calamares/src/modules

Calamares modules

Calamares modules are plugins that provide features like installer pages, batch jobs, etc. An installer page (visible to the user) is called a "view", while other modules are "jobs".

Each Calamares module lives in its own directory.

All modules are installed in $DESTDIR/lib/calamares/modules.

There are two types of Calamares module:

• viewmodule, for user-visible modules. These use C++ and either Widgets or QML
• jobmodule, for not-user-visible modules. These may be done in C++, Python, or as external processes (external processes not recommended).

A viewmodule exposes a UI to the user.

There are three interfaces for Calamares modules:

• qtplugin (viewmodules, jobmodules),
• python (jobmodules only),
• process (jobmodules only, not recommended).

Module directory

Each Calamares module lives in its own directory. The contents of the directory depend on the interface and type of the module.

Module descriptor

A Calamares module must have a module descriptor file, named module.desc. For C++ (qtplugin) modules using CMake as a build- system and using the calamares_add_plugin() function -- this is the recommended way to create such modules -- the module descriptor file is optional, since it can be generated by the build system. For other module interfaces, the module descriptor file is required.

The module descriptor file, if required, is placed in the module's directory. The module descriptor file is a YAML 1.2 document which defines the module's name, type, interface and possibly other properties. The name of the module as defined in module.desc must be the same as the name of the module's directory.

Module descriptors must have the following keys:

• name (an identifier; must be the same as the directory name)
• type ("job" or "view")
• interface (see below for the different interfaces; generally we refer to the kinds of modules by their interface)

Module descriptors for C++ modules may have the following key:

• load (the name of the shared library to load; if empty, uses a standard library name derived from the module name)

Module descriptors for Python modules must have the following key:

• script (the name of the Python script to load, nearly always main.py)

Module descriptors for process modules must have the following key:

• command (the command to run)

Module descriptors for process modules may have the following keys:

• timeout (how long, in seconds, to wait for the command to run)
• chroot (if true, run the command in the target system rather than the host) Note that process modules are not recommended.

Module descriptors may have the following keys:

• emergency (a boolean value, set to true to mark the module as an emergency module; see the section Emergency Modules, below)
• noconfig (a boolean value, set to true to state that the module has no configuration file; defaults to false)
• requiredModules (a list of modules which are required for this module to operate properly)
• weight (a relative module weight, used to scale progress reporting)

Required Modules

A module may list zero (if it has no requirements) or more modules by name. As modules are loaded from the global sequence in settings.conf, each module is checked that all of the modules it requires are already loaded before it. This ensures that if a module needs another one to fill in globalstorage keys, that happens before it needs those keys.

Emergency Modules

If, during an exec step in the sequence, a module fails, installation as a whole fails and the install is aborted. If there are emergency modules in the same exec block, those will be executed before the installation is aborted. Non-emergency modules are not executed.

If an emergency-module fails while processing emergency-modules for another failed module, that failure is ignored and emergency-module processing continues.

Use the EMERGENCY keyword in the CMake description of a C++ module to generate a suitable module.desc. For Python modules, manually add emergency: true to module.desc.

A module that is marked as an emergency module in its module.desc must also set the emergency key to true in its configuration file (see below). If it does not, the module is not considered to be an emergency module after all. This is so that you can have modules that have several instances, only some of which are actually needed for emergencies.

In summary:

• in module.desc, write emergency: true to make it possible to run the module in emergency mode,
• in <modulename>.conf, write emergency: true to make that specific module run in emergency mode.

Module-specific configuration

A Calamares module may read a module configuration file, named <modulename>.conf. If such a file is present in the module's directory, it can be shipped as a default configuration file. This only happens if the CMake-time option INSTALL_CONFIG is on.

The name of the configuration file for a given module can be influenced by the settings.conf of the overall Calamares configuration. By default, though, the module's own name is used.

Modules that have noconfig set to true will not attempt to read a configuration file, and will not warn that one is missing; conversely if noconfig is set to false (or is missing, since the default value is false) if there is no configuration file, a warning is printed during Calamares start-up.

The sample configuration files may work and may be suitable for your distribution, but no guarantee is given about their stability beyond syntactic correctness.

The module configuration file, if it exists, is a YAML 1.2 document which contains a YAML map of anything.

All sample module configuration files are installed in $DESTDIR/share/calamares/modules but can be overridden by files with the same name placed manually (or by the packager) in /etc/calamares/modules.

Module Weights

During the exec phase of an installation, where jobs are run and things happen to the target system, there is a running progress bar. It goes from 0% to 100% while all of the jobs for that exec phase are run. Generally, one module creates one job, but this varies a little (e.g. the partition module can spawn a whole bunch of jobs to deal with each disk, and the users module has separate jobs for the regular user and the root user).

By default, modules all "weigh" the same, and each job is equal. A typical installation has about 30 modules in the exec phase, so there may be 40 jobs or so: each job represents 2.5% of the overall progress of the installation.

The consequence is that the unpackfs module, which needs to write a few hundred MB to disk, gets 2.5% of the progress, and the machineid module, which is essentially instantaneous, also gets 2.5% of the progress. This makes progress reporting seem weird and uneven, and suggests to users that Calamares may be "hanging" during the unpackfs stage.

A module may be assigned a different "weight" in the module.desc file (or via the CMake macros for adding plugins). This gives the module more space in the overall progress: for instance, the unpackfs module now has a weight of 12, so (assuming there are 38 modules in the exec phase with a weight of 1, and unpackfs with a weight of 12) regular modules get 2% (1 in 50 total weight) of the overall progress bar, and the unpackfs module gets 24% (12 in 50). While this doesn't speed anything up, it does make the progress in the unpackfs module more visible.

It is also possible to set a weight on a specific module instance, which can be done in settings.conf. This overrides any weight set in the module descriptor. Doing so is the recommended approach, since that is where the specific installation-process is configured; it is possible to take the whole installation-process into account for determining the relative weights there.

Global Storage keys

Some modules place values in Global Storage so that they can be referenced later by other modules or even other parts of the same module. The following table represents a partial list of the values available as well as where they originate from and which module consume them. Keys whose name is followed by a + are structured data, and have entries (which start with +) below the parent key describing subkeys. Some structured keys refer to other documentation sources.

Key	Source	Consumers	Description
bootloader +	partition		Bootloader location
+ installPath			Device (e.g. /dev/sda) where the bootloader is installed
branding +			See src/branding/README.md
btrfsSubvolumes	mount	fstab	List of maps containing the mountpoint and btrtfs subvolume
btrfsRootSubvolume	mount	bootloader, luksopenswaphook	String containing the subvolume mounted at root
efiSystemPartition	partition	bootloader, fstab	String containing the path to the ESP relative to the installed system
extraMounts	mount	unpackfs	List of maps holding metadata for the temporary mountpoints used by the installer
fullname	users		The full username (e.g. "Jane Q. Public")
hostname	users		A string containing the hostname of the new system
netinstallAdd	packagechooser	netinstall	Data to add to netinstall tree. Same format as netinstall.yaml
netinstallSelect	packagechooser	netinstall	List of group names to select in the netinstall tree
packageOperations +	packagechooser, netinstall	packages	Operations to perform
+ (list data)			See packages.conf
partitions +	partition, rawfs	(many)	List of maps of metadata about each partition
+ device			path to the partition device
+ fs			the name of the file system
+ mountPoint			where the device should be mounted
+ uuid			the UUID of the partition device
rootMountPoint	mount	(many)	A string with the absolute path to the root mountpoint
username	users	networkcfg, plasmainf, preservefiles	A string containing the username of the new user
zfsDatasets	zfs	bootloader, grubcfg, mount	List of maps of zfs datasets including the name and mount information
zfsInfo	partition	mount, zfs	List of encrypted zfs partitions and the encription info
zfsPoolInfo	zfs	mount, umount	List of maps of zfs pool info including the name and mountpoint

C++ modules

Type: viewmodule, jobmodule Interface: qtplugin

Currently the recommended way to write a module which exposes one or more installer pages (viewmodule) is through a C++ and Qt plugin. Viewmodules must implement Calamares::ViewStep. They can also implement Calamares::Job to provide jobs.

To add a Qt plugin module, put it in a subdirectory and make sure it has a CMakeLists.txt with a calamares_add_plugin call. It will be picked up automatically by our CMake magic. The module.desc file is not recommended: nearly all cases can be described in CMake.

Modules can be tested with the loadmodule testing executable in the build directory. See the section on testing modules for more details.

C++ Jobmodule

TODO: this needs documentation

C++ Widgets Viewmodule

TODO: this needs documentation

C++ QML Viewmodule

A QML Viewmodule (or view step) puts much of the UI work in one or more QML files; the files may be loaded from the branding directory or compiled into the module. Which QML is used depends on the deployment and the configuration files for Calamares.

Explicit properties

The QML can access data from the C++ framework though properties exposed to QML. There are two libraries that need to be imported explicitly:

import io.calamares.core 1.0
import io.calamares.ui 1.0

The ui library contains the Branding object, which corresponds to the branding information set through branding.desc. The Branding class (in src/libcalamaresui/Branding.h offers a QObject-property based API, where the most important functions are string() and the convenience functions versionedName() and similar.

The core library contains both ViewManager, which handles overall progress through the application, and Global, which holds global storage information. Both objects have an extensive API. The ViewManager can behave as a model for list views and the like.

These explicit properties from libraries are shared across all the QML modules (for global storage that goes without saying: it is the mechanism to share information with other modules).

Implicit properties

Each module also has an implicit context property available to it. No import is needed. The context property config (note lower case) holds the Config object for the module.

The Config object is the bridge between C++ and QML.

A Config object must inherit QObject and should expose, as Q_PROPERTY, all of the relevant configuration information for the module instance. The general description how to do that is available in the Qt documentation.

Python modules

Modules may use one of the python interfaces, which may be present in a Calamares installation (but also may not be). These modules must have a module.desc file. The Python script must implement the Python jobmodule interface.

To add a Python or process jobmodule, put it in a subdirectory and make sure it has a module.desc. It will be picked up automatically by our CMake magic. For all kinds of Python jobs, the key script must be set to the name of the main python file for the job. This is almost universally main.py.

CMakeLists.txt is not used for Python jobmodules.

Calamares offers a Python API for module developers, the core Calamares functionality is exposed as libcalamares.job for job data, libcalamares.globalstorage for shared data and libcalamares.utils for generic utility functions. Documentation is inline.

All code in Python job modules must obey PEP8, the only exception are libcalamares.globalstorage keys, which should always be camelCaseWithLowerCaseInitial to match the C++ identifier convention.

Modules can be tested with the loadmodule testing executable in the build directory. See the section on testing modules for more details.

Python Jobmodule

Type: jobmodule Interface: python

A Python jobmodule is a Python program which imports libcalamares and has a function run() as entry point. The function run() must return None if everything went well, or a tuple (str,str) with an error message and description if something went wrong.

Python API

The interface from a Python module to Calamares internals is found in the libcalamares module. This is not a standard Python module, and is only available inside the Calamares "runtime" for Python modules (it is implemented in C++ and injected into the Python environment by Calamares).

A module should start by importing the Calamares internals:

import libcalamares

There are three important (sub)modules in libcalamares:

• globalstorage behaves like a dictionary, and interfaces with the global storage in Calamares; use it to transfer information between modules (e.g. the partition module shares the partition layout it creates). Note that some information in global storage is expected to be structured, and it may be dicts-within-dicts.

  An example of using globalstorage:

  if not libcalamares.globalstorage.contains("lala"):
      libcalamares.globalstorage.insert("lala", 72)
  

• job is the interface to the job's behavior, with one important data member: configuration which is a dictionary derived from the configuration file for the module (if there is one, empty otherwise). Less important data is pretty_name (a string) and working_path which are normally not needed. The pretty_name value is obtained by the Calamares internals by calling the pretty_name() function inside the Python module.

  There is one function: setprogress(p) which can be passed a float p between 0 and 1 to indicate 0% to 100% completion of the module's work.

• utils is where non-job-specific functions are placed:

  • debug(s) and warning(s) are logger functions, which send output to the usual Calamares logging functions. Use these over print() which may not be visible at all.
  • mount(device, path, type, options) mounts a filesystem from device onto path, as if running the mount command from the shell. Use this in preference to running mount by hand. In Calamares 3.3 this function also handles privilege escalation.
  • gettext_path() and gettext_languages() are support functions for translations, which would normally be called only once when setting up gettext (see below).
  • obscure(s) is a lousy string obfuscation mechanism. Do not use it.
  • A half-dozen functions for running a command and dealing with its output. These are recommended over using os.system() or the subprocess module because they handle the chroot behavior for running in the target system transparently. In Calamares 3.3 these functions also handle privilege escalation. See below, Running Commands in Python for details.

A module must contain a run() function to do the actual work of the module. The module may define the following functions to provide information to Calamares:

• pretty_name() returns a string that is a human-readable name or short description of the module. Since it is human-readable, return a translated string.
• pretty_status_message() returns a (longer) string that is a human-readable description of the state of the module, or what it is doing. This is primarily of importance for long-running modules. The function is called by the Calamares framework when the module reports progress through the job.setprogress() function. Since the status is human-readable, return a translated string.

Python Translations

Translations in Python modules -- at least the ones in the Calamares core repository -- are handled through gettext. You should import the standard Python gettext module. Conventionally, _ is used to mark translations. That function needs to be configured specifically for use in Calamares so that it can find the translations. A boilerplate solution is this:

import gettext
_ = gettext.translation("calamares-python",
                        localedir=libcalamares.utils.gettext_path(),
                        languages=libcalamares.utils.gettext_languages(),
                        fallback=True).gettext

Error messages should be logged in English, and given to the user in translated form. In particular, when returning an error message and description from the run() function, return translated forms, like the following:

return (
    _("No configuration found"),
    _("<a longer description of the problem>"))

Running Commands in Python

The use of the os.system() function and subprocess modules is discouraged. Using these makes the caller responsible for handling any chroot or other target-versus-host-system manipulation, and in Calamares 3.3 may require additional privilege escalation handling.

The primary functions for running a command from Python are:

• target_env_process_output(command, callback, stdin, timeout)
• host_env_process_output(command, callback, stdin, timeout) They run the given command (which must be a list of strings, like sys.argv or what would be passed to a subprocess module call) either in the target system (within the chroot) or in the host system. Except for command, the arguments are optional.

A very simple example is running ls from a Python module (with libcalamares.utils. qualification omitted):

target_env_process_output(["ls"])

The functions return 0. If the exit code of command is not 0, an exception is raised instead of returning 0. The exception is subprocess.CalledProcessError (as if the subprocess module had been used), and the returncode member of the exception object can be used to determine the exit code.

Parameter stdin may be a string which is fed to the command as standard input. The timeout is in seconds, with 0 (or a negative number) treated as no-timeout.

Parameter callback is special:

• If it is None, no special handling of the command's output is done. The output will be logged, though (if there is any).
• If it is a list, then the output of the command will be appended to the list, one line at a time. Lines will still contain the trailing newline character (if there is one; output may end without a newline). Use this approach to process the command output after it has completed.
• Anything else is assumed to be a callable function that takes one parameter. The function is called once for each line of output produced by the command. The line of output still contains the trailing newline character (if there is one). Use this approach to process the command output while it is running.

Here are three examples of running ls with different callbacks:

# No processing at all, output is logged
target_env_process_output(["ls"])
target_env_process_output(["ls"], None)

# Appends to the list
ls_output = []
target_env_process_output(["ls"], ls_output)

# Calls the function for each line, which then calls debug()
def handle_output(s):
    debug(f"ls said {s}")
target_env_process_output(["ls"], handle_output)

There are additional functions for running commands in the target, which can select what they return and whether exceptions are raised or only an exit code is returned. These functions have an overload that takes a single string (the name of an executable) as well. They should all be considered deprecated by the callback-enabled functions, above.

• target_env_call(command, stdin, timeout) returns the exit code, does not raise.
• check_target_env_call(command, stdin, timeout) raises on a non-zero exit code.
• check_target_env_output(command, stdin, timeout) returns a single string with the output of command, raises on a non-zero exit code.

All of the API functions for running commands set the environment LC_ALL and LANG to "C" for the called command.

Process modules

Use of this kind of module is not recommended. Use shellprocess instead, which is more configurable.

Type: jobmodule Interface: process

A process jobmodule runs a (single) command. The interface is process, while the module type must be job or jobmodule.

The module-descriptor key command should have a string as value, which is passed to the shell -- remember to quote it properly in YAML. It is generally recommended to use a shellprocess job module instead (less configuration, easier to have multiple instances). There is no configuration outside of the module-descriptor. The command undergoes Calamares variable- expansion (e.g. replacing ${ROOT} by the target of the installation). See shellprocess documentation for details.

Optional keys are timeout and chroot.

CMakeLists.txt is not used for process jobmodules.

Testing Modules

For testing purposes there is an executable loadmodule which is built, but not installed. It can be found in the build directory. The loadmodule executable behaves like single-module Calamares: it loads global configuration, job configuration, and then runs a single module which may be a C++ module or a Python module, a Job or a ViewModule.

The same application can also be used to test translations, branding, and slideshows, without starting up a whole Calamares each time. It is possible to run multiple loadmodule executables at the same time (Calamares tries to enforce that it runs only once).

The following arguments can be used with loadmodule (there are more; run loadmodule --help for a complete list):

• --global takes a filename and reads the file to provide data in global storage. The file must be YAML-formatted.
• --job takes a filename and reads that to provide the job configuration (e.g. the .conf file for the module).
• --ui runs a view module with a UI. Without this option, view modules are run as jobs, and most of them are not prepared for that, and will crash.