|nix-collect-garbage(1)||General Commands Manual||nix-collect-garbage(1)|
nix-collect-garbage - delete unreachable store paths
nix-collect-garbage [--delete-old] [-d] [--delete-older-than period] [--max-freed bytes] [--dry-run]
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).
To delete from the Nix store everything that is not used by the current generations of each profile, do
$ nix-collect-garbage -d