Locks out changes to all file systems, and writes system buffers to the disk in preparation for turning off power to the system.

#define INCL_DOSFILEMGR
#include <os2.h>

ULONG     ulShutDownValue;  /*  Flag indicating the shutdown value. */
APIRET    ulrc;             /*  Return Code. */

ulrc = DosShutdown(ulShutDownValue);