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I was playing around with who when I noticed that the who -p option does not give any output. Running the command as root also didn't change the output. I tried this on a CentOS, Ubuntu 12.04 and Ubuntu 13.10.

Is the command deprecated or is it not compatible with newer init systems like upstart or systemd?

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up vote 2 down vote accepted

Taken from the man page for who

-p, --process
print active processes spawned by init"

Looks like no processes are spawned by "init"
http://en.wikipedia.org/wiki/Init
[EDIT]

I did some looking into the wiki page and it turns out that

Traditionally, one of the major drawbacks of init is that it starts tasks serially, waiting for each to finish loading before moving on to the next. When startup processes end up I/O blocked, this can result in long delays during boot. Various efforts have been made to replace the traditional init daemons to address this and other design problems

I'm guessing this might lend a hand to the reason why no processes show up when running who -p. Looks like init daemons are getting run out of town.

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I just checked my processes and /sbin/init indeed doesn't spawn anything. A simple solution to my curiosity.If I recall correctly, init did indeed spawn processes with older init systems. –  cebalrai Oct 8 '13 at 13:35
    
@cebalrai I read into the wiki page a bit and found out they aren't used much anymore, maybe that explains it. I edited the answer with what I found :) –  TopGunCoder Oct 8 '13 at 14:39
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