access system call linux
access – check access permissions of a file or pathname
int access(const char *path, int mode);
MSDOSFS, NFS_CLIENT, UFS
The access function checks the accessibility of the file named by path for the access permissions indicated by mode. The value of mode is 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 an existence test.
F_OK All components of the pathname path are checked for access
permissions (including F_OK).
The real user ID is used instead of the effective user ID, and the real group access list (including the real group ID) are used instead of the effective ID for checking permissions.
Even if a process has appropriate privileges and indicates success for X_OK,R_OK or W_OK, the file may not actually have execute permission bits set.
If path cannot be found or if any of the desired access modes would not be granted, a value of -1 is returned; otherwise a 0 value is returned.
Access to the file is denied if:
[ENOTDIR] A component of the path prefix is not a directory.
[EINVAL] The pathname contains a character with the
high-order bit set.
[ENAMETOOLONG] A component of a pathname exceeded 255
characters, or an entire path name exceeded
[ENOENT] The named file does not exist.
[ELOOP] Too many symbolic links were encountered in
translating the pathname.
[EROFS] Write access is requested for a file on a read-only
[ETXTBSY] Write access is requested for a pure procedure
(shared text) file currently 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. The owner
of a file has permissions checked with respect
to the “owner” read, write, and execute mode
bits. Members of the file’s group other than the
owner have permissions checked with respect
to the “group” mode bits, and all others have
permissions checked with respect to the “other”
[EFAULT] Path points outside the process’s allocated
[EIO] An I/O error occurred while reading from or
writing to the file system.
See attributes(5) for descriptions of the following attributes: