permd

permd is a command-line utility found on some Unix-like operating systems, most notably Solaris. Its primary function is to permanently store data in the system's cache. This means that once data is "permed," it is less likely to be swapped out of memory by the operating system to make room for other processes. This can be beneficial for frequently accessed data or critical system files that require consistent and fast access.

The utility typically takes one or more file paths as arguments. When invoked, permd attempts to read the specified files into memory and then mark them for permanent residency. This process involves interacting with the operating system's virtual memory management system. There are often options to control how much data is permed or to un-perm data if it is no longer needed.

The effectiveness and availability of permd can vary significantly depending on the operating system version and configuration. In modern Linux distributions, similar functionality is often managed by different mechanisms, such as using `mlock` system calls or filesystem mount options like `cache=none` or `cache=direct` for specific devices, although these achieve different outcomes. The concept behind permd, however, remains relevant for performance tuning in environments where predictable memory access is crucial.