SYSTEMD-READAHEAD-REPLAY.SERVICE
Section: systemd-readahead-replay.service (8)
Updated:
Index
Return to Main Contents
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
-
/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
systemd(1)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- COMMANDS
-
- SEE ALSO
-