option

system.stateVersion

Every once in a while, a new NixOS release may change configuration defaults in a way incompatible with stateful data. For instance, if the default version of PostgreSQL changes, the new version will probably be unable to read your existing databases. To prevent such breakage, you can set the value of this option to the NixOS release with which you want to be compatible. The effect is that NixOS will option defaults corresponding to the specified release (such as using an older version of PostgreSQL).

Declarations
Type
signed integer
Default
4