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:

       -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 microseconds 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. For each file, the output lists approximately how much will be read
	   ahead by the replay command.

SEE ALSO

       systemd(1)

systemd 208												       SYSTEMD-READAHEAD-REPLAY.SERVICE(8)