Debian 9 - Installed yesterday on two 64-bit VMs In /etc/ssh/ssh_config there are two parameters, of which I am citing sshd_config(5) man page:
ClientAliveInterval - Sets a timeout interval in seconds after which if no data has been received from the client, sshd(8) will send a message through the encrypted channel to request a response from the client. The default is 0, indicating that these messages will not be sent to the client. This option applies to protocol version 2 only. ClientAliveCountMax - Sets the number of client alive messages (see below) which may be sent without sshd(8) receiving any messages back from the client. If this threshold is reached while client alive messages are being sent, sshd will disconnect the client, terminating the session. I need to have the session expire and the ssh client terminate after an idle time. For testing purposes, I assigned these to unreasonably small values and restarted the daemon with /etc/init.d/ssh restart: ClientAliveInterval 5 ClientAliveCountMax 1 The server is not using protocol version 1, so protocol version 2 is used and thus ClientAliveInterval should be obeyed. I suspected that maybe default settings of the SSH client may be keeping the session alive by delivering scheduled null packets, so I assigned -o ServerAliveInterval 30, a larger value to ensure that such packets aren't delivered in time. But the change doesn't seem to stick, not even after rebooting the machine. mary@mary:/etc/ssh$ w 12:06:03 up 19 min, 3 users, load average: 0.00, 0.00, 0.00 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT mary tty1 - 11:47 1:38 0.20s 0.15s -bash mary pts/0 192.168.1.7 12:02 0.00s 0.05s 0.00s w mary pts/1 192.168.1.19 12:05 1:41 0.04s 0.04s -bash As I write this, the session is idle 5 minutes and just won't hang up. Ironically, it appears most people have the opposite problem of SSH being sporadically closed, and that has really polluted my search results in trying to resolve this. Ideas?