systemd-readahead(8) - phpMan

SYSTEMD-READAHEAD-REPLAY.SERVICE(systemd-readahead-replay.servSYSTEMD-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:

--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.