Kernel decides how much processor time is required for a process based on the nice value. Possible nice value range is: -20 to 20. A process that has a nice value of -20 is very high priority. The process that has a nice value of 20 is very low priority. Use ps axl to display the nice value of all running process as shown below.
Note: Only root user can set a negative nice value. Login as root and try the same. Please note that there is a double dash before the 10 in the nice command below.
# nice --10 ./nice-test.sh &  13060 # ps axl | grep nice-test 4 0 13060 13024 10 -10 5388 964 wait S< pts/1 0:00 /bin/bash ./nice-test.sh [Note: 6th column with value -10 is the nice value of the shell-script.]