Sets a timeout interval in seconds after which if no data has been received from the server, ssh(1) will send a message through the encrypted channel to request a response from the server. This option applies to protocol version 2 only in protocol version 1 there is no mechanism to request a response from the server to the server alive messages, so disconnection is the responsibility of the TCP stack. If, for example, ServerAliveInterval (see below) is set to 15 and ServerAliveCountMax is left at the default, if the server becomes unresponsive, ssh will disconnect after approximately 45 seconds.

$putty ssh config$

The server alive mechanism is valuable when the client or server depend on knowing when a connection has become inactive. The TCP keepalive option enabled by TCPKeepAlive is spoofable.

The server alive messages are sent through the encrypted channel and therefore will not be spoofable. It is important to note that the use of server alive messages is very different from TCPKeepAlive (below). If this threshold is reached while server alive messages are being sent, ssh will disconnect from the server, terminating the session. Sets the number of server alive messages (see below) which may be sent without ssh(1) receiving any messages back from the server. These settings will make the SSH client or server send a null packet to the other side every 300 seconds (5 minutes), and give up if it doesnвЂ™t receive any response after 2 tries, at which point the connection is likely to have been discarded anyway. You can also make your OpenSSH server keep alive all connections with clients by adding the following to /etc/ssh/sshd_config: To enable the keep alive system-wide (root access required), edit /etc/ssh/ssh_config to set the settings for just your user, edit ~/.ssh/config (create the file if it doesnвЂ™t exist). In your session properties, go to Connection and under Sending of null packets to keep session active, set Seconds between keepalives (0 to turn off) to e.g.

To avoid having your SSH sessions become unresponsive after e.g.В 5 minutes, do the following: Sometimes the interval between session drops is 24 hours, but on many commodity firewalls, connections are killed after as little as 300 seconds. Many NAT firewalls time out idle sessions after a certain period of time to keep their trunks clean.

Putty ssh config