Should Rocky Linux Enable NetworkManager‑wait‑online.service or Rely on network‑online.target for Service Startup Ordering?

Enable NetworkManager-wait-online.service. On Rocky Linux 9, network-online.target is a passive target. Without an active wait service, it can be reached before interfaces have addresses, so After=network-online.target does not guarantee that your network stack is ready.

Confirmed facts

NetworkManager-wait-online.service actively holds network-online.target until NetworkManager reports that the configured links are up. This makes the target a real synchronization point. In contrast, Wants=network-online.target alone only pulls the target into the transaction; it does not enforce ordering. You need both Wants= (or Requires=) and After= on the target, plus the wait service, to get strict sequencing.

Likely explanation for intermittent failures

Services that declare After=network-online.target but start before IP assignment will see bind failures or AVC denials. The race is most visible when DHCP is slow or when multiple interfaces initialize out of order.

Boot-time cost

The added delay is not a fixed penalty. It equals the time NetworkManager needs to configure the links. Static or fast-configured interfaces add little; slow DHCP, bonding, or Wi-Fi can add seconds. Measure on your own hardware rather than assuming a universal number.

Rocky Linux 9 specifics

The unit is provided by the NetworkManager package, but its default enabled state can vary by installation image. Verify before assuming it is active. If you use systemd-networkd instead of NetworkManager, the equivalent is systemd-networkd-wait-online.service.

Verification

1. Confirm the unit is present and enabled:
   systemctl is-enabled NetworkManager-wait-online.service
2. Inspect its runtime state:
   systemctl status NetworkManager-wait-online.service
3. Check ordering and delay:
   systemd-analyze critical-chain network-online.target
systemd-analyze blame
4. Look for premature-start symptoms:
   journalctl -u your-service.service -b

Caveats

Reaching network-online.target does not guarantee full routability or DNS. Some services may still race with D-Bus or NetworkManager itself; order those dependencies explicitly if required. If your applications already retry connections internally, you can remove the target dependency and avoid the boot delay entirely.

If your critical services already implement robust connection retries, the wait service may be unnecessary; otherwise enable it.