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When I attempt to run the command ps with the flags/switches/options aux I get the following message. If I run the command without grep, no message is displayed. What am I doing wrong?

ps -aux | grep 'skype'
Warning: bad ps syntax, perhaps a bogus '-'? 
See http://procps.sf.net/faq.html
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Wait, did you even read the link you posted? It answers your question. – Dr Kitty Feb 27 '12 at 5:26
    
@The Electric Muffin - I did however don't understand when it states 'x' refers to a specific user. – PeanutsMonkey Feb 27 '12 at 5:42
    
@The Electric Muffin - Does it mean I can run the command ps -aux{username}? – PeanutsMonkey Feb 27 '12 at 5:50
    
The -u username switch selects processes belonging to username, so ps -upeanuts would select every process belonging to the user peanuts. – Dr Kitty Feb 29 '12 at 3:31
up vote 3 down vote accepted

It should (and did for me) display that warning whether or not it's piped to grep. The real issue is the -aux switch. The manpage says:

Note that "ps -aux" is distinct from "ps aux". The POSIX and UNIX standards require that "ps -aux" print all processes owned by a user named "x", as well as printing all processes that would be selected by the -a option. If the user named "x" does not exist, this ps may interpret the command as "ps aux" instead and print a warning."

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BSD options to ps do not take a dash.

ps aux
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I understand that however what is the difference between ps -aux and ps aux – PeanutsMonkey Feb 27 '12 at 5:48
    
One is incorrect and the other is correct. – Ignacio Vazquez-Abrams Feb 27 '12 at 5:49
    
But why is that? Does x refer to the username of a user? – PeanutsMonkey Feb 27 '12 at 5:50
    
x is a BSD-style option. – Ignacio Vazquez-Abrams Feb 27 '12 at 5:51
    
Sorry for being a n00b but what does that mean? – PeanutsMonkey Feb 27 '12 at 6:16

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