diff --git a/private_dot_config/private_fish/config.fish.tmpl b/private_dot_config/private_fish/config.fish.tmpl
index 625836a..5d1f2e4 100644
--- a/private_dot_config/private_fish/config.fish.tmpl
+++ b/private_dot_config/private_fish/config.fish.tmpl
@@ -121,4 +121,9 @@ if status is-interactive
     if type -q direnv
         direnv hook fish | source
     end
+
+    # run tmux session
+    if not set -q TMUX
+      tmux attach -t build; or tmux new -s build
+    end
 end