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diff --git a/doc/manual/src/architecture/store/relocatability.md b/doc/manual/src/architecture/store/relocatability.md new file mode 100644 index 000000000..c7f869135 --- /dev/null +++ b/doc/manual/src/architecture/store/relocatability.md @@ -0,0 +1,15 @@ +## Advanced Topic: Store object relocation + +Now that we know the fundamentals of the design of the Nix store, let's explore one consequence of that design: the question when it is permissible to relocate a store object to a store with a different mount point. + +Recall from the section on [store paths](./store-paths.md) that concrete store paths look like `<store-dir>/<hash>-<name>`. + +~~The two final restrictions of the previous section yield an alternative view of the same information.~~ +Rather than associating store dirs with the references, we can say a store object itself has a store dir if and only if it has at least one reference. + +This corresponds to the observation that a store object with references, i.e. with a store directory under this interpretation, is confined to stores sharing that same store directory, but a store object without any references, i.e. thus without a store directory, can exist in any store. + +Lastly, this illustrates the purpose of tracking self references. +Store objects without self-references or other references are relocatable, while store paths with self-references aren't. +This is used to tell apart e.g. source code which can be stored anywhere, and pesky non-reloctable executables which assume they are installed to a certain path. +\[The default method of calculating references by scanning for store paths handles these two example cases surprisingly well.\] |