fonts.conf - Font configuration files
Fontconfig is a library designed to provide system-wide font configuration, customization and application access.
Fontconfig contains two essential modules, the configuration module which builds an internal configuration from XML files and the matching module which accepts font patterns and returns the nearest matching font.
The configuration module consists of the FcConfig datatype, libexpat and FcConfigParse which walks over an XML tree and amends a configuration with data found within. From an external perspective, configuration of the library consists of generating a valid XML tree and feeding that to FcConfigParse. The only other mechanism provided to applications for changing the running configuration is to add fonts and directories to the list of application-provided font files.
The intent is to make font configurations relatively static, and shared by as many applications as possible. It is hoped that this will lead to more stable font selection when passing names from one application to another. XML was chosen as a configuration file format because it provides a format which is easy for external agents to edit while retaining the correct structure and syntax.
Font configuration is separate from font matching; applications needing to do their own matching can access the available fonts from the library and perform private matching. The intent is to permit applications to pick and choose appropriate functionality from the library instead of forcing them to choose between this library and a private configuration mechanism. The hope is that this will ensure that configuration of fonts for all applications can be centralized in one place. Centralizing font configuration will simplify and regularize font installation and customization.
While font patterns may contain essentially any properties, there are some well known properties with associated types. Fontconfig uses some of these properties for font matching and font completion. Others are provided as a convenience for the applications' rendering mechanism.
Property Type Description
family String Font family names
familylang String Languages corresponding to each family
style String Font style. Overrides weight and slant
stylelang String Languages corresponding to each style
fullname String Font full names (often includes style)
fullnamelang String Languages corresponding to each fullname
slant Int Italic, oblique or roman
weight Int Light, medium, demibold, bold or black
size Double Point size
width Int Condensed, normal or expanded
aspect Double Stretches glyphs horizontally before hinting
pixelsize Double Pixel size
spacing Int Proportional, dual-width, monospace or charcell
foundry String Font foundry name
antialias Bool Whether glyphs can be antialiased
hinting Bool Whether the rasterizer should use hinting
hintstyle Int Automatic hinting style
verticallayout Bool Use vertical layout
autohint Bool Use autohinter instead of normal hinter
globaladvance Bool Use font global advance data (deprecated)
file String The filename holding the font
index Int The index of the font within the file
ftface FT_Face Use the specified FreeType face object
rasterizer String Which rasterizer is in use (deprecated)
outline Bool Whether the glyphs are outlines
scalable Bool Whether glyphs can be scaled
color Bool Whether any glyphs have color
scale Double Scale factor for point->pixel conversions (deprecated)
dpi Double Target dots per inch
rgba Int unknown, rgb, bgr, vrgb, vbgr,
none - subpixel geometry
lcdfilter Int Type of LCD filter
minspace Bool Eliminate leading from line spacing
charset CharSet Unicode chars encoded by the font
lang String List of RFC-3066-style languages this
fontversion Int Version number of the font
capability String List of layout capabilities in the font
fontformat String String name of the font format
embolden Bool Rasterizer should synthetically embolden the font
embeddedbitmap Bool Use the embedded bitmap instead of the outline
decorative Bool Whether the style is a decorative variant
fontfeatures String List of the feature tags in OpenType to be enabled
namelang String Language name to be used for the default value of
familylang, stylelang, and fullnamelang
prgname String String Name of the running program
postscriptname String Font family name in PostScript
fonthashint Bool Whether the font has hinting
order Int Order number of the font
Fontconfig performs matching by measuring the distance from a provided pattern to all of the available fonts in the system. The closest matching font is selected. This ensures that a font will always be returned, but doesn't ensure that it is anything like the requested pattern.
Font matching starts with an application constructed pattern. The desired attributes of the resulting font are collected together in a pattern. Each property of the pattern can contain one or more values; these are listed in priority order; matches earlier in the list are considered "closer" than matches later in the list.
The initial pattern is modified by applying the list of editing instructions specific to patterns found in the configuration; each consists of a match predicate and a set of editing operations. They are executed in the order they appeared in the configuration. Each match causes the associated sequence of editing operations to be applied.
After the pattern has been edited, a sequence of default substitutions are performed to canonicalize the set of available properties; this avoids the need for the lower layers to constantly provide default values for various font properties during rendering.
The canonical font pattern is finally matched against all available fonts. The distance from the pattern to the font is measured for each of several properties: foundry, charset, family, lang, spacing, pixelsize, style, slant, weight, antialias, rasterizer and outline. This list is in priority order -- results of comparing earlier elements of this list weigh more heavily than later elements.
There is one special case to this rule; family names are split into two bindings; strong and weak. Strong family names are given greater precedence in the match than lang elements while weak family names are given lower precedence than lang elements. This permits the document language to drive font selection when any document specified font is unavailable.
The pattern representing that font is augmented to include any properties found in the pattern but not found in the font itself; this permits the application to pass rendering instructions or any other data through the matching system. Finally, the list of editing instructions specific to fonts found in the configuration are applied to the pattern. This modified pattern is returned to the application.
The return value contains sufficient information to locate and rasterize the font, including the file name, pixel size and other rendering data. As none of the information involved pertains to the FreeType library, applications are free to use any rasterization engine or even to take the identified font file and access it directly.
The match/edit sequences in the configuration are performed in two passes because there are essentially two different operations necessary -- the first is to modify how fonts are selected; aliasing families and adding suitable defaults. The second is to modify how the selected fonts are rasterized. Those must apply to the selected font, not the original pattern as false matches will often occur.
Fontconfig provides a textual representation for patterns that the library can both accept and generate. The representation is in three parts, first a list of family names, second a list of point sizes and finally a list of additional properties:
Values in a list are separated with commas. The name needn't include either families or point sizes; they can be elided. In addition, there are symbolic constants that simultaneously indicate both a name and a value. Here are some examples:
Times-12 12 point Times Roman
Times-12:bold 12 point Times Bold
Courier:italic Courier Italic in the default size
Monospace:matrix=1 .1 0 1 The users preferred monospace font
with artificial obliquing
The '\', '-', ':' and ',' characters in family names must be preceded by a '\' character to avoid having them misinterpreted. Similarly, values containing '\', '=', '_', ':' and ',' must also have them preceded by a '\' character. The '\' characters are stripped out of the family name and values as the font name is read.
To help diagnose font and applications problems, fontconfig is built with a large amount of internal debugging left enabled. It is controlled by means of the FC_DEBUG environment variable. The value of this variable is interpreted as a number, and each bit within that value controls different debugging messages.
Name Value Meaning
MATCH 1 Brief information about font matching
MATCHV 2 Extensive font matching information
EDIT 4 Monitor match/test/edit execution
FONTSET 8 Track loading of font information at startup
CACHE 16 Watch cache files being written
CACHEV 32 Extensive cache file writing information
PARSE 64 (no longer in use)
SCAN 128 Watch font files being scanned to build caches
SCANV 256 Verbose font file scanning information
MEMORY 512 Monitor fontconfig memory usage
CONFIG 1024 Monitor which config files are loaded
LANGSET 2048 Dump char sets used to construct lang values
MATCH2 4096 Display font-matching transformation in patterns
Add the value of the desired debug levels together and assign that (in base 10) to the FC_DEBUG environment variable before running the application. Output from these statements is sent to stdout.
Each font in the database contains a list of languages it supports. This is computed by comparing the Unicode coverage of the font with the orthography of each language. Languages are tagged using an RFC-3066 compatible naming and occur in two parts -- the ISO 639 language tag followed a hyphen and then by the ISO 3166 country code. The hyphen and country code may be elided.
Fontconfig has orthographies for several languages built into the library. No provision has been made for adding new ones aside from rebuilding the library. It currently supports 122 of the 139 languages named in ISO 639-1, 141 of the languages with two-letter codes from ISO 639-2 and another 30 languages with only three-letter codes. Languages with both two and three letter codes are provided with only the two letter code.
For languages used in multiple territories with radically different character sets, fontconfig includes per-territory orthographies. This includes Azerbaijani, Kurdish, Pashto, Tigrinya and Chinese.
Configuration files for fontconfig are stored in XML format; this format makes external configuration tools easier to write and ensures that they will generate syntactically correct configuration files. As XML files are plain text, they can also be manipulated by the expert user using a text editor.
The fontconfig document type definition resides in the external entity "fonts.dtd"; this is normally stored in the default font configuration directory (/etc/fonts ). Each configuration file should contain the following structure:
<?xml version="1.0"?> <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd"> <fontconfig> ... </fontconfig>
This is the top level element for a font configuration and can contain <dir>, <cachedir>, <include>, <match> and <alias> elements in any order.
This element contains a directory name which will be scanned for font files to include in the set of available fonts.
If 'prefix' is set to "default" or "cwd", the current working directory will be added as the path prefix prior to the value. If 'prefix' is set to "xdg", the value in the XDG_DATA_HOME environment variable will be added as the path prefix. please see XDG Base Directory Specification for more details. If 'prefix' is set to "relative", the path of current file will be added prior to the value.
'salt' property affects to determine cache filename. this is useful for example when having different fonts sets on same path at container and share fonts from host on different font path.
This element contains a directory name that is supposed to be stored or read the cache of font information. If multiple elements are specified in the configuration file, the directory that can be accessed first in the list will be used to store the cache files. If it starts with '~', it refers to a directory in the users home directory. If 'prefix' is set to "xdg", the value in the XDG_CACHE_HOME environment variable will be added as the path prefix. please see XDG Base Directory Specification for more details. The default directory is ``$XDG_CACHE_HOME/fontconfig'' and it contains the cache files named ``<hash value>-<architecture>.cache-<version>'', where <version> is the fontconfig cache file version number (currently 7).
This element contains the name of an additional configuration file or directory. If a directory, every file within that directory starting with an ASCII digit (U+0030 - U+0039) and ending with the string ``.conf'' will be processed in sorted order. When the XML datatype is traversed by FcConfigParse, the contents of the file(s) will also be incorporated into the configuration by passing the filename(s) to FcConfigLoadAndParse. If 'ignore_missing' is set to "yes" instead of the default "no", a missing file or directory will elicit no warning message from the library. If 'prefix' is set to "xdg", the value in the XDG_CONFIG_HOME environment variable will be added as the path prefix. please see XDG Base Directory Specification for more details.
This element provides a place to consolidate additional configuration information. <config> can contain <blank> and <rescan> elements in any order.
This element is supposed to hold strings which describe what a config is used for. This string can be translated through gettext. 'domain' needs to be set the proper name to apply then. fontconfig will tries to retrieve translations with 'domain' from gettext.
Fonts often include "broken" glyphs which appear in the encoding but are drawn as blanks on the screen. Within the <blank> element, place each Unicode characters which is supposed to be blank in an <int> element. Characters outside of this set which are drawn as blank will be elided from the set of characters supported by the font.
This element contains a directory name where will be mapped as the path 'as-path' in cached information. This is useful if the directory name is an alias (via a bind mount or symlink) to another directory in the system for which cached font information is likely to exist.
'salt' property affects to determine cache filename as same as <dir> element.
This element removes all of fonts directories where added by <dir> elements. This is useful to override fonts directories from system to own fonts directories only.
The <rescan> element holds an <int> element which indicates the default interval between automatic checks for font configuration changes. Fontconfig will validate all of the configuration files and directories and automatically rebuild the internal datastructures when this interval passes.
This element is used to black/white list fonts from being listed or matched against. It holds acceptfont and rejectfont elements.
Fonts matched by an acceptfont element are "whitelisted"; such fonts are explicitly included in the set of fonts used to resolve list and match requests; including them in this list protects them from being "blacklisted" by a rejectfont element. Acceptfont elements include glob and pattern elements which are used to match fonts.
Fonts matched by an rejectfont element are "blacklisted"; such fonts are excluded from the set of fonts used to resolve list and match requests as if they didn't exist in the system. Rejectfont elements include glob and pattern elements which are used to match fonts.
Glob elements hold shell-style filename matching patterns (including ? and *) which match fonts based on their complete pathnames. This can be used to exclude a set of directories (/usr/share/fonts/uglyfont*), or particular font file types (*.pcf.gz), but the latter mechanism relies rather heavily on filenaming conventions which can't be relied upon. Note that globs only apply to directories, not to individual fonts.
Pattern elements perform list-style matching on incoming fonts; that is, they hold a list of elements and associated values. If all of those elements have a matching value, then the pattern matches the font. This can be used to select fonts based on attributes of the font (scalable, bold, etc), which is a more reliable mechanism than using file extensions. Pattern elements include patelt elements.
Patelt elements hold a single pattern element and list of values. They must have a 'name' attribute which indicates the pattern element name. Patelt elements include int, double, string, matrix, bool, charset and const elements.
This element holds first a (possibly empty) list of <test> elements and then a (possibly empty) list of <edit> elements. Patterns which match all of the tests are subjected to all the edits. If 'target' is set to "font" instead of the default "pattern", then this element applies to the font name resulting from a match rather than a font pattern to be matched. If 'target' is set to "scan", then this element applies when the font is scanned to build the fontconfig database.
This element contains a single value which is compared with the target ('pattern', 'font', 'scan' or 'default') property "property" (substitute any of the property names seen above). 'compare' can be one of "eq", "not_eq", "less", "less_eq", "more", "more_eq", "contains" or "not_contains". 'qual' may either be the default, "any", in which case the match succeeds if any value associated with the property matches the test value, or "all", in which case all of the values associated with the property must match the test value. 'ignore-blanks' takes a boolean value. if 'ignore-blanks' is set "true", any blanks in the string will be ignored on its comparison. this takes effects only when compare="eq" or compare="not_eq". When used in a <match target="font"> element, the target= attribute in the <test> element selects between matching the original pattern or the font. "default" selects whichever target the outer <match> element has selected.
This element contains a list of expression elements (any of the value or operator elements). The expression elements are evaluated at run-time and modify the property "property". The modification depends on whether "property" was matched by one of the associated <test> elements, if so, the modification may affect the first matched value. Any values inserted into the property are given the indicated binding ("strong", "weak" or "same") with "same" binding using the value from the matched pattern element. 'mode' is one of:
Mode With Match Without Match
"assign" Replace matching value Replace all values
"assign_replace" Replace all values Replace all values
"prepend" Insert before matching Insert at head of list
"prepend_first" Insert at head of list Insert at head of list
"append" Append after matching Append at end of list
"append_last" Append at end of list Append at end of list
"delete" Delete matching value Delete all values
"delete_all" Delete all values Delete all values
These elements hold a single value of the indicated type. <bool> elements hold either true or false. An important limitation exists in the parsing of floating point numbers -- fontconfig requires that the mantissa start with a digit, not a decimal point, so insert a leading zero for purely fractional values (e.g. use 0.5 instead of .5 and -0.5 instead of -.5).
This element holds four numerical expressions of an affine transformation. At their simplest these will be four <double> elements but they can also be more involved expressions.
This element holds the two <int> elements of a range representation.
This element holds at least one <int> element of an Unicode code point or more.
This element holds at least one <string> element of a RFC-3066-style languages or more.
Holds a property name. Evaluates to the first value from the property of the pattern. If the 'target' attribute is not present, it will default to 'default', in which case the property is returned from the font pattern during a target="font" match, and to the pattern during a target="pattern" match. The attribute can also take the values 'font' or 'pattern' to explicitly choose which pattern to use. It is an error to use a target of 'font' in a match that has target="pattern".
Holds the name of a constant; these are always integers and serve as symbolic names for common font values:
Constant Property Value
thin weight 0
extralight weight 40
ultralight weight 40
light weight 50
demilight weight 55
semilight weight 55
book weight 75
regular weight 80
normal weight 80
medium weight 100
demibold weight 180
semibold weight 180
bold weight 200
extrabold weight 205
black weight 210
heavy weight 210
roman slant 0
italic slant 100
oblique slant 110
ultracondensed width 50
extracondensed width 63
condensed width 75
semicondensed width 87
normal width 100
semiexpanded width 113
expanded width 125
extraexpanded width 150
ultraexpanded width 200
proportional spacing 0
dual spacing 90
mono spacing 100
charcell spacing 110
unknown rgba 0
rgb rgba 1
bgr rgba 2
vrgb rgba 3
vbgr rgba 4
none rgba 5
lcdnone lcdfilter 0
lcddefault lcdfilter 1
lcdlight lcdfilter 2
lcdlegacy lcdfilter 3
hintnone hintstyle 0
hintslight hintstyle 1
hintmedium hintstyle 2
hintfull hintstyle 3
These elements perform the specified operation on a list of expression elements. <or> and <and> are boolean, not bitwise.
These elements compare two values, producing a boolean result.
Inverts the boolean sense of its one expression element
This element takes three expression elements; if the value of the first is true, it produces the value of the second, otherwise it produces the value of the third.
Alias elements provide a shorthand notation for the set of common match operations needed to substitute one font family for another. They contain a <family> element followed by optional <prefer>, <accept> and <default> elements. Fonts matching the <family> element are edited to prepend the list of <prefer>ed families before the matching <family>, append the <accept>able families after the matching <family> and append the <default> families to the end of the family list.
Holds a single font family name
These hold a list of <family> elements to be used by the <alias> element.
This is an example of a system-wide configuration file
<?xml version="1.0"?> <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd"> <!-- /etc/fonts /fonts.conf file to configure system font access --> <fontconfig> <!-- Find fonts in these directories --> <dir>/usr/share/fonts</dir> <dir>/usr/X11R6/lib/X11/fonts</dir> <!-- Accept deprecated 'mono' alias, replacing it with 'monospace' --> <match target="pattern"> <test qual="any" name="family"><string>mono</string></test> <edit name="family" mode="assign"><string>monospace</string></edit> </match> <!-- Names not including any well known alias are given 'sans-serif' --> <match target="pattern"> <test qual="all" name="family" compare="not_eq"><string>sans-serif</string></test> <test qual="all" name="family" compare="not_eq"><string>serif</string></test> <test qual="all" name="family" compare="not_eq"><string>monospace</string></test> <edit name="family" mode="append_last"><string>sans-serif</string></edit> </match> <!-- Load per-user customization file, but don't complain if it doesn't exist --> <include ignore_missing="yes" prefix="xdg">fontconfig/fonts.conf</include> <!-- Load local customization files, but don't complain if there aren't any --> <include ignore_missing="yes">conf.d</include> <include ignore_missing="yes">local.conf</include> <!-- Alias well known font names to available TrueType fonts. These substitute TrueType faces for similar Type1 faces to improve screen appearance. --> <alias> <family>Times</family> <prefer><family>Times New Roman</family></prefer> <default><family>serif</family></default> </alias> <alias> <family>Helvetica</family> <prefer><family>Arial</family></prefer> <default><family>sans</family></default> </alias> <alias> <family>Courier</family> <prefer><family>Courier New</family></prefer> <default><family>monospace</family></default> </alias> <!-- Provide required aliases for standard names Do these after the users configuration file so that any aliases there are used preferentially --> <alias> <family>serif</family> <prefer><family>Times New Roman</family></prefer> </alias> <alias> <family>sans</family> <prefer><family>Arial</family></prefer> </alias> <alias> <family>monospace</family> <prefer><family>Andale Mono</family></prefer> </alias> <-- The example of the requirements of OR operator; If the 'family' contains 'Courier New' OR 'Courier' add 'monospace' as the alternative --> <match target="pattern"> <test name="family" compare="eq"> <string>Courier New</string> </test> <edit name="family" mode="prepend"> <string>monospace</string> </edit> </match> <match target="pattern"> <test name="family" compare="eq"> <string>Courier</string> </test> <edit name="family" mode="prepend"> <string>monospace</string> </edit> </match> </fontconfig>
This is an example of a per-user configuration file that lives in $XDG_CONFIG_HOME/fontconfig/fonts.conf
<?xml version="1.0"?> <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd"> <!-- $XDG_CONFIG_HOME/fontconfig/fonts.conf for per-user font configuration --> <fontconfig> <!-- Private font directory --> <dir prefix="xdg">fonts</dir> <!-- use rgb sub-pixel ordering to improve glyph appearance on LCD screens. Changes affecting rendering, but not matching should always use target="font". --> <match target="font"> <edit name="rgba" mode="assign"><const>rgb</const></edit> </match> <!-- use WenQuanYi Zen Hei font when serif is requested for Chinese --> <match> <!-- If you don't want to use WenQuanYi Zen Hei font for zh-tw etc, you can use zh-cn instead of zh. Please note, even if you set zh-cn, it still matches zh. if you don't like it, you can use compare="eq" instead of compare="contains". --> <test name="lang" compare="contains"> <string>zh</string> </test> <test name="family"> <string>serif</string> </test> <edit name="family" mode="prepend"> <string>WenQuanYi Zen Hei</string> </edit> </match> <!-- use VL Gothic font when sans-serif is requested for Japanese --> <match> <test name="lang" compare="contains"> <string>ja</string> </test> <test name="family"> <string>sans-serif</string> </test> <edit name="family" mode="prepend"> <string>VL Gothic</string> </edit> </match> </fontconfig>
fonts.conf contains configuration information for the fontconfig library consisting of directories to look at for font information as well as instructions on editing program specified font patterns before attempting to match the available fonts. It is in XML format.
conf.d is the conventional name for a directory of additional configuration files managed by external applications or the local administrator. The filenames starting with decimal digits are sorted in lexicographic order and used as additional configuration files. All of these files are in XML format. The master fonts.conf file references this directory in an <include> directive.
fonts.dtd is a DTD that describes the format of the configuration files.
$XDG_CONFIG_HOME/fontconfig/conf.d and ~/.fonts.conf.d is the conventional name for a per-user directory of (typically auto-generated) configuration files, although the actual location is specified in the global fonts.conf file. please note that ~/.fonts.conf.d is deprecated now. it will not be read by default in the future version.
$XDG_CONFIG_HOME/fontconfig/fonts.conf and ~/.fonts.conf is the conventional location for per-user font configuration, although the actual location is specified in the global fonts.conf file. please note that ~/.fonts.conf is deprecated now. it will not be read by default in the future version.
$XDG_CACHE_HOME/fontconfig/*.cache-* and ~/.fontconfig/*.cache-* is the conventional repository of font information that isn't found in the per-directory caches. This file is automatically maintained by fontconfig. please note that ~/.fontconfig/*.cache-* is deprecated now. it will not be read by default in the future version.
FONTCONFIG_FILE is used to override the default configuration file.
FONTCONFIG_PATH is used to override the default configuration directory.
FONTCONFIG_SYSROOT is used to set a default sysroot directory.
FC_DEBUG is used to output the detailed debugging messages. see Debugging Applications section for more details.
FC_DBG_MATCH_FILTER is used to filter out the patterns. this takes a comma-separated list of object names and effects only when FC_DEBUG has MATCH2. see Debugging Applications section for more details.
FC_LANG is used to specify the default language as the weak binding in the query. if this isn't set, the default language will be determined from current locale.
FONTCONFIG_USE_MMAP is used to control the use of mmap(2) for the cache files if available. this take a boolean value. fontconfig will checks if the cache files are stored on the filesystem that is safe to use mmap(2). explicitly setting this environment variable will causes skipping this check and enforce to use or not use mmap(2) anyway.
SOURCE_DATE_EPOCH is used to ensure fc-cache(1) generates files in a deterministic manner in order to support reproducible builds. When set to a numeric representation of UNIX timestamp, fontconfig will prefer this value over using the modification timestamps of the input files in order to identify which cache files require regeneration. If SOURCE_DATE_EPOCH is not set (or is newer than the mtime of the directory), the existing behaviour is unchanged.
fc-cat(1), fc-cache(1), fc-list(1), fc-match(1), fc-query(1), SOURCE_DATE_EPOCH <URL:https://reproducible-builds.org/specs/source-date-epoch/>.
Fontconfig version 2.14.0
|01 April 2022|