serial: T7484: treat unavailable serial console devices as non-fatal

Instead of failing or starting agetty on an invalid device, we now check
whether the specified serial console device is a valid TTY. If it's not, we
display a warning to the user and skip starting the agetty process.

1 files changed, 13 insertions, 0 deletions

diff --git a/python/vyos/utils/serial.py b/python/vyos/utils/serial.py
index 68aad676e..36b483e91 100644
--- a/python/vyos/utils/serial.py
+++ b/python/vyos/utils/serial.py
@@ -116,3 +116,16 @@ def restart_login_consoles(prompt_user=False, quiet=True, devices: List[str]=[])
             cmd(f'systemctl stop {unit_name}')
 
     return True
+
+def is_tty(name: str) -> bool:
+    """ Check if a given device file (e.g. /dev/ttyS0) is a TTY (teletypewriter)
+    device in Linux
+    """
+    import os
+    path_tty = f'/dev/{name}'
+    if os.path.exists(path_tty):
+        with open(path_tty, 'rb') as f:
+            fd = f.fileno()
+            # True if filename is a TTY
+            return os.isatty(fd)
+    return False