disk_check:
                # testing if some disk has at least 4Go available space
                df | sed '1d' | awk '{print $$4}' | sort -n | tail -n 1 | xargs test 4000000 -lt


memory_check:
                # testing if there is at least 3Go available ram
                free -l | head -n 2 | tail -n 1 | awk '{print $$7}' | xargs test 3000000 -lt


time_check:
                # checking if system have more or less 5 seconds delay with universal time
                ntpdate -q fr.pool.ntp.org | grep -E -o 'offset.+sec$' | awk '{print int($2)}' | tr -d - | xargs test 5 -gt