bootupd: add --pty when stdin is a terminal

From Colin's pointer:
`systemd-run` breaks when forwarding a physical (`/dev/tty*` with
label `tty_device_t`) as opposed to virtual console (`/dev/pts`
with label `user_devpts_t`).
When stdin is a terminal, we should definitely use `-t`.

Fixes #902

Author: HuijingHei

src/cli/bootupctl.rs

@@ -179,8 +179,15 @@ fn ensure_running_in_systemd() -> Result<()> {
             .stderr(Stdio::null())
             .spawn()?
             .wait()?;
+        let mut systemd_args = SYSTEMD_ARGS_BOOTUPD.to_vec();
+        // we need --pty when detect that stdin is a terminal
+        // see discussion in https://github.com/coreos/bootupd/issues/902#issuecomment-2794680163
+        let tty_path = std::fs::read_link("/proc/self/fd/0")?;
+        if tty_path.starts_with("/dev/tty") {
+            systemd_args.push("--pty");
+        }
         let r = Command::new("systemd-run")
-            .args(SYSTEMD_ARGS_BOOTUPD)
+            .args(&systemd_args)
             .args(
                 SYSTEMD_PROPERTIES
                     .into_iter()