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systemd-readahead-replay.service(8) [centos man page]

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)

Check Out this Related Man Page

SD-READAHEAD(7)                                                    sd-readahead                                                    SD-READAHEAD(7)

NAME

       sd-readahead - Reference implementation of APIs for controlling boot-time read-ahead

SYNOPSIS

       #include "sd-readahead.h"

DESCRIPTION

       sd-readahead.c and sd-readahead.h provide a reference implementation for APIs for controlling boot-time read-ahead, as implemented by the
       read-ahead subsystem of the systemd(1) init system.

       See sd_readahead(3) for more information about the function implemented.

NOTES

       This interface is provided by the reference implementation of APIs for controlling boot-time read-ahead and distributed with the systemd
       package. The algorithms it implements are simple, and can easily be reimplemented in daemons if it is important to support this interface
       without using the reference implementation. See the respective function man pages for details.

       In addition, for details about the algorithms check the liberally licensed reference implementation sources:
       http://cgit.freedesktop.org/systemd/systemd/plain/src/readahead/sd-readahead.c resp.
       http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-readahead.h

       These APIs are implemented in the reference implementation's drop-in sd-readahead.c and sd-readahead.h files. It is recommended that
       applications consuming these APIs copy the implementation into their source tree, either verbatim or in excerpts. These interfaces are
       currently not available in a dynamic library.

       The functions provided by this interface become NOPs when -DDISABLE_SYSTEMD is set during compilation. In addition, if sd-readhead.c is
       compiled on non-Linux systems it becomes NOPs.

SEE ALSO

       systemd(1), sd_readahead(3), sd-daemon(7)

AUTHOR

       Lennart Poettering <lennart@poettering.net>
           Developer

systemd                                                             03/16/2012                                                     SD-READAHEAD(7)
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