is used during boot to read files in advance of when they are needed such
that they are already in the page cache, improving boot performance.
When started without any arguments, it checks for the existance and age
of the default pack file
and if not present or older than a month, will discard it and retrace the
boot sequence. The pack will then contain information about the files
opened during boot, and the blocks that were in memory at the completion
of the boot.
If the file exists and is newer than a month old, or an alternate
path is given on the command-line, the files listed in the pack are opened
and the blocks read into the page cache using the
Pack files are automatically optimised for Solid-State Disks or rotational
Hard Drives, depending on which you have.
May be used to report on
operation. In particular, this causes information about the size of the
pack file to be output when reading and a complete dump of the contents of
the pack file after tracing.
into the background once the pack file has been read, or once tracing
has been enabled.
This is ignored when reading on rotational hard drives, since it's
important for performance reasons not to contend with other processes
Discards all pack files and forces re-tracing.
Normally when tracing,
will wait for a
signal before concluding and generating the pack file. This option
instead sets a timeout after which tracing is terminated.
Dump the contents of the pack file to standard output in a pretty format,
does not trace or read the contents into memory.
to sort the output.
The default is
which is the order that the files will be opened.
sorts by path name,
sorts by on-disk location, and
sorts by the amount of data that will be read for that file.
OTHER MOUNT POINTS
need not be the filename of a pack, instead it may be the name of a mount
point (or indeed any non-file within the filesystem), in which case the
pack for that device is read instead. This allows
to be called in the style
for filesystems split across multiple devices.
Pack files for these other devices are also stored under
and are named
When tracing, these will be automatically generated.