How to monitor CPU usage automatically and return results when it reaches a threshold - linux

Question

I am new to shell script , i want to write a script to monitor CPU usage and if the CPU usage reaches a threshold it should print the CPU usage by top command ,here is my script , which is giving me error bad number and also not storing any value in the log files
while sleep 1;do if [ "$(top -n1 | grep -i ^cpu | awk '{print $2}')">>sy.log - ge "$Threshold" ]; then echo "$(top -n1)">>sys.log;fi;done

Answer 1

Your script HAS to be indented and stored to a file, especially if you are new to shell !
#!/bin/sh
while sleep 1
do
if [ "$(top -n1 | grep -i ^cpu | awk '{print $2}')">>sy.log - ge "$Threshold" ]
then
echo "$(top -n1)" >> sys.log
fi
done
Your condition looks a bit odd. It may work, but it looks really complex. Store intermediate results in variables, and evaluate them.
Then, you will immediately see the syntax error on the “-ge”.
You HAVE to store logfiles within an absolute path for security reasons. Use variables to simplify the reading.
#!/bin/sh
LOGFILE=/absolute_path/sy.log
WHOLEFILE=/absolute_path/sys.log
Thresold=80
while sleep 1
do
TOP="$(top -n1)"
CPU="$(echo $TOP | grep -i ^cpu | awk '{print $2}')"
echo $CPU >> $LOGFILE
if [ "$CPU" -ge "$Threshold" ] ; then
echo "$TOP" >> $WHOLEFILE
fi
done

Answer 2

You have a couple of errors.
If you write output to sy.log with a redirection then that output is no longer available to the shell. You can work around this with tee.
The dash before -ge must not be followed by a space.
Also, a few stylistic remarks:
grep x | awk '{y}' is a useless use of grep; this can usefully and more economically (as well as more elegantly) be rewritten as awk '/x/{y}'
echo "$(command)" is a useless use of echo -- not a deal-breaker, but you simply want command; there is no need to capture what it prints to standard output just so you can print that text to standard output.
If you are going to capture the output of top -n 1 anyway, there is no need really to run it twice.
Further notes:
If you know the capitalization of the field you want to extract, maybe you don't need to search case-insensitively. (I could not find a version of top which prints a CPU prefix with the load in the second field -- it the expression really correct?)
The shell only supports integer arithmetic. Is this a bug? Maybe you want to use Awk (which has floating-point support) to perform the comparison? This also allows for a moderately tricky refactoring. We make Awk output an exit code of 1 if the comparison fails, and use that as the condition for the if.
#!/bin/sh
while sleep 1
do
if top=$(top -n 1 |
awk -v thres="$Threshold" '1; # print every line
tolower($1) ~ /^cpu/ { print $2 >>"sy.log";
exitcode = ($2 >= thres ? 0 : 1) }
END { exit exitcode }')
then
echo "$top" >>sys.log
fi
done
Do you really mean to have two log files with nearly the same name, or is that a typo? Including a time stamp in the log might be useful both for troubleshooting and for actually using the log files.