Flags for the linux syscall open in /usr/include/bits/fcntl.h

fcntl.h

#define O_ACCMODE          0003
#define O_RDONLY             00
#define O_WRONLY             01
#define O_RDWR               02
#define O_CREAT            0100 /* not fcntl */
#define O_EXCL             0200 /* not fcntl */
#define O_NOCTTY           0400 /* not fcntl */
#define O_TRUNC           01000 /* not fcntl */
#define O_APPEND          02000
#define O_NONBLOCK        04000
#define O_NDELAY        O_NONBLOCK
#define O_SYNC         04010000
#define O_FSYNC          O_SYNC
#define O_ASYNC          020000