1169 /* 1170 * If the new process will be in a different pid namespace 1171 * don't allow the creation of threads. 1172 */ 1173 if ((clone_flags & (CLONE_VM|CLONE_NEWPID)) && 1174 (task_active_pid_ns(current) != current->nsproxy->pid_ns)) 1175 return ERR_PTR(-EINVAL); Navigating through these calls, I discovered that task_active_pid_ns calls task_pid(), which gets the struct pid attached to the task_struct, and use this struct as an argument to ns_of_pid() ( E.G: return ns_of_pid(task_pid(tsk)) ). Reading the code carefully, I realized that ns_of_pid() returns the higher level pid_namespace attached to the struct pid. Thus, I think that the higher level pid_namespace in the struct pid will always be the active pid_namespace. When would task_active_pid_ns(current) be different than current->nsproxy->pid_ns? Sorry if this question was already asnwered somewhere, I didn't find it. Regards, Raphael S. Carvalho.