To identify multiple VNC servers running on a Linux system, use the
ps aux | grep vnc command to list all processes containing "vnc" in their name. This output reveals the specific process IDs and command-line arguments, which often include the display number or port configuration, allowing you to distinguish between different instances effectively.
Identifying Running Processes with ps and grep
The most direct method for troubleshooting VNC server instances involves examining the active process table. The
ps utility provides a snapshot of current processes, while
grep filters that output for relevant keywords. When multiple VNC services are active, they typically appear as separate entries in the process list, each associated with a unique display number or port.
Run the following command in your terminal:
ps aux | grep -i vnc
The
-i flag ensures case-insensitive matching, capturing variations like "VNC", "vnc", or "tigervnc". The output will show the user, process ID (PID), CPU and memory usage, and the full command used to start the service. For example, you might see entries like
/usr/bin/Xvnc :1 or
vncserver :5901. Each line represents a distinct session. If you see multiple lines referencing similar binaries but different display numbers (such as
:1,
:2, etc.), you have confirmed that multiple VNC servers are indeed running simultaneously.
It is important to note that some modern setups use systemd units rather than standalone daemon processes. In such cases, the
ps output might be less descriptive. However, for traditional VNC implementations like TightVNC, TigerVNC, or RealVNC, the process list remains the primary diagnostic tool. You can also check for related X server processes, as VNC often relies on an underlying X display server. Look for
Xvnc or
Xorg processes that correspond to the VNC sessions.
Determining Ports and Display Numbers
Once you have identified the processes, the next step is to determine which network ports they are listening on. VNC servers typically bind to ports starting at 5900, where display
:0 corresponds to port 5900, display
:1 to 5901, and so on. You can verify this mapping by looking at the command-line arguments in the
ps output or by using network utilities.
Use the
netstat or
ss command to list active connections and listening ports. The following command filters for VNC-related ports:
sudo ss -tlnp | grep 590
This command lists all TCP listening sockets (
-t) with numerical addresses (
-n) and shows the program name (
-p). The filter
grep 590 isolates the standard VNC port range. You should see entries indicating which PID is bound to which port. This confirms exactly which VNC instance is accessible over the network. If you find a port open but no corresponding
ps entry, the process might have crashed or exited, leaving the socket in a TIME_WAIT state. In such scenarios, restarting the networking stack or waiting for the timeout to clear may be necessary.
For more detailed information about the specific VNC server software being used, check the binary path shown in the
ps output. Different VNC implementations handle port allocation slightly differently. Some allow manual port specification via command-line flags, while others strictly adhere to the display-to-port mapping rule. Understanding this distinction helps in configuring firewalls correctly, ensuring that only intended ports are exposed to the network.
Managing Multiple Instances
If you discover unintended VNC servers running, it is crucial to manage them properly to avoid resource exhaustion or security vulnerabilities. Each VNC session consumes significant system resources, including memory and CPU cycles, particularly if they are serving graphical desktop environments. You can stop specific instances using the
vncserver command with the kill option.
To terminate a specific display, use:
vncserver -kill :1
Replace
:1 with the actual display number identified from your earlier checks. This command sends a termination signal to the Xvnc process and cleans up temporary files associated with that session. Be cautious when killing processes, as abrupt termination can lead to data loss in unsaved work within those VNC sessions. It is always better to notify users connected to those sessions before executing kill commands.
In cases where you need to audit all running VNC services across the system, consider checking the systemd service status if your distribution uses it. Commands like
systemctl list-units --type=service | grep vnc provide a high-level overview of managed services. This approach is particularly useful in server environments where multiple administrators might configure remote access independently. Proper documentation and centralized management tools can prevent the accumulation of orphaned or duplicate VNC instances.
For further insights into securing your server environment, you might want to review guides on establishing secure connections. See
Unable to SSH into Ubuntu Server: Log in Locally First for context on local access methods. Additionally, understanding how other services interact with your network ports can help diagnose conflicts. Check
Unintended Ubuntu Server Access on Port 8080: WeKan Instance to learn about managing unexpected port bindings.
Frequently Asked Questions
How do I find the PID of a specific VNC server?
You can find the Process ID by running
ps aux | grep vnc and looking at the second column in the output. This column displays the numeric PID associated with each running VNC process, which you can then use for management commands.
Can multiple VNC servers run on the same port?
No, only one process can bind to a specific TCP port at a time. If you attempt to start a new VNC server on an occupied port, it will fail with an address already in use error unless you force the previous process to release the port.
What is the difference between display :1 and port 5901?
Display
:1 is a logical identifier for the X server session, while port 5901 is the network address clients connect to. By default, VNC maps display
n to port
5900 + n, so display
:1 automatically listens on port 5901.
How can I stop all VNC servers at once?
There is no single command to kill all VNC instances simultaneously because they are independent processes. You must iterate through the PIDs found in
ps aux and send a kill signal to each one individually, or restart the VNC service daemon if it manages them collectively.
Why does netstat show a VNC port but ps shows no process?
This usually indicates a zombie process or a socket in the TIME_WAIT state after the process has terminated. The operating system holds the port open briefly to ensure any lingering packets are delivered. Waiting a few minutes or rebooting the network interface will clear this state.