Question

#!/bin/bash
#
module add apps/java/1.6 
java -Xmx1024m HelloWorld

I need to set -XmxYm where Y should be the 95% of available memory on the system in Mb.

Answer 1

Here is a script that calls Java with the required heap size.

#!/bin/bash

# Total memory in KB
totalMemKB=$(awk '/MemTotal:/ { print $2 }' /proc/meminfo)

# Percentage of memory to use for Java heap
usagePercent=95

# heap size in KB
let heapKB=$totalMemKB*$usagePercent/100

# heap size in MB
let heapMB=$heapKB/1024

module add apps/java/1.6 
java -Xmx${heapMB}m HelloWorld

I strongly advise you to use a lower usagePercent, since a Java application uses more memory than the heap size (for eg. for the PermGen).