Index: sys/compat/linux/linux_misc.c
===================================================================
--- sys/compat/linux/linux_misc.c
+++ sys/compat/linux/linux_misc.c
@@ -1077,6 +1077,9 @@
 	} else if (args->pid < 0) {
 		idtype = P_PGID;
 		id = (id_t)-args->pid;
+	} else if (args->pid == 0) {
+		idtype = P_PGID;
+		id = td->td_ucred->cr_rgid;
 	} else {
 		idtype = P_PID;
 		id = (id_t)args->pid;