prelinking

Prelinking is a technique used in some Unix-like operating systems to reduce the startup time of dynamically linked programs by performing relocation work in advance. It relies on a prelinking tool that analyzes shared libraries and executables, computes the final addresses for symbols, and rewrites binaries so that much of the dynamic linker work can be avoided at run time. The process typically runs with root privileges and maintains a prelink database.

How it works: The prelinking tool scans installed libraries and binaries, resolves relocations, and rewrites them to use fixed, precomputed addresses. At runtime, the dynamic linker can then skip or shorten relocation processing, which can lead to faster application launches, especially on systems with extensive use of shared libraries. The prelinking step may be performed periodically or during package installations.

Benefits and limitations: The main benefit is faster startup for many dynamic binaries. However, prelinking can conflict with security features such as Address Space Layout Randomization (ASLR), which relies on randomizing addresses at runtime. It also introduces maintenance overhead: after libraries are updated, prelinking must be re-run to ensure correctness, and moving or removing prelinked binaries can cause failures if the precomputed addresses no longer match. In modern systems, concerns about security and compatibility, along with improvements in dynamic linking techniques and ASLR, have reduced the prevalence of prelinking.

History and status: Prelinking enjoyed popularity on several Linux distributions in the past, but its use has waned in many environments. Some distributions still provide prelink tooling, while others have deprecated or disabled it in favor of ASLR and other performance optimizations.