Here is how to keep your ssh session from freezing and how to keep ssh alive.

Edit your ssh config file. Change to the following variables

# nano /etc/ssh/sshd_config

TCPKeepAlive yes
ClientAliveInterval 60
ClientAliveCountMax 10000

Then, restart ssh

On CentOS:

# service sshd restart
Stopping sshd:                                             [  OK  ]
Starting sshd:                                             [  OK  ]

• TCPKeepAlive – is there to ensure that certain firewalls don’t drop idle connections.
• ClientAliveInterval – the server will wait 60 seconds before sending a null packet to the client to keep the connection alive.
• ClientAliveCountMax – server will send alive messages to the client even though it has not received any message back from the client.

Using Putty Settings

1. Start PuTTY.
2. Load pone of your saved sessions.
3. In the Category pane, click Connection.
4. Look for ” Sending of null packets to keep session active”.
5. In the Seconds between keepalives (0 to turn off), type 300. (With this configuration, PuTTY sends a packet to the server every 300 seconds -5 minutes – to keep the connection alive.
6. In the Category pane, click Session.
7. Click Save.
8. Connect to your account and monitor the connection. If it still drops, gradually decrease the keepalive interval until the connection is stable.