These are build steps that remain "busy" in the database even though they have finished, because they couldn't be updated (e.g. due to a PostgreSQL connection problem). To prevent them from showing up as busy in the "Machine status" page, we now periodically purge them.
To start hacking on Hydra, run:
$ nix-shell
$ ./configure $configureFlags --prefix=/opt/hydra
$ make
$ make install
Or, if you just want to build from source (on x86_64-linux):
$ nix-build -A build.x86_64-linux release.nix
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