What Happens When you Run ./configure on Source Code

When you run ./configure on Linux to build a program from source, it’s executing a shell script that prepares the build environment for compilation. Here’s what it does:

Main Functions

System Detection: The configure script examines your system to determine:

Operating system type and version
CPU architecture
Available system libraries and their versions
Compiler presence and capabilities (gcc, g++, etc.)
Build tools like make, ar, and ld

Dependency Checking: It verifies that all required dependencies are present:

Checks for necessary libraries (like libxml2, openssl, etc.)
Confirms required header files exist
Tests that dependencies meet minimum version requirements
Identifies optional features that can be enabled based on what’s available

Build Customisation: The script processes various options you can pass to customise the build:

--prefix=/path to set the installation directory
--enable-feature or --disable-feature flags
--with-library or --without-library options
Optimisation and debugging flags

File Generation: Based on its findings, configure generates several important files:

Makefile: The primary build instructions that make will use
config.h: A C header file containing system-specific definitions and feature flags
config.log: A detailed log of all tests performed
config.status: A script that can recreate the current configuration

The Process Flow

The configure script typically works by compiling and running small test programs to verify functionality. For example, it might compile a tiny program that uses a specific library function to confirm that library is working correctly on your system.

If everything checks out, you’ll see a summary of what was configured and can proceed with make to actually compile the program. If something is missing, configure will usually stop and tell you what’s needed.

This system, part of the GNU Autotools suite (autoconf/automake), allows the same source code to be built on many different Unix-like systems by adapting to each system’s specific characteristics.