The access() function checks the file named by the pathname pointed to by the path argument for accessibility according to the bit pattern contained in amode, using the real user ID in place of the effective
user ID and the real group ID in place of the effective group ID. This allows a setuid process to verify that the user running it would have had permission to access this file.
The value of amode is either the bitwise inclusive OR of the access permissions to be checked (R_OK, W_OK, X_OK) or the existence test, F_OK.
These constants are defined in <unistd.h> as follows:
R_OK
Test for read permission.
W_OK
Test for write permission.
X_OK
Test for execute or search permission.
F_OK
Check existence of file
See Intro(2) for additional information about "File Access Permission".
If any access permissions are to be checked, each will be checked individually, as described in Intro(2). If the process has appropriate privileges, an implementation
may indicate success for X_OK even if none of the execute file permission bits are set.
RETURN VALUES
If the requested access is permitted, access() succeeds and returns 0. Otherwise, -1 is returned and errno is set to indicate the error.
ERRORS
The access() function will fail if:
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
path points to an illegal address.
EINTR
A signal was caught during the access() function.
ELOOP
Too many symbolic links were encountered in resolving path.
ELOOP
A loop exists in symbolic links encountered during resolution of the path argument.
ENAMETOOLONG
The length of the path argument exceeds {PATH_MAX}, or a pathname component is longer than {NAME_MAX} while _POSIX_NO_TRUNC is in effect.
ENOENT
A component of path does not name an existing file or path is an empty string.
ENOLINK
path points to a remote machine and the link to that machine is no longer active.
ENOTDIR
A component of the path prefix is not a directory.
ENXIO
The path argument points to a character or block device special file and the corresponding device has been retired by the fault management framework.
EROFS
Write access is requested for a file on a read-only file system.
The access() function may fail if:
EINVAL
The value of the amode argument is invalid.
ENAMETOOLONG
Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.
ETXTBSY
Write access is requested for a pure procedure (shared text) file that is being executed.
USAGE
Additional values of amode other than the set defined in the description might be valid, for example, if a system has extended access controls.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
