For a namespace clean function, implement _execve, otherwise implement execve. The implementation of this functionality will be tightly bound to any operating infrastructure for handling multiple processes.

A minimal implementation, such as that for bare metal coding, only offers a single user thread of control. It is thus impossible to start a new process, so this function always fails.

#include <errno.h>

#undef errno;
extern int  errno;

int
_execve (char  *name,
         char **argv,
         char **env)
{
  errno = ENOMEM;
  return -1;                    /* Always fails */

}       /* _execve () */
	  

The choice of errno is somewhat arbitrary. However no value for "no processes available" is provided, and ENOMEM is the closest in meaning to this.