Run ‘top’ Command Once and Exit – How to Guide

monitoringosxtop

I find the output of the shell command top to be a simple and familiar way to get a rough idea of the health of a machine. I'd like to serve top's output (or something very similar to it) from a tiny web server on a machine for crude monitoring purposes.

Is there a way to get top to write its textual output exactly once, without formatting characters? I've tried this:

(sleep 1; echo 'q') | top > output.txt

This seems to be close to what I want, except that (1) there's no guarantee that I won't get more or less than one screenful of info and (2) I have to strip out all the terminal formatting characters.

Or is there some other top-like command that lists both machine-wide and process-level memory/CPU usage/uptime info?

(Ideally, I'd love a strategy that's portable to both Linux and Mac OS X, since our devs use Macs and our prod environment is Linux.)

Best Answer

In Linux, you can try this:

top -bn1 > output.txt

From man top:

-b : Batch-mode operation
            Starts top in 'Batch' mode, which could be useful for sending
            output from top to other programs or  to  a  file.   In  this
            mode, top will not accept input and runs until the iterations
            limit you've set with the '-n' command-line option  or  until
            killed.
....
-n : Number-of-iterations limit as:  -n number
            Specifies  the  maximum  number of iterations, or frames, top
            should produce before ending.

With OS X, try:

top -l 1

From top OSX manpage:

 -l <samples>
              Use logging mode and display <samples> samples, even if 
              standard output is a terminal. 0 is treated  as  infinity.   
              Rather than redisplaying, output is periodically printed in 
              raw form. Note that the first sample displayed will have an 
              invalid %CPU displayed for each process,  as it is calculated 
              using the delta between samples.

Related Solutions

Valid alternative to top for OpenBSD

Htop 2.0 adds OpenBSD support. I just compiled it on OpenBSD 5.9 and it works very well: http://hisham.hm/htop/

Linux Top Command – How to Keep Track of Values?

The answer to this question can range from a simple command, to complex monitoring tools, depending on your needs.

You can start by simply running top -b -n 1 >> file.txt (-b for batch mode, -n 1 for running a single iteration of top) and store the output (appended) in the file.txt. You can filter also "top" output like top -b -n 1 | grep init to see only the data for the "init" process or top -b -n 1 | grep "init" | head -1 |awk '{print $9}' to get the 9th column of the init process data (the CPU value).

If you want to use in a shell script, you could:

CPU=$(top -b -n1 | grep "myprocess" | head -1 | awk '{print $9}')
MEM=$(top -b -n1 | grep "myprocess" | head -1 | awk '{print $10}')

Or, with a single execution of top:

read CPU MEM <<<$(top -b -n1 | grep "myprocess" | head -1 | awk '{print $9 " " $10}')

(note that grep, head and awk could be merged in a single awk command but for the shake of simplicity I'm using separate commands).

We used top in this example but there are alternate methods for other metrics (check sar, iostat, vmstat, iotop, ftop, and even reading /proc/*).

Now you have a way to access the data (CPU usage). And in our example we are appending it to a text file. But you can use other tools to store the data and even graph them: store in csv and graph with gnuplot/python/openoffice, use monitoring&graping tools like zabbix, rrdtools, cacti, etc. There is a big world of monitoring tools that allow to collect and graph the data like CPU usage, memory usage, disk io, and even custom metrics (number of mysql connections, etc).

EDIT: finally, to specifically answering your question, if you want to keep track of changes easily for a simple test, you can run top -b -n 1 >> /tmp/file.txt in your /etc/crontab file, by running top every 5 minutes (or any other time interval if you replace the /5 below).

0-59/5 * * * * root top -b -n1 >>/tmp/output.txt

(and a grep + head -1 in the command above if you're only intestered in a single process data).

Note that the output.txt will grow, so if you want to reset it daily or weekly, you can "rm" it with another crontab entry.

Best Answer

Related Solutions

Valid alternative to top for OpenBSD

Linux Top Command – How to Keep Track of Values?

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