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SimplySimplified
Asked: 2017-08-24 00:42:43 +0800 CST

Simplify command in top

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I'm using the following command to gather the information of child-PID: 

top -b -n1 -p 719011,719012,719013,719014,719015,719016,719017 | sed -e 's/USER/----/' -e 's/root/----/' -e 's/PR/--/' -e 's/20/--/' -e 's/VIRT/----/' -e 's/538m/----/' -e 's/RES/---/' -e 's/12m/---/' -e 's/SHR/---/' -e 's/1348/----/' -e 's/NI/--/' -e 's/S/-/' | tail -9 > file1

It works just fine, but is a little long winded! I want to know if there is anyway to gather the information just by using the pPID? Thus saving having to type every child process ID. I don't want the full answer just a pointer in the right direction so I can figure it out myself!

Okay, so I have tidied up the command to:

ps -o pid= --ppid 719008 | top -b -n4 | awk '{print $1,$9,$10,$12}' | tail -9 > file

But instead of giving the output for the child processes I get the output for every process on the system! What am I missing?

$ pstree -p 719008
dvaudio_server(719008)─┬─{dvaudio_server}(719011)
                       ├─{dvaudio_server}(719012)
                       ├─{dvaudio_server}(719013)
                       ├─{dvaudio_server}(719014)
                       ├─{dvaudio_server}(719015)
                       ├─{dvaudio_server}(719016)
                       └─{dvaudio_server}(719017)

And the output of pgrep is:

pgrep: option requires an argument -- 'd'
Usage: pgrep [-flvx] [-d DELIM] [-n|-o] [-P PPIDLIST] [-g PGRPLIST] [-s SIDLIST]
    [-u EUIDLIST] [-U UIDLIST] [-G GIDLIST] [-t TERMLIST] [PATTERN]
command-line

2 Answers

  1. Best Answer

    You can obtain the direct children of a process using pgrep:

    -P, --parent ppid,...
      Only match processes whose parent process ID is listed.

    And:

    -d, --delimiter delimiter
      Sets  the  string  used to delimit each process ID in the output
      (by default a newline).  (pgrep only.)

    So:

    top ... -p $(pgrep -P <PPID> -d,) | ...
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  2. You can use ps to display a list of processes. It understands the --ppid PPIDLIST argument which allows you to filter the processes by a comma-separated list of parent process IDs.

    From man ps:

    --ppid pidlist

Select by parent process ID. This selects the processes with a parent process ID in pidlist. 
That is, it selects processes that are children of those listed in pidlist.

    So probably you should try something like 

    ps aux --ppid 12345
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