zebrasrv - Zebra Server
zebrasrv [-install] [-installa] [-remove] [-a file] [-v level]
[-l file] [-u uid] [-c config] [-f vconfig] [-C fname]
[-t minutes] [-k kilobytes] [-d daemon] [-w dir] [-p pidfile]
Zebra is a high-performance, general-purpose structured text indexing
and retrieval engine. It reads structured records in a variety of input
formats (e.g. email, XML, MARC) and allows access to them through exact
boolean search expressions and relevance-ranked free-text queries.
zebrasrv is the Z39.50 and SRU frontend server for the Zebra search
engine and indexer.
On Unix you can run the zebrasrv server from the command line - and put
it in the background. It may also operate under the inet daemon. On
WIN32 you can run the server as a console application or as a WIN32
The options for zebrasrv are the same as those for YAZ' yaz-ztest.
Option -c specifies a Zebra configuration file - if omitted zebra.cfg
Specify a file for dumping PDUs (for diagnostic purposes). The
special name - (dash) sends output to stderr.
Don't fork or make threads on connection requests. This is good for
debugging, but not recommended for real operation: Although the
server is asynchronous and non-blocking, it can be nice to keep a
software malfunction (okay then, a crash) from affecting all
current users. The server can only accept a single connection in
Like -S but after one session the server exits. This mode is for
Operate the server in threaded mode. The server creates a thread
for each connection rather than a fork a process. Only available on
UNIX systems that offers POSIX threads.
Use the SR protocol (obsolete).
Use the Z39.50 protocol (default). This option and -s complement
each other. You can use both multiple times on the same command
line, between listener-specifications (see below). This way, you
can set up the server to listen for connections in both protocols
concurrently, on different local ports.
Specify an output file for the diagnostic messages. The default is
to write this information to stderr
Read configuration information from config-file. The default
configuration is ./zebra.cfg
This specifies an XML file that describes one or more YAZ frontend
virtual servers. See section VIRTUAL HOSTS for details.
Sets SSL certificate file name for server (PEM).
The log level. Use a comma-separated list of members of the set
Set user ID. Sets the real UID of the server process to that of the
given user. It's useful if you aren't comfortable with having the
server run as root, but you need to start it as such to bind a
The server changes to this working directory during before
listening on incoming connections. This option is useful when the
server is operating from the inetd daemon (see -i).
Specifies that the server should write its Process ID to file given
by pidfile. A typical location would be /var/run/zebrasrv.pid.
Use this to make the the server run from the inetd server (UNIX
only). Make sure you use the logfile option -l in conjunction with
this mode and specify the -l option before any other options.
Use this to make the server put itself in the background and run as
a daemon. If neither -i nor -D is given, the server starts in the
Use this to install the server as an NT service (Windows NT/2000/XP
only). Control the server by going to the Services in the Control
Use this to install and activate the server as an NT service
(Windows NT/2000/XP only). Control the server by going to the
Services in the Control Panel.
Use this to remove the server from the NT services (Windows
Idle session timeout, in minutes. Default is 60 minutes.
Maximum record size/message size, in kilobytes. Default is 1024 KB
Set name of daemon to be used in hosts access file. See
hosts_access(5) and tcpd(8).
A listener-address consists of an optional transport mode followed by a
colon (:) followed by a listener address. The transport mode is either
a file system socket unix, a SSL TCP/IP socket ssl, or a plain TCP/IP
socket tcp (default).
For TCP, an address has the form
hostname | IP-number [: portnumber]
The port number defaults to 210 (standard Z39.50 port) for privileged
users (root), and 9999 for normal users. The special hostname "@" is
mapped to the address INADDR_ANY, which causes the server to listen on
any local interface.
The default behavior for zebrasrv - if started as non-privileged user -
is to establish a single TCP/IP listener, for the Z39.50 protocol, on
To start the server listening on the registered port for Z39.50, or on
a filesystem socket, and to drop root privileges once the ports are
bound, execute the server like this from a root shell:
zebrasrv -u daemon @
zebrasrv -u daemon tcp:@:210
zebrasrv -u daemon unix:/some/file/system/socket
Here daemon is an existing user account, and the unix socket
/some/file/system/socket is readable and writable for the daemon
Z39.50 PROTOCOL SUPPORT AND BEHAVIOR
During initialization, the server will negotiate to version 3 of the
Z39.50 protocol, and the option bits for Search, Present, Scan,
NamedResultSets, and concurrentOperations will be set, if requested by
the client. The maximum PDU size is negotiated down to a maximum of 1
MB by default.
The supported query type are 1 and 101. All operators are currently
supported with the restriction that only proximity units of type "word"
are supported for the proximity operator. Queries can be arbitrarily
complex. Named result sets are supported, and result sets can be used
as operands without limitations. Searches may span multiple databases.
The server has full support for piggy-backed retrieval (see also the
The present facility is supported in a standard fashion. The requested
record syntax is matched against the ones supported by the profile of
each record retrieved. If no record syntax is given, SUTRS is the
default. The requested element set name, again, is matched against any
provided by the relevant record profiles.
The attribute combinations provided with the termListAndStartPoint are
processed in the same way as operands in a query (see above).
Currently, only the term and the globalOccurrences are returned with
the termInfo structure.
Z39.50 specifies three different types of sort criteria. Of these Zebra
supports the attribute specification type in which case the use
attribute specifies the "Sort register". Sort registers are created for
those fields that are of type "sort" in the default.idx file. The
corresponding character mapping file in default.idx specifies the
ordinal of each character used in the actual sort.
Z39.50 allows the client to specify sorting on one or more input result
sets and one output result set. Zebra supports sorting on one result
set only which may or may not be the same as the output result set.
If a Close PDU is received, the server will respond with a Close PDU
with reason=FINISHED, no matter which protocol version was negotiated
during initialization. If the protocol version is 3 or more, the server
will generate a Close PDU under certain circumstances, including a
session timeout (60 minutes by default), and certain kinds of protocol
errors. Once a Close PDU has been sent, the protocol association is
considered broken, and the transport connection will be closed
immediately upon receipt of further data, or following a short timeout.
Zebra maintains a "classic" Z39.50 Explain database on the side.
This database is called IR-Explain-1 and can be searched using the
attribute set exp-1.
The records in the explain database are of type grs.sgml. The root
element for the Explain grs.sgml records is explain, thus explain.abs
is used for indexing.
Zebra must be able to locate explain.abs in order to index the
Explain records properly. Zebra will work without it but the
information will not be searchable.
THE SRU SERVER
In addition to Z39.50, Zebra supports the more recent and web-friendly
IR protocol SRU. SRU can be carried over SOAP or a REST-like
protocol that uses HTTP GET or POST to request search responses. The
request itself is made of parameters such as query, startRecord,
maximumRecords and recordSchema; the response is an XML document
containing hit-count, result-set records, diagnostics, etc. SRU can be
thought of as a re-casting of Z39.50 semantics in web-friendly terms;
or as a standardisation of the ad-hoc query parameters used by search
engines such as Google and AltaVista; or as a superset of A9's
OpenSearch (which it predates).
Zebra supports Z39.50, SRU GET, SRU POST, SRU SOAP (SRW) - on the same
port, recognising what protocol is used by each incoming requests and
handling them accordingly. This is a achieved through the use of Deep
Magic; civilians are warned not to stand too close.
Running zebrasrv as an SRU Server
Because Zebra supports all protocols on one port, it would seem to
follow that the SRU server is run in the same way as the Z39.50 server,
as described above. This is true, but only in an uninterestingly
vacuous way: a Zebra server run in this manner will indeed recognise
and accept SRU requests; but since it doesn't know how to handle the
CQL queries that these protocols use, all it can do is send failure
It is possible to cheat, by having SRU search Zebra with a PQF
query instead of CQL, using the x-pquery parameter instead of
query. This is a non-standard extension of CQL, and a very naughty
thing to do, but it does give you a way to see Zebra serving SRU
‘‘right out of the box''. If you start your favourite Zebra server
in the usual way, on port 9999, then you can send your web browser
This will display the XML-formatted SRU response that includes the
first record in the result-set found by the query mineral. (For
clarity, the SRU URL is shown here broken across lines, but the
lines should be joined together to make single-line URL for the
browser to submit.)
In order to turn on Zebra's support for CQL queries, it's necessary to
have the YAZ generic front-end (which Zebra uses) translate them into
the Z39.50 Type-1 query format that is used internally. And to do this,
the generic front-end's own configuration file must be used. See the
section called “YAZ SERVER VIRTUAL HOSTS”; the salient point for SRU
support is that zebrasrv must be started with the -f frontendConfigFile
option rather than the -c zebraConfigFile option, and that the
front-end configuration file must include both a reference to the Zebra
configuration file and the CQL-to-PQF translator configuration file.
A minimal front-end configuration file that does this would read as
The <config> element contains the name of the Zebra configuration file
that was previously specified by the -c command-line argument, and the
<cql2rpn> element contains the name of the CQL properties file
specifying how various CQL indexes, relations, etc. are translated into
A zebra server running with such a configuration can then be queried
using proper, conformant SRU URLs with CQL queries:
&query=title=utah and description=epicent*
SRU PROTOCOL SUPPORT AND BEHAVIOR
Zebra running as an SRU server supports SRU version 1.1, including CQL
version 1.1. In particular, it provides support for the following
elements of the protocol.
SRU Search and Retrieval
Zebra supports the SRU searchRetrieve operation.
One of the great strengths of SRU is that it mandates a standard query
language, CQL, and that all conforming implementations can therefore be
trusted to correctly interpret the same queries. It is with some shame,
then, that we admit that Zebra also supports an additional query
language, our own Prefix Query Format (PQF). A PQF query is
submitted by using the extension parameter x-pquery, in which case the
query parameter must be omitted, which makes the request not valid SRU.
Please feel free to use this facility within your own applications; but
be aware that it is not only non-standard SRU but not even
syntactically valid, since it omits the mandatory query parameter.
Zebra supports SRU scan operation. Scanning using CQL syntax is the
default, where the standard scanClause parameter is used.
In addition, a mutant form of SRU scan is supported, using the
non-standard x-pScanClause parameter in place of the standard
scanClause to scan on a PQF query clause.
Zebra supports SRU explain.
The ZeeRex record explaining a database may be requested either with a
fully fledged SRU request (with operation=explain and version-number
specified) or with a simple HTTP GET at the server's basename. The
ZeeRex record returned in response is the one embedded in the YAZ
Frontend Server configuration file that is described in the the section
called “YAZ SERVER VIRTUAL HOSTS”.
Unfortunately, the data found in the CQL-to-PQF text file must be added
by hand-craft into the explain section of the YAZ Frontend Server
configuration file to be able to provide a suitable explain record. Too
bad, but this is all extreme new alpha stuff, and a lot of work has yet
to be done ..
There is no linkage whatsoever between the Z39.50 explain model and the
SRU explain response (well, at least not implemented in Zebra, that is
..). Zebra does not provide a means using Z39.50 to obtain the ZeeRex
Other SRU operations
In the Z39.50 protocol, Initialization, Present, Sort and Close are
separate operations. In SRU, however, these operations do not exist.
· SRU has no explicit initialization handshake phase, but commences
immediately with searching, scanning and explain operations.
· Neither does SRU have a close operation, since the protocol is
stateless and each request is self-contained. (It is true that
multiple SRU request/response pairs may be implemented as multiple
HTTP request/response pairs over a single persistent TCP/IP
connection; but the closure of that connection is not a
· Retrieval in SRU is part of the searchRetrieve operation, in which
a search is submitted and the response includes a subset of the
records in the result set. There is no direct analogue of Z39.50's
Present operation which requests records from an established result
set. In SRU, this is achieved by sending a subsequent
searchRetrieve request with the query cql.resultSetId=id where id
is the identifier of the previously generated result-set.
· Sorting in CQL is done within the searchRetrieve operation - in
v1.1, by an explicit sort parameter, but the forthcoming v1.2 or
v2.0 will most likely use an extension of the query language, CQL
It can be seen, then, that while Zebra operating as an SRU server does
not provide the same set of operations as when operating as a Z39.50
server, it does provide equivalent functionality.
Surf into http://localhost:9999 to get an explain response, or use
See number of hits for a query
Fetch record 5-7 in Dublin Core format
Even search using PQF queries using the extended naughty parameter
Or scan indexes using the extended extremely naughty parameter
Don't do this in production code! But it's a great fast debugging aid.
YAZ SERVER VIRTUAL HOSTS
The Virtual hosts mechanism allows a YAZ frontend server to support
multiple backends. A backend is selected on the basis of the TCP/IP
binding (port+listening address) and/or the virtual host.
A backend can be configured to execute in a particular working
directory. Or the YAZ frontend may perform CQL to RPN conversion,
thus allowing traditional Z39.50 backends to be offered as a SRU
service. SRU Explain information for a particular backend may also be
For the HTTP protocol, the virtual host is specified in the Host
header. For the Z39.50 protocol, the virtual host is specified as in
the Initialize Request in the OtherInfo, OID
Not all Z39.50 clients allows the VHOST information to be set. For
those the selection of the backend must rely on the TCP/IP
information alone (port and address).
The YAZ frontend server uses XML to describe the backend
configurations. Command-line option -f specifies filename of the XML
The configuration uses the root element yazgfs. This element includes a
list of listen elements, followed by one or more server elements.
The listen describes listener (transport end point), such as TCP/IP,
Unix file socket or SSL server. Content for a listener:
The CDATA for the listen element holds the listener string, such as
tcp:@:210, tcp:server1:2100, etc.
attribute id (optional)
identifier for this listener. This may be referred to from server
We expect more information to be added for the listen section in a
future version, such as CERT file for SSL servers.
The server describes a server and the parameters for this server type.
Content for a server:
attribute id (optional)
Identifier for this server. Currently not used for anything, but it
might be for logging purposes.
attribute listenref (optional)
Specifies listener for this server. If this attribute is not given,
the server is accessible from all listener. In order for the server
to be used for real, however, the virtual host must match (if
specified in the configuration).
element config (optional)
Specifies the server configuration. This is equivalent to the
config specified using command line option -c.
element directory (optional)
Specifies a working directory for this backend server. If
specified, the YAZ frontend changes current working directory to
this directory whenever a backend of this type is started (backend
handler bend_start), stopped (backend handler hand_stop) and
element host (optional)
Specifies the virtual host for this server. If this is specified a
client must specify this host string in order to use this backend.
element cql2rpn (optional)
Specifies a filename that includes CQL to RPN conversion for
this backend server. See CQL section in YAZ manual. If given,
the backend server will only "see" a Type-1/RPN query.
element explain (optional)
Specifies SRU ZeeRex content for this server - copied verbatim
to the client. As things are now, some of the Explain content seems
redundant because host information, etc. is also stored elsewhere.
The format of the Explain record is described in detail, with
examples, on the file at the ZeeRex web-site.
The XML below configures a server that accepts connections from two
ports, TCP/IP port 9900 and a local UNIX file socket. We name the
TCP/IP server public and the other server internal.
<server id="server3" listenref="internal">
There are three configured backend servers. The first two servers,
"server1" and "server2", can be reached by both listener addresses -
since no listenref attribute is specified. In order to distinguish
between the two a virtual host has been specified for each of server in
the host elements.
For "server2" elements for CQL to RPN conversion is supported and
explain information has been added (a short one here to keep the
The third server, "server3" can only be reached via listener
1. Z39.50 Explain
3. SRU searchRetrieve
5. SRU scan
6. SRU explain
7. CQL sorting