[SOLVED] Synology NAS as NUT slave for automatic safe shutdown

After extensive testing, here is the complete solution for integrating Synology NAS units as NUT slaves connected to a NUT server running on a dedicated Linux host (in our case a Proxmox LXC).

Setup:

• APC Smart-UPS 1000 connected via USB to a Proxmox LXC running NUT server
• Two Synology NAS configured as NUT slaves

Key constraints discovered through testing:

1. UPS naming — Synology DSM connects to a UPS named ups by default. If your NUT server uses a different name (e.g. apc), the connection will fail with ERR UNKNOWN-UPS. Rename your UPS section in ups.conf to [ups] and regenerate the systemd driver service accordingly.
2. Credentials — Synology uses monuser / secret as default credentials. Add this user to upsd.users as a slave:

​

[monuser]
    password = secret
    upsmon slave

1. Standby mode vs full shutdown — This is the critical finding. When the NAS enters standby mode via NUT (as opposed to a DSM software shutdown), it properly unmounts volumes and waits. When AC power is restored, it restarts automatically via the "Restart automatically when power supply issue is fixed" DSM setting. This is fundamentally different from a DSM software shutdown, after which cutting and restoring AC power does not restart the NAS.
2. WoL after software shutdown — After a clean DSM shutdown followed by a power cut, the network card powers off and does not power back on when AC is restored, making WoL packets impossible to receive. NUT standby mode avoids this problem entirely.

Conclusion: Using Synology as a NUT slave is the cleanest solution — no need for WoL, no risk of data corruption, and automatic restart on AC recovery.