SYSTEMD−READAHEAD−REPLAY.SERVICE
NAMESYNOPSIS
DESCRIPTION
OPTIONS
COMMANDS
SEE ALSO
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:
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
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