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readahead is a system call of the Linux kernel that loads a file's contents into the page cache, providing that way a file prefetching technology. When a file is subsequently accessed, its contents are read from the main memory (RAM) rather than from a hard disk drive (HDD), resulting in much lower file access latencies due to much higher performance of the main memory.[1][2]

Many Linux distributions use readahead on a list of commonly used files to speed up booting. In such a setup, if the kernel is booted with the profile boot parameter, it will record all file accesses during bootup and write a new list of files to be read during later boot sequences. This will make additional installed services start faster, because they are not included in the default readahead list.[3]

In Linux distributions that use systemd, readahead binary (as part of the boot sequence) is replaced by systemd-readahead.[4][5] However, support for readahead was removed from systemd in its version 219, being described as unmaintained and unable to provide expected performance benefits.[6]

Certain experimental page-level prefetching systems have been developed to further improve performance.[7]


  1. ^ Jonathan Corbet (2005-10-12). "Adaptive file readahead". Retrieved 2014-08-20. 
  2. ^ "readahead(2) - Linux manual page". Retrieved 2014-04-09. 
  3. ^ Michael Opdenacker (2007-06-15). "Readahead: time-travel techniques for desktop and embedded systems" (PDF). pp. 5–6. Retrieved 2014-05-01. 
  4. ^ "Readahead". Retrieved 2014-04-09. 
  5. ^ "systemd-readahead-replay.service". 2014-03-26. Retrieved 2014-04-09. 
  6. ^ "systemd/systemd – System and Session Manager: Changes with 219". Retrieved 2015-02-15. 
  7. ^ Krzysztof Lichota (2008). "Linux solution for prefetching necessary data during application and system startup" (PDF). Retrieved 2014-07-28.