Circos > Documentation > Tutorials > Configuration > Configuration Files

Use the latest version of Circos and read Circos best practices—these list recent important changes and identify sources of common problems.

If you are having trouble, post your issue to the Circos Google Group and include all files and detailed error logs. Please do not email me directly unless it is urgent—you are much more likely to receive a timely reply from the group.

Don't know what question to ask? Read Points of View: Visualizing Biological Data by Bang Wong, myself and invited authors from the Points of View series.

1 — Configuration and Installation

3. Configuration Files - Syntax, Colors, Fonts and Units

If you are having trouble with installation of Perl or modules, use online resources that explain the details of how to download Perl, get it working (Linux, Mac OS X, Windows [ wiki, ActiveState, Strawberry]), and how to install modules (UNIX, Windows). If you're still stuck, post your questions to the Circos group.

Try the Active State Perl build for Circos. It includes all the necessary modules.

Need to install modules? See A Guide to Installing Modules and its corresponding tutorial for Windows users.

Having trouble with libgd and GD? See the Perl Monks libgd/GD Tutorial, Shaun Jackman's Homebrew formula, Wang's install zlib/libpng/jpeg/freetype/libgd/GD on Mavericks as well as my own guide for installation of libpng, freetype, libgd and GD on Mac OS X Mavericks. There are some useful threads in the Google Group about this.

Need to run Bash shell batch files in Windows? You'll need to install a UNIX command line shell, like Cygwin.

Stumped by an error? A good strategy is to Google the error message (e.g. mkdir /usr/local/share/man: permission denied) to find the solution.

Want to learn more about Perl? Try or read through the Perl Journal archive.

Circos generates static images. The image generation process is driven by a central configuration file. This file usually imports other configuration files, such as global color and font settings.

There is no interface to Circos. Workflow typically proceeds as follows

  • determining how the data is to be shown (this is the hard part)
  • parsing data files into Circos format
  • constructing a configuration file, either from scratch or using one of the tutorials as template
  • running Circos to create PNG and SVG files
  • editing PNG/SVG files for publication (adding a legend, additional text labels, etc).

configuration syntax

Configuration files are parsed using Config::General module. All pertinent features are described below, but for those so inclined, refer to this module's man page to learn about the details of the syntax and parsing of these files.

Settings are defined in configuration files using the format

variable = value

Note that although Config::General supports a whitespace as an assignment delimiter, Circos requires that you use = for all definitions.

Some settings are grouped in blocks, to create a hierarchical structure.

 thickness = 30p
 fill      = yes

Some blocks can have multiple instances, such as data tracks. Typically, these are enlosed in another block, here <links>.


 file      = data/set1.txt
 color     = black

 file      = data/set2.txt
 color     = red


Please ensure that all your configuration blocks are correctly terminated with an appropriate close block tag.

<ideogram> # <-- if this is missing, an error will result

4 ways to specify configuration parameters: global, track, data and rules

There are four places in which a configuration parameter can be specified.

In order of increasing importance

  • globally for all data points in all plot tracks (in the <plots>or <links> block)
  • locally for all data points in a given plot track (in the <plot> or <link> block)
  • specifically for a single data point (in the data file)
  • using a rule (in a <rule> block)

A parameter set by a rule overrides any specified in the data file. A data file parameter overrides any in a <plot> or <link> block, which in turn override any global parameters in a <plots> or <links> block.


# global parameter
fill_color = white


... # other plot parameters, such as file, type, position, etc

# local to this track - overrides the fill_color=white value
fill_color = grey

# in data.txt:
# ...
# hs1 10 20 0.50 fill_color=dblue
# ...
# The data point will be purple, overriding both fill_color=red and fill_color=green values. 

condition  = var(value) < 0.33
# specific to data points matching the condition, overrides any previously specified
# fill_color value, (global, local, data file)
fill_color = orange



If you are plotting a large number of similar tracks (e.g. groups of histograms, heat maps, etc), it is useful to apply global parameters where possible. This is particularly effective when combined with automated track placement with track counters. In the example below, each plot will be a heatmap with the same min/max value and color map. Within individual <plot> blocks, only the parameters specific to that block need to be specified.


type  = heatmap
min   = 0
max   = 1
# this color name is a list - see below about color lists
color = spectral-4-div

file = data.1.txt
r1   = 0.6r
r0   = 0.5r

file = data.2.txt
r1   = 0.7r
r0   = 0.6r

file = data.3.txt
r1   = 0.8r
r0   = 0.7r

file = data.4.txt
r1   = 0.9r
r0   = 0.8r



external imports

Some settings never or rarely change, such as colors and fonts. To keep the main configuration file modular, the files for these static values are imported using the <<include ...>> directive.

Two files should always be imported from etc/ in the Circos distribution. These are

# colors, fonts and fill patterns
<<include etc/colors_fonts_patterns.conf>>
# system and debug parameters
<<include etc/housekeeping.conf>>

The etc/colors_fonts_patterns.conf file itself imports several files from the Circos distribution.

# etc/colors_fonts_patterns.conf




Circos requires that these blocks be present and populated with definitions.

Conventionally, I store configuration for ideograms in an external file (ideogram.conf) and for tick mark formatting (ticks.conf). The reason for this is that these settings are fairly verbose, but are not related to a data set. By importing ideogram and tick mark settings from an external file

<<include ideogram.conf>>
<<include ticks.conf>>

the main configuration file is kept more succinct. Moreover, if you are creating multiple images with different data sets, you are likely to use the same settings for ideogram and tick mark formats. Storing these settings separately just makes sense.

Usually both ideogram.conf and ticks.conf are placed in the same directory as circos.conf, so no path (relative or absolute) needs to be added to the filename in the <<include >> directive.

If you have parameters that rarely change, consider creating external configuration files for these.

You can use the <<include >> directive anywhere in the configuration file, such as in plot blocks.

file = data.4.txt
r0 = 0.8r
r1 = 0.9r
<<include plotsettings.conf>>

Inclusion can be arbitrarily nested. In other words, included files can themselves include others, and so on.

When you include a file using <<include CONFIG_FILE_PATH/CONFIG_FILE>>, Circos will search the following paths for the file

  • relative to the location of CONFIG_FILE
  • relative to CONFIG_FILE_PATH/etc
  • CIRCOS_PATH/../etc

dynamically evaluated parameters

In the configuration file, parameters are typically set to constants using the syntax

variable = value

For example,

color = blue

There will be times when you'll want to specify the value of a configuration parameter using the value or a function of another.

accessing configuration values

Any parameter can be set to the value of another parameter using the syntax

parameter2 = conf(parameter1)

or, for parameters which are found in blocks

parameter2 = conf(block1,parameter1)
parameter2 = conf(block1,block2,parameter1)

For example,

track_color = blue
color = conf(track_color)

When the configuration file is parsed, simple substitution is exhaustively made until all conf(parameter) strings have been replaced by values.

Make sure that you include the full block path of the parameter when using this syntax. Thus for

parameter1 = ...

you would use conf(block1,block2,parameter1).

performing operations on parameters

Any parameter can be written as Perl code and evaluated at run-time. To use this feature, enclose the parameter in an eval() function.

thickness = eval(1+1)
color     = eval("b"."l"."u"."e")

The eval() feature is very useful when used to refer to and manipulate other configuration parameters.

For example,

track_color = blue
track_width = 100
track_start = 0.5


# color=blue
color = conf(track_color)
# r0 = 0.5r
r0    = eval(conf(track_start) . "r")
# r1 = 0.5r+100p
r1    = eval(conf(track_start) . "r" + conf(track_width) . "p")

If you are defining a parameter by a single conf(parameter) value, you do not need eval(), since only a substitution is required. However, if you need to manipulate this value (e.g. append a string, perform arithmetic), then eval() is required since the expression must be evaluated as code.

Because eval()calls require that you write correct Perl syntax, the chance of a mistake and therefore fatal error is high. Double check! It is common to forget to quote text in these calls — verify that you are not using a value as a bare word.

## OK
x = eval( 1.05 . "r" )
## NOT OK - r is meant to be a string, but without quotes Perl will 
## interpret it as a bare word, producing an error
x = eval( 1.05 . r )

Parameters with eval() in <rule> blocks are evaluated independently for each data point.

Automated Counters

Circos keeps a running count of the tracks as they are drawn. You can use these variables to fully automate track placement.

See Automating Tracks.


By including the etc/colors_fonts_patterns.conf file in the main configuration file

# circos.conf
<<include etc/colors_fonts_patterns.conf>>

you are including definitions for primary RGB and HSV colors. Also defined are Brewer palette colors and the conventional human chromosome color palette. To learn more about Brewer palettes, see my Color Palettes Matter presentation.

The etc/colors.conf file, which is included by etc/colors_fonts_patterns.conf, itself includes these various color definitions

# etc/colors.conf

# primary RGB colors

# Brewer palettes
# see etc/colors.brewer.conf
<<include colors.brewer.conf>>

# UCSC genome browser human chromosome colors
# see etc/colors.ucsc.conf
<<include colors.ucsc.conf>>

# HSV pure colors
# see etc/colors.hsv.conf
<<include colors.hsv.conf>>

using colors

Colors are referenced using their RGB values or their names (see below).

# using RGB values
color = 107,174,241

# using name
color = blue

When passing a color as an option in data files, the RGB values need to be delimited by (...). For example, if you want to add a color to a link

# using a color name
chr1 100 200 chr2 200 250 color=blue,thickness=2

# using RGB value
chr1 100 200 chr2 200 250 color=(107,174,241),thickness=2

color names

Colors in Circos are defined by their RGB or HSV values and specified by a name (e.g. red, orange, etc). Many named colors are pointers to Brewer palette equivalents.

# pure orange
porange  = 255,127,0

# dark pure orange
dporange = 234,110,0

# points to Brewer color...
orange = oranges-7-seq-4

# ...which is defined in colors.brewer.conf as
oranges-7-seq-4 = 253,141,60

color name syntax

Typically for a given color root name (e.g. orange), there are corresponding shades of the color with prefixed d (dark), l (light). The light version may be prefixed by one or more v (very). These shades point to a sequential Brewer palette for the color. For example, oranges point to the 7-color 'oranges' Brewer palette

vvlorange = oranges-7-seq-1
vlorange  = oranges-7-seq-2
lorange   = oranges-7-seq-3
orange    = oranges-7-seq-4
dorange   = oranges-7-seq-5
vdorange  = oranges-7-seq-6
vvdorange = oranges-7-seq-7

which is defined in colors.brewer.conf as

oranges-7-seq-1 = 254,237,222 
oranges-7-seq-2 = 253,208,162 
oranges-7-seq-3 = 253,174,107 
oranges-7-seq-4 = 253,141,60 
oranges-7-seq-5 = 241,105,19 
oranges-7-seq-6 = 217,72,1  
oranges-7-seq-7 = 140,45,4 

If you want the pure, saturated version of the color, use the p prefix. For example, porange is a pure bright orange.

vvlporange = 255,182,106
vlporange  = 255,164,82
lporange   = 255,146,54
porange    = 255,127,0
dporange   = 234,110,0
vdporange  = 213,92,0
vvdporange = 193,75,0

Check etc/colors for the full list of colors.

I suggest that you try using the Brewer colors (e.g. orange vs porange), because they are perceptually uniform. However, they will appear less punchy and saturated than their pure equivalents. In particular, the Brewer reds may appear pinkish and light when used on their own.

Experiment, but be aware of the perceptual aspects of color, which will influence how your figure is perceived (see my Color Palettes Matter presentation).

Brewer colors

Brewer colors are categorized into one of three palette types: sequential, diverging and qualitative. For a given palette type (e.g. sequential), there are a variety of palettes (e.g. reds, greens, blues). Each palette is available for various number of colors (e.g. 3, 4, 5, ...).

The syntax for a Brewer color name is palettename-ncolors-palettetype-index. The palette names, for each type, are

# sequential (-seq-) (3-9 colors)

# diverging (-div-) (3-11 colors)

# qualitative (-qual-) (3-8 colors, some up to 12 colors)
accent (3-8 colors)
dark2 (3-8 colors)
paired (3-12 colors)
pastel1 (3-9 colors)
pastel2 (3-8 colors)
set1 (3-9 colors)
set2 (3-8 colors)
set3 (3-12 colors)

For example, purple-orange diverging 9-color palette colors are puor-9-div-1, puor-9-div-2, ..., puor-9-div-9.

HSV colors

You can use the HSV color space to define colors. To do so, specify the HSV values as hsv(h,s,v). For example,

red = hsv(0,1,1)

All pure HSV colors (s = 1, v = 1) are defined in colors.hsv.conf.

hue000 = hsv(0,1,1)
hue001 = hsv(1,1,1)
hue359 = hsv(359,1,1)
hue360 = hsv(360,1,1) # same as hue000

unix colors

The file etc/colors.unixnames.txt defines a large number (700+) of named colors, taken from UNIX's rgb.txt file. This file is not included by default.

Many definitions in this file duplicate definitions in colors.conf (e.g. colors.unixnames.txt defines blue as 0,0,255 but in colors.conf it is blues-7-seq-4, which is 107,174,214). Including colors.unixnames.txt together with (colors.conf) will result in an error.

colors with alpha channels (transparency)

You can assign an alpha channel value to a color (transparency) by including a fourth component.

# 0 < alpha < 1 
# 0 opaque
# 1 transparent
red_faint = 255,255,255,0.8

# or alpha 0-127
# 0   opaque
# 127 transparent
red_also_faint = 255,255,255,102

You can use either the [0,1] range for the alpha value, or [0,127]. In both cases, the right end of the interval corresponds to transparent. For example, if alpha is in the range 0-127 then a=0 corresponds to fully opaque, and a=127 to fully transparent.

Please see Transparent Link tutorial for discussion about automating definition of these colors.

full transparency

To create a fully transparent color (e.g. for an image with transparent background), you'll need to define a color named transparent. A transparent color still requires an RGB value (a strange artefact in gd implementation). Choose an RGB value that you aren't using elsewhere. Typically something like 1,0,0 will be suitable.

# in color.conf
transparent = 1,0,0

The transparent color will be available using the name transparent. A synonym clear is also provided. To use the transparent color (e.g. for background),

background = transparent # 'clear' also works here 

The names transparent and clear are reserved. Do not use these two color names for other colors.

color synonyms

You can include synonyms for colors, by defining one color using the name of another color, instead of RGB or RGBA values.

favourite        = green
almost_favourite = orange
green  = 51,204,94
orange = 255,136,0

Be careful not to create infinite lookup loops — these produce an error.

# don't do this
favourite = green
green     = favourite

color lists

A color list can be defined by specifying a comma-delimited list of existing colors

red_list = dred,red,lred,vlred

or, more conveniently, a regular expression. The results will be sorted by the value of any capture buffers. The order will be reasonable (numerically or alphanumerically depending on the value of the capture buffer). If you want to sort the matches in reverse, wrap the regular expression in rev().

For example, to create a list of the 9-color spectral Brewer palette,

spectral9 = spectral-9-div-(\d+)

and to create a reversed list

spectral9r = rev(spectral-9-div-(\d+))

Color lists are used with heat maps.

Brewer palette Lists

Lists for all Brewer palettes are predefined (see etc/brewer.lists.conf). For a given color set name-ncolors-type-index, two lists are available

  • name-ncolors-type Brewer palette color list (e.g. reds-8-seq = reds-8-seq-1,reds-8-seq-2,...)
  • name-ncolors-type-rev corresponding palette, with colors in reverse order (e.g. reds-8-seq-rev = reds-8-seq-8,reds-8-seq-7,...)

For example, the 6-color Brewer palette lists that are defined are

# sequential

# diverging

# qualitative

Each has a -rev (reversed) counterpart (e.g. spectral-6-div and spectral-6-div-rev).

These lists are automatically imported from etc/colors.brewer.lists.conf via etc/colors.brewer.conf. Thus, if you import the Brewer colors (done by default), you are automatically including all Brewer lists.

HSV color lists

Brewer palettes provide sets of perceptually uniform colors and should be used whenever possible (i.e., always).

Additionally, color sets of pure HSV colors (s = 1, v = 1) are defined in colors.hsv.conf. Two kind of HSVG color lists are defined.

Lists of colors by hue step are named hue-sH, for a set of colors that vary by a change in hue of H. For example, hue-s45 includes the colors hue000, hue045, hue090, hue135, hue180, hue225, hue270, hue315. Lists for steps 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180 and 360 are defined.

The other set of lists are named hue-N, for a set of N uniformly spaced colors. For example, hue-7 includes the colors hue000, hue051, hue103, hue154, hue206, hue257, and hue309. Lists for 3 to 30 colors are defined.

color list cache

Generating the color lists can take several seconds. For this reason, Circos employs a caching mechanism to store color lists definitions. By default, the cache file is /tmp/circos.colorlist.dat. If the cache is older than the configuration file, or color definitions, it is recomputed. The length of time required is a function of the total number of colors (color definitions multiplied by automatic transparency levels) and the number of lists. If you are trying to optimize image generation speed, and do not wish to count on caching, remove any list definitions you are not using and reduce the number of automatic transparency levels.

chromosome color scheme

A set of colors named after chromosomes is also defined and corresponds to the chromosome color scheme used by UCSC Genome Browser and other online resources. This is a standardized palette.

chr1 = 153,102,0
chr2 = 102,102,0
chr3 = 153,153,30
chrX = 153,153,153
chrY = 204,204,204

Another set of colors is named after cytogenetic band colors, typically reported in karyotype files. These colors define the G-staining shades seen in ideograms.

gpos100 = 0,0,0
gpos    = 0,0,0
gpos75  = 130,130,130
gpos66  = 160,160,160
gpos50  = 200,200,200
gpos33  = 210,210,210
gpos25  = 200,200,200
gvar    = 220,220,220
gneg    = 255,255,255
acen    = 217,47,39
stalk   = 100,127,164

creating your own colors

I strongly suggest that you place new color definitions in a separate file. Modularity will make maintenance easier. And given that you'll likely want access to your custom colors for all images, include them globally rather than on an image-by-image basis.

For example, if you create your own blue

# in mycolors.conf
niceblue = 17,111,227

you can include this file like this

# all default color definitions
<<include colors_fonts_patterns.conf>>

# this will append your definitions to the <colors> block
<<include mycolors.conf>>

You can quickly add colors directly

# all default color definitions
<<include colors_fonts_patterns.conf>>

# this will append your definitions to the <colors> block
<<include mycolors.conf>>
niceblue2 = 37,101,179


Circos uses CMU Modern fonts. These are found in fonts/ in the distribution and are associated with unique definitions (e.g. light, bold, italic) used in configuration files.

light          = fonts/modern/cmunbmr.otf # CMUBright-Roman
normal         = fonts/modern/cmunbmr.otf # CMUBright-Roman
default        = fonts/modern/cmunbmr.otf # CMUBright-Roman
semibold       = fonts/modern/cmunbsr.otf # CMUBright-Semibold
bold           = fonts/modern/cmunbbx.otf # CMUBright-Bold
italic         = fonts/modern/cmunbmo.otf # CMUBright-Oblique
bolditalic     = fonts/modern/cmunbxo.otf # CMUBright-BoldOblique
italicbold     = fonts/modern/cmunbxo.otf # CMUBright-BoldOblique

To use a specific font for an element, specify its label (e.g. normal, bold) in the configuration file. The default fonts are shown here.

To add your own fonts, copy the TTF file to fonts/ and add a new label to the font in the fonts.conf configuration.

To render very small labels, you should consider using bitmapped fonts. These fonts are designed to be used at a specific size and without anti-aliasing. One such family is the Mini Font set from

Other legible fonts, commonly used in terminals and text editors are

  • andale mono
  • anonymous
  • aurulent sans mono
  • vera sans mono
  • courier
  • dejavu sans mono
  • droid sans mono
  • inconsolata
  • liberation mono
  • lucida console
  • lucida typewriter
  • monofur
  • pragmata
  • profont
  • proggy
  • saxmono
  • the sans mono

These fonts are shown in the image section of this tutorial.


If you suspect there may be a problem with drawing images, please run

> bin/gddiag

and look at the output gddiag.png. It should look like the image in this tutorial.


Many quantities defined in the configuration files require units, which are one of

  • b (bases) - used to indicate distance along the ideogram
  • p (pixels) - used for quantities defined in absolute pixel size, such as track radius, label size, glyph size, and others.
  • r (relative) - quantifies a parameter relative to another value, which is sometimes more intuitive than using absolute pixel values. For example, label radial padding is relative to label width and label angular padding is relative to label height
  • u (chromosome units) - special relative unit which expresses distance long ideogram in terms of the chromosomes_unit value
  • n (no unit) - explicit suffix for unitless values

Unit designations are suffixed to the value and may be mixed

# 1 pixel padding
padding = 1p 
# relative padding (e.g. relative to label width)
padding = -0.25r

# radius of track (relative to inner ideogram radius)
r0 = 0.5r
# combination of relative and pixel values
r1 = 0.5r+200p

The reason why Circos insists on units is to reduce the strain of interpreting the configuration file parameters - a large number of custom values can quickly make the file opaque to quick inspection.