How to stop a infinite running process (ztail) started by a ssh session after that session is closed

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http://unix.stackexchange.com – I have a peculiar problem. My server supports multiple ssh session simultaneously, so that multiple admins can manage (via command line interface) it simultaneously. We have a command which calls ztail to show the compressed log files. Now when the current ssh session is closed (without pressing Ctrl-C, to stop the ztail command), this command should ideally stop working. But what I observed when I start a new ssh session that, the process (ztail) is still running in background and consuming my CPU, even though the previous session was closed. Now how can I know when the session was closed, so (HowTos)