Need help with a script to test for memory usage

To create a crontab entry via a Bash script you'll need to change this line:

*/5 * * * * $path/$cronfile

To something like this:

# Write out current crontab
crontab -l > mycron

# Echo new cron into cron file
echo "*/5 * * * * $path/$cronfile" >> mycron

# Install new cron file
crontab mycron
rm mycron

You could also get fancy and do it all with this one liner:

cat <(crontab -l) <(echo "*/5 * * * $path/$cronfile") | crontab -

Your script

Here's a modified version of your script that works for me.

#!/bin/sh

cronfile=memory_protect.sh    #NOTE THIS SHOULD DETECT IT'S SELF
path=$(pwd)                   #this is the path to the file 
percent_allowed=80            #this should be max memory before action

has_cron(){
    #is the file in the cron?
    #return 0 #returning this just to test should
    #be the next line but it's not working
    if crontab -l | egrep -v '^$|^#' | grep -q $cronfile; then
      return 1
    else
      return 0
    fi
}
test_memory(){
    memusage=$(top -n 1 -b | grep "Mem")
    MAXMEM=$(echo $memusage | cut -d" " -f2 | awk '{print substr($0,1,length($0)-1)}')
    USEDMEM=$(echo $memusage | cut -d" " -f4 | awk '{print substr($0,1,length($0)-1)}')

    USEDMEM1=$(expr $USEDMEM \* 100)
    PERCENTAGE=$(expr $USEDMEM1 / $MAXMEM)
    #if it's above 80% alert
    [[ $PERCENTAG>$percent_allowed ]] && return 1 || return 0
}

if has_cron;
then
    #was not here so add
    #run this script every 5 mins
    #crontab -e */5 * * * $path/$cronfile
    #cat <(crontab -l) <(echo "*/5 * * * $path/$cronfile") | crontab -
    crontab -l > mycron

    # Echo new cron into cron file
    echo "*/5 * * * * $path/$cronfile" >> mycron

    # Install new cron file
    crontab mycron
    rm mycron
else
    echo "cron present"
fi

if test_memory;
then
    #clear some memory
    echo "/etc/init.d/nginx restart"
    echo "/etc/init.d/php-fpm restart"
fi

Example

$ ./memory_protect.sh 
/etc/init.d/nginx restart
/etc/init.d/php-fpm restart

$ crontab -l
*/5 * * * * /home/saml/tst/91789/memory_protect.sh

The script needs to have these two lines modified so that it will actually restart the nginx and php-fpm services.

Change these lines: echo "/etc/init.d/nginx restart" echo "/etc/init.d/php-fpm restart"

To these:

    /etc/init.d/nginx restart
    /etc/init.d/php-fpm restart

I did this just so I could see that the script was running correctly. NOTE: that these restart lines should be prefixed with sudo if this script is running as anyone other than root!

        sudo /etc/init.d/nginx restart         sudo /etc/init.d/php-fpm restart

This use will likely need to have NOPASSWD privileges at least on these 2 scripts otherwise it will be waiting for the user that owns the cron to supply a password.

Crontab entry doesn't exist?

You'll encounter this problem when your crontab hasn't been created yet in the directory, /var/sppol/cron. You'll encounter it when you run crontab -l like this:

$ crontab -l
no crontab for saml

Double check:

$ sudo ls -l /var/spool/cron/
total 0
-rw------- 1 root root 0 Sep 16 23:47 root

So just simply make like you're going to edit it, and save the empty file to create it:

$ crontab -e

# now you're in the vim editor, add a empty line
# type "i", hit return, hit Escape,
# and do a Shift + Z + Z to save!

Now you should see this:

$ crontab -l
$ 

And this:

$ sudo ls -l /var/spool/cron/
total 0
-rw------- 1 root root 0 Sep 16 23:47 root
-rw------- 1 saml root 0 Sep 21 16:20 saml

Restarting the services

Another issue you'll run into is if this crontab entry is running as user, user1, then user1 will require sudo rights to restart them.