There are a number of issues with RHEL 8 RH124, Chapter 8, section 5:
"their" should be "the"
Also, the entire sentence is awkward. Perhaps something like this could be used, "Signals may be sent to the foreground process by using various key sequences: Ctrl+c to terminate, Ctrl+\ to perform a core dump then terminate, and Ctrl+z to suspend. To send signals to background process(es) or to process(es) in other sessions, commands are used with the signal as an option. The signal that is to be sent can be specified by name (i.e.: -HUP or -SIGHUP) or by number (-1)."
This output is incorrect, it puts the output from the kill command after the ps aux command:
Here's what it looks like when you do it:
This tells the student to get the PIDs, but then doesn't use them (or why you'd want them in the first place). It simply uses SIGKILL to log the user off irrespective of any PID.
A correction: I said that this output is incorrect:
In reality, it depends on the sequence of events. It turns out that the kill command will not print any output until (1) Enter is pressed in the command line [how I was doing it] or (2) the next command is entered [how the instructions were doing it].
Neither way is incorrect, just different.