An Apptainer plugin is a package that can be dynamically loaded by the Apptainer runtime, augmenting Apptainer with experimental, non-standard and/or vendor-specific functionality.

Plugins can influence the behaviour of Apptainer in specific ways:

  • A cli plugin can use the Command callback to add or modify CLI subcommands and/or flags.

  • A cli plugin can use the ApptainerEngineConfig callback to change the container configuration before it is passed to the runtime, e.g. adding bind mounts etc.

  • A runtime plugin can use the MonitorContainer callback to watch the container process as it is executing.

  • A runtime plugin can use the PostStartProcess callback to carry out a task after the container has been started.

  • A runtime plugin can use the RegisterImageDriver callback to implement an alternative way of providing a container image to execute.

Limitations / Requirements

The way that plugin functionality is implemented in the Go language, which Apptainer is written with, is quite restrictive.

Go plugins must be built with the same Go version, and set of dependencies, as the main program they will be loaded into. This means it is generally impractical to develop and build plugins except in lock-step with the main Apptainer source tree.

Functionality that can be implemented with plugins is limited to the scope of the exposed plugin callbacks. Container runtimes such as Apptainer execute using multiple processes, with distinct boundaries that limit the influence a plugin can have.

If you are considering writing a plugin for Apptainer you may wish to investigate whether the feature can be contributed to the main source tree directly via a PR. This simplifies future maintenance, and avoids the limitations of Go plugins.

Using Plugins

The list command prints the currently installed plugins.

$ apptainer plugin list
There are no plugins installed.

Plugins are packaged and distributed as binaries encoded with the versatile Singularity Image Format (SIF). However, plugin authors may also distribute the source code of their plugins. A plugin can be compiled from its source code with the compile command. A number of example plugins are included in the examples/plugins directory of the Apptainer source.

$ apptainer plugin compile examples/plugins/cli-plugin/
INFO:    Plugin built to: /home/dtrudg/Git/apptainer/examples/plugins/cli-plugin/cli-plugin.sif

Upon successful compilation, a SIF file will appear in the directory of the plugin’s source code.

$ ls examples/plugins/cli-plugin/ | grep sif


Due to the structure of the Apptainer project, and the strict requirements of Go plugin compilation, all plugins must be compiled from within the Apptainer source code tree.

The ability to compile plugins outside of the Apptainer tree, that previously existed, has been removed due to incompatible changes in Go 1.18.

Every plugin encapsulates various information such as the plugin’s author, the plugin’s version, etc. To view this information about a plugin, use the inspect command.

$ apptainer plugin inspect examples/plugins/cli-plugin/cli-plugin.sif
Description: This is a short example CLI plugin for Apptainer
Author: Apptainer Team
Version: 0.1.0

To install a plugin, use the install command. This operation requires root privilege.

$ sudo apptainer plugin install examples/plugins/cli-plugin/cli-plugin.sif
$ apptainer plugin list

After successful installation, the plugin will automatically be enabled. Any plugin can be disabled with the disable command and re-enabled with the enable command. Both of these operations require root privilege.

$ sudo apptainer plugin disable
$ apptainer plugin list

$ sudo apptainer plugin enable
$ apptainer plugin list

Finally, to uninstall a plugin, use the uninstall command. This operation requires root privilege.

$ sudo apptainer plugin uninstall
Uninstalled plugin "".

$ apptainer plugin list
There are no plugins installed.

Writing a Plugin

Developers interested in writing Apptainer plugins can get started by reading the Go documentation for the plugin package.

Example plugins can be found in the Apptainer source code.