NAME         top

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

SYNOPSIS         top





       /usr/lib/systemd/systemd-readahead/systemd-readahead [OPTIONS...]
                                                            [DIRECTORY | FILE]

DESCRIPTION         top

       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

       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         top

       systemd-readahead understands the following options:

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

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

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

       -h, --help
           Print a short help text and exit.

           Print a short version string and exit.

COMMANDS         top

       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         top


COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see 
       ⟨⟩.  This
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systemd 216                              SYSTEMD-READAHEAD-REPLAY.SERVICE(8)