Option A: Remove the Serial Port (if unused)
Option B: Configure it to Connect at Power On
If you want the port active but connected to nothing (to suppress the warning), you must trick VMware into thinking it has a valid backing: virtual device serial0 will start disconnected
The VM will now think it has a valid serial port and will not log the disconnected warning.
Option C: Use Named Pipe to Nowhere (Advanced) Option A: Remove the Serial Port (if unused)
For most users: No. The warning is completely harmless.
For certain users: Yes, you need to address it. Option B: Configure it to Connect at Power
You should fix this if:
A student attempted to build a Frame Relay switch using a Cisco 3640 in GNS3. After configuring the Frame Relay map statements and inverse ARP, the PVCs remained inactive. The student spent six hours checking DLCI numbers and encapsulation types.
The root cause? The console log from boot clearly showed: "Virtual device serial0 will start disconnected" and "Virtual device serial1 will start disconnected". The student had never connected the cables from the router to the Frame Relay switch.
Moral of the story: Always read the console boot messages. That "disconnected" line is not a warning; it is a direct status report.