Admin Quick Start

This quick start gives an overview of installation of Apptainer from source, a description of the architecture of Apptainer, and pointers to configuration files. More information, including alternate installation options and detailed configuration options can be found later in this guide.

Architecture of Apptainer

Apptainer is designed to allow containers to be executed as if they were native programs or scripts on a host system. No daemon is required to build or run containers, and the security model is compatible with shared systems.

As a result, integration with clusters and schedulers such as Univa Grid Engine, Torque, SLURM, SGE, and many others is as simple as running any other command. All standard input, output, errors, pipes, IPC, and other communication pathways used by locally running programs are synchronized with the applications running locally within the container.

Apptainer favors an ‘integration over isolation’ approach to containers. By default only the mount namespace is isolated for containers, so that they have their own filesystem view. Access to hardware such as GPUs, high speed networks, and shared filesystems is easy and does not require special configuration. Default access to user home directories, /tmp space, and installation specific mounts makes it simple for users to benefit from the reproducibility of containerized applications without major changes to their existing workflows. Where more complete isolation is important, Apptainer can use additional Linux namespaces and other security and resource limits to accomplish this.

Apptainer Security

Note

See also the security section of this guide, for more detail.

Apptainer uses a number of strategies to provide safety and ease-of-use on both single-user and shared systems. Notable security features include:

  • The user inside a container is the same as the user who ran the container. This means access to files and devices from the container is easily controlled with standard POSIX permissions.

  • Container filesystems are mounted nosuid and container applications run with the PR_SET_NO_NEW_PRIVS flag. This means that applications in a container cannot gain additional privileges. A regular user cannot sudo or otherwise gain root privilege on the host via a container.

  • The Singularity Image Format (SIF) supports encryption of containers, as well as cryptographic signing and verification of their content.

  • SIF containers are immutable and their payload is run directly, without extraction to disk. This means that the container can always be verified, even at runtime, and encrypted content is not exposed on disk.

  • Restrictions can be configured to limit the ownership, location, and cryptographic signatures of containers that are permitted to be run.

To support the SIF image format, automated networking setup etc., and older Linux distributions without user namespace support, Apptainer runs small amounts of privileged container setup code via a starter-setuid binary. This is a ‘setuid root’ binary, so that Apptainer can perform filesystem loop mounts and other operations that need privilege. The setuid flow is the default mode of operation, but can be disabled on build, or in the apptainer.conf configuration file if required.

Note

Running Apptainer in non-setuid mode requires unprivileged user namespace support in the operating system kernel and does not support all features, most notably direct mounts of SIF images. This impacts integrity/security guarantees of containers at runtime.

See the non-setuid installation section for further detail on how to install Apptainer to run in non-setuid mode.

Installation from Source

Apptainer can be installed from source directly, or by building an RPM package from the source. Linux distributions may also package Apptainer, but their packages may not be up-to-date with the upstream version on GitHub.

To install Apptainer directly from source, follow the procedure below. Other methods are discussed in the Installation section.

Note

This quick-start that you will install as root using sudo, so that Apptainer uses the default setuid workflow, and all features are available. See the non-setuid installation section of this guide for detail of how to install as a non-root user, and how this affects the functionality of Apptainer.

Install Dependencies

On Red Hat Enterprise Linux or CentOS install the following dependencies:

$ sudo yum update -y && \
     sudo yum groupinstall -y 'Development Tools' && \
     sudo yum install -y \
     openssl-devel \
     libuuid-devel \
     libseccomp-devel \
     wget \
     squashfs-tools \
     cryptsetup

On Ubuntu or Debian install the following dependencies:

$ sudo apt-get update && sudo apt-get install -y \
    build-essential \
    uuid-dev \
    libgpgme-dev \
    squashfs-tools \
    libseccomp-dev \
    wget \
    pkg-config \
    git \
    cryptsetup-bin

Install Go

Apptainer is written primarily in Go, and you will need Go 1.16 or above installed to compile it from source. Versions of Go packaged by your distribution may not be new enough to build Apptainer.

The method below is one of several ways to install and configure Go.

Note

If you have previously installed Go from a download, rather than an operating system package, you should remove your go directory, e.g. rm -r /usr/local/go before installing a newer version. Extracting a new version of Go over an existing installation can lead to errors when building Go programs, as it may leave old files, which have been removed or replaced in newer versions.

Visit the Go download page and pick a package archive to download. Copy the link address and download with wget. Then extract the archive to /usr/local (or use other instructions on go installation page).

$ export VERSION=1.17.6 OS=linux ARCH=amd64 && \
    wget https://dl.google.com/go/go$VERSION.$OS-$ARCH.tar.gz && \
    sudo tar -C /usr/local -xzvf go$VERSION.$OS-$ARCH.tar.gz && \
    rm go$VERSION.$OS-$ARCH.tar.gz

Then, set up your environment for Go.

$ echo 'export GOPATH=${HOME}/go' >> ~/.bashrc && \
    echo 'export PATH=/usr/local/go/bin:${PATH}:${GOPATH}/bin' >> ~/.bashrc && \
    source ~/.bashrc

Download Apptainer from a GitHub release

You can download Apptainer from one of the releases. To see a full list, visit the GitHub release page. After deciding on a release to install, you can run the following commands to proceed with the installation.

$ export VERSION=1.0.0 && # adjust this as necessary \
    wget https://github.com/apptainer/apptainer/releases/download/v${VERSION}/apptainer-${VERSION}.tar.gz && \
    tar -xzf apptainer-${VERSION}.tar.gz && \
    cd apptainer

Compile & Install Apptainer

Apptainer uses a custom build system called makeit. mconfig is called to generate a Makefile and then make is used to compile and install.

$ ./mconfig && \
    make -C ./builddir && \
    sudo make -C ./builddir install

By default Apptainer will be installed in the /usr/local directory hierarchy. You can specify a custom directory with the --prefix option, to mconfig:

$ ./mconfig --prefix=/opt/apptainer

This option can be useful if you want to install multiple versions of Apptainer, install a personal version of Apptainer on a shared system, or if you want to remove Apptainer easily after installing it.

For a full list of mconfig options, run mconfig --help. Here are some of the most common options that you may need to use when building Apptainer from source.

  • --sysconfdir: Install read-only config files in sysconfdir. This option is important if you need the apptainer.conf file or other configuration files in a custom location.

  • --localstatedir: Set the state directory where containers are mounted. This is a particularly important option for administrators installing Apptainer on a shared file system. The --localstatedir should be set to a directory that is present on each individual node.

  • -b: Build Apptainer in a given directory. By default this is ./builddir.

Configuration

Apptainer is configured using files under etc/apptainer in your --prefix, or --syconfdir if you used that option with mconfig. In a default installation from source without a --prefix set you will find them under /usr/local/etc/apptainer. In a default installation from RPM or Deb packages you will find them under /etc/apptainer.

You can edit these files directly, or using the Apptainer config global command as the root user to manage them.

apptainer.conf contains the majority of options controlling the runtime behavior of Apptainer. Additional files control security, network, and resource configuration. Head over to the Configuration files section where the files and configuration options are discussed.

Test Apptainer

You can run a quick test of Apptainer using a small alpine container:

$ apptainer exec docker://alpine cat /etc/alpine-release
3.9.2

See the user guide for more information about how to use Apptainer.