`dataDir` is a an option present in all the services, allowing users to specify the directory where a given service will store its data files. Essentially, it is to persist the state of the service even when you exit the `process-compose` window.
The `dataDir` of these services tend to take *relative* paths, which are usually relative to the project root. As such, when you run these services using `nix run`, their data files are created relative to whichever directory you are in. If you want these data files to always reside relative to the project directory, instead of using `nix run` consider wrapping the process-compose packages in script, via either [mission-control](https://community.flake.parts/mission-control) module or a [justfile](https://just.systems/). `services-flake` uses the latter.
{#default-structure}
## Default data directory structure
Let's say your project defines the following services:
Some services create unix domain socket files under the data directory. As the unix socket length is limited to [about 100 chars](https://linux.die.net/man/7/unix), if your data directory is nested too deep, you will have to set `dataDir` option of the service to a shorter path as a workaround.