It can be solved setting properly the environment variable LD_LIBRARY_PATH in the configuration file /etc/apache2/apache2.conf

Add below the ServerRoot path:
ServerRoot "/etc/apache2"


the following line:
SetEnv LD_LIBRARY_PATH="/opt/oracle/instantclient_10_2"


Don’t forget to let us know if the solution is working also for you ;)

Get the OCI8 module working on a Mac require several settings. I wrote a script to automate the procedure that install and configure SqlPlus, the Oracle Client v10.2, Apache2, PHP5 and the OCI8 on a Mac OS X running Leopard. The script was tested on a Leopard 10.5.4 machine. I have never tested it on Tiger but I don’t recommend to test it there without having an idea of how to backup and restore all the Apache configuration files.

Pre-installation:
1. Download from the Oracle website the Oracle Client for Mac OS X (Intel x86) Version 10.2.0.4 and the SqlPlus:
- the Oracle Client ‘Instant Package – Basic’ [instantclient-basic-macosx-10.2.0.4.0.zip]
- the Oracle Client ‘Instant Package – SDK’ [instantclient-sdk-macosx-10.2.0.4.0.zip]
- the Oracle Client ‘Instant Package – SqlPlus‘ [instantclient-sqlplus-macosx-10.2.0.4.0.zip]
2. Download the bash script MacOracleViaPHP.sh. Last version can be found in the script page.
3. Download the last version of the following programs respecting the file format
- Apache2 [httpd-X.X.X.tar.gz]
- PHP5 [php-5.X.X.tar.gz]
- OCI8 [oci8-X.X.X.tgz]

Installation:
1. Copy all these files in your Mac directory /var/root in the following way
- Create a folder on the desktop and move all the files in this folder
- Open the terminal
- If you don’t have a root password set you will need to set one
# sudo passwd
- Log in as root
# su -
- Copy the files inside the folder you created into the root directory /var/www
cp /Users/YOUR_MAC_USERNAME/Desktop/FOLDER_YOU_CREATED/* .
(don’t forget the dot ‘.’ at the end of the command)
- Check that the files are in the right place
# cd /var/root
# ls
2. Enter the home directory of the user root, change the permissions of the installation script and execute it.
# cd
# chmod 755 MacOracleViaPHP.sh
# ./MacOracleViaPHP.sh
3. Type: Oracle SID, Oracle Server, Oracle Server Port, Oracle Database Username, Oracle Database Password.

Installation Check:
1. To connect the Oracle DB via SqlPlus you can run the following command:
# sqlplus DB_USER/DB_PASS@//DB_SERVER:DB_PORT/DB_SID
2. To check that PHP can connect Oracle, opening the page http://localhost/info.php you could see the OCI8 module enabled, and opening the page http://localhost/test.php you could connect the Oracle DB.

Your comment, error reports and improvement requests are always welcome ;D

Pre-installation:
1. Download from the Oracle website the Oracle Client for Mac OS X (Intel x86) Version 10.2.0.4 and the SqlPlus:
- the Oracle Client ‘Instant Package – Basic’ [instantclient-basic-macosx-10.2.0.4.0.zip]
- the Oracle Client ‘Instant Package – SqlPlus‘ [instantclient-sqlplus-macosx-10.2.0.4.0.zip]
2. Download the bash scripts MacSqlPlus.sh and TNSconnectMac.sh. Last version can be found in the script page.

Installation:
1. Set a root password and log in as root
# sudo passwd
# su -
2. Copy the files instantclient-basic-macosx-10.2.0.4.0.zip, instantclient-sqlplus-macosx-10.2.0.4.0.zip, MacSqlPlus.sh and TNSconnectMac.sh into the directory /var/root.
3. Enter the home directory of the user root, change the permissions of the scripts and execute the installation script.
# cd
# chmod 755 MacSqlPlus.sh TNSconnectMac.sh
# ./MacSqlPlus.sh

Post-Installation: [Steps Required]
1. Make sure you know SID, SERVER and PORT of the server you want to connect.
2. Execute the script TNSconnectMac.sh
# cd
# ./TNSconnectMac.sh
3. Type: Oracle SID, Oracle Server, Oracle Server Port, Oracle Database Username, Oracle Database Password.

Installation Check:
1. To connect the Oracle DB via SqlPlus you can run the following command:
# sqlplus DB_USER/DB_PASS@//DB_SERVER:DB_PORT/DB_SID

Your comment, error reports and improvement requests are always welcome ;D

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Connecting an Oracle Database via PHP, requires a not easy procedure. The bash scripts OracleViaPHP.sh and TNSconnect.sh will automate the set up process for you.
The scripts are tested on a virtual machine running OS Linux Ubuntu Server 8.04.1 i386 created on a Mac OS X running Leopard 10.5.3. OracleViaPHP.sh will install and configure Apache2, PHP5, the Oracle Client v10.2 and the OCI8 and TNSconnect.sh will create the file tnsnames.ora to connect the Oracle DB. The scripts should also work on Ubuntu 9.x.

Pre-installation:
1. Download Ubuntu Server 8.04.1 from www.ubuntu.com
2. Download from the Oracle website the Oracle Client for Linux x86 Version 10.2.0.4 and the SDK:
- the Oracle Client ‘Instant Package – Basic Lite’ [oracle-instantclient-basiclite-10.2.0.4-1.i386.zip]
- the Oracle Client ‘Instant Package – SDK’ [oracle-instantclient-devel-10.2.0.4-1.i386.zip]  
3. Download the bash scripts OracleViaPHP.sh and TNSconnect.sh. Last version can be found in the script page.
4. Install Ubuntu Server 8.04.1 

Installation:
1. Set a root password and log in as root
# sudo passwd
# su -
2. Copy the files oracle-instantclient-basiclite-10.2.0.4-1.i386.zip, oracle-instantclient-devel-10.2.0.4-1.i386.zip, OracleViaPHP.sh and TNSconnect.sh into the /root directory.
3. Enter the /root directory and execute the installation script.
# cd /root
# ./OracleViaPHP.sh 

Post-Installation: [Steps Required]
1. Make sure you know SID, SERVER and PORT of the server you want to connect.
2. Execute the script TNSconnect.sh
# cd /root
# ./TNSconnect.sh
3. Type: Oracle SID, Oracle Server, Oracle Server Port, Oracle Database Username, Oracle Database Password.

Installation Check:
1. Connecting http://your_ip_address/info.php you should get the PHP info page showing the module oci8 installed.
2. Connecting http://your_ip_address/test.php you should be able to connect the Oracle DB you defined.

Trouble Shooting
If you get the error:
Warning: ocilogon() [function.ocilogon]: ORA-12154: TNS:could not resolve the connect identifier specified in /var/www/test.php on line 2
Could not connect to Oracle database!

It is possible that: 
1. You typed the Oracle Server details in a wrong way. You can edit manually this information in the files /opt/oracle/tns/tnsnames.ora and /var/www/test.php
2. The permission to the file /opt/oracle/tns/tnsnames.ora are not right. You can to execute the following command:
# chmod 777 /opt/oracle/tns/tnsnames.ora
3. The environment variables in the file /etc/init.d/apache2 are not defined properly. Make sure that the file /etc/init.d/apache2 contains at the beginning the following string:
ENV=”env -i LANG=C PATH=/usr/local/bin:/usr/bin:/bin 
ORACLE_HOME=/opt/oracle/instantclient_10_2 
TNS_ADMIN=/opt/oracle/tns 
LD_LIBRARY_PATH=/opt/oracle/instantclient_10_2″

If you get the error:
/usr/bin/ld: skipping incompatible /opt/oracle/instantclient_10_2/libclntsh.so when searching for -lclntsh
/usr/bin/ld: cannot find -lclntsh
collect2: ld returned 1 exit status
make: *** [oci8.la] Error 1
ERROR: `make' failed
it’s possible that your server has a 64-bit architecture. You will need to download from the Oracle website the Oracle Client and the SDK package for Linux 64-bit architecture and manually unzip the files in the directory /opt/oracle/instantclient_10_2.

Your comment, error reports and improvement requests are always welcome ;D