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nix/doc/manual/src/command-ref/nix-store/optimise.md
Alexander Bantyev 36b059748d Split nix-env and nix-store documentation per-subcommand
Documentation on "classic" commands with many sub-commands are
notoriously hard to discover due to lack of overview and anchor links.
Additionally the information on common options and environment variables
is not accessible offline in man pages, and therefore often overlooked
by readers.

With this change, each sub-command of nix-store and nix-env gets its
own page in the manual (listed in the table of contents), and each own
man page.

Also, man pages for each subcommand now (again) list common options
and environment variables. While this makes each page quite long and
some common parameters don't apply, this should still make it easier
to navigate as that additional information was not accessible on the
command line at all.

It is now possible to run 'nix-store --<subcommand> --help` to display
help pages for the given subcommand.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
2023-03-30 09:46:28 +02:00

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Markdown

# Name
`nix-store --optimise` - reduce disk space usage
## Synopsis
`nix-store` `--optimise`
## Description
The operation `--optimise` reduces Nix store disk space usage by finding
identical files in the store and hard-linking them to each other. It
typically reduces the size of the store by something like 25-35%. Only
regular files and symlinks are hard-linked in this manner. Files are
considered identical when they have the same NAR archive serialisation:
that is, regular files must have the same contents and permission
(executable or non-executable), and symlinks must have the same
contents.
After completion, or when the command is interrupted, a report on the
achieved savings is printed on standard error.
Use `-vv` or `-vvv` to get some progress indication.
{{#include ./opt-common.md}}
{{#include ../opt-common.md}}
{{#include ../env-common.md}}
## Example
```console
$ nix-store --optimise
hashing files in `/nix/store/qhqx7l2f1kmwihc9bnxs7rc159hsxnf3-gcc-4.1.1'
...
541838819 bytes (516.74 MiB) freed by hard-linking 54143 files;
there are 114486 files with equal contents out of 215894 files in total
```