User:Dan Nessett/Technical/How to set up a CZ clone on CentOS 5

These instructions describe how to set up a LAPP stack (Linux Apache2 Postgres PHP stack) on CentOS 5.4. They are intended as an alternative to the instructions for creating a LAPP stack on Ubuntu for the purpose of creating a local CZ clone.

It must be noted that unlike Ubuntu, CentOS is much more expert friendly and much less novice friendly. For those without significant experience with Linux systems (specifically, installing and administering them), the recommended OS for a CZ clone is Ubuntu. However, the production version of the CZ wiki runs on CentOS, so for those with the requisite experience and skills, implementing a CZ clone for development work on CentOS has certain advantages. But with those advantages comes risks. The yum software installation system on CentOS is prone to significant configuration problems, especially when setting up its repositories. So, those choosing to use CentOS do so at their own risk. Caveat Emptor.

Installing postgres

The version of postgres we want is not available through the normal CentOS software repositories. So, we have to modify the repository information to direct yum to install the correct version. (Note: these instructions are based on those given at Yet Another Guide.

First find out what is the latest install package for postgres 8.3 (install packages for CentOS have the suffix rpm). Using a new tab or browser window, follow the link postgres rpms. Three files should display in the browser window. One of these will have the name pgdg-centos-8.3-x.noarch.rpm, where x will be a number, such as 6. Now download the appropriate yum repository configuration by entering the following at a terminal command prompt (replacing the x in the file name with the integer just discovered):

cd /tmp
sudo wget http://yum.pgsqlrpms.org/reporpms/8.3/pgdg-centos-8.3-x.noarch.rpm

Then install this information using the following command (again changing the x to the appropriate integer):

sudo chmod +x pgdg-centos-8.3-x.noarch.rpm
sudo rpm -ivf pgdg-centos-8.3-x.noarch.rpm

If you are working on a CentOS installation on which some other software has already been installed, it is possible that other repositories are indicated in the yum configuration files that may interfere with the installation of postgres 8.3. You can determine this as folows. Execute the following commands:

cd /etc/yum.repos.d
sudo gedit CentOS-base.repo &

If this file is non-empty, then do the following. (If the file is empty, simply close it without making any changes). There are sections in the configuration file each headed by a word in square brackets. If there are two sections labeled [base] and [updates] then at the bottom of those sections add the line:

exclude=postgresql*

Click on the Save button at the top of the edit window and close it.

Now execute the following commands:

sudo yum install postgresql
sudo yum install postgresql-server

For each command a bunch of text is displayed followed by a line that specifies the total download size. The next line is a prompt: Is this ok [y/N]:. You must type y. The default is N, which (of course) means no and taking it will abort the install.

The install of postgres on CentOS does not initialize the directory that postgres uses to store database information. So, the next step is to do this. Execute the following commands:

sudo /etc/rc.d/init.d/postgresql initdb

Installing postgres doesn't mean the server starts up when the system boots. We have to configure the system to do that. First, check that chkconfig is in your execution path. At a command prompt enter:

chkconfig

If the error bash: chkconfig: command not found is returned, you will have to add /sbin to $PATH. This requires editing .bash_profile (remember to cd to your home directory):

gedit .bash_profile &

In the edit window there should be a line starting with $PATH. At the end of this line add :/sbin (don't forget the colon at the beginning of this text and there should be no space between the colon and the rest of the line). Then save the edit, exit the editor and type:

source .bash_profile
chkconfig

This should result in an error message about usage. When chkconfig is working, enter the following commands:

sudo chkconfig --add postgresql
sudo chkconfig postgresql on

Now reboot you system and when that completes open a terminal window. Type:

su
su postgres
psql

A welcome message should display, followed by hints on psql commands and then the prompt postgres=#. At this prompt type \q.

Your terminal identity was changed from your CentOS username to root and then to postgres. Get back to root by typing:

exit

You should see a # prompt. There is one more thing we have to do before proceeding. In CentOS, the default trust model is ident based. This causes problems when configuring the postgres databases using pgAdmin III. So, we need to make one change to the postgres configuration file. Execute the following commands at a terminal window prompt:

cd /var/lib/pgsql/data
gedit pg_hba.conf &

An edit window should appear. Scroll to the end of the file and find the entry with the comment # IPv4 local connections:. The next entry controls access when connections to the postgres server comes from the local host. Copy it and paste a copy below the current entry. Now comment out the original entry and change the last part of the copied line from ident sameuser to trust. The entry should now look like the following (you can simply copy and paste the following text over the existing entry to save time):

# IPv4 local connections:
#host    all         all         127.0.0.1/32          ident sameuser
host    all         all         127.0.0.1/32          trust

Save the file and exit the editor. Now restart the postgres server with the following command:

/etc/rc.d/init.d/postgresql restart

This change allows you to manipulate postgres through pgAdmin III without changing your CentOS user identity using su or sudo. The install of postgres is now complete.

Installing apache2 and PHP

Installing postgres is a lot of work. Fortunately, installing the other two components of the LAPP stack takes much less effort. First, we will install the apache2 web server. In a terminal window execute the following command:

sudo yum install httpd

Follow the normal install procedure by answering y to the question. You may be prompted with a question whether it is OK to import a GPG key. If so, answer y.

After the install completes, execute the following two commands:

sudo chkconfig --levels 235 httpd on
sudo /etc/init.d/httpd start

Then in your favorite browser, create a new tab or window and in the URL field type: http://localhost. An apache2 test page should display. If so, apache2 is installed. If not, then make sure you correctly executed all of the commands specified above.

To install PHP5 is even simpler. Execute the following commands:

sudo yum install php
sudo yum install mod_php

If you want to test that PHP5 is working properly, cd to /var/www/html and execute:

sudo gedit phpinfo.php

When the empty edit window appears, enter the following information:

<?php
phpinfo();
?>

Save the edit and then execute:

sudo /etc/init.d/httpd restart

This command restarts the apache2 server so it is aware that PHP5 is available. Now in a browser create a new tab or window and in the URL field type:

http://localhost/phpinfo.php

A page containing information about the PHP5 installation should appear, followed by information about installed PHP5 extensions.

Finishing up

In order to install the CZ software, the installer must use the subversion client. CentOS 5.4 doesn't come with subversion , so it must be manually installed. At a terminal prompt execute:

sudo yum install mod_dav_svn subversion

After this installation completes, the LAPP stack and other software for creating a CZ clone is available. Return to the page on How to set up a CZ Clone and continue with LAPP stack conguration. You may skip the first part of the Configure Apache2 section, since you have already tested that PHP5 is correctly working. (Furthermore, document root on CentOS is different than that on Ubuntu, so there are some differences in how to carry out this test).