ps command

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# 1  
ps command

What is the difference between ps -ax and ps -x? I got the meaning here but don't understand it clearly.

-a List information about all processes most frequently requested: all those except process group leaders and processes not associated with a terminal.

-x includes processes not attached to terminals

what are proccess group leaders and processes not associated with a terminal? processes not attached to terminals?

Can please someone explain this to me.
# 2  
These options are describing the BSD ps syntax (ps -x is invalid) so should not be prefixed by a dash.

process group leaders are processes that created a process group, commonly used with shell job control.

processes not associated with / attached to terminals are usually daemons and similar processes that do not use a terminal (tty) to read their input / write their output.
# 3  
Thank you so much for your reply.

I'm not sure about ps x. I read it from the book and it can run well when I type in the terminal.
# 4  
Originally Posted by muffle
I'm not sure about ps x. I read it from the book and it can run well when I type in the terminal.
That depends on the OS you use. It runs with a warning on Gnu/Linux but fails on Solaris.

$ ps -x
Warning: bad ps syntax, perhaps a bogus '-'? See
 1611 ?        Ssl    0:00 gnome-session
 1642 ?        Ss     0:00 /usr/bin/ssh-agent /usr/bin/dbus-launch --exit-with-s

$ ps -x
ps: illegal option -- x
usage: ps [ -aAdeflcjLPyZ ] [ -o format ] [ -t termlist ]
        [ -u userlist ] [ -U userlist ] [ -G grouplist ]
        [ -p proclist ] [ -g pgrplist ] [ -s sidlist ] [ -z zonelist ]
  'format' is one or more of:
        user ruser group rgroup uid ruid gid rgid pid ppid pgid sid taskid ctid
        pri opri pcpu pmem vsz rss osz nice class time etime stime zone zoneid
        f s c lwp nlwp psr tty addr wchan fname comm args projid project pset

# 5  
As a side note, the Berkeley version of some Unix programs could be found in /usr/ucb on Solaris (ucb = University of California, Berkeley):

bash-3.2$ uname -sr; /usr/ucb/ps -x
SunOS 5.10
 18261 ?        S  0:00 /usr/lib/ssh/sshd
 18270 pts/4    S  0:00 -ksh
 18296 pts/4    S  0:00 bash
 18446 pts/4    O  0:00 /usr/ucb/ps -x

SunOS/BSD Compatibility Package Commands                   ps(1B)

     ps - display the status of current processes

     /usr/ucb/ps [-aceglnrSuUvwx] [-t term] [num]

     The ps command displays information  about  processes.  Nor-
     mally,  only  those  processes  that  are  running with your
     effective user ID and are attached to a controlling terminal
     (see    termio(7I))  are  shown.  Additional  categories  of
     processes can be added to the display using various options.
     In particular, the -a option allows you to include processes
     that are not owned by you (that do not have your  user  ID),
     and  the  -x  option allows you to include processes without
     controlling terminals. When you specify both -a and -x,  you
     get processes owned by anyone, with or without a controlling
     terminal. The -r option  restricts  the  list  of  processes
     printed to running and runnable processes.

Last edited by radoulov; 05-21-2012 at 12:18 PM..
# 6  
Thanks to both jlliagre & radoulov. I understand now.

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