nixos/doc: Add chapter “necessary system state”

Suggested in the discussion of #268995.

1 files changed, 13 insertions, 0 deletions

diff --git a/nixos/doc/manual/administration/nixos-state.section.md b/nixos/doc/manual/administration/nixos-state.section.md
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+# NixOS {#sec-nixos-state}
+
+NixOS itself obviously needs `/nix` to be persistent, so the system environment
+can be linked from the nix store during activation.
+
+Moreover, `/boot` should also be persistent, as it contains the kernel, initrd,
+and the command-line determining the system environment's path in the nix store.
+
+Lastly, `users.mutableUsers` should be false, *or* the following files under
+`/etc` should all persist:
+- {manpage}`passwd(5)` and {manpage}`group(5)`,
+- {manpage}`shadow(5)` and {manpage}`gshadow(5)`,
+- {manpage}`subuid(5)` and {manpage}`subgid(5)`.