When all SSH sessions have been idle for more than a minute, shut down the machine

Question

Idle is defined as when no foreground program is running and the terminal is waiting for user input, but the user does not make any input.

Actually, my ultimate goal is: shutdown when all SSH sessions are idle and x-window is also idle.
The idle time of x-window can be determined with xprintidle. So for now I just need to determine if all SSH sessions are idle or not.
I've looked for many ways to determine if a machine is idle in Linux, but most of them are based on x-window to determine if the desktop is idle.

Answer 1

in /etc/ssh/sshd_config

# default values
ClientAliveInterval                        0
ClientAliveCountMax                        3

If you set ClientAliveInterval to 600 {seconds} along with ClientAliveCountMax to 0 then that will close any SSH session that has been idle for 10 minutes. By using this mechanism you could have any SSH session cleanly close after a specific timeout or idle period of your choosing. Then check to see if there are any SSH sessions or processes present and if not then do a shutdown.

Recommend you also read up on those two SSH parameters before using them to be sure,

https://man.openbsd.org/sshd_config

What do options `ServerAliveInterval` and `ClientAliveInterval` in sshd_config do exactly?

because someone doesn't believe me... edit /etc/ssh/sshd_config to have ClientAliveInterval 61 and ClientAliveCountMax 0 and then have the below script run via crontab every minute and watch your machine shut down

#!/bin/bash
ssh_idle_shutdown.bash
the first num (a) in file /var/run/sshidleshutdown.txt is 0 or 1 based on if a ssh connection has happened
if a == 1 and count == 0 then do something
if [ ! -f /var/run/sshidleshutdown.txt ]
then
    echo 0 > /var/run/sshidleshutdown.txt
fi
count=netstat -tnpa | grep 'ESTABLISHED.*sshd' | wc -l
str=head /var/run/sshidleshutdown.txt
astr=${str:0:1}
a=$((astr))
if [ $a -eq 0 ] && [ $count -gt 0 ]
then
   echo 1 > /var/run/sshidleshutdown.txt
elif [ $a -eq 1 ] && [ $count -eq 0 ]
then
   echo -n "ssh idle condition met system shutdown called at " >> /var/log/sshidleshutdownlog.txt
   date >> /var/log/sshidleshutdownlog.txt
   rm -f /var/run/sshidleshutdown.txt
execute /sbin/shutdown
fi

put this in /etc/crontab

1 * * * * *  root   /path_to/ssh_idle_shutdown.bash

and also do

chown root.root  /path_to/ssh_idle_shutdown.bash
chmod 700 /path_to/ssh_idle_shutdown.bash

this is letting the SSH server identify what idle sessions are, and then the ssh server is closing them. Once we have seen at least one established ssh session then we begin checking until no ssh sessions are left via netstat, because the ssh server will have closed idle sessions based on ClientAlive Interval and ClientAliveCountMax in sshd_config. Adjust ClientAliveInterval and /etc/crontab frequency for running this ssh_idle_shutdown.bash accordingly.