CACHEFILESD.CONF(5) Cache Files Utilities CACHEFILESD.CONF(5)NAME
/etc/cachefilesd.conf - Local file caching configuration file
The configuration file for cachefilesd which can manage a persistent
cache for a variety of network filesystems using a set of files on an
already mounted filesystem as the data store.
This configuration file can contain a number of commands. Each one
should be on a separate line. Blank lines and lines beginning with a
'#' character are considered to be comments and are discarded.
The only mandatory command is:
This command specifies the directory containing the root of the
cache. It may only specified once per configuration file.
All the other commands are optional:
Specify an LSM security context as which the kernel will perform
operations to access the cache. The default is to use
cachefilesd's security context. Files will be created in the
cache with the label of directory specified to the 'dir' com‐
These commands configure the culling limits. The defaults are
7% (run), 5% (cull) and 1% (stop) respectively. See the section
on cache culling for more information.
The commands beginning with a 'b' are file space (block) limits,
those beginning with an 'f' are file count limits.
This command specifies a tag to FS-Cache to use in distinguish‐
ing multiple caches. This is only required if more than one
cache is going to be used. The default is "CacheFiles".
This command specifies the size of the tables holding the lists
of cullable objects in the cache. The bigger the number, the
faster and more smoothly that culling can proceed when there are
many objects in the cache, but the more memory will be consumed
The quantity is specified as log2 of the size actually required,
for example 12 indicates a table of 4096 entries and 13 indi‐
cates 8192 entries. The permissible values are between 12 and
20, the latter indicating 1048576 entries. The default is 12.
nocull Disable culling. Culling and building up the cull table take up
a certain amount of a systems resources, which may be undesir‐
able. Supplying this option disables all culling activity. The
cache will keep building up to the limits set and won't be
shrunk, except by the removal of out-dated cache files.
This command specifies a numeric bitmask to control debugging in
the kernel module. The default is zero (all off). The follow‐
ing values can be OR'd into the mask to collect various informa‐
1 Turn on trace of function entry (_enter() macros)
2 Turn on trace of function exit (_leave() macros)
4 Turn on trace of internal debug points (_debug())
This mask can also be set through /sys/module/cachefiles/parame‐
As an example, consider the following:
This places the cache storage objects in a directory called
"/var/cache/fscache", names the cache "mycache", permits the cache to
run freely as long as there's at least 10% free space on
/var/cache/fscache/, starts culling the cache when the free space drops
below 7% and stops writing new stuff into the cache if the amount of
free space drops below 3%. If the cache is suspended, it won't reacti‐
vate until the amount of free space rises again to 10% or better.
Furthermore, this will tell the kernel module the security context it
should use when accessing the cache (SELinux is assumed to be the LSM
in this example). In this case, SELinux would use cachefiles_kernel_t
as the key into the policy.
The cache may need culling occasionally to make space. This involves
discarding objects from the cache that have been used less recently
than anything else. Culling is based on the access time of data
objects. Empty directories are culled if not in use.
Cache culling is done on the basis of the percentage of blocks and the
percentage of files available in the underlying filesystem. There are
frun If the amount of free space and the number of available files in
the cache rises above both these limits, then culling is turned
fcull If the amount of available space or the number of available
files in the cache falls below either of these limits, then
culling is started.
fstop If the amount of available space or the number of available
files in the cache falls below either of these limits, then no
further allocation of disk space or files is permitted until
culling has raised things above these limits again.
These must be configured thusly:
0 <= bstop < bcull < brun < 100
0 <= fstop < fcull < frun < 100
Note that these are percentages of available space and available files,
and do not appear as 100 minus the percentage displayed by the df pro‐
The userspace daemon scans the cache to build up a table of cullable
objects. These are then culled in least recently used order. A new
scan of the cache is started as soon as space is made in the table.
Objects will be skipped if their atimes have changed or if the kernel
module says it is still using them.
Culling can be disabled with the nocull option.
SEE ALSOcachefilesd(8), df(1), /usr/share/doc/cachefilesd-*/README
David Howells <firstname.lastname@example.org>
Linux 14 November 2005 CACHEFILESD.CONF(5)