The following problems with Compaq PVM were known at the time of release:
A process that has called a PVM routine may fail if it calls execl, execv, execle, execve, execlp, or execvp. The exec routine returns EWOULDBLOCK. The problem can be avoided if the process calls fork, and calls the exec routine in the child process.
When a process that has called a PVM routine forks, the child process sometimes loses some virtual memory resources. If an application uses multiple generations of processes (parent makes PVM call then forks child, which makes a PVM call then forks, and so on), the application may run out of vm-mapentries. The number of vm-mapentries available to an application can be changed using the sysconfig(8) command.