bproc_chgrp changes the group of node to group. A process can chagne the group to any group that that process is a member of.
On success, bproc_chgrp will return 0. On error, bproc_chgrp will return -1 and errno will be set appropriately.
The calling process isn't permitted to change the node's group or the caller isn't a member of group.
node is an invalid node number or node is down.
The BProc system is not running.