section is required;
the others are optional, but they must be in the order listed here.

Syntax The following keywords are valid in a configuration file: access, allow, deny,
group, database, data, index, filter, prefilter, postfilter, name, include, user,
authonly, site. Keywords are case sensitive. String arguments that contain spaces
should be surrounded by double quotes. Without quoting, strings may contain
alphanumeric characters and _, -, ., and *, but not spaces. Strings can be
continued between lines. \", \\, \n, \<NL> are treated as double quote, backslash,
new line and no symbol respectively. Comments start with # and extend to the end
of the line.

Global Settings Section

global { global settings specification }
Used to set global dictd setting such as log file, syslog facility, locale
and so on.

EXAMPLE:
See examples/dictd4.conf file from the distribution.

Access Section

access { access specification }
This section contains access restrictions for the server and all of the
databases collectively. Per-database control is specified in the Database
Section.

EXAMPLE:
See examples/dictd3.conf file from the distribution.

Database Section

database string { database specification }
The string specifies the name of the database (e.g., wn or web1913). (This
is an arbitrary name selected by the administrator, and is not necessarily
related to the file name or any name listed in the data file. A short, easy
to type name is often selected for easy use with dict -d.)

EXAMPLE: See examples/dictd*.conf files from the distribution.

NOTE: If the files specified in the database specification do not exist on
the system, dictd may silently fail.

database_virtual string { virtual database specification }
This section specifies the virtual database. The string specifies the name
of the database (e.g., en-ru or fren).

EXAMPLE: See examples/dictd_virtual.conf or examples/dictd_complex.conf
files from the distribution.

database_plugin string { plugin specification }
This section specifies the plugin. The string specifies the name of the
database.

EXAMPLE: See examples/dictd_plugin_dbi.conf or examples/dictd_complex.conf
files from the distribution.

database_mime string { mime specification }
Traditionally, databases created for dictd contained plain text only because
dictd releases before 1.10.0 didn't have full support of OPTION MIME option
(consult with RFC-2229). This section describes the special database which
behaves differently depending on whether OPTION MIME command was received
from client or was not, i.e. the database created by this section allows one
to return to the client either a plain text or specially formatted content
depending on whether DICT client supports (or wants to receive) MIMEized
content or doesn't. The string specifies the name of the database.

NOTE: All this is about DEFINE command only. MATCH, SHOW DB, SHOW STRAT,
SHOW INFO, SHOW SERVER and HELP commands return texts prepended with empty
line only.

EXAMPLE: See examples/dictd_mime.conf file from the distribution.

database_exit
Excludes following databases from the '*' database. By default '*' means
all databases available. Look at 'examples/dictd_virtual.conf' file for
example configuration.

NOTE: If you use 'virtual' dictionaries, you should use this directive,
otherwise you will search the same dictionary twice.

User Section

user string string
The first string specifies the username, and the second string
specifies the shared secret for this username. When the AUTH command
is used, the client will provide the username and a hashed version of
the shared secret. If the shared secret matches, the user is said to
have authenticated, and will have access to databases whose access
specifications allow that user (by name, or by wildcard). If
present, this section must appear last in the configuration file.
There may be many user entries. The shared secret should be kept
secret, as anyone who has access to it can access the shared
databases (assuming access is not denied by domain name).

Access Specification
Access specifications may occur in the Access Section or in the Database
Section. The access specification will be described here.

For allow, deny, and authonly, a star (*) may be used as a wild card that
matches any number of characters. A question mark (?) may be used as a
wildcard that matches a single character. For example, 10.0.0.* and *.edu
are valid strings.

Further, a range of IP addresses and an IP address followed by a netmask may
be specified. For example, 10.0.0.0:10.0.0.255, 10.0.0.0/24, and 10.0.0.*
all specify the same range of IP numbers. Notation cannot be combined on
the same line. If the notation does not make sense, access will be denied
by default. Use the --debug auth option to debug related problems.

Note that these specifications take only one string per specification line.
However, you can have multiple lines of each type.

The syntax is as follows:

allow string
The string specifies a domain name or IP address which is allowed
access to the server (in the Access Section) or to a database (in the
Database Section). Note that more than one string is not permitted
for a single "allow" line, but more than one "allow" lines are
permitted in the configuration file.

deny string
The string specifies a domain name or IP address which is denied
access to the server (in the Access Section) or to a database (in the
Database Section). Note that if reverse DNS is not working, then
only the IP number will be checked. Therefore, it is essential to
deny networks based on IP number, since a denial based on domain name
may not always be checked.

authonly string
This form is only useful in the Access Section. The string specifies
a domain name or IP address which is allowed access to the server but
not to any of the databases. All commands are valid except DEFINE,
MATCH, and SHOW DB. More specifically AUTH is a valid command, and
commands which access the databases are not allowed.

user string
This form is only useful in the Database Section. The string
specifies a username that is allowed to access this database after a
successful AUTH command is executed.

Global Settings Specification
This section describes the following parameters:

port string_or_number
Specifies the port or service name (e.g., 2628). The default is 2628, as
specified in the DICT Protocol RFC, but may be changed in the defs.h file at
compile time (DICT_DEFAULT_SERVICE).

site string
Used to specify the filename for the site information file, a flat text file
which will be displayed in response to the SHOW SERVER command.

EXAMPLE: See examples/dictd4.conf file from the distribution.

site_no_banner boolean
By default SHOW SERVER command outputs information about dictd version and
an operating system type. This option disables this.

site_no_uptime boolean
By default SHOW SERVER command outputs information about uptime of dictd , a
number of forks since startup and forks per hour. This option disables
this.

site_no_dblist boolean
By default SHOW SERVER command outputs internal information about databases,
such as a number of headwords, index size and so on. This option disables
this.

delay number
Specifies the number of seconds a client may be idle before the server will
close the connection. Idle time is defined to be the time the server is
waiting for input and does not include the time the server spends searching
the database. The default is 0 seconds (no limit), but may be changed in the
defs.h file at compile time (DICT_DEFAULT_DELAY).

NOTE: Setting delay option disables limit_time option. Only one of them
(last specified in dictd.conf ) is in effect.

NOTE: Connections are closed without warning since no provision for
premature connection termination is specified in the DICT protocol RFC.

depth number
Specify the queue length for listen(2). Specifies the number of pending
socket connections which are queued by the operating system. Some operating
systems may silently limit this value to 5 (older BSD systems) or 128
(Linux). The default is 10 but may be changed in the defs.h file at compile
time (DICT_QUEUE_DEPTH).

limit_childs number
Specifies the number of daemons that may be running simultaneously. Each
daemon services a single connection. If the limit is exceeded, a
(serialized) connection will be made by the server process, and a response
code 420 (server temporarily unavailable) will be sent to the client. This
parameter should be adjusted to prevent the server machine from being
overloaded by dict clients, but should not be set so low that many clients
are denied useful connections. The default is 100, but may be changed in the
defs.h file at compile time (DICT_DAEMON_LIMIT_CHILDS).

limit number
Synonym for limit_childs. For backward compatibility only.

limit_matches number
Specifies the maximum number of matches that can be returned by MATCH query.
Zero means no limit. The default is 2000.

limit_definitions number
Specifies the maximum number of definitions that can be returned by DEFINE
query. Zero means no limit. The default is 200.

limit_time number
Specifies the number of seconds a client may talk to the server before the
server will close the connection. The default is 600 seconds (10 minutes),
but may be changed in the defs.h file at compile time
(DICT_DEFAULT_LIMIT_TIME).

NOTE: Setting limit_time option disables delay option. Only one of them
(last specified in dictd.conf ) is in effect.

NOTE: Connections are closed without warning since no provision for
premature connection termination is specified in the DICT protocol RFC.

limit_queries number
Specifies the number of queries (MATCH, DEFINE, SHOW DB etc.) that client
may send to the server before the server will close the connection. Zero
means no limit. The default is 2000, but may be changed in the defs.h file
at compile time (DICT_DEFAULT_LIMIT_QUERIES).

timestamp number
How often a timestamp should be logged (int minutes). (This is effective
only if logging has been enabled with the -s or -L option, or with a
debugging option.)

log_option option
Specify a logging option. This is effective only if logging has been
enabled with the -s or -L option or in configuration file, or logging to the
console has been activated with a debugging option (e.g., --debug nodetach.
Only one option may be set with each invocation of this option; however,
multiple invocations of this option may be made in configuration file or
dictd command line. For instance:
dictd -s --log stats --log found --log notfound
is a valid command line, and sets three logging options.

Some of the more verbose logging options are used primarily for debugging
the server code, and are not practical for normal use.

server Log server diagnostics. This is extremely verbose.

connect
Log all connections.

stats Log all children terminations.

command
Log all commands. This is extremely verbose.

client Log results of CLIENT command.

found Log all words found in the databases.

notfound
Log all words not found in the databases.

timestamp
When logging to a file, use a full timestamp like that which syslog
would produce. Otherwise, no timestamp is made, making the files
shorter.

host Log name of foreign host.

auth Log authentication failures.

min Set a minimal number of options. If logging is activated (to a file,
or via syslog), and no options are set, then the minimal set of
options will be used. If options are set, then only those options
specified will be used.

all Set all of the options.

none Clear all of the options.

To facilitate location of interesting information in the log file, entries
are marked with initial letters indicating the class of the line being
logged:

I Information about the server, connections, or termination statistics.
These lines are generally not designed to be parsed automatically.

E Error messages.

C CLIENT command information.

D Definitions found in the databases searched.

M Matches found in the database searched.

N Matches which were not found in the databases searched.

T Trace of exact line sent by client.

A Authentication information.

To preserve anonymity of the client, do not use the connect or host options.
Clients may or may not send host information using the CLIENT command, but
this should be an option that is selectable on the client side.

debug_option string
Activate a debugging option. There are several, all of which are only
useful to developers. They are documented here for completeness. A list
can be obtained interactively by using -d with an illegal option.

verbose
The same as -v or --verbose. Adds verbosity to other options.

scan Debug the scanner for the configuration file.

parse Debug the parser for the configuration file.

search Debug the character folding and binary search routines.

init Report database initialization.

port Log client-side port number to the log file.

lev Debug Levenshtein search algorithm.

auth Debug the authorization routines.

nodetach
Do not detach as a background process. Implies that a copy of the
log file will appear on the standard output.

nofork Do not fork daemons to service requests. Be a single-threaded
server. This option implies nodetach, and is most useful for using a
debugger to find the point at which daemon processes are dumping
core.

alt Debugs altcompare in index.c.

locale string
Specifies the locale used for searching. If no locale is specified, the "C"
locale is used. The locale used for the server should be the same as that
used for dictfmt when the database was built (specifically, the locale under
which the index was sorted). The locale should be specified for both 8-bit
and UTF-8 formats. If locale contains utf8 or utf-8 substring, UTF-8 format
is expected. Note that if your database is not in ASCII7 or UTF-8 format,
then the dictd server will not be compliant to RFC 2229.

NOTE If utf-8 or 8-bit dictionaries are included in the configuration file,
and the appropriate --locale has not been specified, dictd will fail to
start. This implies that dictd will not run with both utf-8 and 8-bit
dictionaries in the configuration file.

add_strategy strategy_name description
Adds strategy strategy_name with the description description. This new
search strategy may be implemented with a help of plugins. Both
strategy_name and description are strings.

default_strategy string
Set the server's default search strategy for MATCH search type. The
compiled-in default is 'lev'. It is also possible to set default strategy
per database. See default_strategy keyword in Database specification
section.

disable_strategy string
Disable specified strategies. By default all implemented search strategies
are enabled. It is also possible to disable strategies per database. See
disable_strategy keyword in Database specification section.

listen_to string
Binds socket to the specified address. If you want to allow connections to
dict server from localhost only, apply
listen_to 127.0.0.1

syslog string
Log using the syslog(3) facility.

syslog_facility string
Specifies the syslog facility to use. The use of this option implies the -s
option to turn on logging via syslog. When the operating system libraries
support SYSLOG_NAMES, the names used for this option should be those listed
in syslog.conf(5). Otherwise, the following names are used (assuming the
particular facility is defined in the header files): auth, authpriv, cron,
daemon, ftp, kern, lpr, mail, news, syslog, user, uucp, local0, local1,
local2, local3, local4, local5, local6, and local7.

log_file string
Specify the file for logging. The filename specified is recomputed on each
use using the strftime(3) call. For example, a filename ending in ".%Y%m%d"
will write to log files ending in the year, month, and date that the log
entry was written.
NOTE: If dictd does not have write permission for this file, it will
silently fail.

pid_file string
The specified filename will be created to contain the process id of the main
dictd process. The default is /var/run/dictd.pid

fast_start
By default, dictd creates (in memory) additional index to make the search
faster. This option disables this behaviour and makes startup faster.

without_mmap
do not use the mmap(2) function and read entire files into memory instead.
Use this option, if you know exactly what you are doing.

Database Specification
The database specification describes the database:

data string
Specifies the filename for the flat text database. If the filename does not
begin with '.' or '/', it is prepended with $datadir/. It is a compile time
option. You can change this behaviour by editing Makefile or running
./configure --datadir=...

index string
Specifies the filename for the index file. Path matter is similar to that
described above in "data" option .

index_suffix string
This is optional index file to make 'suffix' search strategy faster (binary
search). It is generated by 'dictfmt_index2suffix'. Run
"dictfmt_index2suffix --help" for more information. Path matter is similar
to that described above in "data" option .

index_word string
This is optional index file to make 'word' search strategy faster (binary
search). It is generated by 'dictfmt_index2word'. Run "dictfmt_index2word
--help" for more information. Path matter is similar to that described
above in "data" option .

prefilter string
Specifies the prefilter command. When a chunk of the compressed database
is read, it will be filtered with this filter before being decompressed.
This may be used to provide some additional compression that knows about
the data and can provide better compression than the LZ77 algorithm used by
zlib.

postfilter string
Specifies the postfilter command. When a chunk of the compressed database
is read, it will be filtered with this filter before the offset and length
for the entry are used to access data. This is provided for symmetry with
the prefilter command, and may also be useful for providing additional
database compression.

filter string
Specifies the filter command. After the entry is extracted from the
database, it will be filtered with this filter. This may be used to provide
formatting for the entry (e.g., for html).

name string
Specifies the short name of the database (e.g., "1913 Webster's"). If the
string begins with @, then it specifies the headword to look up in the
dictionary to find the short name of the database. The default is
"@00-database-short", but this may be changed in the defs.h file at compile
time (DICT_SHORT_ENTRY_NAME).

info string
Specifies the information about database. If the string begins with @, then
it specifies the headword to look up in the dictionary to find information.
The default is "@00-database-info", but this may be changed in the defs.h
file at compile time (DICT_INFO_ENTRY_NAME).

invisible
Makes dictionary invisible to the clients i.e. this dictionary will not be
recognized or shown by DEFINE, MATCH, SHOW INFO, SHOW SERVER and SHOW DB
commands. If some definitions or matches are found in invisible dictionary,
the name of the upper visible virtual dictionary is returned. Dictionaries
'*' and '!' don't include invisible ones. NOTE: Invisible dictionaries are
completely inaccessible (and invisible) to the client unless they are
included to the virtual or MIME dictionary (See database_virtual or
database_mime database sections).

disable_strategy string
Disables the specified strategy for database. This may be useful for slow
dictionaries (plugins) or for dictionaries included to virtual ones. For an
example see file examples/dictd_complex.conf.

default_strategy string
Specifies the strategy which will be used if the database is accessed using
the strategy '.'. I.e. this directive is the way to set the preferred
search strategy per database. For example, instead of strategy lev , the
strategy word may be preferred for databases mainly containing the multiword
phrases but the single words.

Virtual Database Specification
The virtual database specification describes the virtual database:

database_list string
Specifies a list of databases which are included into the virtual database.
Database names are in the string and are separated by comma.

name string
Specifies the short name of the database. See database specification

info string
Specifies the information about database. See database specification

invisible
Makes dictionary invisible to the clients. See database specification

disable_strategy string
Disables the specified strategy for database. See database specification

Plugin Specification

plugin string
Specifies a filename of the plugin.

data string
Specifies data for initializing plugin.

name string
Specifies the short name of the database. See Database Specification for
more information.

info string
Specifies the information about database. See Database Specification for
more information.

invisible
Makes dictionary invisible to the clients. See Database Specification for
more information.

disable_strategy string
Disables the specified strategy for database. See Database Specification
for more information.

default_strategy string
Sets the default search strategy for database. See Database Specification
for more information.

Mime Specification

dbname_nomime string
Specifies the real database name which is used in case OPTION MIME command
was NOT received from a client.

dbname_mime string
Specifies the real database name which is used in case OPTION MIME command
WAS received from a client. A necessary MIME header is set while creating a
database. See dictfmt(1) for option --mime-header.

name string
Specifies the short name of the database. See Database Specification for
more information.

info string
Specifies the information about database. See Database Specification for
more information.

invisible
Makes dictionary invisible to the clients. See Database Specification for
more information.

disable_strategy string
Disables the specified strategy for database. See Database Specification
for more information.

default_strategy string
Sets the default search strategy for database. See Database Specification
for more information.

include string
The text of the file "string" (usually a database specification) will be read as if
it appeared at this location in the configuration file. Nested includes are not
permitted.

DETERMINATION OF ACCESS LEVEL

When a client connects, the global access specification is scanned, in order, until a
specification matches. If no access specification exists, all access is allowed (e.g.,
the action is the same as if "allow *" was the only item in the specification). For each
item, both the hostname and IP are checked. For example, consider the following access
specification:
allow 10.42.*
authonly *.edu
deny *
With this specification, all clients in the 10.42 network will be allowed access to
unrestricted databases; all clients from *.edu sites will be allowed to authenticate, but
will be denied access to all databases, even those which are otherwise unrestricted; and
all other clients will have their connection terminated immediately. The 10.42 network
clients can send an AUTH command and gain access to restricted databases. The *.edu
clients must send an AUTH command to gain access to any databases, restricted or
unrestricted.

When the AUTH command is sent, the access list for each database is scanned, in order,
just as the global access list is scanned. However, after authentication, the client has
an associated username. For example, consider the following access specification:
user u1
deny *.com
user u2
allow *
If the client authenticated as u1, then the client will have access to this database, even
if the client comes from a *.com site. In contrast, if the client authenticated as u2,
the client will only have access if it does not come from a *.com site. In this case, the
"user u2" is redundant, since that client would also match "allow *".

Warning: Checks are performed for domain names and for IP addresses. However, if reverse
DNS for a specific site is not working, it is possible that a domain name may not be
available for checking. Make sure that all denials use IP addresses. (And consider a
future enhancement: if a domain name is not available, should denials that depend on a
domain name match anything? This is the more conservative viewpoint, but it is not
currently implemented.)

SEARCH ALGORITHMS

The DICT standard specifies a few search algorithms that must be implemented, and permits
others to be supported on a server-dependent basis. The following search strategies are
supported by this server. Note that all strategies are case insensitive. Most ignore
non-alphanumeric, non-whitespace characters.

exact An exact match. This algorithm uses a binary search and is one of the fastest
search algorithms available.

lev The Levenshtein algorithm (string edit distance of one). This algorithm searches
for all words which are within an edit distance of one from the target word. An
"edit" means an insertion, deletion, or transposition. This is a rapid algorithm
for correcting spelling errors, since many spelling errors are within a Levenshtein
distance of one from the original word.

prefix Prefix match. This algorithm also uses a binary search and is very fast.

nprefix
Like prefix but returns the specified range of matches. For example, when prefix
strategy returns 1000 matches, you can get only 100 ones skipping the first 800
matches. This is made by specified these limits in a query like this: 800#100#app,
where 800 is skip count, 100 is a number of matches you want to get and "app" is
your query. This strategy allows one to implement DICT client with fast
autocompletion (although it is not trivial) just like many standalone dictionary
programs do.

NOTE: If you access the dictionary "*" (or virtual one) with nprefix strategy, the
same range is set for each database in it, but globally for all matches found in
all databases.

NOTE: In case you access non-english dictionary the returned matches may be (and
mostly will be) NOT ordered in alphabetic order.

re POSIX 1003.2 (modern) regular expression search. Modern regular expressions are
the ones used by egrep(1). These regular expressions allow predefined character
classes (e.g., [[:alnum:]], [[:alpha:]], [[:digit:]], and [[:xdigit:]] are useful
for this application); uses * to match a sequence 0 or more matches of the previous
atom; uses + to match a sequence of 1 or more matches of the previous atom; uses ?
to match a sequence of 0 or 1 matches of the previous atom; used ^ to match the
beginning of a word, uses $ to match the end of a word, and allows nested
subexpression and alternation with () and |. For example, "(foo|bar)" matches all
words that contain either "foo" or "bar". To match these special characters, they
must be quoted with two backslashes (due to the quoting characteristics of the
server). Warning: Regular expression matches can take 10 to 300 times longer than
substring matches. On a busy server, with many databases, this can required more
than 5 minutes of waiting time, depending on the complexity of the regular
expression.

regexp Old (basic) regular expressions. These regular expressions don't support |, +, or
?. Groups use escaped parentheses. While modern regular expressions are generally
easier to use, basic regular expressions have a back reference feature. This can
be used to match a second occurrence of something that was already matched. For
example, the following expression finds all words that begin and end with the same
three letters:
^\$...\$.*\\1$

Note the use of the double backslashes to escape the special characters. This is
required by the DICT protocol string specification (a single backslash quotes the
next character -- we use two to get a single backslash through to the regular
expression engine). Warning: Note that the use of backtracking is even slower than
the use of general regular expressions.

soundex
The Soundex algorithm, a classic algorithm for finding words that sound similar to
each other. The algorithm encodes each word using the first letter of the word and
up to three digits. Since the first letter is known, this search is relatively
fast, and it sometimes good for correcting spelling errors when the Levenshtein
algorithm doesn't help.

substring
Match a substring anywhere in the headword. This search strategy uses a modified
Boyer-Moore-Horspool algorithm. Since it must search the whole index file, it is
not as fast as the exact and prefix matches.

suffix Suffix match. This search strategy also uses a modified Boyer-Moore-Horspool
algorithm, and is as fast as the substring search. If the optional index_suffix
string file is listed in the configuration file this search is much faster.

word Match any single word, even if part of a multi-word entry. If the optional
index_word string file is listed in the configuration file this search strategy
works much faster.

first Match the first word that begins a multi-word entry.

last Match the last word that ends a multi-word entry. If the optional index_suffix
string file is listed in the configuration file this search strategy works much
faster.

DATABASE FORMAT

Databases for dictd are distributed separately. A database consists of two files. One is
a flat text file, the other is the index.

The flat text file contains dictionary entries (or any other suitable data), and the index
contains tab-delimited tuples consisting of the headword, the byte offset at which this
entry begins in the flat text file, and the length of the entry in bytes. The offset and
length are encoded using base 64 encoding using the 64-character subset of International
Alphabet IA5 discussed in RFC 1421 (printable encoding) and RFC 1522 (base64 MIME).
Encoding the offsets in base 64 saves considerable space when compared with the usual base
10 encoding, while still permitting tab characters (ASCII 9) to be used for delimiting
fields in a record. Each record ends with a newline (ASCII 10), so the index file is
human readable.

Some headwords are used by dictd especially

00-database-info Contains the information about database which is returned by SHOW INFO
command, unless it is specified in the configuration file.

00-database-short Contains the short name of the database which is returned by SHOW DB
command, unless it is specified in the configuration file. See dictfmt -s.

00-database-url URL where original dictionary sources were obtained from. See dictfmt -u.
This headword is not used by dictd

00-database-utf8 Presents if dictionary is encoded using UTF-8. See dictfmt --utf8

00-database-8bit-new Presents if dictionary is encoded using 8-BIT character set (not
ASCII and not UTF8). See dictfmt --locale.

The flat text file may be compressed using gzip(1) (not recommended) or dictzip(1) (highly
recommended). Optimal speed will be obtained using an uncompressed file. However, the
gzip compression algorithm works very well on plain text, and can result in space savings
typically between 60 and 80%. Using a file compressed with gzip(1) is not recommended,
however, because random access on the file can only be accomplished by serially
decompressing the whole file, a process which is prohibitively slow. dictzip(1) uses the
same compression algorithm and file format as does gzip(1), but provides a table that can
be used to randomly access compressed blocks in the file. The use of 50-64kB blocks for
compression typically degrades compression by less than 10%, while maintaining acceptable
random access capabilities for all data in the file. As an added benefit, files
compressed with dictzip(1) can be decompressed with gzip(1) or zcat(1). (Note:
recompressing a dictzip'd file using, for example, znew(1) will destroy the random access
characteristics of the file. Always compress data files using dictzip(1).)

SIGNALS

       SIGHUP causes dictd to reread configuration file and reinitialize databases.

       SIGUSR1 causes dictd to unload databases. Then dictd returns 420 status (instead of  220).
       To load databases again, send SIGHUP signal. Because database files are mmap'ed(2) , it is
       impossible to update them while dictd is running.  So, if  you  need  to  update  database
       files  and  reread  configuration  file,  first,  send  SIGUSR1  signal to dictd to unload
       databases, update files, and then send SUGHUP signal to load them again.

COPYING

       The main source files for the dictd  server  and  the  dictzip  compression  program  were
       written  by  Rik  Faith  (faith@dict.org)  and  are distributed under the terms of the GNU
       General Public License.  If you need to distribute under other terms, write to the author.

       The main libraries used by these programs (zlib,  regex,  libmaa)  are  distributed  under
       different  terms,  so  you  may  be  able  to use the libraries for applications which are
       incompatible with the GPL -- please see the copyright notices and license information that
       come  with  the  libraries for more information, and consult with your attorney to resolve
       these issues.

BUGS

       The regular expression searches do not ignore non-whitespace, non-alphanumeric  characters
       as do the other searches.  In practice, this isn't much of a problem.

WARNINGS

       Conformance  of  regular  expressions (used by 're' and 'regexp' search strategies) to ERE
       and BRE depends on library you build dictd with.   Whether  're'  and  'regex'  strategies
       support utf8 depends on library you build dictd with.

FILES

       /etc/dictd/dictd.conf
              dictd configuration file

       /usr/sbin/dictd
              dictd daemon itself

       /var/run/dictd.pid
              File for storing pid of dictd daemon

       /usr/share/dictd
              The default directory for dictd databases (.index and .dict[.dz] files)