--verbose / -v Increases the level of verbosity of diagnostic messages printed on standard error. For each Nix operation, the information printed on standard output is well-defined; any diagnostic information is printed on standard error, never on standard output. This option may be specified repeatedly. Currently, the following verbosity levels exist: 0 Errors only: only print messages explaining why the Nix invocation failed. 1 Informational: print useful messages about what Nix is doing. 2 Talkative: print more informational messages. 3 Chatty: print even more informational messages. 4 Debug: print debug information: 5 Vomit: print vast amounts of debug information.