Wraprun is a utility that enables independent applications to be launched on Cray resources under a single instance of aprun.
The OLCF enforces a policy limit of 50 parallel aprun instances per batch job due to inordinate consumption of shared resources that is proportional to the number of aprun calls. To overcome this policy limit, it is possible to combine
tasks taking approximately the same walltime into a single bundled ensemble using wraprun, which invokes aprun only once.
Wraprun is compatible with both dynamically-linked MPI applications and arbitrarily-linked serial programs. For cases where an ensemble consists of a single binary (SIMD) that does not use a GPU (on Eos for example), wraprun can launch data-independent instances of the binary on the same node, increasing task density compared to the traditional approach of parallel aprun invocations.