SYSTEMD-READAHEAD-REPLAsystemd-readahead-reSYSTEMD-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

       /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 215                                SYSTEMD-READAHEAD-REPLAY.SERVICE(8)

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