1SYSTEMD-READAHEAD-REPLAYs.ySsEtReVmIdC-Er(e8a)dahead-repSlYaSyT.EsMeDr-vRiEcAeDAHEAD-REPLAY.SERVICE(8)
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NAME

6       systemd-readahead-replay.service, systemd-readahead-collect.service,
7       systemd-readahead-done.service, systemd-readahead-done.timer, systemd-
8       readahead - Disk read ahead logic
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SYNOPSIS

11       systemd-readahead-replay.service
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13       systemd-readahead-collect.service
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15       systemd-readahead-done.service
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17       systemd-readahead-done.timer
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19       /usr/lib/systemd/systemd-readahead/systemd-readahead [OPTIONS...]
20                                                            COMMAND
21                                                            [DIRECTORY | FILE]
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DESCRIPTION

24       systemd-readahead-collect.service is a service that collects disk usage
25       patterns at boot time.  systemd-readahead-replay.service is a service
26       that replays this access data collected at the subsequent boot. Since
27       disks tend to be magnitudes slower than RAM, this is intended to
28       improve boot speeds by pre-loading early at boot all data on disk that
29       is known to be read for the complete boot process.
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31       systemd-readahead-done.service is executed a short while after boot
32       completed and signals systemd-readahead-collect.service to end data
33       collection. On this signal, this service will then sort the collected
34       disk accesses and store information about them in /.readahead.
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36       Normally, both systemd-readahead-collect.service and
37       systemd-readahead-replay.service are activated at boot so that access
38       patterns from the preceding boot are replayed and new data collected
39       for the subsequent boot. However, on read-only media where the
40       collected data cannot be stored, it might be a good idea to disable
41       systemd-readahead-collect.service.
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43       On rotating media, when replaying disk accesses at early boot,
44       systemd-readahead-replay.service will order read requests by their
45       location on disk. On non-rotating media, they will be ordered by their
46       original access timestamp. If the file system supports it,
47       systemd-readahead-collect.service will also defragment and rearrange
48       files on disk to optimize subsequent boot times.
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OPTIONS

51       systemd-readahead understands the following options:
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53       --files-max=
54           Maximum number of files to read ahead. Only valid for thes collect
55           command.
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57       --file-size-max=
58           Maximum size of files in bytes to read ahead. Only valid for the
59           collect and replay commands.
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61       --timeout=
62           Maximum time in microseconds to spend collecting data. Only valid
63           for the collect command.
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65       -h, --help
66           Print a short help text and exit.
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68       --version
69           Print a short version string and exit.
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COMMANDS

72       The following commands are understood by systemd-readahead:
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74       collect [DIRECTORY]
75           Collect read-ahead data on early boot. When terminating, it will
76           write out a pack file to the indicated directory containing the
77           read-ahead data.
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79       replay [DIRECTORY]
80           Perform read-ahead on the specified directory tree.
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82       analyze [FILE]
83           Dumps the content of the read-ahead pack file to the terminal. For
84           each file, the output lists approximately how much will be read
85           ahead by the replay command.
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SEE ALSO

88       systemd(1)
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92systemd 219                                SYSTEMD-READAHEAD-REPLAY.SERVICE(8)
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