Linux – Piping PS output into a Text file

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

It seems to be a misleading error message.

If you look at the procps source, file common.h line 290:

extern unsigned        format_modifiers; /* -c -j -y -P -L... */

-j implied format_modifiers flag to be set, which cause the error if used with user defined output:

if(format_list){
  if(format_flags) return "Conflicting format options.";
  if(format_modifiers) return "Can't use output modifiers with user-defined output";
  if(thread_flags&TF_must_use) return "-L/-T with H/m/-m and -o/-O/o/O is nonsense";
  return NULL;
}

A message like Can't use output format modifiers with user-defined output would be better.

FreeBSD ps doesn't have this issue, -j option cause ps to print information about user, pid, ppid, pgid, sid, jobc, state, tt, time, and command. Adding -o makes the output aggregated:

$ ps -j -o ppid,sid
USER     PID PPID PGID  SID JOBC STAT TT     TIME COMMAND          PPID  SID
cuonglm 1196 1195 1196 1196    0 Ss    0  0:00.02 -sh (sh)         1195 1196
cuonglm 1233 1196 1233 1196    1 R+    0  0:00.00 ps -j -o ppid,si 1196 1196

Output modifiers control how information displayed, while output format controls control what information displayed.

Example the s options is an output format control, because it added process signal information to ps output:

$ ps s
  UID   PID          PENDING          BLOCKED          IGNORED           CAUGHT STAT TTY        TIME COMMAND
 1000 12831 0000000000000000 0000000000000002 0000000000384004 0000000188013003 Ss   pts/1      0:00 zsh
 1000 13067 0000000000000000 0000000000000000 0000000000000000 0000000073d3fef9 R+   pts/1      0:00 ps s

f is an output modifier, because it changed how the output displayed:

$ ps f
  PID TTY      STAT   TIME COMMAND
12831 pts/1    Ss     0:00 zsh
13238 pts/1    R+     0:00  \_ ps f

Here the output was displayed as hierarchy.