Store UID in env and run self-check with that UID

src/cli/mod.rs

@@ -133,6 +133,16 @@ pub fn ensure_root() -> eyre::Result<()> {
             env_list.push("NIX_INSTALLER_CI=1".to_string());
         }
 
+        // Record the current user's UID so that we can run the self-tests as this user.
+        // This works around issues where root users have a shell profile / config file that e.g.
+        // runs `mesg n` (which changes the permissions of `/dev/tty` and prevents SSH from doing
+        // certain things), as happens with Ubuntu 24.04.
+        // https://github.com/DeterminateSystems/nix-installer/issues/1412
+        env_list.push(format!(
+            "NIX_INSTALLER_CURRENT_UID={}",
+            nix::unistd::Uid::current()
+        ));
+
         if !env_list.is_empty() {
             arg_vec_cstring
                 .push(CString::new("env").wrap_err("Building a `env` argument for `sudo`")?);

src/self_test.rs

@@ -77,17 +77,24 @@ impl Shell {
     #[tracing::instrument(skip_all)]
     pub async fn self_test(&self) -> Result<(), SelfTestError> {
         let executable = self.executable();
-        let mut command = match &self {
-            // On Mac, `bash -ic nix` won't work, but `bash -lc nix` will.
+
+        let mut command = if let Ok(uid) = std::env::var("NIX_INSTALLER_CURRENT_UID") {
+            let mut command = Command::new("sudo");
+            command.arg("-u");
+            command.arg(format!("#{uid}"));
+            command.arg(executable);
+            command
+        } else {
+            Command::new(executable)
+        };
+
+        match &self {
+            // On macOS and Ubuntu (at least), `bash -ic nix` won't work, but `bash -lc nix` will.
             Shell::Sh | Shell::Bash => {
-                let mut command = Command::new(executable);
                 command.arg("-lc");
-                command
             },
             Shell::Zsh | Shell::Fish => {
-                let mut command = Command::new(executable);
                 command.arg("-ic");
-                command
             },
         };