I am connecting via SSH from PuTTY running on Windows 10 to an OpenSSH server on Rocky Linux 8. I am using the Bash shell. These sessions close after a period of inactivity. I have not measured the timeout, but it seems to be on the order of a small number of hours. I am trying to understand how these sessions are being closed. I will explain below the potential causes I’ve ruled out.
sshd_config ClientAliveInterval
/etc/ssh/sshd_config has ClientAliveInterval set to 0.
Bash Environment Variable TMOUT
I have searched for TMOUT in all regular files in the entire file system. This environment variable is not set anywhere.
Network Infrastructure
It occurred to me that perhaps a firewall sitting between my client and server might be monitoring connections and actively closing (via TCP FIN, perhaps) those that have been idle for some time. I have ruled out this possibility by noting that sessions from the same Windows host to other Linux hosts (not Rocky 8) do not close. These other hosts are behind the same firewall as the problematic Rocky 8 host and also have ClientAliveInterval and TMOUT set as described above.
Request for Help
What other mechanisms might be closing sessions due to inactivity?
Thank you in advance.
