Prelink

Prelink is a system optimization tool used on some Unix-like operating systems to speed up the startup of dynamically linked programs by precomputing and embedding fixed addresses for shared libraries. By coordinating the load addresses of libraries across a system, prelink aims to reduce the work performed by the dynamic linker at run time.

How it works: The prelink program analyzes binaries and their shared libraries, assigns suggested fixed load addresses, and patches the executables to assume these addresses. It maintains a database of this information and updates the binaries so that relocations can be resolved more quickly when a program starts. When correctly maintained, the dynamic linker can skip or shorten many relocation steps, resulting in faster process startup.

Maintenance and usage: Prelink typically runs with elevated privileges, often via scheduled tasks or system initialization. After installing or upgrading libraries, prelink must be re-run to reflect changes; otherwise, mismatches can cause startup failures. Some systems allow disabling prelink entirely or removing its database if dynamic linking needs to rely on current address layouts.

Impact and considerations: The main benefit is reduced startup time for programs with many dynamic dependencies. However, prelink can conflict with security features such as address space layout randomization (ASLR), and updated or moved libraries can render prelinked addresses invalid. Because of these risks, many distributions have reduced or eliminated the use of prelink in favor of ASLR and on-demand relocation, while some still provide it as an opt-in option or legacy feature.

History and status: Prelink originated in Unix-like environments to improve startup performance on systems with numerous dynamically linked binaries. Over time, its usefulness waned as ASLR and modern dynamic linkers improved, leading to its decline in many distributions.