-o comm= means user output should be the command name only, but without any column title. E.g. if you do
-o comm=COMMAND, it will print you a column title
$ ps -o comm= -p $PPID
$ ps -o comm=COMMAND -p $PPID
-p $PPID selects the process by the given parent's
-o comm= -p $PPID are two independent options.
So your command essentially does give you the name of the parent process by its
E.g. if I start
tmux, it has the
PID of 1632. Now I start several
bash in each pane, which each have the PPID of 1632, but have their own PID.
You can learn more in What are PID and PPID?
I am not sure, but
ps might look at
/proc/$PPID/comm to determine the parent's command name.
In my case, executing this command gives you the name of the parent's process, without using
$ cat /proc/$PPID/comm
$ cat /proc/1632/comm