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Occasionally as a Linux administrator you will be in the situation where working on a remote server and you are left with no option but to force a reboot the system. This may be for a number of reasons, but where I have found it most frequent is when working on Linux clusters in a remote location.

When the "reboot" or "shutdown" commands are executed daemons are gracefully stopped and storage volumes unmounted.
This is usually accomplished via scripts in the /etc/init.d directory which will wait for each daemon to shut down gracefully before proceeding on to the next one. This is where a situation can develop where your Linux server fails to shutdown cleanly leaving you unable to administer the system until it is inspected locally. This is obviously not ideal so the answer is to force a reboot on the system where you can guarantee that the system will power cycle and come back up. The method will not unmount file systems nor sync delayed disk writes, so use this at your own discretion.

To force the kernel to reboot the system we will be making use of the magic SysRq key.

The magic_SysRq_key provides a means to send low level instructions directly to the kernel via the /proc virtual file system.


To enable the use of  the magic SysRq option type the following at the command prompt:

 

    echo 1 > /proc/sys/kernel/sysrq

 

Then to reboot the machine simply enter the following:

 

    echo b > /proc/sysrq-trigger


Voilà! Your system will instantly reboot.
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In this article Chris Mavin, explains and details how to use the Recital Database Server with the Open Source Servlet Container Apache Tomcat.

Overview

PHP has exploded on the Internet, but its not the only way to create web applications and dynamic websites. Using Java Servlets, JavaServer Pages and Apache Tomcat you can develop web applications in a more powerful full featured Object Oriented Language, that is easier to debug, maintain, and improve.

Tomcat Installation

There are a number of popular Java application servers such as IBM Web Sphere and BEA WebLogic but today we will be talking about the use of Apache Tomcat 5, the Open Source implementation of the Java Servlet and JavaServer Pages technologies developed at the Apache Software Foundation. The Tomcat Servlet engine is the official reference implementation for both the Servlet and JSP specifications, which are developed by Sun under the Java Community Process. What this means is that the Tomcat Server implements the Servlet and JSP specifications as well or better than most commercial application servers.

Apache Tomcat is available for free but offers many of the same features that commercially available Web application containers boast.

Tomcat 5 supports the latest Servlet and JSP specifications, Servlet 2.4, and JSP 2.0, along with features such as:

  • Tomcat can run as a standalone webserver or a Servlet/JSP engine for other Web Servers.

  • Multiple connectors - for enabling multiple protocol handlers to access the same Servlet engine.

  • JNDI - The Java Naming and Domain Interface is supported.

  • Realms - Databases of usernames and passwords that identify valid users of a web application.

  • Virtual hosts - a single server can host applications for multiple domain names. You need to edit server.xml to configure virtual hosts.

  • Valve chains.

  • JDBC - Tomcat can be configured to use any JDBC driver.

  • DBCP - Tomcat can use the Apache commons DBCP for connection pooling.

  • Servlet reloading (Tomcat monitors any changes to the classes deployed within that web server.)

  • HTTP functionality - Tomcat functions as a fully featured Web Server.

  • JMX, JSP and Struts-based administration.

Tomcat Installation

In this next two sections we will walk through the install and setup of Tomcat for use with the Recital database server.

To download Tomcat visit the Apache Tomcat web site is at http://jakarta.apache.org/tomcat.
Follow the download links to the binary for the hardware and operating system you require.

For Tomcat to function fully you need a full Java Development Kit (JDK). If you intend to simply run pre compiled JavaServer pages you can do so using just the Java Runtime Environment(JRE).

The JDK 1.5 is the preferred Java install to work with Tomcat 5, although it is possible to run Tomcat 5 with JDK 1.4 but you will have to download and install the compat archive available from the Tomcat website.

For the purpose of this article we will be downloading and using Tomcat 5 for Linux and JDK 5.0, 
you can download the JDK at http://java.sun.com/javase/downloads/index.jsp.

Now we have the JDK, if the JAVA_HOME environment variable isn't set we need to set it to refer to the base JDK install directory.

Linux/Unix:
$ JAVA_HOME= /usr/lib/j2se/1.4/
$ EXPORT $JAVA_HOME
Windows NT/2000/XP:

Follow the following steps:

1. Open Control Panel.
2. Click the System icon.
3. Go to the Advanced tab.
4. Click the Environment Variables button.
5. Add the JAVA_HOME variable into the system environment variables.


The directory structure of a Tomcat installation comprises of the following:

/bin 			- Contains startup, shutdown and other scripts. 
	/common  	- Common classes that the container and web applications can use.
	/conf 		- Contains Tomcat XML configuration files XML files.
	/logs 		- Serlvet container and application logs.
	/server 		- Classes used only by the Container.
	/shared 		- Classes shared by all web application.
	/webapps 	- Directory containing the web applications.
	/work 		- Temporary directory for files and directories.

The important files that you should know about are the following:

  • server.xml

The Tomcat Server main configuration file is the [tomcat install path]\conf\server.xml file. This file is mostly setup correctly for general use. It is within this file where you specify the port you wish to be running the server on. Later in this article I show you how to change the default port used from 8080 to port 80.

  • web.xml

The web.xml file provides the configuration for your web applications. There are two locations where the web.xml file is used, 
web-inf\web.xml provides individual web application configurations and [tomcat install path]conf\web.xml contains the server wide configuration.

Setting up Tomcat for use

We'll start by changing the port that Tomcat will be listening on to 80.

To do this we need to edit [tomcat install path]/conf/server.xml and change the port attribute of the connector element from 8080 to 80.

After you have made the alteration the entry should read as:

<!-- Define a non-SSL HTTP/1.1 Connector on port 8080 -->
<Connector port="80" maxHttpHeaderSize="8192"

Next we want to turn on Servlet reloading, this will cause the web application to be recompiled each time it is accessed, allowing us to make changes to the files without having to worry about if the page is being recompiled or not.

To enable this you need to edit [tomcat install path]/conf/context.xml and change <Context> element to <Context reloadable="true">.

After you have made the alteration the entry should read as:

<Context reloadable="true">
<WatchedResource>WEB-INF/web.xml</WatchedResource>
</Context>

Next we want to enable the invoker Servlet.

The "invoker" Servlet executes anonymous Servlet classes that have not been defined in a web.xml file.  Traditionally, this Servlet is mapped to the URL pattern "/servlet/*", but you can map it to other patterns as well.  The extra path info portion of such a request must be the fully qualified class name of a Java class that implements Servlet, or the Servlet name of an existing Servlet definition.

To enable the invoker Servlet you need to edit the to [tomcat install path]/conf/web.xml and uncomment the Servlet and Servlet-mapping elements that map the invoker /servlet/*.

After you have made the alteration the entry should read as:

<servlet>
<servlet-name>invoker</servlet-name>
<servlet-class>org.apache.catalina.servlets.InvokerServlet</servlet-class>
<init-param>
<param-name>debug</param-name>
<param-value>0</param-value>
</init-param>
<load-on-startup>2</load-on-startup>
</servlet>

<servlet-mapping>
<servlet-name>invoker</servlet-name>
<url-pattern>/servlet/*</url-pattern>
</servlet-mapping>

If you are you not interested in setting up your own install of Tomcat there are prebuilt versions Tomcat that has all of the above changes already made, and has the test HTML, JSP, and Servlet files already bundled. Just unzip the file, set your JAVA_HOME

Next we will give Tomcat and your web applications access to the Recital JDBC driver.

For the purposes of this article we are going to install the Recital JDBC driver in the /[tomcat install path]/common/lib/ this gives Tomcat and your web applications access to the Recital JDBC driver. The driver can be installed in a number of places in the Tomcat tree, giving access to the driver to specific application or just to the web application and not the container. For more information refer to the Tomcat documentation.

Copy the recitalJDBC.jar which is located at /[recital install path]/drivers/recitalJDBC.jar to the /[tomcat install path]/common/lib/ directory.

Linux:
$cp /[recital install path]/drivers/recitalJDBC.jar /[tomcat install path]/common/lib/
Once you have completed all the steps detailed above, fire up the server using the script used by your platform's Tomcat installation.

Linux/Unix:
[tomcat install path]/bin/startup.sh
Windows:
[tomcat install path]/bin/startup

If you are having problems configuring your Tomcat Installation or would like more detail visit the online documentation a the Apache Tomcat site.

Example and Links

Now we have setup our Tomcat installation, lets get down to it with a JSP example which uses the Recital JDBC driver to access the demonstration database (southwind) shipped with the Recital Database Server.

The example provided below is a basic JDBC web application, where the user simply selects a supplier from the listbox and requests the products supplied by that supplier.

To run the example download and extract the tar archive or simple save each of the two jsp pages individually into /[tomcat install path]/webapps/ROOT/ on your server.

By enabling the invoker Servlet earlier we have removed the need to set the example up as a web application in the Tomcat configuration files.

You can now access the example web application at http://[Server Name]/supplier.jsp if the page doesn't display, check you have followed all the Tomcat installation steps detailed earlier in this article and then make sure both Tomcat and a licensed Recital UAS are running.

Downloads:
Archive: jspExample.tar

Right click and save as individual files and rename as .jsp files:
supplier.txt details.txt

Further Reading on JSP and JDBC can be found at http://www-128.ibm.com/developerworks/java/library/j-webdata/

Final Thoughts

Recital and Apache tomcat are a powerful combination, using Java Servlet technology you can separate application logic and the presentation extremely well. Tomcat, JSP, Java Servlets and the Recital database server form a robust platform independent, easily maintained and administered solution with which to unlock the power of your Recital, Foxpro, Foxbase, Clipper, RMS and C-SAM data.

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Occasionally subversion can get itself confused about what is and what is not in a working copy. This usually occurs if you have replaced the contents of a directory such as when you upgrade a component in Joomla!

You receive a message such containing this:

"working copy admin area is missing"

How to resolve this: 

Step 1 -- Rename the directory that is causing the error from a shell prompt and prefix it with __ 

mv com_docman __com_docman

Step 2 -- Using your subversion client refresh your working copy, then "update" the directory that is causing the problem e.g. update com_docman.

Step 3 -- Now you can commit the __com_docman directory.

After you have done this follow these steps, using your subversion client:

Step 4 -- delete the com_docman directory from your working copy
Step 5 -- rename __com_docman back to com_docman

Now "commit all" and both your working copy and repository will be in sync.
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Privacy Policy

We respect and are committed to protecting your privacy.

We require that you provide some personal information, to allow us to provide the services we do to the users of recitalsoftware.com, and to improve recitalsoftware.com. The type of information we collect, how we use it, and what choices you have, are detailed in this policy.

Information Collection and Use

We collect the information you provide when you register for an account or complete an information request form.

We use this information to satisfy your requests for further information, to customize our responses and our future communication with you, and to contact you, regarding development and events in the projects or areas of recitalsofware.com that you have expressed interest in, or in recitalsoftware.com, in general.

We make every effort to allow you to opt-in and opt-out of receiving messages from recitalsoftware.com. However, if you are receiving messages from us and cannot find a way to unsubscribe, please contact us at This email address is being protected from spambots. You need JavaScript enabled to view it..

Information Sharing

We will not release your personal information to anyone by any method, including selling, renting, or sharing, unless:

  • you grant us permission
  • we are required to do so by law

We will not share personal identification information data, either for single individuals or groups, with any parties, including those affiliated with recitalsoftware.com, such as members or sponsors.

How We Use Cookies

This website uses cookies. A cookie is a small amount of text data, sent from our webserver to your browser, and stored on your device. The cookie is sent back to the webserver each time the browser connects to this site. We use cookies to personalize the site and to streamline your interaction with the site.

It may be possible to configure your browser to refuse cookies, or to ask you to accept each time a cookie is offered. If you choose not to accept cookies, areas of this site may have reduced functionality or performance.

Software on our servers, or third party web statics services, may store your IP address, and other information passed on by your browser (such as browser version, operating system, screen size, language, etc). recitalsoftware.com and/or third party services will aggregate this information to provide usages statistics for this website. We use this information to optimize the design, structure, and performance of this site. In particular, we use Google Analytics to provide usage statistics. For more information, read the Google Analytics Privacy Policy.

Data Security

recitalsoftware.com is also committed to the security of your personal information. We train those who work on recitalsoftware.com on this privacy policy. On our site, we use SSL (Secure Sockets Layer) to protect your personal information, by encrypting your information when you send it to recitalsoftware.com.

Public Forum Content

recitalsoftware.com makes available to its users communication forums, such as mail lists, blogs, and others. Be aware that any information or messages you share in these forums becomes public information immediately. Exercise caution in determining whether to disclose any of your personal information. recitalsoftware.com reserves the right to act as necessary to preserve the integrity of the site and its forums, including removing any and all posts deemed vulgar or inappropriate.

Children's Online Privacy

Regarding children under the age of 13, recitalsoftware.com does not knowingly:

  • accept personal information from them
  • allow them to become registered members of our web site

Updates to this Privacy Policy

We may update this policy. We will contact you if we make any substantial changes in how we use your personal information.

This privacy policy was last updated on July 1, 2010.

Contact Information

If you have any questions about this privacy policy itself, or on how we use personal information on recitalsoftware.com, please contact us at This email address is being protected from spambots. You need JavaScript enabled to view it..

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For Recital to run correctly on 64bit Linux you require the ia32 shared libraries.

The 64bit port of Recital requires these libraries to allow access to 32bit Xbase and C-ISAM data files which are 32bit.

If you do not have these libraries installed you will either get a "can't find db.exe" or an "error loading shared libraries" when trying to run or license Recital.

Installing the ia32 shared libraries

Redhat EL 5 / Centos 5 / Fedora 10

  1. Insert the Red Hat Enterprise Linux 5 Supplementary CD, which contains the ia32el package.

  2. After the system has mounted the CD, change to the directory containing the Supplementary packages. For example:

    cd /media/cdrom/Supplementary/

  3. Install the ia32el package:

    rpm -Uvh ia32el-<version>.ia64.rpm

Alternatively: Note you must have the required repo's enabled.
 yum install ia32el

Ubuntu / Debian

sudo apt-get install ia32-libs

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Recital 10 introduced the ECHO command. This command operates in the same way as the PHP ECHO command. It does not append a newline to the output but rather operates in the same way as the existing ?? command in Recital. The string being output can contain C-style string escapes \n \t or \r (newline, tab and carriage return respectively) e.g.
echo "Hello world\n"
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In this article Barry Mavin, CEO and Chief Software Architect for Recital, details on how to use the Client Drivers provided with the Recital Database Server to work with local or remote server-side JDBC data sources.

Overview

The Recital Universal .NET Data Provider provides connectivity to the Recital Database Server running on any supported platform (Windows, Linux, Unix, OpenVMS) using the RecitalConnection object.

The Recital Universal JDBC Driver provides the same functionality for java applications.

The Recital Universal ODBC Driver provides the same functionality for applications that use ODBC.

Each of the above Client Drivers use a connection string to describe connections parameters.

The basic format of a connection string consists of a series of keyword/value pairs separated by semicolons. The equals sign (=) connects each keyword and its value.

The following table lists the valid names for keyword/values.


Name Default Description

Data Source
-or-
Server
-or-Nodename

  The name or network address of the instance of the Recital Database Server which to connect to.
Directory   The target directory on the remote server where data to be accessed resides. This is ignored when a Database is specified.

Encrypt
-or-
Encryption

false When true, DES3 encryption is used for all data sent between the client and server.
Initial Catalog
-or-
Database
  The name of the database on the remote server.
Password
-or-
Pwd
  The password used to authenticate access to the remote server.
User ID   The user name used to authenticate access to the remote server.

Connection Pooling
-or-
Pool

false Enable connection pooling to the server. This provides for one connection to be shared.
Logging false Provides for the ability to log all server requests for debugging purposes
Rowid true When Rowid is true (the default) a column will be post-fixed to each SELECT query that is a unique row identifier. This is used to provide optimised UPDATE and DELETE operations. If you use the RecitalSqlGrid, RecitalSqlForm, or RecitalSqlGridForm components then this column is not visible but is used to handle updates to the underlying data source.
Logfile   The name of the logfile for logging
Gateway  

Opens an SQL gateway(Connection) to a foreign SQL data source on the remote server.
Using Gateways, you can transparently access the following local or remote data sources:

  • Recital
  • Oracle
  • ODBC (Server-side ODBC data sources)
  • JDBC (Server-side JDBC data sources)
  • ADO (Use this to connect to SQL Server and other Native Windows OLEDB data sources)
  • MySQL
  • PostgreSQL
The gateway can be specified in several formats:
servertype@nodename:username/password-database
e.g.
oracle@nodename:username/password-database
mysql@nodename:username/password-database
postgresql@nodename:username/password-database
-or-
odbc:odbc_data_source_name_on_server
oledb:oledb_connection_string_on_server
jdbc:jdbc_driver_path_on_server;jdbc:Recital:args

To connect to a server-side JDBC data source, you ue the gateway=value key/value pair in the following way.

gateway=jdbc:jdbc_driver_path_on_server;jdbc:Recital:args

You can find examples of connection strings for most ODBC and OLE DB data sources by clicking here.

Example in C# using the Recital Universal .NET Data Provider:
////////////////////////////////////////////////////////////////////////
// include the references below
using System.Data;
using Recital.Data;

////////////////////////////////////////////////////////////////////////
// The following code example creates an instance of a DataAdapter that 
// uses a Connection to the Recital Database Server, and a gateway to
// Recital Southwind database. It then populates a DataTable 
// in a DataSet with the list of customers via the JDBC driver. 
// The SQL statement and Connection arguments passed to the DataAdapter 
// constructor are used to create the SelectCommand property of the
// DataAdapter.
public DataSet SelectCustomers()
{
	string gateway = "jdbc:/usr/java/lib/RecitalJDBC/Recital/sql/RecitalDriver;"+
			"jdbc:Recital:Data Source=localhost;database=southwind";       
	RecitalConnection swindConn = new
			RecitalConnection("Data Source=localhost;gateway=\""+gateway+"\");
	RecitalCommand selectCMD = new
			RecitalCommand("SELECT CustomerID, CompanyName FROM Customers", swindConn);
	selectCMD.CommandTimeout = 30;
	RecitalDataAdapter custDA = new RecitalDataAdapter();    
	custDA.SelectCommand = selectCMD;    
	swindConn.Open();    
	DataSet custDS = new DataSet();
	custDA.Fill(custDS, "Customers");    
	swindConn.Close();
	return custDS;
}
Example in Java using the Recital Universal JDBC Driver:
////////////////////////////////////////////////////////////////////////
// standard imports required by the JDBC driver
import java.sql.*;
import java.io.*;
import java.net.URL;
import java.math.BigDecimal;
import Recital.sql.*;

////////////////////////////////////////////////////////////////////////
// The following code example creates a Connection to the Recital // Database Server, and a gateway to the Recital Southwind database. // It then retrieves all the customers via the JDBC driver. public void SelectCustomers() { // setup the Connection URL for JDBC String gateway = "jdbc:/usr/java/lib/RecitalJDBC/Recital/sql/RecitalDriver;"+ "jdbc:Recital:Data Source=localhost;database=southwind"; String url = "jdbc:Recital:Data Source=localhost;gateway=\""+gateway+"\";
// load the Recital Universal JDBC Driver new RecitalDriver(); // create the connection Connection con = DriverManager.getConnection(url); // create the statement Statement stmt = con.createStatement(); // perform the SQL query ResultSet rs = stmt.executeQuery("SELECT CustomerID, CompanyName FROM Customers"); // fetch the data while (rs.next()) { String CompanyID = rs.getString("CustomerID"); String CompanyName = rs.getString("CompanyName"); // do something with the data... } // Release the statement stmt.close(); // Disconnect from the server con.close(); }
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Subclipse is an Eclipse Team Provider plug-in providing support for Subversion within the Eclipse IDE. This plugin is required in order to use the recital eclipse workspace.
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If you have a live linux site that is running vmware virtual machines, you can pause the virtual machines when you want to perform a backup, I use acronis for linux which does incremental backups and you can specify a command to run before and after the backup, this allows backups to be performed at scheduled times daily without any intervention. In my examples below, the virtual machine i want to control is in /root/vmware/Recital/Recital.vmx

To pause the virtual machine on linux:

# vmrun pause /root/vmware/Recital/Recital.vmx


and then to unpause after the backup has completed:

# vmrun unpause /root/vmware/Recital/Recital.vmx


That is basicallty it, no need to attend the backup and it can be perfomed at a suitable time so no users are affected.

Incidentally, vmrun lets you startup a virtual machine at system startup too, without needing the GUI:

# vmrun start /root/vmware/Recital/Recital.vmx


Or alternatively stop it:

# vmrun stop /root/vmware/Recital/Recital.vmx


There are lots of other capabilities of this command, running applications inside the virtual machine etc etc. For full details just type vmrun in a terminal window.



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Recital 10 enhances the APPEND FROM command. The enhancement added the following syntax ;
APPEND FROM  TYPE CSV <file-name.csv> 
The TYPE keyword has now been enhanced to support a comma separated values (CSV) format
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