This page explains how themes work and takes you through the process of creating your own theme for Webmin. It covers both basic features such as image replacement and advanced capabilities like writing an alternate header function.

Introduction to themes

Webmin themes are sets of alternate user interfaces, graphics and color schemes. A user can choose which theme he wants by going into the Webmin Configuration module and clicking on Webmin Themes link. Multiple themes can be installed, but only one can be active for a Webmin user at any one time - or if no theme is active, the default colors and layout are used.

If no theme is active, the very basic default Webmin layout is used. This is different from the framed layout that you see when Webmin is first installed - that is generated by the gray-theme theme, which adds the left menu, new icons, table highlighting, many CSS improvements and more. Thus creating your own theme gives you a lot of power over Webmin’s layout, but requires quite a lot of work.

If you just want to modify the colors, icons or CSS of the default Blue Framed theme, the easier method is via creating an overlay theme, which is simpler but has less control over the layout.

Theme files

Like a module, a theme is a directory under the Webmin root directory that contains certain files. The most important is the theme.info file, which has the same format as the module.info file - lines of text with names and values separated by the = character. The only required entry is:

  • desc

    A description for this theme, such as My Webmin Theme. This is the text that will appear in the theme selection menu. Other useful entries are:

  • version

    The theme’s version number

  • depends

    The version of Webmin that the theme requires. This can also contain module dependencies, like in the module.info file. A theme can also contain a config file, also in the same format. The values defined in this file control the behaviour of the standard header and footer functions. Supported names and their values are:

  • cs_page

    A six-character hex string in RRGGBB format for the background color of Webmin pages.

  • cs_link

    A six-character hex string in RRGGBB format for the color of visited and unvisited links on Webmin pages.

  • cs_text

    A six-character hex string in RRGGBB format for the color of normal text.

  • bgimage

    A relative URL (like /images/background.gif) for a background image to be displayed on all pages.

  • noindex

    If set to 1, the HTML generated by the header function will not include a Webmin Index link. Useful if another frame is used for the main index.

  • brand

    HTML for an image or text to be displayed in the top-right corner of the main index page. Note, this can only be used with the old Legacy Theme.

  • brand_url

    A URL to which the brand image is linked. These two options are usually combined to create a company icon that links to its homepage in customized versions of Webmin. NOTE - this can only be used with the old Legacy Theme.

  • headhtml

    HTML that will be included inside the <head> section of each Webmin page.

  • headinclude

    The name of a file in your theme directory whose contents will be included inside the section of each page.

  • inbody

    Text that will be included inside the <body> tag itself.

  • prebody

    HTML that will be included at the top of the <body> section of each page. The following substitutions will be done in the HTML:

    • %HOSTNAME% will be replaced with the system’s hostname.
    • %VERSION% will be replaced with the Webmin version.
    • %USER% will be replaced with the current user’s login.
    • %OS% will be replaced with the OS name and version.

  • texttitles

    If set to 1, the titles on all pages will be displayed as HTML text rather than using letter images.

  • postbody

    HTML that will be included at the bottom of the <body> section on each page. The same substitutions as prebody are done.

  • tb

    Text that will be included inside the <tr> tag in table header rows.

  • cb

    Text that will be included inside the <tr> tag in table rows below the header.

  • functions

    The name of a file in your theme’s directory that contains Perl functions for overriding the default header, footer andf UI functions. See the Theme functions section below for more details.

  • noicons

    If set to 1, the standard generate_icon and icons_table functions will display only a name instead of an icon. This can be useful if your theme is designed for text-only or low bandwidth use. Many of these options will not work automatically if your theme uses the functions option to create its own replacement for the header function. Normally they are checked for and implemented by the standard header function, so if you define your own it will need to check the %tconfig global hash and interpret the values that it contains in the same way, if you still want them to be configurable in the theme’s config file.

Just like modules, themes can also be packaged as RPMs, which are suitable for installing on servers on which the RPM version of Webmin itself is already installed. You can download a script called makemodulerpm.pl that can package up a theme directory into an RPM by creating the spec file automatically.

Similarly, you can create a Debian package of a module using makemoduledeb.pl file. The resulting .deb file is placed in the /tmp directory. The package name is always webmin- followed by the directory name, for both modules and themes.

Overriding images and programs

In addition to changing the default colors, a theme can be used to selectively override any icon or CGI program used by Webmin. When a theme is chosen, its directory becomes an overlay root directory for the Webmin webserver. Thus, if your theme subdirectory contains a file called images/newlogo.gif, it will replace the logo on the main menu when it is displayed, because the webserver will look in the theme directory first before looking for images/newlogo.gif under the top-level directory.

In this way any of the module icons can be overridden, as can the images used to make up the titles at the top of pages. For example, if your theme directory contained a file called useradmin/images/icon.gif, it would be used as the icon for the Users and Groups module on the main menu. Because this replacement does not actually change the real images, the user can switch between themes or back to the default theme easily.

CGI programs can also be overridden as well, in exactly the same way. This can be used to do things like changing the way the main menu is displayed, by putting a custom index.cgi script in your theme directory. However, this ability should be used carefully as changes to the real CGI may break your custom script if its behaviour is different to the one it replaces. Also, note that when a theme CGI is executed, it will be in the real directory and not the theme subdirectory.

If your theme does replace an existing script, be sure to read it carefully so that your replacement implements all of the same functionality. The most common reason to replace the top-level index.cgi is to generate your own menu of modules. Some of the things to keep in mind when replacing this script are:

  • The function get_available_module_infos can be used to get a list of modules available to the current Webmin user, for use when generating any tables of icons.
  • If $gconfig{'gotoone'} is set to 1 and the user has only one module, your index.cgi should re-direct the browser directly to that module instead of displaying a menu. Users can set this in the Index Page Options page of the Webmin Configuration module.
  • The get_goto_module function should be called to get the name of a module to display initially, if selected by the user on the Index Page Options page.
  • If your menu program normally categorizes modules, when then $gconfig{'notabs'} variable is set categorization should be turned off so that all modules appear on a single page. Again, this is set on the Index Page Options page.
  • If your program arranges module icons in a table and the variable $gconfig{'nocols'} is set, it should be used as the number of columns to display.
  • If $gconfig{'deftab'} is set and your program categorizes modules, it should be used to decide which category to open by default.
  • The API function list_categories should be used to build a list of all categories with their correct descriptions, and the modules in them.
  • If your program displays a logout link, it should only appear if neither of the following environment variables are defined. They both indicate that a form of authentication has been used that makes logging out impossible or irrelevant. $ENV{'SSL_USER'} indicates that the current user has logged in with SSL client authentication. $ENV{'LOCAL_USER'} indicates that the user is connecting from localhost and that his Unix username matches his Webmin login.
  • If the variable $main::session_id is set, Webmin is in session (or cookie) authentication mode. You should generate a link to /session_login.cgi?logout=1 labeled Logout or something similar. However, if that variable is not set then Webmin is using HTTP authentication. Instead your code should create a link to /switch_user.cgi labeled Switch User, as the normal logout link above will not work.

It is not mandatory to implement all of the suggestions above - however, it will make your theme behave more like those included as standard with Webmin.

Theme functions

A Webmin theme can override some of the common HTML-generating functions by adding a line like functions=theme.pl to the config file and creating a theme.pl script in the theme’s directory. This script can then contain the following (optional) functions:

  • theme_header

    Overrides the standard header (and thus ui_print_header) functions.

  • theme_footer

    Overrides the standard footer and ui_print_footer functions.

  • theme_error

    Overrides the standard error function.

All of these take the same parameters as the functions they override, and should perform the same behavior, modified to fit your theme’s UI style.

In addition, all of the ui_ functions documented at API can be overridden by creating alternate functions whose names have theme_ pre-pended.

These functions give you a lot of power to create themes that significantly change the Webmin layout. However, for them to work properly they must handle all the parameters that they are passed in exactly the same way that the standard functions do.

The most complex is the theme_header function, due to the large number of parameters that it takes and the other global variables that it can make use of. When writing it, consider the following:

  • All parameters should be checked an interpreted in the same was the real header function.
  • There is no need for your function to call PrintHeader or output the Content-Type HTTP header, as this will be done automatically before it is called. It can just go ahead and start producing HTML.
  • HTML produced should be valid and complete. That means starting with <html>, followed by a <head> section containing the <title> and then the start of the <body> section.
  • The core API function get_html_title can be used to get the page title to display, with hostname, login or OS information added.
  • In all cases the function get_webmin_version can be used to get the version of Webmin, and get_display_hostname the hostname to show to users.
  • The <body> tag that your code produces may contain bgcolor, link and text parameters containing the values from the global variables $gconfig{'cs_page'}, $gconfig{'cs_link'} and $gconfig{'cs_text'}, if they are set. This ensures that color preferences set by the user on the User Interface page of the Webmin Configuration module are used. However, feel free to ignore them if your theme only looks good with a certain color scheme.
  • If every page includes a Logout or Switch User link, they should follow the rules described above for the index.cgi page.
  • If the variable $ENV{'HTTP_WEBMIN_SERVERS'} is set, your page heading should include a link to the URL in that variable labeled Webmin Servers. This is set when connecting via a tunnel in the Webmin Servers Index module, and the URL refers to that module on the originating system. This gives user an easy way to return to the list of servers.
  • Unless your heading is very similar to the default, the theme_footer function should be defined as well. It must produce closing HTML that matches that produced by theme_header, followed by </body> and </html> tags. Be sure to interpret and display the multiple return links that can be supplied to the footer function as well.
  • Some themes normally put all page content into a table by outputting an un-closed <table> tag in the header function. If the global variable $theme_no_table is set, this should be turned off as it indicates that the CGI program will be slowly producing some progressive output. Many browsers will not display a table’s content until it has been completely output. Similarly, your theme_footer function should not produce a closing </table> tag when $theme_no_table is set.
  • The special CGI program session_login.cgi that displays Webmin’s login form will call theme_header as well. However, at this point the browser has not logged into Webmin and so will not be able to access any images that your header refers to. For this reason, when called with the first two parameters set to undef (as it will be in this case), your function should not produce any <img> tags. Or they should always refer to the special /unauthenticated URL path, to which access is always allowed even to clients that have not logged in.

Reading the header function in web-lib.pl and the theme_header function is gray-theme/theme.pl should give you a good idea of how the various parameters and global variables should be handled.