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+Title: nix-collect-garbage
+
+# Name
+
+`nix-collect-garbage` - delete unreachable store paths
+
+# Synopsis
+
+`nix-collect-garbage` [`--delete-old`] [`-d`] [`--delete-older-than` *period*] [`--max-freed` *bytes*] [`--dry-run`]
+
+# Description
+
+The command `nix-collect-garbage` is mostly an alias of [`nix-store
+--gc`](nix-store.md#operation---gc), that is, it deletes all
+unreachable paths in the Nix store to clean up your system. However,
+it provides two additional options: `-d` (`--delete-old`), which
+deletes all old generations of all profiles in `/nix/var/nix/profiles`
+by invoking `nix-env --delete-generations old` on all profiles (of
+course, this makes rollbacks to previous configurations impossible);
+and `--delete-older-than` *period*, where period is a value such as
+`30d`, which deletes all generations older than the specified number
+of days in all profiles in `/nix/var/nix/profiles` (except for the
+generations that were active at that point in time).
+
+# Example
+
+To delete from the Nix store everything that is not used by the current
+generations of each profile, do
+
+```console
+$ nix-collect-garbage -d
+```