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The ps command has a ww output modifier (man page says this is "wide output, unlimited length"). This modifier seems to not work if prefixed with a hyphen (-ww) AND ps reports on a single process (with the -p option).

For more than one process OR if a hyphen isn't used, it works.

Why so? Have I misunderstood what "wide output" means? This is on Redhat RHEL 6.5.

$ ps -w -p 2180
  PID TTY          TIME CMD
 2180 tty1     00:00:00 mingetty

$ ps -w -p 2180 2182
  PID TTY      STAT   TIME COMMAND
 2180 tty1     Ss+    0:00 /sbin/mingetty /dev/tty1
 2182 tty2     Ss+    0:00 /sbin/mingetty /dev/tty2

An output format specifier changes from 'CMD' to 'COMMAND', depending on whether one or more PIDs were fed to '-p'.

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8

ps has two syntaxes, the BSD and the System V syntax. If you start your options with a hyphen, you are using System V syntax. The w flag is a BSD syntax flag. In BSD syntax, you can just specify the process ID without any option. So I think the command you just want is:

ps ww 2180 2182

(where 2180, 2182 are example PIDs).

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  • … and if you give a non-option argument PID, you get (sloppy) SysV syntax again, right? Hence ps -w -p 2180 2182 is (sloppy) SysV syntax, while ps -w -p 2180 -p 2182 (where each PID has a -p) is BSD syntax. … right? – The Sidhekin Nov 16 '15 at 23:30
  • Thanks user318..., the issue seems to an output format specifier is switched from COMMAND to CMD if a single process is reported on in my example. Switching to a 'pure BSD' format works fine (i.e. drop the "-p", or remove the hyphen from "-w"). – Happyblue Nov 17 '15 at 0:14
  • Thanks 'The Sid...'. But " ps -w -p" seems to force the use of the CMD output format specifier (does not report the command line) by default – Happyblue Nov 17 '15 at 0:24
  • I think its a bug in ps implementation (The man page states "-ww" and "ww" are equivalent, yet default output format specifier changes if more than one process is reported on). – Happyblue Nov 17 '15 at 22:40
  • @Happyblue: I think having two totally different modes is confusing, but the man page is correct. It says "BSD options, which may be grouped and must not be used with a dash." So even though the descriptions of w and -w are the same, the two options are not the same (one is BSD, one UNIX). man7.org/linux/man-pages/man1/ps.1.html – user3188445 Nov 18 '15 at 6:57

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