Installing and Configuring LXP

To install LXP, you must have the Apache web server installed and configured to support mod_so. This is the Apache Shared Object module. If you have not built Apache with this module, you will need to reconfigure it, making sure to include the - -enable-module=so configuration option before compiling.

Warning

If you choose to manually compile Apache, be sure that you remove any existing Apache RPMs first. You can usually identify these with the rpm -qa |grep apache command.

If Apache is installed, and the Shared Object module is enabled, you may insert the CD included with this book, mount it, and proceed with the installation. You will need to be logged in as root in order to successfully install LXP, since it requires access to system-level files and directories.

Installing LXP

There are two ways to install LXP as of Version 0.8; you may use the lxpinstall.sh script, found in the lxp directory on the CD, or you may install it manually. The lxpinstall.sh script is intended to both install the required LXP files and to configure your httpd.conf file to load and enable the LXP module.

If you encounter any errors during the installation from lxpinstall.sh, see the following section about manual configuration.

Using lxpinstall.sh

The lxpinstall.sh script is extremely straightforward. On a fresh system, the only option you should be prompted to respond to is at the end of the script, when it asks you whether or not to automatically restart Apache (as must be done, to enable LXP). You may run it again afterward in case something goes wrong, though it will prompt you whether or not certain files should be overwritten.

Example 13-1 changes to the lxp directory on the CD (mounted in /mnt/cdrom, in this case), and runs the lxpinstall.sh file.

Example 13-1. Installing LXP with lxpinstall.sh

[root@host root]# cd /mnt/cdrom/lxp
[root@host lxp]# ./lxpinstall.sh
===================================================================
Thank you for installing Command Prompt LXP, 0.8.0.
Copyright (c) 1999-2001, Command Prompt, Inc.
See the LICENSE file for licensing restrictions.
==================================================================
[cmd] Checking for PostgreSQL libs (this may take a moment) ...
[cmd] Found PostgreSQL libpq library.
[cmd] Using apxs: '/usr/local/apache/bin/apxs'
[cmd] Using '/usr/local/apache/libexec/' for shared object file
 
==================================================================
[cmd] Installing 'liblxp.so'
[activating module `lxp' in /usr/local/apache/conf/httpd.conf]
cp lib/liblxp.so /usr/local/apache/libexec/liblxp.so
chmod 755 /usr/local/apache/libexec/liblxp.so
cp /usr/local/apache/conf/httpd.conf /usr/local/apache/conf/httpd.conf.bak
cp /usr/local/apache/conf/httpd.conf.new /usr/local/apache/conf/httpd.conf
rm /usr/local/apache/conf/httpd.conf.new
 
==================================================================
[cmd] Using '/usr/local/apache/conf/httpd.conf' for configuration
[cmd] Backing up original configuration file...
/usr/local/apache/conf/httpd.conf -> /usr/local/apache/conf/httpd.conf.lxp_backup
[cmd] Backing up original configuration file...
/usr/local/apache/conf/srm.conf -> /usr/local/apache/conf/srm.conf.lxp_backup
[cmd] Adding LXP directives to httpd.conf...
 
==================================================================
[cmd] Installing 'lxp.conf' into /usr/local/cmd/etc ...
conf/lxp.conf-dist -> /usr/local/cmd/etc/lxp.conf
 
==================================================================
[cmd] Re-start Apache with '/usr/local/apache/bin/apachectl'? (y/n) y
/usr/local/apache/bin/apachectl stop: httpd stopped 
/usr/local/apache/bin/apachectl start: httpd started
[cmd] Command Prompt LXP 0.8.0 successfully installed.

Note: In case there is a problem with your httpd.conf reconfiguration, remember that LXP creates a backup of your original configuration called httpd.conf.lxp_backup in the same directory as your httpd.conf before making any modifications.

You may receive the following error when running the lxpinstall.sh script:

[cmd] ERROR: LXP requires Apache be configured with Shared Object support,
[cmd] but we couldn't find Apache's apxs script.
[cmd] Please make sure it is in your path, if you know mod_so is enabled.
[cmd] exit error 1

This error indicates that apxs, the Apache Extension tool, could not be found on your system. It is typically found in /usr/local/apache/bin, though it may be missing if your Apache web server was not built with mod_so support enabled, or if you have not installed the apache-devel RPM for your system. If you know it is installed, be sure that the directory it resides within is in your PATH environment variable.

Alternatively, you may get an error message similar to the following:

[cmd] ERROR: apxs couldn't find your configuration file
[cmd] (Tried /usr/local/apache/conf/httpd.conf)
[cmd] exit error 3

If you are not using a configuration file with a standard name (i.e., httpd.conf ), you will need to manually configure it. See the next section instructions.

Manual installation

This section describes how to manually install LXP if the lxpinstall.sh script does not work for you. If you've already installed LXP successfully through this script, you may skip this section.

There are three steps to manually installing LXP:

  • Installing the LXP shared-object file

  • Installing the LXP configuration file

  • Configuring Apache's httpd.conf file

The liblxp.so file (located in the /lxp/lib directory on the CD) must be copied to the directory that your Apache web server is configured to load external modules from. This is typically /usr/local/apache/libexec for manual installations of Apache, and /etc/httpd/modules for RPM installations. Note that this directory varies wildly, and may be different in your distribution. You should be able to install into this directory through the use of apxs, however, with the following syntax:

apxs -i -n module -a shared_object

Example 13-2 demonstrates using the apxs script to install and configure the liblxp.so file directly into Apache's module directory.

Example 13-2. Manually installing liblxp.so

[root@host lib]# apxs -i -n "lxp" -a lib/liblxp.so
cp lib/liblxp.so /usr/local/apache/libexec/liblxp.so
chmod 755 /usr/local/apache/libexec/liblxp.so
[activating module `lxp' in /usr/local/apache/conf/httpd.conf]

If you do not have PostgreSQL installed, the libpq.so.2.2 file (also located in the /lxp/lib directory on the CD) should be copied to the /usr/local/cmd/lib directory. A symbolic link named libpq.so.2 should also be created to point to this file. If you have not run lxpinstall.sh, you may need to create this directory. Example 13-3 demonstrates this process.

Example 13-3. Manually installing libpq.so.2.2

[root@host lib]# mkdir -p /usr/local/cmd/lib
[root@host lib]# cp -iv libpq.so.2.2 /usr/local/cmd/lib/
libpq.so.2.2 -> /usr/local/cmd/lib/libpq.so.2.2
[root@host lib]# ln -s /usr/local/cmd/lib/libpq.so.2.2 /usr/local/cmd/lib/libpq.so.2

Next, the lxp.conf file must be installed in the /usr/local/cmd/etc directory. This is the configuration file for LXP 0.8, discussed in detail in the next section. The distributed configuration file is found in the lxp/conf directory on the CD, and is named lxp.conf-dist. Copy this file to /usr/local/cmd/etc from the lxp/conf directory on the CD, as shown in Example 13-4. If you have not run lxpinstall.sh at all, you may need to create this directory. Be sure to rename it from lxp.conf-dist to lxp.conf  !

Example 13-4. Manually installing lxp.conf

[root@host lxp]# mkdir -p /usr/local/cmd/etc
[root@host lxp]# cp -v conf/lxp.conf-dist /usr/local/cmd/etc/lxp.conf
conf/lxp.conf-dist -> /usr/local/cmd/etc/lxp.conf
[root@host lxp]#

Finally, Apache's httpd.conf file must be configured for the LXP content type.

Warning

In some circumstances, httpd.conf may have been renamed to something else (such as httpsd.conf, in the case of ApacheSSL).

There are two lines that must be added to this file for LXP to be configured. These are shown in Example 13-5.

Example 13-5. Configuring httpd.conf for LXP

DirectoryIndex index.html index.lxp
AddType application/x-httpd-lxp .lxp

A line similar to the first line in Example 13-5 should already exist in your httpd.conf file. You must add index.lxp as a value to this directive if you wish for Apache to automatically look for an LXP index in a directory request.

The second line must be added from scratch. This AddType directive should be entered exactly as it is shown in Example 13-5. This line enables the LXP module to process files ending in .lxp.

It is generally not important where you put these last two directives within the httpd.conf file, though you may wish to place them with similarly named directives that already exist, to keep the configuration file organized.

Once you have finished, you must restart Apache for the changes to take effect. This is typically done with either the apachectl command, or the httpd service script.

Nuts and Bolts: Configuring lxp.conf

After installing LXP, you will find the lxp.conf file in the /usr/local/cmd/etc directory. This file defines the database settings with which LXP connects to the PostgreSQL database for persistent connections. The file also contains a pair of debugging options.

The lxp.conf file is a simple configuration file using common conventions. The format of this file can consist of comments, directives, and associated values for each directive.

Comments are always prefixed with a hash mark (#). They can be at the beginning of a line, or follow a directive and value. They are totally ignored by LXP when the configuration is loaded, and are only useful for remembering notes on why directives are set and what possible options there may be. You can add your own comments without harming the functionality of LXP as long as you remember to precede the comment with a hash mark (#).

Directives have a very basic affect upon the functionality of LXP. They typically start at the beginning of a line, have a name (without spaces), and are followed by their associated value. The directive name defines a behavior to affect, while the value sets how to affect that behavior. Some directives accept multiple values, which are separated by either tabs or spaces. Here is example syntax:

# Here's an example directive.

MyDirective	SomeValue	# MyDirective defines some arbitrary value.

You may never need to make serious alterations in your lxp.conf file, but it's a good idea to know what it is, and what it does, in case you ever need to change one of these basic behaviors. As of LXP 0.8, the lxp.conf file is broken up into two sections; general settings and database settings.

General settings

The first two directives under the General settings section are Debug and MaxIncludeDepth:

#######################
# General LXP settings.
#######################

Debug            No  # (Yes|No)
MaxIncludeDepth  15  # (Number)

Setting the Debug directive to Yes adds a debugging-header to the top of all LXP documents. This can be useful for tracking down unexplained behavior of LXP files and included scripts. The debug header includes the name of the LXP document requested, any cookies found for the given domain, any GET/POST variables that are passed, and maximum depth inclusion.

The maximum depth inclusion is the highest number of includes LXP will traverse down before stopping and displaying an error. This is used to prevent accidental infinite includes (e.g., a.lxp includes b.lxp, which includes a.lxp). Set this value with the MaxIncludeDepth directive. The default value is 15.

Note: The value assigned to MaxIncludeDepth does not limit the total number of files that can be included within a document. It describes only the deepest level LXP can go in sub-inclusions (e.g., a.lxp includes b.lxp, which includes c.lxp, which includes d.lxp, etc).

Database settings

The next six directives pertain to database connectivity with PostgreSQL. Most of the default options are usable on most systems, but you may wish to modify these if you have special needs for your PostgreSQL installation:

#############################################
# PostgreSQL persistent connectivity options.
#############################################

UseDb   No        # (Yes|No) Set to Yes if you wish to connect to the database.

DbName  template1 # The database to use. By default, "template1".
DbHost  localhost # The database host to use. By default, "localhost".
DbPort  5432      # The port to connect to PostgreSQL on.
DbUser  postgres  # The username to connect with. By default, "postgres".
DbPass            # The password to connect with. By default, empty

If you wish to enable LXP's persistent connections to a database, set UseDb to Yes. If set to No, you will still be able to use the Direct SQL Interface to dynamically open up connections (see the Section called Including SQL Content"), but you will incur the cost of a new PostgreSQL backend connection for each connection request.

The remaining options—DbName, DbHost, DbPort, DbUser, and DbPass—should be familiar to anyone with experience connecting to PostgreSQL. The defaults will usually work fine, but you might wish to change them if you have special needs (for example, if you wish to store your data on a separate database server, you would change DbHost to point to the appropriate machine).

Warning

When utilizing the persistent connections between Apache and LXP's PostgreSQL database, it is important to recognize that there will be a separate postmaster binary running for each httpd process. Be sure that your system is configured to be capable of loading as many PostgreSQL postmaster backends as Apache requires (i.e., the number defined by the MaxClients directive in Apache's httpd.conf ) file.