A package consists of one or more files placed in a directory or its subdirectories. It must have a manifest.json file and follow certain naming conventions.

The name of a package is the name of the directory.

The name of the package must be ASCII alphanumeric, and may contain an underscore. Names of directories and files in the package must consist of ASCII alphanumeric along with dash, underscore, dot, and comma. No spaces are allowed.

Cockpit uses the data directories from the XDG Base Directory Specification to locate packages. The $XDG_DATA_DIRS represents a colon separate list of system data directories, and $XDG_DATA_HOME is a user specific data directory. If the environment variables are not set, defaults are used, according to the spec. If cockpit has been built with an alternate --prefix=/path then the $prefix/share/cockpit is used by default.

A cockpit/ subdirectories in any of these data directories is the location where packages are loaded by Cockpit. If Cockpit finds a package with the same name, in multiple data directories, then the first one wins. According to the spec the first data directory is $XDG_DATA_HOME and then $XDG_DATA_DIRS in order.

This means that, by default the following directories are searched for cockpit packages, and in this order:

Packages placed in $XDG_DATA_HOME are not cached by Cockpit or the web browser. Other packages are cached aggressively, and are accessed using a checksum of the files in the packages and their names.

You can use the following command to list the packages installed on a server. You'll note that it's output may change when you run the command as different users, if there are packages installed in the user's home directory.

$ cockpit-bridge --packages
...

To further clarify things, here is an example package called "my-package" and its file layout:

/usr/share/cockpit/
    my-package/
        manifest.json
        file.html
        some.js

Place or symlink packages in your ~/.local/share/cockpit directory (or appropriate $XDG_DATA_HOME location) that you would like to modify and develop. System installed packages should not change while Cockpit is running.

Each package has a manifest.json file. It is a JSON object. The following fields may be present in the manifest:

In addition, the following keys contain information about where components of the package should appear in Cockpit's user interface. Each of these keys is optional and contains an object mapping unique identifiers to menu items, which are described below. (The naming of these fields doesn't perfectly match the current user interface for historical reasons.)

Menu items and tools are registered using JSON objects that have the following properties:

Keyword items are registered using JSON objects that have the following properties:

An example manifest.json with some optional properties set:

{
  "version": 0,
  "require": {
      "cockpit": "120"
  },
  "tools": {
     "mytool": {
        "label": "My Tool",
        "path": "tool.html"
     }
  }
}

A file called override.json may be placed next to the manifest. containing overrides to the information in the manifest. These override files are in the simple JSON Merge Patch format.

When referring to files in your package, such as in a hyperlink or a <style> tag or <script> tag, simply use a relative path, and refer to the files in the same directory. When you need to refer to files in another package use a relative link.

For example here's how to include the base cockpit.js script in your HTML from the latest package:

<script src="../base1/cockpit.js"></script>

Do not assume you can link to any file in any other package. Refer to the list of API packages for those that are available for use.

In order to support language specific files, gzipped and/or minified data, the files in a package are loaded using content negotiation logic.

If a file does not exist at the expected path, Cockpit tries to insert .min before its extension. It also tries adding a .gz to both of those file names. If the file is still not found, and the request path has more than one extension, the second to the last extension is popped off, and the above process repeats.

This means that for the file test.de.js in the package named mypackage the following files would be tried in this order:

mypackage/test.de.js
mypackage/test.de.min.js
mypackage/test.de.js.gz
mypackage/test.de.min.js.gz
mypackage/test.js
mypackage/test.min.js
mypackage/test.js.gz
mypackage/test.min.js.gz

When packages are loaded from a system directory, Cockpit optimizes the file system lookups above, by pre-listing the files. This is one of the reasons that you should never change packages installed to a system directory while Cockpit is running.

Cockpit has API available for writing packages. There is no API available for external callers to invoke via HTTP, REST or otherwise.

API from various packages can be used to implement Cockpit packages. Each package listed here has some API available for use. Only the API explicitly documented should be used.

To include javascript from the API, simply load it into your HTML using a script tag. Alternatively you can use an javascript loader.

On the server side the cockpit-bridge connects to various system APIs that the front end UI requests it to. There are additional bridges for specific tasks that the main cockpit-bridge cannot handle, such as using the PCP C library API.

These additional bridges can be registered in a "bridges" section of a package's manifest.json file. Building such a bridge is a complex tasks, and we will skip over that here. However it is useful to adjust how these additional bridges are called, and so we'll look at how they are registered.

An example manifest.json with a bridges section:

{
    "bridges": [
        {
            "match": { "payload": "metrics1" },
            "spawn": [ "/usr/libexec/cockpit-pcp" ]
        }
    ]
}

The bridges are considered in the order they are listed in the array. Use the manifest.json"priority" field to control order between packages. The bridges are registered using JSON objects that have the following properties:

The spawn and environ values can be dynamically taken from a matching open command values. When a value in either the spawn or environ array contains a named variable wrapped in ${}, the variable will be replaced with the value contained in the matching open command. Only named variables are supported and name can only contain letters, numbers and the following symbols: ._-

For example a bridges section like:

{
  "bridges": [
    {
      "match": { "payload": "example" },
      "environ": [ "TAG=${tag}" ],
      "spawn: [ "/example-bridge", "--tag", "${tag}" ],
      "problem": "access-denied"
    }
  ]
}

when a open command is received with a payload of example with tag value of tag1. The following command will be spawned

TAG=tag1 /example-bridge --tag tag1

Processes that are reused so if another open command with a "tag" of tag1 is received. The open command will be passed to existing process, rather than spawning a new one. However a open command with an tag of tag2 will spawn a new command:

TAG=tag2 /example-bridge --tag tag2

If you need to include ${}, as an actual value in your arguments you can escape it by prefixing it with a \

If the functionality in a package replaces that of another package then it can replace that package by claiming the same name and a higher priority.

For example, a package in the /usr/share/cockpit/disks directory could replace Cockpit's storage package with a manifest.json like this:

{
  "version": 0,
  "name": "storage",
  "priority": 10,
  "menu": {
     "index": {
        "label": "Disk Storage",
        "order": 15
     }
  }
}

It is also possible to hide or change labels on the menu items of an existing package by including a override.json in that existing package's directory.

For example an /usr/share/cockpit/systemd/override.json could hide the Logs menu item and move the Services menu item to the top of the menu.

{
  "menu": {
    "logs": null,
    "services": {
      "order": -1
    }
  }
}