Re: Basic ps Tips

Joerg Mertens <joerg-mertens@t-online.de> wrote:

Rene Kita <mail@rkta.de> wrote:

Ed Morton <mortonspam@gmail.com> wrote:

On 8/3/2024 2:08 AM, Rene Kita wrote:

Jerry Peters <jerry@example.invalid> wrote:

Lawrence D'Oliveiro <ldo@nz.invalid> wrote:

On Sat, 27 Jul 2024 00:40:49 -0000 (UTC), I wrote:

[...]

     ps -p$(pgrep -d, bash) -wwo pid,ppid,lstart,tty,etime,cmd
>
says not to truncate the output, which is handy for long command lines.

 
Or just use ps -C <command>:

[...]

Does noone know about -C? I keep seeing things like 'ps -ef | grep
<something> in scripts to see if <something is running, rather than
using 'ps -C'.

 
I did not know about it.
 
The man page on OpenBSD does not mention -C, but calling 'ps -C' does
not give an error. But:
#v+
$ ps -C ksh
ps: /dev/mem: Permission denied'
#v-
 
Dunno what to make out of it, but apparently one reason to use grep
instead of -C is portability.

 
Its described in the man page for FreeBSD ps,
https://man.freebsd.org/cgi/man.cgi?ps(1), as:
 
    -C      Change  the  way         the  CPU  percentage is calculated by
using a
           "raw" CPU calculation that ignores "resident" time  (this  nor-
           mally has no effect).
 
so maybe you're running FreeBSD instead of the OpenBSD version.

 
I'm pretty sure I know which version of BSD I'm running and I would be
very surprised if OpenBSD would ship the FreeBSD version of ps...
 
But let's have a look at the source:
#v+
        while ((ch = getopt(argc, argv,
            "AaCcefgHhjkLlM:mN:O:o:p:rSTt:U:uvW:wx")) != -1)
                switch (ch) {
                case 'A':
                        all = 1;
                        xflg = 1;
                        break;
                case 'a':
                        all = 1;
                        break;
                case 'C':
                        break;                  /* no-op */
#v-
 
'-C' does nothing. I did not look further to see where that error is
coming from.

 
The error message also is printed, when you run ps with a valid
flag plus some string, like `ps -a xyz´, so it seems to be independent
of the `-C´-option.  Maybe it has to do with parsing of the old-style
flags vs. the dashed ones.

You got me curious and I got my debugger out for my morning coffee.

The error message comes from a function kvm_openfiles, which is called
after the flag parsing is done. From a quick glance, this function takes
what looks like three file names. If the second one is NULL, it will
default to /dev/mem. Trying to open /dev/mem it will error out - which
could be due to me being on a VPS.

While the man page mentions kvm(3) in the SEE ALSO section, there is no
mentioning nor explanation what additional arguments can be passed to
ps.

Regards