open(2)

       #include <fcntl.h>

       int open(const char *pathname, int flags);
       int open(const char *pathname, int flags, mode_t mode);

       int creat(const char *pathname, mode_t mode);

       int openat(int dirfd, const char *pathname, int flags);
       int openat(int dirfd, const char *pathname, int flags, mode_t mode);

       /* Documented separately, in openat2(2): */
       int openat2(int dirfd, const char *pathname,
                   const struct open_how *how, size_t size);

Description

flags

access modes
- O_RDONLY
- O_WRONLY
- O_RDWR
file creation flags, file status flags
- O_CLOEXEC enable close-on-exec flag
- O_CREAT if pathname does not exist, create it as a regular file
- O_DIRECTORY if pathname is not a directory, cause the open to fail
- O_EXCL
- O_NOCTTY
- O_NOFOLLOW
- O_TMPFILE
- O_APPEND open in append mode
- O_ASYNC enable signal-driven io

자주 쓰는 플래그: 여러 프로세스들 간에 독점적인 읽기를 보장해주는 옵션. 일종의 lock 파일처럼 쓸 수 있게된다.

O_CREAT | O_EXCL