# cat one.sh
#!/bin/ksh

if [ -f /tmp/lockfile ]; then
        exit
fi
touch /tmp/lockfile
echo "Process one doing work..."
sleep 10
echo "Process one completed work..."
rm /tmp/lockfile
# cat two.sh
#!/bin/ksh

if [ -f /tmp/lockfile ]; then
        exit
fi
touch /tmp/lockfile
echo "Process two doing work..."
sleep 10
echo "Process two completed work..."
rm /tmp/lockfile
# ./one.sh &
[1] 7377
# Process one doing work...

# ./two.sh
# ./two.sh
Process one completed work...
# ./two.sh
Process two doing work...
Process two completed work...
#