DOKK / manpages / debian 13 / nix-bin / nix-env-delete-generations.1.en
nix-env --delete-generations(1) General Commands Manual nix-env --delete-generations(1)

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

nix-env --delete-generations generations

This operation deletes the specified generations of the current profile.

generations can be a one of the following:

•
<number>...
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.
•
The special value old
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 curent 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.
•
<number>d
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.
•
+<number>
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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$ 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.

$ 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).

$ 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).

$ nix-env --profile other_profile --delete-generations old