---
name: "systemd-readahead-collect.service"
section: "8"
platform: "linux"
package: "systemd"
version: "215-17+deb8u7"
release: "Debian 8 (Jessie)"
platforms: ["linux"]
url: "https://new.carta.tech/systemd-readahead-replay.service"
---

# systemd-readahead-collect.service(8)

Disk read ahead logic

Part of [systemd-readahead-replay.service(8)](/systemd-readahead-replay.service/8.md).

## NAME

systemd-readahead-replay.service, systemd-readahead-collect.service, systemd-readahead-done.service, systemd-readahead-done.timer, systemd-readahead - Disk read ahead logic

## SYNOPSIS

systemd-readahead-replay.service

systemd-readahead-collect.service

systemd-readahead-done.service

systemd-readahead-done.timer

**/lib/systemd/systemd-readahead/systemd-readahead** \[OPTIONS...\] COMMAND \[DIRECTORY \| FILE\]

## DESCRIPTION

systemd-readahead-collect.service is a service that collects disk usage patterns at boot time. systemd-readahead-replay.service is a service that replays this access data collected at the subsequent boot. Since disks tend to be magnitudes slower than RAM, this is intended to improve boot speeds by pre-loading early at boot all data on disk that is known to be read for the complete boot process.

systemd-readahead-done.service is executed a short while after boot completed and signals systemd-readahead-collect.service to end data collection. On this signal, this service will then sort the collected disk accesses and store information about them in /.readahead.

Normally, both systemd-readahead-collect.service and systemd-readahead-replay.service are activated at boot so that access patterns from the preceding boot are replayed and new data collected for the subsequent boot. However, on read-only media where the collected data cannot be stored, it might be a good idea to disable systemd-readahead-collect.service.

On rotating media, when replaying disk accesses at early boot, systemd-readahead-replay.service will order read requests by their location on disk. On non-rotating media, they will be ordered by their original access timestamp. If the file system supports it, systemd-readahead-collect.service will also defragment and rearrange files on disk to optimize subsequent boot times.

## OPTIONS

systemd-readahead understands the following options:

**--files-max=**

Maximum number of files to read ahead. Only valid for thes **collect** command.

**--file-size-max=**

Maximum size of files in bytes to read ahead. Only valid for the **collect** and **replay** commands.

**--timeout=**

Maximum time in microseconds to spend collecting data. Only valid for the **collect** command.

- **-h**, **--help**

  Print a short help text and exit.

- **--version**

  Print a short version string and exit.

## COMMANDS

The following commands are understood by systemd-readahead:

**collect \[***DIRECTORY***\]**

Collect read-ahead data on early boot. When terminating, it will write out a pack file to the indicated directory containing the read-ahead data.

**replay \[***DIRECTORY***\]**

Perform read-ahead on the specified directory tree.

**analyze \[***FILE***\]**

Dumps the content of the read-ahead pack file to the terminal. For each file, the output lists approximately how much will be read ahead by the **replay** command.

## SEE ALSO

[**systemd**(1)](/systemd/1.md)