diff --git a/config.nix b/config.nix
index 87644a2b..d07280fd 100644
--- a/config.nix
+++ b/config.nix
@@ -33,15 +33,16 @@ let
         ];
 
       launchd.daemons.nix-daemon =
-        { serviceConfig.Program = "/nix/var/nix/profiles/default/bin/nix-daemon";
+        { serviceConfig.Program = "${pkgs.nix}/bin/nix-daemon";
           serviceConfig.KeepAlive = true;
           serviceConfig.RunAtLoad = true;
-          serviceConfig.EnvironmentVariables.SSL_CERT_FILE = "/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt";
+          serviceConfig.EnvironmentVariables.SSL_CERT_FILE = "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt";
           serviceConfig.EnvironmentVariables.TMPDIR = "/nix/tmp";
           serviceConfig.SoftResourceLimits.NumberOfFiles = 4096;
           serviceConfig.ProcessType = "Background";
         };
 
+      programs.tmux.loginShell = "${pkgs.zsh}/bin/zsh";
       programs.tmux.enableSensible = true;
       programs.tmux.enableMouse = true;
       programs.tmux.enableVim = true;
@@ -49,14 +50,16 @@ let
       environment.variables.EDITOR = "vim";
       environment.variables.HOMEBREW_CASK_OPTS = "--appdir=/Applications/cask";
 
-      environment.variables.GIT_SSL_CAINFO = "/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt";
-      environment.variables.SSL_CERT_FILE = "/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt";
+      environment.variables.GIT_SSL_CAINFO = "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt";
+      environment.variables.SSL_CERT_FILE = "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt";
 
       environment.shellAliases.l = "ls -lh";
       environment.shellAliases.ls = "ls -G";
+      environment.shellAliases.tmux = "${pkgs.tmux}/bin/tmux -f ${config.environment.etc."tmux.conf".source}";
+      environment.shellAliases.zsh = "${pkgs.zsh}/bin/zsh";
 
       environment.etc."tmux.conf".text = ''
-        source-file ${config.system.build.setTmuxOptions}
+        ${config.programs.tmux.config}
         bind 0 set status
 
         set -g status-bg black
@@ -100,6 +103,9 @@ let
 
         export NIX_PATH=nixpkgs=$HOME/.nix-defexpr/nixpkgs
 
+        typeset -U NIX_PATH
+        typeset -U PATH
+
         # Set up secure multi-user builds: non-root users build through the
         # Nix daemon.
         if [ "$USER" != root -a ! -w /nix/var/nix/db ]; then
@@ -107,13 +113,13 @@ let
         fi
 
         nixdarwin-rebuild () {
-          case $1 in
-            'build')  nix-build --no-out-link '<nixpkgs>' -A nixdarwin.toplevel ;;
-            'repl')   nix-repl "$HOME/.nixpkgs/config.nix" ;;
-            'shell')  nix-shell '<nixpkgs>' -p nixdarwin.toplevel --run "zsh -l" ;;
-            'switch') nix-env -f '<nixpkgs>' -iA nixdarwin.toplevel && nix-shell '<nixpkgs>' -A nixdarwin.toplevel --run 'sudo $out/activate'  && exec zsh -l ;;
-            "")       return 1 ;;
-          esac
+            case $1 in
+                'build')  nix-build --no-out-link '<nixpkgs>' -A nixdarwin.toplevel ;;
+                'repl')   nix-repl "$HOME/.nixpkgs/config.nix" ;;
+                'shell')  nix-shell '<nixpkgs>' -p nixdarwin.toplevel --run "${pkgs.zsh}/bin/zsh -l" ;;
+                'switch') nix-env -f '<nixpkgs>' -iA nixdarwin.toplevel && nix-shell '<nixpkgs>' -A nixdarwin.toplevel --run 'sudo $out/activate'  && exec ${pkgs.zsh}/bin/zsh -l ;;
+                "")       return 1 ;;
+            esac
         }
 
         source $HOME/.zshrc.local
diff --git a/modules/tmux.nix b/modules/tmux.nix
index 369e1c29..a983d19f 100644
--- a/modules/tmux.nix
+++ b/modules/tmux.nix
@@ -14,6 +14,14 @@ let
 in {
   options = {
 
+    programs.tmux.loginShell = mkOption {
+      type = types.path;
+      default = "$SHELL";
+      description = ''
+        Configure default login shell.
+      '';
+    };
+
     programs.tmux.enableSensible = mkOption {
       type = types.bool;
       default = false;
@@ -41,9 +49,16 @@ in {
       '';
     };
 
+    programs.tmux.config = mkOption {
+      type = types.lines;
+      description = ''
+        Configuration options.
+      '';
+    };
+
     programs.tmux.text = mkOption {
       internal = true;
-      type = types.attrsOf types.str;
+      type = types.attrsOf types.lines;
       default = {};
     };
 
@@ -51,8 +66,13 @@ in {
 
   config = {
 
-    system.build.setTmuxOptions = pkgs.writeText "set-tmux-options"
-      (lib.concatStringsSep "\n" tmuxConfigs);
+    programs.tmux.config = lib.concatStringsSep "\n" tmuxConfigs;
+
+    programs.tmux.text.login-shell = if stdenv.isDarwin then ''
+      set -g default-command "reattach-to-user-namespace -l ${cfg.loginShell}"
+    '' else ''
+      set -g default-command "${cfg.loginShell}"
+    '';
 
     programs.tmux.text.sensible = mkIf cfg.enableSensible (''
       set -g default-terminal "screen-256color"