1OPEN(2) Linux Programmer's Manual OPEN(2)
2
6 open, openat, creat - open and possibly create a file
7
9 #include <sys/types.h>
10 #include <sys/stat.h>
11 #include <fcntl.h>
12 int open(const char *pathname, int flags);
14 int open(const char *pathname, int flags, mode_t mode);
15 int creat(const char *pathname, mode_t mode);
17 int openat(int dirfd, const char *pathname, int flags);
19 int openat(int dirfd, const char *pathname, int flags, mode_t mode);
20 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22 openat():
24 Since glibc 2.10:
25 _POSIX_C_SOURCE >= 200809L
26 Before glibc 2.10:
27 _ATFILE_SOURCE
28
30 The open() system call opens the file specified by pathname. If the
31 specified file does not exist, it may optionally (if O_CREAT is speci‐
32 fied in flags) be created by open().
33 The return value of open() is a file descriptor, a small, nonnegative
35 integer that is used in subsequent system calls (read(2), write(2),
36 lseek(2), fcntl(2), etc.) to refer to the open file. The file descrip‐
37 tor returned by a successful call will be the lowest-numbered file
38 descriptor not currently open for the process.
39 By default, the new file descriptor is set to remain open across an
41 execve(2) (i.e., the FD_CLOEXEC file descriptor flag described in
42 fcntl(2) is initially disabled); the O_CLOEXEC flag, described below,
43 can be used to change this default. The file offset is set to the
44 beginning of the file (see lseek(2)).
45 A call to open() creates a new open file description, an entry in the
47 system-wide table of open files. The open file description records the
48 file offset and the file status flags (see below). A file descriptor
49 is a reference to an open file description; this reference is unaf‐
50 fected if pathname is subsequently removed or modified to refer to a
51 different file. For further details on open file descriptions, see
52 NOTES.
53 The argument flags must include one of the following access modes:
55 O_RDONLY, O_WRONLY, or O_RDWR. These request opening the file read-
56 only, write-only, or read/write, respectively.
57 In addition, zero or more file creation flags and file status flags can
59 be bitwise-or'd in flags. The file creation flags are O_CLOEXEC,
60 O_CREAT, O_DIRECTORY, O_EXCL, O_NOCTTY, O_NOFOLLOW, O_TMPFILE, and
61 O_TRUNC. The file status flags are all of the remaining flags listed
62 below. The distinction between these two groups