--- name: "access" section: "2" platform: "macos" package: "xnu" version: "12377.121.6" release: "macOS 26.5" platforms: ["linux", "freebsd", "macos"] url: "https://new.carta.tech/access/2" --- # access(2) check accessibility of a file ## NAME **access**, **faccessat** – check accessibility of a file ## SYNOPSIS **#include \** *int*\ **access**(*const char \*path*, *int mode*); *int*\ **faccessat**(*int fd*, *const char \*path*, *int mode*, *int flag*); ## DESCRIPTION The **access**() system call checks the accessibility of the file named by the *path* argument for the access permissions indicated by the *mode* argument. The value of *mode* is either the bitwise-inclusive OR of the access permissions to be checked (R\_OK for read permission, W\_OK for write permission, and X\_OK for execute/search permission), or the existence test (F\_OK). For additional information, see the File Access Permission section of [intro(2)](/intro/2.md). The **access**() system call uses the real user ID in place of the effective user ID, the real group ID in place of the effective group ID, and the rest of the group access list. The **faccessat**() system call is equivalent to **access**() except in the case where *path* specifies a relative path. In this case the file whose accessibility is to be determined is located relative to the directory associated with the file descriptor *fd* instead of the current working directory. If **faccessat**() is passed the special value AT\_FDCWD in the *fd* parameter, the current working directory is used and the behavior is identical to a call to **access**(). Values for *flag* are constructed by a bitwise-inclusive OR of flags from the following list, defined in ⟨fcntl.h⟩: - AT\_EACCESS The checks for accessibility are performed using the effective user and group IDs instead of the real user and group ID as required in a call to **access**(). - AT\_SYMLINK\_NOFOLLOW If *path* names a symbolic link, the status of the symbolic link is returned. - AT\_SYMLINK\_NOFOLLOW\_ANY If *path* names a symbolic link, the status of the symbolic link is returned and if the path has any other symbolic links, an error is returned. - AT\_RESOLVE\_BENEATH If *path* does not reside in the hierarchy beneath the starting directory, an error is returned. - AT\_UNIQUE If *path* resolves to a vnode with multiple hard links, an error is returned. Even if a process has appropriate privileges and indicates success for X\_OK, the file may not actually have execute permission bits set. Likewise for R\_OK and W\_OK. ## RETURN VALUES The **access()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ## ERRORS **access**() or **faccessat**() will fail if: - \[EINVAL\] The value of the *mode* argument is invalid. - \[ENOTDIR\] A component of the path prefix is not a directory. - \[ENAMETOOLONG\] A component of a pathname exceeded {NAME\_MAX} characters, or an entire path name exceeded {PATH\_MAX} characters. - \[ENOENT\] The named file does not exist. - \[ELOOP\] Too many symbolic links were encountered in translating the pathname. - \[ELOOP\] AT\_SYMLINK\_NOFOLLOW\_ANY was passed and a symbolic link was encountered in translating the pathname. - \[EROFS\] Write access is requested for a file on a read-only file system. - \[ETXTBSY\] Write access is requested for a pure procedure (shared text) file presently being executed. - \[EACCES\] Permission bits of the file mode do not permit the requested access, or search permission is denied on a component of the path prefix. - \[EFAULT\] The *path* argument points outside the process's allocated address space. - \[EIO\] An I/O error occurred while reading from or writing to the file system. Also, the **faccessat**() system call may fail if: - \[EBADF\] The *path* argument does not specify an absolute path and the *fd* argument is neither AT\_FDCWD nor a valid file descriptor. - \[EINVAL\] The value of the *flag* argument is not valid. - \[ENOTDIR\] The *path* argument is not an absolute path and *fd* is neither AT\_FDCWD nor a file descriptor associated with a directory. - \[ENOTCAPABLE\] if AT\_RESOLVE\_BENEATH was passed and *path* does not reside in the directory hierarchy beneath the starting directory. - \[ENOTCAPABLE\] if AT\_UNIQUE was passed and *path* resolves to a vnode with multiple links. ## SEE ALSO [chmod(2)](/chmod/2.md), [intro(2)](/intro/2.md), [stat(2)](/stat/2.md) ## STANDARDS The **access**() system call is expected to conform to ISO/IEC 9945-1:1990 (“POSIX.1”). The **faccessat**() system call is expected to conform to POSIX.1-2008 . ## HISTORY The **access**() function appeared in Version 7 AT&T UNIX. ## SECURITY CONSIDERATIONS The result of **access**() should not be used to make an actual access control decision, since its response, even if correct at the moment it is formed, may be outdated at the time you act on it. **access**() results should only be used to pre-flight, such as when configuring user interface elements or for optimization purposes. The actual access control decision should be made by attempting to execute the relevant system call while holding the applicable credentials, and properly handling any resulting errors; and this must be done even though **access**() may have predicted success. Additionally, set-user-ID and set-group-ID applications should restore the effective user or group ID, and perform actions directly rather than use **access**() to simulate access checks for the real user or group ID.