Question: Reading the Output of Top

[Janina Sajka]

The observation that the data provided by top is directly available in
the /proc file system tree is actually very useful, because you can
simply write a script or two to query for common concerns.

I have a script, which I alias to a command called lav, for checking the
current system load average in a running, real time report:

<begin script>
while true; do cat /proc/loadavg |cut -b 1-5; sleep 5; done
<end script>

Just Ctrl+C to stop.

I have a variant, this time written as a simple bash script, that also
uses the ps command to report the process which top would report as the
heaviest resource consumer like so:

<begin script>
#!/bin/bash
while true; do
        cat /proc/loadavg |cut -b 1-5
	        sleep .5
		#Sort pids to greatest consumer
		for APP in $(ps -e --sort %cpu |cut -b 17-); do
		        echo $APP >/dev/null
			done
			echo $APP
			sleep 4
			done
			<end script>

The above works on Fedora 23 for me right now. Note that your distro may
do things a bit differently, but the data is most certainly going to be
available if you look in the write place.

The value of checking for the top cpu hog is that load averages are
often the result of a process gone out of control somehow. I simply kill
the offender, and 99% of the time my machine returns to a sane state.
That's why I've found having this data directly available in a script
useful, it takes less time to get at than listening to the complete
output of top, or even faster than hitting ScrollLock on top and finding
the top cpu hog manually.

			hth

			Janina

Willem van der Walt writes:
> Hi John,
> Thanks for this. I am about to try it now.
> Regards, Willem
> 
> 
> On Sat, 7 May 2016, John G. Heim wrote:
> 
> >Okay, I threw together a script to linearize table output from programs
> >like top. It's at:
> >http://www.math.wisc.edu/~jheim/pub/linearize
> >
> >You can get it with wget:
> >
> >$ wget http://www.math.wisc.edu/~jheim/pub/linearize
> >
> >To run it, type linearize and your command after it. For example, to use
> >it with top, do this:
> >
> >linearize top -bn1
> >
> >The keys you have to use are configured at the top of the script. I had to
> >choose keys that would not interfere with speakup or orca so I picked i to
> >move up a line, the comma to move down a line, j to move left a cell, and
> >l to move right a cell. They form a little cross on the keyboard. But you
> >can easily change them to whatever you like by editing the script. Let me
> >know if you think there is a more logical set of keys that don't interfere
> >with other functions.
> >
> >One tricky thing. There is a key defined to set the column headings. Press
> >the h key and the script will use the current line for column headings.
> >Behaviour of the left and right keys is undefined until you do this. So if
> >you are using the script with top, you'd want to use the comma to move
> >down several times until you hear the first line of the table listing
> >processes. Then press the h key. From then on you can move around as if
> >you are in a table.
> >
> >
> >On 05/07/2016 06:24 AM, Parham Doustdar wrote:
> >>
> >>Hi John,
> >>
> >>    I doubt that there is an answer to your first question. You could
> >>    probably write a script to do it.
> >>
> >>Top is unusable without such a feature, but you and other people
> >>replying to this thread seem to be using it just fine. So, what tricks
> >>do people use in order to memorize what column is for what value? I have
> >>this problem when reading the output of commands like |free -m|, too.
> >>
> >>Thanks!
> >>
> >>On 5/6/2016 6:00 PM, John G Heim wrote:
> >>
> >>>I doubt that there is an answer to your first question. You could
> >>>probably write a script to do it.
> >>>
> >>>As for your second question, I run top thusly, 'top -bn1 | more'. This
> >>>runs top in batch mode and has it retrieve the data just once. Piping
> >>>the output to more keeps the data from scrolling off the top. What you
> >>>get is a snapshot of the data at the moment you run the top command.
> >>>
> >>>PS: You can also set the refresh rate for top to something high enough
> >>>for you to listen to the output.
> >>>
> >>>
> >>>
> >>>On 05/06/2016 01:59 AM, Parham Doustdar wrote:
> >>>>Hi all,
> >>>>
> >>>>What do you do when you want to read content of a command like
> >>>>|top|? There are two issues with it:
> >>>>
> >>>>1. There is no way of knowing the title of a column without first
> >>>>   navigating to the headers. I want to be able to go to the
> >>>>   next/previous column, know the title of a column, etc.
> >>>>2. The output keeps changing. For example, while I’m reading one line,
> >>>>   its CPU usage might drop and cause it to be reordered in the list.
> >>>>
> >>>>How do you get through these issues?
> >>>>
> >>>>Thanks!
> >>>>
> >>>>
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> >>>
> >>
> >
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-- 

Janina Sajka,	Phone:	+1.443.300.2200
			sip:janina at asterisk.rednote.net
		Email:	janina at rednote.net

Linux Foundation Fellow
Executive Chair, Accessibility Workgroup:	http://a11y.org

The World Wide Web Consortium (W3C), Web Accessibility Initiative (WAI)
Chair, Accessible Platform Architectures	http://www.w3.org/wai/apa