nologin: add page (#2943)

pages/linux/nologin.md

@@ -0,0 +1,11 @@
+# nologin
+
+> Alternative shell that prevents a user from logging in.
+
+- Set a user's login shell to `nologin` to prevent the user from logging in:
+
+`chsh -s {{user}} nologin`
+
+- Customize message for users with the login shell of `nologin`:
+
+`echo "{{declined_login_message}}" > /etc/nologin.txt`