Interaction with Mock

Mock is crucial component for building in Koji. Most build types use mock to prepare a fresh, isolated environment for building content.

For further reading on the mock tool itself, see the mock documentation.

Mock config files

For each buildroot Koji prepares a configuration file for mock to use. The content of the file depends in part on some administrator’s decisions and can be tweaked by options in the build tag. These files are managed by kojid and stored under /etc/mock/koji on the build host.

Since Koji 1.34.1, builds will save the mock configuration file as a log named mock_config.log and store it alongside other logs from the build.

The contents of this file are generated by Koji and are affected by:

You can generate mock configs locally in the same way that kojid does. See Local mock configs

Site defaults

In addition to the mock configuration file for the buildroot, the mock command also consults /etc/mock/site-defaults.cfg on the build host. You can use this file to set global defaults on your builders.

The following settings are recommended for use with Koji:

  • use_bootstrap = False - Bootstrap is a) not needed in most cases b) slows down the build c) e.g. in combination with next option could lead to unreproducible build. While this feature is pretty useful in some cases, it should be turned off as default and could be selectively turned on for specific buildroots per tag configuration.

  • use_bootstrap_image - As noted before, this is generally unsafe option, especially if used with image tags which are expected to be moved (e.g. “latest”). Note, that to use this option (even via tag’s configuration), you need to explicitly allow it in kojid.conf via mock_bootstrap_image = True.

  • nspawn_args - if you want to apply rlimit settings for mock with nspawn isolation, you will need to use this option. See RLIMIT settings below.

  • macros - some rpm macros could be defined every time for every build based on builder itself. Typical usecase is to limit usage of CPUs on given builder by setting config_opts['macros']['%_smp_ncpus_max'] = 2.

  • plugin_conf - Various plugins could be enabled and configured to be available in build environment. Example is rpmautospec which allows various %auto* macros in spec files.

RLIMIT settings

When mock uses simple isolation (aka old-chroot), the RLIMIT_* settings from kojid.conf will propagate to mock.

However, when mock uses nspawn isolation (aka new-chroot, controlled by the mock.new_chroot tag extra option), these limits are not propagated automatically. To apply such limits to the mock nspawn chroots, you can add them to the nspawn_args option in site-defaults.cfg. For example, you might set:

config_opts['nspawn_args'] = ['--rlimit=RLIMIT_NOFILE=16384:16384']

If your system uses a mix of mock isolation settings, then you will likely want to apply rlimit settings in both kojid.conf and site-defaults.cfg for consistency.

Local mock configs

The koji mock-config command can be used to generate a mock config file locally in the same way that the builders do. These can be useful for local testing or debugging.

$ koji mock-config --help
Usage: koji mock-config [options]
(Specify the --help global option for a list of other help options)

  -h, --help            show this help message and exit
  -a ARCH, --arch=ARCH  Specify the arch
  -n NAME, --name=NAME  Specify the name for the buildroot
  --tag=TAG             Create a mock config for a tag
  --target=TARGET       Create a mock config for a build target
  --task=TASK           Duplicate the mock config of a previous task
  --latest              use the latest redirect url
                        Duplicate the mock config for the specified buildroot
  --mockdir=DIR         Specify mockdir
  --topdir=DIR          Specify topdir, topdir tops the topurl
  --topurl=URL          URL under which Koji files are accessible, when topdir
                        is specified, topdir tops the topurl
                        Change the distribution macro
                        Specify a yum proxy
  -o FILE               Output to a file