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I am reading the ps man page and there is something I don't understand.

-f    does full-format listing. This option can be combined with many other
      UNIX-style options to add additional columns. It also causes the
      command arguments to be printed. When used with -L, the NLWP (number of 
      threads) and LWP (thread ID) columns will be added. See the c option,
      the format keyword args, and the format keyword comm.

I just want to add sid to the output of ps -f

But I was confused by the following output, my understanding is -o should just add sid to the output of -f but looks like -o overwrites -f completely.

I know I can specify all the options I want, like pid,ppid,pgid,sid,user,comm etc etc but is there a way just add one additional column to output of -f ? That is what the man page says, correct ?

[njia@cst-cgxfile01 ~]$ ps -f
UID        PID  PPID  C STIME TTY          TIME CMD
njia      3397 26106  0 12:23 pts/1    00:00:00 ps -f
njia     26106 26105  0 09:45 pts/1    00:00:00 -bash
[njia@ ~]$ ps -f -o sid
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.8/FAQ
  SID
26106
26106
25875
25875
25875
25875
25875
[njia@ ~]$

In addition, ps -ef -o sid will limit the process selection to those owned my me, that was a surprise as well.

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2 Answers 2

up vote 2 down vote accepted

To answer the first part of your question, there are several flags you can add to -f. They include -l, -j, -m, and -L. Unfortunately -o <format> can't be combined with -f.

Indeed, the best way to get exactly what you want, is to specify exactly what you want, e.g.

ps -e -o pid,ppid,pgid,sid,user,comm

But you can get really close by adding -j to -f, to make ps -efj. This adds both the PGID and SID columns.

Demonstrating without the -e flag to make the output shorter, compare:

$ ps -f
UID        PID  PPID  C STIME TTY          TIME CMD
myuser     123  4513  0 18:20 pts/26   00:00:00 zsh
myuser     1282  123  0 18:20 pts/26   00:00:00 ps -f

$ ps -fj
UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
myuser     123  4513   123   123  0 18:20 pts/26   00:00:00 zsh
myuser     1402  123  1402   123  0 18:20 pts/26   00:00:00 ps -fj

To answer the second part of your question, the reason ps -ef -o sid only shows your own processes, is it switches to BSD mode when it decides your flags weren't POSIX compliant. This is indicated by the message

Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.8/FAQ

So it's equivalent to running ps ef o sid.

In BSD mode, e means it will print the process's environment, and f means "forest". And BSD mode defaults to printing all processes owned by the current user that have any terminal, not just those on the current terminal.

Try changing the -o sid to -o sid,cmd to see the effects of e and f options.

$ ps ef o sid
SID
12345
  567
  567
...

$ ps ef o sid,cmd
  SID CMD
12345 -zsh USER=... LOGNAME=...
  567 zsh PWD=... LANG=...
  567  \_ ps ef o sid,cmd LANG=... PWD=...
...

And compare to ps u to see that the processes shown are the same (I added | wc -l for brevity).

$ ps ef o cmd | wc -l
20
$ ps u | wc -l
20
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I think you're absolutely right, I don't get this error message on my Debian though. –  terdon Feb 11 at 2:19
    
ps -eO sid f worked for me but that is even more wired. There are -f in output format control and f in output modifier. I can do this ps -f f and it gives me all the fields included by ps -f but in ps f format. This becomes more interesting. –  Ask and Learn Feb 11 at 2:29
    
ps ef sid,cmd gives me a syntax error, do you mean ps ef o sid,cmd ? –  Ask and Learn Feb 11 at 2:32
    
Yes, thanks. Fixed. –  Mikel Feb 11 at 2:55

Everything you state is correct, ps will only list processes owned by you unless you tell it otherwise with x or a or similar options. -o sets the format, it is not cumulative. So, to get the output of ps -f with SID added, you will need to specify the whole thing using -o:

$ ps -f 
UID        PID  PPID  C STIME TTY          TIME CMD
terdon   27452 27436  0 02:48 pts/3    00:00:00 /bin/bash
terdon   30622 27452  0 02:51 pts/3    00:00:00 ps -f
$ ps -o user,pid,sid,ppid,c,stime,tty,time,cmd
USER       PID   SID  PPID  C STIME TT           TIME CMD
terdon   27452 27452 27436  0 02:48 pts/3    00:00:00 /bin/bash
terdon   30905 27452 27452  0 02:51 pts/3    00:00:00 ps -o user,pid,sid,ppid,c,stime,tty,time,cmd

To get the same output for all users, use this:

ps -axo user,pid,sid,ppid,c,stime,tty,time,cmd

The closest you can get to adding to as opposed to overwriting the output format is using -O (that's O as in Oliver, not 0):

-O format
    Like -o, but preloaded with some default columns.  
    Identical to -o pid,format,state,tname,time,command or
                 -o pid,format,tname,time,cmd

So, for example:

$ ps -O sid
  PID   SID S TTY          TIME COMMAND
 4879 27452 R pts/3    00:00:00 ps -O sid
27452 27452 S pts/3    00:00:00 /bin/bash
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thanks for the reply, I am still confused by ps -ef -O sid only list processes owned by myself, what happened to -e option. Looks like ps just ignored it. It works if I do this ps -eO sid f. –  Ask and Learn Feb 11 at 2:11
    
@AskandLearn the ps man page is one of the most complex I've ever seen. I agree that the -f seems to be eating -e but have no idea why. –  terdon Feb 11 at 2:17
    
The -f isn't eating the -e. The -f and the -o conflict, so ps tries to parse it in BSD mode instead. And in BSD mode -e means something different. –  Mikel Feb 11 at 3:15
    
@Mikel yes, I understood when I read your answer, thanks! –  terdon Feb 11 at 3:18

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