other versions
- jessie 215-17+deb8u7
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 logicSYNOPSIS¶
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)systemd 215 |