OMP_STACKSIZE environment variable

The OMP_STACKSIZE environment variable indicates the stack size of threads created by the OpenMP run time. OMP_STACKSIZE sets the value of the stacksize-var internal control variable. OMP_STACKSIZE does not control the stack size of the master thread. The syntax is as follows:
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>>-OMP_STACKSIZE=----size--------------------------------------><

By default, the size value is represented in Kilobytes. You can also use the suffixes B, K, M, or G if you want to indicate the size in Bytes, Kilobytes, Megabytes, or Gigabytes respectively. White space is allowed between and around the size value and the suffix. For example, these two examples both indicate a stack size of 10 Megabytes.
setenv OMP_STACKSIZE 10M
setenv OMP_STACKSIZE " 10 M "
If OMP_STACKSIZE is not set, the initial value of the stacksize-var internal control variable is set to the default value. The default value for 32-bit mode is 256M. For 64-bit mode, the default is up to the limit imposed by system resources. If the compiler cannot use the stack size specified or if OMP_STACKSIZE does not conform to the correct format, the compiler sets the environment variable to the default value. If the STACK suboption of the XLSMPOPTS environment variable and the OMP_STACKSIZE environment are specified, the OMP_STACKSIZE environment variable takes precedence.