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Mock » Feature container for bootstrap

A 'simple' chroot build environment manager for building RPMs.

Container image for bootstrap

In past, we had some incompatibilities between host and build target. They were, in fact, small. Like using a different package manager. Some were big. Like, the introduction of Weak and Rich dependencies. For this reason, we introduced bootstrap. But then comes zstd payload. This is a new type of payload. And to install packages with this payload, you need rpm binary, which supports this payload. This is true for all current Fedoras. Unfortunately, neither RHEL 8 nor RHEL 7 supports this payload. So even bootstrap will not help you to build Fedora packages on RHEL 8.

We come up with a nice feature. Mock will not install bootstrap chroot itself. Instead, it will download the container image, extract the image, and use this extracted directory as a bootstrap chroot. And from this bootstrapped chroot install the final one.

Using this feature, any incompatible feature in either RPM or DNF can be used in the target chroot. Now or in future. And you will be able to install the final chroot. You do not even need to have RPM on a host. So this should work on any system. Even Debian based. The only requirement for this feature is Podman. Do not forget to install the podman package.

This feature is available since 1.4.20 and enabled by default from 5.0. You can disable it using:

config_opts['use_bootstrap_image'] = False

It can be enabled or disabled on the command line using --use-bootstrap-image or --no-bootstrap-image options.

Note however that also this is prerequisite:

config_opts['use_bootstrap_container'] = True # or --bootstrap-chroot option

To specify which image should be used for bootstrap container you can put in config:

config_opts['bootstrap_image'] = ''

This is a general config. Each config has specified its own image specified. E.g. CentOS 7 has config_opts['bootstrap_image'] = 'centos:7' in config. So unless you use your own config, you can enable this feature, and the right image will be used.

The image contents are typically suboptimal for Mock’s use-case. In particular, Mock needs to have a correct package manager (as specified in the package_manager configuration option) installed inside the image, along with the builddep functionality (typically provided by python3-dnf-plugins-core). This is why Mock still has to ‘update the downloaded bootstrap’ somehow. If you happen to have an image with builddep pre-installed, you can set bootstrap_image_ready to ‘True’:

config_opts['bootstrap_image_ready'] = True

This option will significantly reduce the bootstrap preparation time, as no package management actions need to be performed for the bootstrap (no need to download and initialize package manager caches).

There is one known issue:

Technically, you can use any container, as long as there is the required package manager (DNF or YUM). The rest of the needed packages will be installed by mock.