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doc/manual/source/command-ref/nix-env/delete-generations.md
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# Name

`nix-env --delete-generations` - delete profile generations

# Synopsis

`nix-env` `--delete-generations` *generations*

# Description

This operation deletes the specified generations of the current profile.

*generations* can be a one of the following:

- <span id="generations-list">[`<number>...`](#generations-list)</span>

  A list of generation numbers, each one a separate command-line argument.

  Delete exactly the profile generations given by their generation number.
  Deleting the current generation is not allowed.

- <span id="generations-old">[The special value `old`](#generations-old)</span>

  Delete all generations except the current one.

  > **WARNING**
  >
  > Older *and newer* generations will be deleted by this operation.
  >
  > One might expect this to just delete older generations than the current one, but that is only true if the current generation is also the latest.
  > Because one can roll back to a previous generation, it is possible to have generations newer than the current one.
  > They will also be deleted.

- <span id="generations-time">[`<number>d`](#generations-time)</span>

  The last *number* days

  *Example*: `30d`

  Delete all generations created more than *number* days ago, except the most recent one of them.
  This allows rolling back to generations that were available within the specified period.

- <span id="generations-count">[`+<number>`](#generations-count)</span>

  The last *number* generations up to the present

  *Example*: `+5`

  Keep the last *number* generations, along with any newer than current.

Periodically deleting old generations is important to make garbage collection
effective.
The is because profiles are also garbage collection roots — any [store object] reachable from a profile is "alive" and ineligible for deletion.


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# Examples

## Delete explicit generation numbers

```console
$ nix-env --delete-generations 3 4 8
```

Delete the generations numbered 3, 4, and 8, so long as the current active generation is not any of those.

## Keep most-recent by count (number of generations)

```console
$ nix-env --delete-generations +5
```

Suppose `30` is the current generation, and we currently have generations numbered `20` through `32`.

Then this command will delete generations `20` through `25` (`<= 30 - 5`),
and keep generations `26` through `31` (`> 30 - 5`).

## Keep most-recent by time (number of days)

```console
$ nix-env --delete-generations 30d
```

This command will delete all generations older than 30 days, except for the generation that was active 30 days ago (if it currently exists).

## Delete all older

```console
$ nix-env --profile other_profile --delete-generations old
```
Chunks
dfd9158b (1st chunk of `doc/manual/source/command-ref/nix-env/delete-generations.md`)
Title: nix-env --delete-generations: Deleting Nix Profile Generations
Summary
The `nix-env --delete-generations` command is used to remove specified generations from the current Nix profile. It offers several ways to select generations for deletion: by providing a list of specific generation numbers (excluding the current one), using the special value `old` to delete all generations except the current one (including those newer than the current if it's not the latest), specifying a time period like `30d` to delete generations older than a certain number of days (keeping the most recent of those), or using `+<number>` to keep only the most recent specified number of generations. Deleting old generations is crucial for effective garbage collection, as profiles act as garbage collection roots, preventing reachable store objects from being deleted.