diff --git a/modules/base.nix b/modules/base.nix
index 41550e6..0d507a7 100644
--- a/modules/base.nix
+++ b/modules/base.nix
@@ -4,11 +4,13 @@
 
 { lib, pkgs, config, ...}:
 let
-  inherit (lib) mkEnableOption mkOption types isDerivation hasAttr ;
+  inherit (lib) mkEnableOption mkOption types isDerivation hasAttr concatStringsSep;
   inherit (pkgs.pseudofile) dir symlink;
   inherit (pkgs.liminix.networking) address interface;
   inherit (pkgs.liminix.services) bundle;
 
+  # TODO: escape shell argument.
+  exportVar = name: value: "export ${name}=\"${value}\"";
   type_service = pkgs.liminix.lib.types.service;
 
 in {
@@ -22,6 +24,24 @@ in {
           /run/current-system, we just add the paths in /etc/profile
         '';
       };
+
+      environmentVariables = mkOption {
+        type = types.attrsOf types.str;
+        description = ''
+          Attribute set of environment variables to make available
+          in a login shell.
+
+          The value is assumed to be escaped and the name to be valid.
+        '';
+      };
+
+      prompt = mkOption {
+        type = types.str;
+        default = "$(whoami)@$(hostname) # ";
+        description = ''
+          Prompt string (PS1) for the shell.
+        '';
+      };
     };
     services = mkOption {
       type = types.attrsOf type_service;
@@ -111,6 +131,8 @@ in {
 
     defaultProfile.packages = with pkgs;
       [ s6 s6-init-bin execline s6-linux-init s6-rc ];
+    # Set the useful PS1 prompt by default.
+    defaultProfile.environmentVariables.PS1 = lib.mkDefault config.defaultProfile.prompt;
 
     boot.commandLine = [
       "panic=10 oops=panic init=/bin/init loglevel=8"
@@ -181,9 +203,10 @@ in {
       etc = let
         profile = symlink
           (pkgs.writeScript ".profile" ''
-           PATH=${lib.makeBinPath config.defaultProfile.packages}:/bin
+            PATH=${lib.makeBinPath config.defaultProfile.packages}:/bin
             export PATH
-            '');
+            ${concatStringsSep "\n" (map exportVar config.defaultProfile.environmentVariables)}
+          '');
       in dir {
         inherit profile;
         ashrc = profile;