Setting it to `0` disallows building on the local machine, which is useful when you want builds to happen only on remote builders.

- <span id="opt-cores">[`--cores`](#opt-cores)</span>

  Sets the value of the `NIX_BUILD_CORES` environment variable in the invocation of builders.
  Builders can use this variable at their discretion to control the maximum amount of parallelism.
  For instance, in Nixpkgs, if the derivation attribute `enableParallelBuilding` is set to `true`, the builder passes the `-jN` flag to GNU Make.
  It defaults to the value of the `cores` configuration setting, if set, or `1` otherwise.
  The value `0` means that the builder should use all available CPU cores in the system.

- <span id="opt-max-silent-time">[`--max-silent-time`](#opt-max-silent-time)</span>

  Sets the maximum number of seconds that a builder can go without producing any data on standard output or standard error.
  The default is specified by the `max-silent-time` configuration setting.
  `0` means no time-out.

- <span id="opt-timeout">[`--timeout`](#opt-timeout)</span>

  Sets the maximum number of seconds that a builder can run.
  The default is specified by the `timeout` configuration setting.
  `0` means no timeout.

- <span id="opt-keep-going">[`--keep-going`](#opt-keep-going)</span> / `-k`

  Keep going in case of failed builds, to the greatest extent possible.
  That is, if building an input of some derivation fails, Nix will still build the other inputs, but not the derivation itself.
  Without this option, Nix stops if any build fails (except for builds of substitutes), possibly killing builds in progress (in case of parallel or distributed builds).

- <span id="opt-keep-failed">[`--keep-failed`](#opt-keep-failed)</span> / `-K`

  Specifies that in case of a build failure, the temporary directory (usually in `/tmp`) in which the build takes place should not be deleted.
  The path of the build directory is printed as an informational message.

- <span id="opt-fallback">[`--fallback`](#opt-fallback)</span>

  Whenever Nix attempts to build a derivation for which substitutes are known for each output path, but realising the output paths through the substitutes fails, fall back on building the derivation.

  The most common scenario in which this is useful is when we have registered substitutes in order to perform binary distribution from, say, a network repository.
  If the repository is down, the realisation of the derivation will fail.
  When this option is specified, Nix will build the derivation instead.
  Thus, installation from binaries falls back on installation from source.
  This option is not the default since it is generally not desirable for a transient failure in obtaining the substitutes to lead to a full build from source (with the related consumption of resources).

- <span id="opt-readonly-mode">[`--readonly-mode`](#opt-readonly-mode)</span>

  When this option is used, no attempt is made to open the Nix database.
  Most Nix operations do need database access, so those operations will fail.

- <span id="opt-arg">[`--arg`](#opt-arg)</span> *name* *value*

  This option is accepted by `nix-env`, `nix-instantiate`, `nix-shell` and `nix-build`.
  When evaluating Nix expressions, the expression evaluator will automatically try to call functions that it encounters.
  It can automatically call functions for which every argument has a [default value](@docroot@/language/syntax.md#functions) (e.g., `{ argName ?  defaultValue }: ...`).

  With `--arg`, you can also call functions that have arguments without a default value (or override a default value).
  That is, if the evaluator encounters a function with an argument named *name*, it will call it with value *value*.

  For instance, the top-level `default.nix` in Nixpkgs is actually a function:

  ```nix
  { # The system (e.g., `i686-linux') for which to build the packages.
    system ? builtins.currentSystem