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SYSTEMD-READAHEAD-REPLAY.SERVICE(8)        systemd-readahead-replay.service       SYSTEMD-READAHEAD-REPLAY.SERVICE(8)



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 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:

       systemd(1)



systemd 219                                                                       SYSTEMD-READAHEAD-REPLAY.SERVICE(8)