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

       /usr/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 disk 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:

       -h, --help
           Prints a short help text and exits.

       --max-files=
           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 usec) to to spend collecting data. Only valid for the collect command.

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. The output lists approximately for
           each file how much will be read-ahead by the replay command.

SEE ALSO

       systemd(1)

systemd 204                                                                  SYSTEMD-READAHEAD-REPLAY.SERVICE(8)