When compiling PHP from source (specifically version 5.2.5 in this case), the configure script failing to find OpenSSL headers is a common issue that can stem from several causes:

configure: error: Cannot find OpenSSL's <evp.h>

Even when you have multiple OpenSSL versions installed (like libssl1.0.0, libssl0.9.8, and openssl-dev packages), the compiler might still fail to locate the necessary headers.

First, let's verify what OpenSSL packages are actually installed:

dpkg -l | grep -i openssl

And check where the development headers are located:

find /usr -name "evp.h"

1. Install Missing Development Packages

For Ubuntu/Debian systems:

sudo apt-get install libssl-dev

2. Specify Correct OpenSSL Path

The most reliable solution is to explicitly tell configure where to find OpenSSL:

./configure --with-openssl=/usr \
    --with-openssl-dir=/usr \
    --with-openssl-inc=/usr/include/openssl

Alternatively, if you know the exact path:

./configure --with-openssl=/usr/local/ssl \
    --with-openssl-dir=/usr/local/ssl

3. Symbolic Link Solution

Sometimes creating symlinks helps:

sudo ln -s /usr/include/openssl /usr/local/include/openssl

When you get the "Cannot find OpenSSL's libraries" error, try:

export LD_LIBRARY_PATH=/usr/local/ssl/lib:$LD_LIBRARY_PATH
./configure --with-openssl

Or check library locations with:

ldconfig -p | grep libssl

Here's a complete configure command that typically works:

LDFLAGS="-L/usr/local/ssl/lib" \
CPPFLAGS="-I/usr/local/ssl/include" \
./configure --with-openssl=/usr/local/ssl \
    --with-openssl-dir=/usr/local/ssl \
    --with-openssl-inc=/usr/local/ssl/include/openssl

Remember to adapt paths to match your system's OpenSSL installation.

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When compiling PHP from source on Ubuntu, you might encounter the frustrating error:

configure: error: Cannot find OpenSSL's <evp.h>

or alternatively:

configure: error: Cannot find OpenSSL's libraries

This typically occurs when:

• OpenSSL development headers are missing
• The OpenSSL path specified is incorrect
• Multiple OpenSSL versions are installed causing conflicts
• 32-bit vs 64-bit library mismatch exists

First, ensure all required packages are installed:

sudo apt-get update
sudo apt-get install openssl libssl-dev

If you're still getting the error, try specifying the correct OpenSSL path:

./configure --with-openssl=/usr --other-php-options

For some systems, you might need to explicitly point to the include directory:

./configure --with-openssl-dir=/usr/include/openssl --other-php-options

If the issue persists, check where your OpenSSL files are actually located:

sudo find / -name evp.h

Then use the parent directory in your configure command. For example, if you find evp.h at /usr/local/ssl/include/openssl/evp.h, use:

./configure --with-openssl=/usr/local/ssl --other-php-options

If you have multiple OpenSSL versions installed, you might need to:

sudo update-alternatives --config openssl

Then select the appropriate version before reconfiguring PHP.

After successful configuration, check the PHP configuration to verify OpenSSL support:

php -i | grep -i openssl

This should show OpenSSL support is enabled with the correct version.