.\" -*- nroff -*-

.\" Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.

.\" Written by David Howells (dhowells@redhat.com)

.\"

.\" This program is free software; you can redistribute it and/or

.\" modify it under the terms of the GNU General Public License

.\" as published by the Free Software Foundation; either version

.\" 2 of the License, or (at your option) any later version.

.\"

.TH CACHEFILESD.CONF 5 "14 November 2005" Linux "Cache Files Utilities"

.SH NAME

/etc/cachefilesd.conf \- Local file caching configuration file

.SH SYNOPSIS

.P

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.

.SH DESCRIPTION

.P

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.

.P

The only mandatory command is:

.TP

.B dir <path>

This command specifies the directory containing the root of the cache.  It may

only specified once per configuration file.

.P

All the other commands are optional:

.TP

.B secctx <label>

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'

command.

.TP

.B brun <N>%

.TP

.B bcull <N>%

.TP

.B bstop <N>%

.TP

.B frun <N>%

.TP

.B fcull <N>%

.TP

.B fstop <N>%

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.

.IP

The commands beginning with a 'b' are file space (block) limits, those

beginning with an 'f' are file count limits.

.TP

.B tag <name>

This command specifies a tag to FS-Cache to use in distinguishing multiple

caches.  This is only required if more than one cache is going to be used.  The

default is "CacheFiles".

.TP

.B culltable <log2size>

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 by cachefilesd.

.IP

The quantity is specified as log2 of the size actually required, for example 12

indicates a table of 4096 entries and 13 indicates 8192 entries.  The

permissible values are between 12 and 20, the latter indicating 1048576

entries.  The default is 12.

.TP

.B nocull

Disable culling.  Culling and building up the cull table take up a certain

amount of a systems resources, which may be undesirable.  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.

.TP

.B resume_thresholds <blocks> <files>

This command specifies the amount of blocks or files that the kernel should let

go of before the daemon should resume from culling table scan suspension.

.IP

Scanning to refill the cull table is suspended when all the objects in a cache

are pinned by a live network filesystem in the kernel and there's nothing to

cull.

.IP

Either value can be "-" to indicate that this threshold should be ignored.

.TP

.B debug <mask>

This command specifies a numeric bitmask to control debugging in the kernel

module.  The default is zero (all off).  The following values can be OR'd into

the mask to collect various information:

.RS

.TP

.B 1

Turn on trace of function entry (_enter() macros)

.TP

.B 2

Turn on trace of function exit (_leave() macros)

.TP

.B 4

Turn on trace of internal debug points (_debug())

.RE

.IP

This mask can also be set through /sys/module/cachefiles/parameters/debug.

.RE

.SH EXAMPLES

.P

As an example, consider the following:

.P

.RS

dir /var/cache/fscache

.br

secctx cachefiles_kernel_t

.br

tag mycache

.br

brun 10%

.br

bcull 7%

.br

bstop 3%

.br

secctx system_u:system_r:cachefiles_kernel_t:s0

.RE

.P

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 reactivate until the amount of free space rises

again to 10% or better.

.P

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.

.SH CACHE CULLING

.P

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.

.P

Cache culling is done on the basis of the percentage of blocks and the

percentage of files available in the underlying filesystem.  There are six

"limits":

.TP

.B brun

.TP

.B 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 off.

.TP

.B bcull

.TP

.B 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.

.TP

.B bstop

.TP

.B 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.

.P

These must be configured thusly:

.IP

0 <= bstop < bcull < brun < 100

.br

0 <= fstop < fcull < frun < 100

.P

Note that these are percentages of available space and available files, and do

\fInot\fP appear as 100 minus the percentage displayed by the \fBdf\fP program.

.P

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.

.P

Culling can be disabled with the \fBnocull\fP option.

.SH SEE ALSO

\fBcachefilesd\fR(8), \fBdf\fR(1), /usr/share/doc/cachefilesd/README

.SH AUTHORS

.br

David Howells <dhowells@redhat.com>