DS-Client service fails to start with 'Address is in use (ds-user, UDP)' port error

DS-Client service fails to start with 'Address is in use (ds-user, UDP)' port error

Machine-distilled from a resolved support ticket on 2026-09-28. Source ref: eb3641edeae4. Verify before relying on it.

Applies to: DS-Client on Windows (version not specified in the source ticket)

Symptom: The DS-Client service will not start, so scheduled backups stop running. The Windows Event Viewer shows 'Failed to open ports (Address is in use (ds-user, UDP))'. It may also show a message saying there is no free space on the disk(s) hosting the DS-Client database, even though the disk has plenty of free space.

Cause: Another process is already holding the port the DS-Client needs to start (port 4403, ds-user). This is most likely a leftover DS-Client process from an earlier unclean stop. The disk space message is a misleading secondary error. The port conflict is the real reason the service cannot start.

Resolution: 1. Check that the database disk really has free space. If it does, treat the disk space message as a red herring and focus on the port error.

2. Reboot the DS-Client machine (out of hours if needed). This frees the held port.

3. After the reboot, check that the DS-Client service and the DS-Client-PostgreSQL service have both started cleanly.

4. Check that scheduled backups run again.

5. If the same port error comes back after the reboot, open an administrator command prompt and run: netstat -ano | findstr 4403

6. Note the process ID (PID) shown by that command, then look it up in Task Manager or with tasklist to find which process is holding the port. Stop that process, or reconfigure it, then start the DS-Client service again.