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a713476790
move together all syntactic and semantic information into one page, and add a page on data types, which in turn links to the syntax and semantics. also split out the note on scoping rules into its own page. Co-authored-by: Ryan Hendrickson <ryan.hendrickson@alum.mit.edu>
209 lines
9.7 KiB
Markdown
209 lines
9.7 KiB
Markdown
# Common Options
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Most Nix commands accept the following command-line options:
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- <span id="opt-help">[`--help`](#opt-help)</span>
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Prints out a summary of the command syntax and exits.
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- <span id="opt-version">[`--version`](#opt-version)</span>
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Prints out the Nix version number on standard output and exits.
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- <span id="opt-verbose">[`--verbose`](#opt-verbose)</span> / `-v`
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Increases the level of verbosity of diagnostic messages printed on standard error.
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For each Nix operation, the information printed on standard output is well-defined;
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any diagnostic information is printed on standard error, never on standard output.
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This option may be specified repeatedly.
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Currently, the following verbosity levels exist:
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- `0` “Errors only”
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Only print messages explaining why the Nix invocation failed.
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- `1` “Informational”
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Print *useful* messages about what Nix is doing.
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This is the default.
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- `2` “Talkative”
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Print more informational messages.
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- `3` “Chatty”
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Print even more informational messages.
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- `4` “Debug”
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Print debug information.
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- `5` “Vomit”
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Print vast amounts of debug information.
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- <span id="opt-quiet">[`--quiet`](#opt-quiet)</span>
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Decreases the level of verbosity of diagnostic messages printed on standard error.
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This is the inverse option to `-v` / `--verbose`.
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This option may be specified repeatedly.
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See the previous verbosity levels list.
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- <span id="opt-log-format">[`--log-format`](#opt-log-format)</span> *format*
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This option can be used to change the output of the log format, with *format* being one of:
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- `raw`
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This is the raw format, as outputted by nix-build.
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- `internal-json`
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Outputs the logs in a structured manner.
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> **Warning**
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>
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> While the schema itself is relatively stable, the format of
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> the error-messages (namely of the `msg`-field) can change
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> between releases.
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- `bar`
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Only display a progress bar during the builds.
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- `bar-with-logs`
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Display the raw logs, with the progress bar at the bottom.
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- <span id="opt-no-build-output">[`--no-build-output`](#opt-no-build-output)</span> / `-Q`
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By default, output written by builders to standard output and standard error is echoed to the Nix command's standard error.
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This option suppresses this behaviour.
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Note that the builder's standard output and error are always written to a log file in `prefix/nix/var/log/nix`.
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- <span id="opt-max-jobs">[`--max-jobs`](#opt-max-jobs)</span> / `-j` *number*
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Sets the maximum number of build jobs that Nix will perform in parallel to the specified number.
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Specify `auto` to use the number of CPUs in the system.
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The default is specified by the `max-jobs` configuration setting, which itself defaults to `1`.
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A higher value is useful on SMP systems or to exploit I/O latency.
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Setting it to `0` disallows building on the local machine, which is useful when you want builds to happen only on remote builders.
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- <span id="opt-cores">[`--cores`](#opt-cores)</span>
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Sets the value of the `NIX_BUILD_CORES` environment variable in the invocation of builders.
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Builders can use this variable at their discretion to control the maximum amount of parallelism.
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For instance, in Nixpkgs, if the derivation attribute `enableParallelBuilding` is set to `true`, the builder passes the `-jN` flag to GNU Make.
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It defaults to the value of the `cores` configuration setting, if set, or `1` otherwise.
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The value `0` means that the builder should use all available CPU cores in the system.
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- <span id="opt-max-silent-time">[`--max-silent-time`](#opt-max-silent-time)</span>
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Sets the maximum number of seconds that a builder can go without producing any data on standard output or standard error.
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The default is specified by the `max-silent-time` configuration setting.
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`0` means no time-out.
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- <span id="opt-timeout">[`--timeout`](#opt-timeout)</span>
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Sets the maximum number of seconds that a builder can run.
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The default is specified by the `timeout` configuration setting.
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`0` means no timeout.
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- <span id="opt-keep-going">[`--keep-going`](#opt-keep-going)</span> / `-k`
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Keep going in case of failed builds, to the greatest extent possible.
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That is, if building an input of some derivation fails, Nix will still build the other inputs, but not the derivation itself.
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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).
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- <span id="opt-keep-failed">[`--keep-failed`](#opt-keep-failed)</span> / `-K`
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Specifies that in case of a build failure, the temporary directory (usually in `/tmp`) in which the build takes place should not be deleted.
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The path of the build directory is printed as an informational message.
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- <span id="opt-fallback">[`--fallback`](#opt-fallback)</span>
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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.
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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.
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If the repository is down, the realisation of the derivation will fail.
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When this option is specified, Nix will build the derivation instead.
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Thus, installation from binaries falls back on installation from source.
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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).
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- <span id="opt-readonly-mode">[`--readonly-mode`](#opt-readonly-mode)</span>
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When this option is used, no attempt is made to open the Nix database.
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Most Nix operations do need database access, so those operations will fail.
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- <span id="opt-arg">[`--arg`](#opt-arg)</span> *name* *value*
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This option is accepted by `nix-env`, `nix-instantiate`, `nix-shell` and `nix-build`.
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When evaluating Nix expressions, the expression evaluator will automatically try to call functions that it encounters.
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It can automatically call functions for which every argument has a [default value](@docroot@/language/syntax.md#functions) (e.g., `{ argName ? defaultValue }: ...`).
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With `--arg`, you can also call functions that have arguments without a default value (or override a default value).
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That is, if the evaluator encounters a function with an argument named *name*, it will call it with value *value*.
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For instance, the top-level `default.nix` in Nixpkgs is actually a function:
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```nix
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{ # The system (e.g., `i686-linux') for which to build the packages.
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system ? builtins.currentSystem
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...
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}: ...
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```
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So if you call this Nix expression (e.g., when you do `nix-env --install --attr pkgname`), the function will be called automatically using the value [`builtins.currentSystem`](@docroot@/language/builtins.md) for the `system` argument.
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You can override this using `--arg`, e.g., `nix-env --install --attr pkgname --arg system \"i686-freebsd\"`.
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(Note that since the argument is a Nix string literal, you have to escape the quotes.)
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- <span id="opt-argstr">[`--argstr`](#opt-argstr)</span> *name* *value*
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This option is like `--arg`, only the value is not a Nix expression but a string.
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So instead of `--arg system \"i686-linux\"` (the outer quotes are to keep the shell happy) you can say `--argstr system i686-linux`.
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- <span id="opt-attr">[`--attr`](#opt-attr)</span> / `-A` *attrPath*
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Select an attribute from the top-level Nix expression being evaluated.
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(`nix-env`, `nix-instantiate`, `nix-build` and `nix-shell` only.)
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The *attribute path* *attrPath* is a sequence of attribute names separated by dots.
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For instance, given a top-level Nix expression *e*, the attribute path `xorg.xorgserver` would cause the expression `e.xorg.xorgserver` to be used.
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See [`nix-env --install`](@docroot@/command-ref/nix-env/install.md) for some concrete examples.
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In addition to attribute names, you can also specify array indices.
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For instance, the attribute path `foo.3.bar` selects the `bar`
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attribute of the fourth element of the array in the `foo` attribute
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of the top-level expression.
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- <span id="opt-expr">[`--expr`](#opt-expr)</span> / `-E`
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Interpret the command line arguments as a list of Nix expressions to be parsed and evaluated, rather than as a list of file names of Nix expressions.
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(`nix-instantiate`, `nix-build` and `nix-shell` only.)
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For `nix-shell`, this option is commonly used to give you a shell in which you can build the packages returned by the expression.
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If you want to get a shell which contain the *built* packages ready for use, give your expression to the `nix-shell --packages ` convenience flag instead.
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- <span id="opt-I">[`-I`](#opt-I)</span> *path*
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Add an entry to the [Nix expression search path](@docroot@/command-ref/conf-file.md#conf-nix-path).
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This option may be given multiple times.
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Paths added through `-I` take precedence over [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH).
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- <span id="opt-option">[`--option`](#opt-option)</span> *name* *value*
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Set the Nix configuration option *name* to *value*.
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This overrides settings in the Nix configuration file (see nix.conf5).
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- <span id="opt-repair">[`--repair`](#opt-repair)</span>
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Fix corrupted or missing store paths by redownloading or rebuilding them.
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Note that this is slow because it requires computing a cryptographic hash of the contents of every path in the closure of the build.
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Also note the warning under `nix-store --repair-path`.
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> **Note**
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>
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> See [`man nix.conf`](@docroot@/command-ref/conf-file.md#command-line-flags) for overriding configuration settings with command line flags.
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