nix/doc/manual/rl-next/nix-copy-flags.md

synopsis	prs
`nix copy` supports `--profile` and `--out-link`	11657

The nix copy command now has flags --profile and --out-link, similar to nix build. --profile makes a profile point to the top-level store path, while --out-link create symlinks to the top-level store paths.

For example, when updating the local NixOS system profile from a NixOS system closure on a remote machine, instead of

# nix copy --from ssh://server $path
# nix build --profile /nix/var/nix/profiles/system $path

you can now do

# nix copy --from ssh://server --profile /nix/var/nix/profiles/system $path

The advantage is that this avoids a time window where path is not a garbage collector root, and so could be deleted by a concurrent nix store gc process.