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# Name
`nix-store --realise` - realise specified store paths
# Synopsis
`nix-store` {`--realise` | `-r`} *paths…* [`--dry-run`]
# Description
The operation `--realise` essentially “builds” the specified store
paths. Realisation is a somewhat overloaded term:
- If the store path is a *derivation*, realisation ensures that the
output paths of the derivation are [valid] (i.e.,
the output path and its closure exist in the file system). This
can be done in several ways. First, it is possible that the
outputs are already valid, in which case we are done
immediately. Otherwise, there may be [substitutes]
that produce the outputs (e.g., by downloading them). Finally, the
outputs can be produced by running the build task described
by the derivation.
- If the store path is not a derivation, realisation ensures that the
specified path is valid (i.e., it and its closure exist in the file
system). If the path is already valid, we are done immediately.
Otherwise, the path and any missing paths in its closure may be
produced through substitutes. If there are no (successful)
substitutes, realisation fails.
[valid]: @docroot@/glossary.md#gloss-validity
[substitutes]: @docroot@/glossary.md#gloss-substitute
The output path of each derivation is printed on standard output. (For
non-derivations argument, the argument itself is printed.)
The following flags are available:
- `--dry-run`\
Print on standard error a description of what packages would be
built or downloaded, without actually performing the operation.
- `--ignore-unknown`\
If a non-derivation path does not have a substitute, then silently
ignore it.
- `--check`\
This option allows you to check whether a derivation is
deterministic. It rebuilds the specified derivation and checks
whether the result is bitwise-identical with the existing outputs,
printing an error if that’s not the case. The outputs of the
specified derivation must already exist. When used with `-K`, if an
output path is not identical to the corresponding output from the
previous build, the new output path is left in
`/nix/store/name.check.`
{{#include ../status-build-failure.md}}
{{#include ./opt-common.md}}
{{#include ../opt-common.md}}
{{#include ../env-common.md}}
# Examples
This operation is typically used to build [store derivation]s produced by
[`nix-instantiate`](@docroot@/command-ref/nix-instantiate.md):
[store derivation]: @docroot@/glossary.md#gloss-store-derivation
```console
$ nix-store --realise $(nix-instantiate ./test.nix)
/nix/store/31axcgrlbfsxzmfff1gyj1bf62hvkby2-aterm-2.3.1
```
This is essentially what [`nix-build`](@docroot@/command-ref/nix-build.md) does.
To test whether a previously-built derivation is deterministic:
```console
$ nix-build '<nixpkgs>' --attr hello --check -K
```
Use [`nix-store --read-log`](./read-log.md) to show the stderr and stdout of a build:
```console
$ nix-store --read-log $(nix-instantiate ./test.nix)
```
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