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Start with the exact symptom and error
Write down the complete error text and note whether the viewer ever reaches a login prompt or desktop. RealVNC groups failures such as refusal, unreachable host, name resolution, authentication, and security negotiation separately; its remedies are not interchangeable. For RealVNC-specific error details, see RealVNC Connect Error Messages.
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- No connection or a refusal: check the server process, address, route, listening port, and network filtering.
- A connection reaches the host but access is rejected: follow the authentication, access-control, or encryption error rather than changing display settings.
- The connection opens but the desktop is black, blank, stale, or incomplete: investigate the remote graphical session and display capture.
If Viewer cannot establish a connection
Confirm the server and destination address
On the remote computer, confirm that the VNC server is running and listening on the port configured for that server. Verify that the hostname resolves to the intended machine or try its correct IP address, and confirm that the viewer’s network has a route to it. A wrong host, stopped service, or unreachable network path can look similar from the viewer, so use the exact error to narrow the cause.
Check the configured port and inbound filtering
For RealVNC direct connections, the documented default is port 5900 over TCP/UDP; an administrator may configure a different port. Check the actual server setting, then allow inbound traffic on that port in the host firewall and any applicable network security policy. Antivirus or other endpoint filtering may also block a connection. RealVNC’s guidance is at Configuring firewalls to allow direct connections.
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Do not open a port broadly to the internet simply to test a connection. Limit any firewall rule to the intended interface and trusted source networks, and follow the security requirements for the system.
Use the access or security error to guide login fixes
If the server is reachable but rejects the session, check the precise message. RealVNC documents possibilities including account or sign-in state, a server waiting for user acceptance, client-address restrictions, server licensing or version conditions, and incompatible encryption settings. Correct the condition identified by the server and your administrator; do not weaken encryption or expand permitted users as a generic troubleshooting step. These conditions are specific to RealVNC and may differ in other VNC implementations.
If Viewer connects but the desktop is blank
A successful connection followed by a black or incomplete image is a rendering or capture symptom, not evidence that port 5900 or credentials are wrong. RealVNC documents display-capture issues on both Linux and Windows, including headless computers and powered-off monitors. The relevant checks depend on the operating system and whether the session is a physical or virtual desktop.
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Linux: check Wayland and the active graphical session
RealVNC’s Wayland guidance says RealVNC Connect does not currently support Wayland, and associates affected setups with errors such as “Cannot currently show the desktop” and pre-login access problems. This is vendor- and version-specific guidance, not a claim about all VNC servers. Verify the distribution, display manager, and active session before changing configuration. RealVNC’s page describes disabling Wayland for named distributions; consult it and current distribution documentation before applying those steps: How do I disable Wayland to use RealVNC Connect?.
On an affected system, the session may need a user to be logged in before remote access works. This can make pre-login access fail even when an already-started desktop session is viewable.
Linux: distinguish physical display capture from Virtual Mode
For a headless Linux computer or one connected to a powered-off HDMI or DisplayPort monitor, the server may not have a usable display signal to capture. RealVNC lists an EDID emulator as a possible workaround for relevant cases, but says its example emulator was not tested. It is optional and will not fix a refusal, routing problem, credentials, or encryption mismatch. See Display issues when connecting to RealVNC Server running on Linux.
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If the problem is specifically a blank or gray desktop in RealVNC Virtual Mode, the built-in X server may not work with some modern desktop environments, including GNOME. RealVNC documents a SystemXorg option for supported configurations, but excludes SLES and Raspberry Pi OS. Confirm that the distribution, RealVNC version, and mode are supported before switching. Also account for the operational consequence of the documented dummy Xorg driver route: a connected physical monitor will display blank while that configuration is in use. Details are in Configuring RealVNC Server’s Virtual Mode to use SystemXorg mode.
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On Windows, RealVNC likewise identifies headless systems and powered-off displays as possible causes of black, blank, or incomplete rendering. Its Windows guidance prefers RealVNC Virtual Display Driver in most cases; this remedy is specific to RealVNC rather than a universal VNC setting. Review Display issues when connecting to RealVNC Connect for Windows for the applicable setup.
Quick Recap
Choose the remedy that matches the failure
| What you see | First checks | Scope and caution |
|---|---|---|
| Refused, unreachable, or name-resolution error | Server status, destination name or IP, route, configured port, and inbound filtering | Port 5900 TCP/UDP is RealVNC’s direct-connection default, not a universal setting. |
| Host reached but access or security rejected | Exact authentication, access acceptance, client restriction, version/licensing, or encryption message | Do not loosen access or encryption as a blanket fix. |
| Connected, but Linux desktop is blank or unavailable | Wayland/session state, display availability, and whether the connection uses Virtual Mode | Wayland and SystemXorg advice is RealVNC-specific and distribution/version dependent. |
| Connected, but Windows desktop is blank or incomplete | Monitor/display availability and RealVNC’s display-driver guidance | RealVNC identifies its Virtual Display Driver as preferred in most cases. |
| Headless Linux display-capture issue | Determine whether an EDID emulator is appropriate for the display setup | Optional workaround; RealVNC says its example was not tested. |
Make one change at a time
- Capture the exact error and establish whether the viewer connects at all.
- For connection failures, verify the remote service, address, route, actual listening port, and inbound rules in that order.
- For a rejected login, address the specific authentication or security condition reported by the server.
- For a blank desktop, identify the OS, display session, physical versus virtual mode, and monitor state before changing display configuration.
- After each change, reconnect and note whether the symptom changed; revert changes that do not address the identified cause.
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