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220 lines
9.3 KiB
Markdown
220 lines
9.3 KiB
Markdown
# Common Options
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Most Nix commands accept the following command-line options:
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- [`--help`]{#opt-help}\
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Prints out a summary of the command syntax and exits.
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- [`--version`]{#opt-version}\
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Prints out the Nix version number on standard output and exits.
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- [`--verbose`]{#opt-verbose} / `-v`\
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Increases the level of verbosity of diagnostic messages printed on
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standard error. For each Nix operation, the information printed on
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standard output is well-defined; any diagnostic information is
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printed on standard error, never on standard output.
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This option may be specified repeatedly. Currently, the following
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verbosity levels exist:
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- 0\
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“Errors only”: only print messages explaining why the Nix
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invocation failed.
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- 1\
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“Informational”: print *useful* messages about what Nix is
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doing. This is the default.
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- 2\
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“Talkative”: print more informational messages.
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- 3\
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“Chatty”: print even more informational messages.
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- 4\
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“Debug”: print debug information.
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- 5\
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“Vomit”: print vast amounts of debug information.
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- [`--quiet`]{#opt-quiet}\
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Decreases the level of verbosity of diagnostic messages printed on
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standard error. This is the inverse option to `-v` / `--verbose`.
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This option may be specified repeatedly. See the previous verbosity
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levels list.
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- [`--log-format`]{#opt-log-format} *format*\
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This option can be used to change the output of the log format, with
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*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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- [`--no-build-output`]{#opt-no-build-output} / `-Q`\
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By default, output written by builders to standard output and
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standard error is echoed to the Nix command's standard error. This
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option suppresses this behaviour. Note that the builder's standard
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output and error are always written to a log file in
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`prefix/nix/var/log/nix`.
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- [`--max-jobs`]{#opt-max-jobs} / `-j` *number*\
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Sets the maximum number of build jobs that Nix will perform in
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parallel to the specified number. Specify `auto` to use the number
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of CPUs in the system. The default is specified by the `max-jobs`
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configuration setting, which itself defaults to `1`. A higher
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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
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useful when you want builds to happen only on remote builders.
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- [`--cores`]{#opt-cores}\
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Sets the value of the `NIX_BUILD_CORES` environment variable in
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the invocation of builders. Builders can use this variable at
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their discretion to control the maximum amount of parallelism. For
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instance, in Nixpkgs, if the derivation attribute
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`enableParallelBuilding` is set to `true`, the builder passes the
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`-jN` flag to GNU Make. It defaults to the value of the `cores`
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configuration setting, if set, or `1` otherwise. The value `0`
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means that the builder should use all available CPU cores in the
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system.
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- [`--max-silent-time`]{#opt-max-silent-time}\
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Sets the maximum number of seconds that a builder can go without
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producing any data on standard output or standard error. The
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default is specified by the `max-silent-time` configuration
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setting. `0` means no time-out.
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- [`--timeout`]{#opt-timeout}\
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Sets the maximum number of seconds that a builder can run. The
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default is specified by the `timeout` configuration setting. `0`
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means no timeout.
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- [`--keep-going`]{#opt-keep-going} / `-k`\
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Keep going in case of failed builds, to the greatest extent
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possible. That is, if building an input of some derivation fails,
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Nix will still build the other inputs, but not the derivation
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itself. Without this option, Nix stops if any build fails (except
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for builds of substitutes), possibly killing builds in progress (in
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case of parallel or distributed builds).
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- [`--keep-failed`]{#opt-keep-failed} / `-K`\
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Specifies that in case of a build failure, the temporary directory
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(usually in `/tmp`) in which the build takes place should not be
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deleted. The path of the build directory is printed as an
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informational message.
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- [`--fallback`]{#opt-fallback}\
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Whenever Nix attempts to build a derivation for which substitutes
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are known for each output path, but realising the output paths
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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
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registered substitutes in order to perform binary distribution from,
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say, a network repository. If the repository is down, the
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realisation of the derivation will fail. When this option is
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specified, Nix will build the derivation instead. Thus, installation
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from binaries falls back on installation from source. This option is
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not the default since it is generally not desirable for a transient
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failure in obtaining the substitutes to lead to a full build from
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source (with the related consumption of resources).
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- [`--readonly-mode`]{#opt-readonly-mode}\
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When this option is used, no attempt is made to open the Nix
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database. Most Nix operations do need database access, so those
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operations will fail.
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- [`--arg`]{#opt-arg} *name* *value*\
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This option is accepted by `nix-env`, `nix-instantiate`,
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`nix-shell` and `nix-build`. When evaluating Nix expressions, the
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expression evaluator will automatically try to call functions that
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it encounters. It can automatically call functions for which every
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argument has a [default
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value](../expressions/language-constructs.md#functions) (e.g.,
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`{ argName ? defaultValue }: ...`). With `--arg`, you can also
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call functions that have arguments without a default value (or
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override a default value). That is, if the evaluator encounters a
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function with an argument named *name*, it will call it with value
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*value*.
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For instance, the top-level `default.nix` in Nixpkgs is actually a
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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 -iA
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pkgname`), the function will be called automatically using the
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value [`builtins.currentSystem`](../expressions/builtins.md) for
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the `system` argument. You can override this using `--arg`, e.g.,
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`nix-env -iA pkgname --arg system \"i686-freebsd\"`. (Note that
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since the argument is a Nix string literal, you have to escape the
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quotes.)
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- [`--argstr`]{#opt-argstr} *name* *value*\
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This option is like `--arg`, only the value is not a Nix
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expression but a string. So instead of `--arg system
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\"i686-linux\"` (the outer quotes are to keep the shell happy) you
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can say `--argstr system i686-linux`.
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- [`--attr`]{#opt-attr} / `-A` *attrPath*\
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Select an attribute from the top-level Nix expression being
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evaluated. (`nix-env`, `nix-instantiate`, `nix-build` and
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`nix-shell` only.) The *attribute path* *attrPath* is a sequence
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of attribute names separated by dots. For instance, given a
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top-level Nix expression *e*, the attribute path `xorg.xorgserver`
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would cause the expression `e.xorg.xorgserver` to be used. See
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[`nix-env --install`](nix-env.md#operation---install) for some
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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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- [`--expr`]{#opt-expr} / `-E`\
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Interpret the command line arguments as a list of Nix expressions to
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be parsed and evaluated, rather than as a list of file names of Nix
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expressions. (`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
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which you can build the packages returned by the expression. If you
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want to get a shell which contain the *built* packages ready for
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use, give your expression to the `nix-shell -p` convenience flag
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instead.
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- [`-I`]{#opt-I} *path*\
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Add a path to the Nix expression search path. This option may be
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given multiple times. See the `NIX_PATH` environment variable for
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information on the semantics of the Nix search path. Paths added
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through `-I` take precedence over `NIX_PATH`.
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- [`--option`]{#opt-option} *name* *value*\
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Set the Nix configuration option *name* to *value*. This overrides
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settings in the Nix configuration file (see nix.conf5).
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- [`--repair`]{#opt-repair}\
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Fix corrupted or missing store paths by redownloading or rebuilding
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them. Note that this is slow because it requires computing a
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cryptographic hash of the contents of every path in the closure of
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the build. Also note the warning under `nix-store --repair-path`.
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