Multi-User fail if already has /nix

scripts/install-multi-user.sh

@@ -58,6 +58,7 @@ readonly EXTRACTED_NIX_PATH="$(dirname "$0")"
 
 readonly ROOT_HOME=~root
 
+
 if [ -t 0 ] && [ -z "${NIX_INSTALLER_YES:-}" ]; then
     readonly IS_HEADLESS='no'
 else
@@ -96,6 +97,12 @@ is_os_darwin() {
     fi
 }
 
+if [ -d "/nix" ]; then
+    echo "$(tput setaf 1)Error: /nix already exists on your system.$(tput sgr0)"
+    echo "$(tput setaf 2)To remove it, you can use the following command: sudo rm -rf /nix$(tput sgr0)"
+    exit 1
+fi
+
 contact_us() {
     echo "You can open an issue at"
     echo "https://github.com/NixOS/nix/issues/new?labels=installer&template=installer.md"