diff --git a/Makefile b/Makefile
index 08372ea..0ee66a2 100644
--- a/Makefile
+++ b/Makefile
@@ -81,7 +81,7 @@ else ifneq (,$(filter $(I),base lang))
 ifeq ($(I),lang)
 	@: $${L}
 endif
-	docker run -it --rm --hostname $(I) -v $(VOLUME_MOUNT):/src --label riju-install-target=yes $(SHELL_PORTS) $(SHELL_ENV) $(IMAGE_HASH) riju:$(LANG_TAG) $(BASH_CMD)
+	docker run -it --rm --hostname $(LANG_TAG) -v $(VOLUME_MOUNT):/src --label riju-install-target=yes $(SHELL_PORTS) $(SHELL_ENV) $(IMAGE_HASH) riju:$(LANG_TAG) $(BASH_CMD)
 else ifeq ($(I),runtime)
 	docker run -it --rm --hostname $(I) -v $(VOLUME_MOUNT):/src -v /var/run/docker.sock:/var/run/docker.sock $(SHELL_PORTS) $(SHELL_ENV) $(IMAGE_HASH) riju:$(I) $(BASH_CMD)
 else
diff --git a/backend/langs.js b/backend/langs.js
index 63716b0..f477050 100644
--- a/backend/langs.js
+++ b/backend/langs.js
@@ -13,10 +13,9 @@ export let langs = {};
 // Map from language aliases and IDs to canonical language IDs.
 export let aliases = {};
 
-// Read languages from JSON files in /opt/riju/langs, and update the
-// global langs variable in this module. Never throw an error. If
-// there is a problem then just leave the languages as they previously
-// were.
+// Read languages from YAML, and update the global langs variable in
+// this module. Never throw an error. If there is a problem then just
+// leave the languages as they previously were.
 async function updateLangsFromDisk() {
   try {
     const newLangs = {};
diff --git a/backend/sandbox.bash b/backend/sandbox.bash
index a08e84d..8c6f6ec 100644
--- a/backend/sandbox.bash
+++ b/backend/sandbox.bash
@@ -5,10 +5,13 @@ if [[ -z "$L" ]]; then
     exit 1
 fi
 
-cfg="$(< "/opt/riju/langs/$L.json")" || exit 1
+if [[ -z "$LANG_CONFIG" ]]; then
+    echo 'environment variable unset: $LANG_CONFIG' >&2
+    exit 1
+fi
 
 function get {
-    jq -r ".$1" <<< "${cfg}"
+    jq -r ".$1" <<< "${LANG_CONFIG}"
 }
 
 function has {
diff --git a/backend/sandbox.js b/backend/sandbox.js
index a89d79e..19fb2fd 100644
--- a/backend/sandbox.js
+++ b/backend/sandbox.js
@@ -2,14 +2,17 @@ import { spawn } from "child_process";
 import { promises as fs } from "fs";
 import process from "process";
 
+import pty from "node-pty";
 import { quote } from "shell-quote";
 
-import { getUUID } from "./util.js";
-
+import { readLangConfig } from "../lib/yaml.js";
 import {
-  privilegedSetup,
-  privilegedSpawn,
-  privilegedTeardown,
+  bash,
+  getUUID,
+  privilegedExec,
+  privilegedPty,
+  privilegedSession,
+  privilegedWait,
   run,
 } from "./util.js";
 
@@ -28,22 +31,40 @@ async function main() {
   if (!lang) {
     die("environment variable unset: $L");
   }
+  const langConfig = await readLangConfig(lang);
   const uuid = getUUID();
-  await run(privilegedSetup({ uuid }), log);
-  const args = privilegedSpawn({ uuid }, [
-    "bash",
-    "-c",
-    `exec env L='${lang}' bash --rcfile <(cat <<< ${quote([sandboxScript])})`,
-  ]);
+  console.log(`Starting session with UUID ${uuid}`);
+  const sessionArgs = privilegedSession({ uuid, lang });
+  const session = pty.spawn(sessionArgs[0], sessionArgs.slice(1), {
+    name: "xterm-color",
+  });
+  await run(privilegedWait({ uuid }), log);
+  console.log(
+    bash(
+      `env L='${lang}' LANG_CONFIG=${quote([
+        JSON.stringify(langConfig),
+      ])} bash --rcfile <(cat <<< ${quote([sandboxScript])})`
+    )[2]
+  );
+  const args = privilegedPty(
+    { uuid },
+    bash(
+      `env L='${lang}' LANG_CONFIG=${quote([
+        JSON.stringify(langConfig),
+      ])} bash --rcfile <(cat <<< ${quote([sandboxScript])})`
+    )
+  );
   const proc = spawn(args[0], args.slice(1), {
     stdio: "inherit",
   });
-  await new Promise((resolve, reject) => {
-    proc.on("error", reject);
-    proc.on("close", resolve);
-  });
-  await run(privilegedTeardown({ uuid }), log);
-  await returnUser();
+  try {
+    await new Promise((resolve, reject) => {
+      proc.on("error", reject);
+      proc.on("close", resolve);
+    });
+  } finally {
+    session.kill();
+  }
 }
 
 main().catch(die);