MobaXterm and WinSCP Disconnect from My Connection Due to Sudden Inactivity

SSH sessions dropping due to inactivity occur because intermediate firewalls or NAT devices close idle connections. You can resolve this by configuring client-side keepalives in MobaXterm and WinSCP, and adjusting server-side timeouts on your Ubuntu Linux system to maintain the connection state.

Understanding the Root Cause

When you establish an SSH connection using tools like MobaXterm or WinSCP, the data stream travels through various network nodes. Many corporate firewalls, cloud load balancers, and residential routers are configured to drop TCP connections that remain silent for a specific duration, often ranging from five minutes to thirty minutes. This is not a bug in your terminal emulator; it is a security and resource management feature designed to clean up stale sockets. The "sudden inactivity" mentioned in your query refers to periods where no keyboard input or file transfer activity occurs. To the network infrastructure, the connection appears dead, so it sends a RST (Reset) packet or simply drops the state table entry. When you eventually try to type again, the client receives a "Connection Reset by Peer" error because the other side has already forgotten the session exists. To fix this, we must implement two layers of protection: keeping the tunnel alive at the protocol level and ensuring the server process does not terminate the shell prematurely.

Configuring MobaXterm Keepalives

MobaXterm provides a graphical interface to manage SSH settings, but the default configuration often lacks aggressive keepalive settings required for unstable networks. You need to enable the TCP keepalive option explicitly. Navigate to Settings > Configuration > SSH. Look for the section labeled "TCP keepalive". Ensure this checkbox is selected. By enabling this, MobaXterm will send small, invisible packets over the SSH channel at regular intervals. These packets trick the firewall into thinking the connection is active, preventing the timeout. If you are experiencing frequent drops even with this setting, you may need to adjust the interval. While MobaXterm does not always expose the raw interval time in the GUI, you can verify the behavior by observing if the connection persists during long pauses. For advanced users, editing the underlying OpenSSH configuration file used by MobaXterm can provide finer control. You should also check the "Forward X11" and "Agent forwarding" settings. Sometimes, background processes associated with these features can cause minor stalls, though they rarely trigger full disconnects. The primary culprit remains the lack of periodic heartbeat signals. For more details on managing Ubuntu network stability, see How do Ubuntu-server network interfaces work?.

Adjusting WinSCP Settings

WinSCP operates similarly but offers more granular control over the SSH protocol parameters directly within its connection dialog. If you are using WinSCP to manage files and find that sessions drop when you leave the computer, you must configure the keepalive mechanism before connecting. Open the Session Details window. Click on the "Advanced" button located at the bottom right. Navigate to the "Connection" category in the left-hand tree menu. Here, you will find the "Keepalive interval" setting. Change this value from 0 (disabled) to a reasonable number, such as 60 seconds. This setting instructs WinSCP to send a null packet every minute. This is sufficient to bypass most firewall timeouts without generating excessive network traffic. If you are connecting through a highly restrictive proxy, you might need to lower this to 30 seconds. Additionally, ensure that the "Enable SSH agent forwarding" is checked only if necessary. Unnecessary features can sometimes introduce latency or complexity that exacerbates timeout issues on weak connections. After applying these changes, save the session profile. Next time you connect, WinSCP will automatically send heartbeats. If you still experience disconnections, verify that your local machine is not entering sleep mode, which can suspend network adapters.

Server-Side Configuration on Ubuntu

Client-side keepalives are effective, but they are not the only solution. Your Ubuntu server itself may be configured to terminate idle SSH sessions. This is controlled by the SSH daemon configuration file. Log into your Ubuntu server via console or another stable connection. Open the SSH daemon configuration file using a text editor with root privileges:

sudo nano /etc/ssh/sshd_config

Search for the following two directives:

• ClientAliveInterval
• ClientAliveCountMax

By default, these might be commented out or set to zero, meaning the server never checks on the client. To enforce a keepalive policy from the server side, uncomment these lines and set appropriate values. For example:

ClientAliveInterval 60
ClientAliveCountMax 3

This configuration tells the SSH daemon to send a message through the channel every 60 seconds. If three consecutive messages go unanswered (meaning the client is truly gone), the server will disconnect the session. This prevents zombie processes from accumulating on the server while keeping the connection alive for idle clients. After editing the file, restart the SSH service to apply the changes:

sudo systemctl restart sshd

This approach ensures that even if your client software fails to send keepalives, the server maintains the socket state actively. It is particularly useful in shared hosting environments or when managing multiple servers with varying client configurations. For insights into how Docker interacts with server connections, refer to Ubuntu Linux Server Randomly Loses Connection: Troubleshooting Docker Host.

Frequently Asked Questions

Why does my connection drop only after exactly 5 minutes?

This usually indicates a specific firewall rule or NAT timeout setting on your network router. Most consumer routers have a TCP idle timeout of roughly 300 seconds. You cannot change this from the client side alone; you must either increase the keepalive frequency below this threshold or contact your network administrator to adjust the router's timeout settings.

Can I use Putty instead of MobaXterm to fix this?

Yes, PuTTY has a very robust keepalive setting. In the PuTTY Configuration window, go to Connection > Seconds between keepalives (0 to turn off) and set it to 30 or 60. This is often simpler than configuring MobaXterm if you do not require the additional X11 or SFTP features.

Does enabling keepalives increase bandwidth usage significantly?

No. The keepalive packets sent by SSH are extremely small, typically just a few bytes. Sending one every 60 seconds adds negligible overhead to your network connection and will not impact your internet speed or data caps.

What if I get 'Permission denied' when editing sshd_config?

You must use sudo to gain root privileges. The command is sudo nano /etc/ssh/sshd_config. If you receive a permission error, ensure you are running the command in a terminal with administrative access. Never edit this file as a standard user.

Will these settings affect my ability to log in remotely?

No, these settings only affect established connections. They do not interfere with the authentication process or the initial login handshake. They merely maintain the state of an active session against idle timeouts.