Official builds of MassOS, produced by the developers of the MassOS Project, are made available on this web server. These builds can be directly downloaded, or used with the new MassOS upgrade utility.
You can browse all the available builds here - both the Live CD ISO images (.iso) and plain rootfs tarballs (.tar.zst) are provided. Note that builds are now in architecture-specific directories - for most systems, you therefore want the x86_64 subdirectory. For instructions on how to install MassOS, please refer to the the official installation guide.
Please note that the previously-used build directory, named massos-builds, is now transparently symlinked to the new x86_64 directory, so older workflows using it will continue to function normally without breaking. However we recommend migrating current and future workflows to the new directory layout, primarily because it helps improve support for multiple architectures.
Blake-2 checksum files (.b2) are provided alongside all builds. These can be used to verify the integrity of your download. Builds are also published with a detached GPG signature file (.asc) signed by this GPG key. Validating the GPG signature of a build can be done instead of or as well as checking the Blake-2 checksum, to verify the integrity of your download. All current and past GPG keys used to sign official MassOS builds can be found in the SIGNING-KEYS subdirectory.
MassOS builds are signed for UEFI secure boot. In most cases you will not need to download the secure boot certificates directly, as they are embedded into the bootable section of the MassOS ISO images, and the UEFI secure boot guide explains how to import the certificate from the ISO image. However, if for some reason you want/need to obtain them separately, you can download them from here.
Builds produced in 2026 and onwards are and will be signed by the updated 2026 MassOS secure boot certificate, which has a CN of MassOS Project Secure Boot Signing 2026. Builds from 2025 were signed by the older 2025 MassOS secure boot certificate, which has a CN of MassOS Project Official SB Signing 2025. The main reason for the migration was due to the old certificate lacking the Code Signing EKU, as well as because it was used to sign builds which (at the time) were not properly locked down and hardened under UEFI secure boot like newer builds are.
The MassOS developers have mirrored some source tarballs on this web server, for use in 'source-urls' as part of the MassOS build system. This is primarily for packages which are known (or have previously been found) to have unreliable origin web servers. It also contains some custom source tarballs created by the MassOS developers from upstream git checkouts, when (for any reason) a package skip-ahead to the latest git revision is required, but there are no reliable ways to obtain the snapshot without a direct git checkout (which the MassOS build system doesn't support for source URLs). These individual sources can be found here.
Furthermore, a very small number of packages used by the MassOS build system, even fewer of which are included in output builds, have to be precompiled for practical reasons. In this case, they can be found here (unless they are available elsewhere on the internet which can also be a possibility).
Occasionally, full source dumps for stages 1 and 2 of the MassOS build system will be published, only under exceptional circumstances (e.g. a large portion of the upstream servers used by the build system's source URLs are down). When this happens, the source dumps can be found here. The version that a source dump corresponds to will be visible in its file name. After downloading a source dump, it is sufficient to simply extract the dump into the MassOS source tree, which will automatically populate the sources/ directory which the retrieve-sources.sh script would ordinarily save its downloaded files to.