Privileged builds

It is never recommended to invoke a build with elevated (e.g. root) privileges. A builder invoking in an elevated environment runs the risk of a misconfigured releng-tool project dirtying or destroying the builder's host environment.

releng-tool will generate a warning when an elevated run has been detected. For certain cases when using a container image that operates in a single-user mode, the image can define the environment variable RELENG_IGNORE_RUNNING_AS_ROOT to suppress these warnings.