ACCESS(2) Linux Programmer's Manual ACCESS(2)
access - check user's permissions for a file
int access(const char *pathname, int mode);
access checks whether the process would be allowed to read, write or test for existence of
the file (or other file system object) whose name is pathname. If pathname is a symbolic
link permissions of the file referred to by this symbolic link are tested.
mode is a mask consisting of one or more of R_OK, W_OK, X_OK and F_OK.
R_OK, W_OK and X_OK request checking whether the file exists and has read, write and exe-
cute permissions, respectively. F_OK just requests checking for the existence of the
The tests depend on the permissions of the directories occurring in the path to the file,
as given in pathname, and on the permissions of directories and files referred to by sym-
bolic links encountered on the way.
The check is done with the process's real uid and gid, rather than with the effective ids
as is done when actually attempting an operation. This is to allow set-UID programs to
easily determine the invoking user's authority.
Only access bits are checked, not the file type or contents. Therefore, if a directory is
found to be "writable," it probably means that files can be created in the directory, and
not that the directory can be written as a file. Similarly, a DOS file may be found to be
"executable," but the execve(2) call will still fail.
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.
On success (all requested permissions granted), zero is returned. On error (at least one
bit in mode asked for a permission that is denied, or some other error occurred), -1 is
returned, and errno is set appropriately.
access shall fail if:
EACCES The requested access would be denied to the file or search permission is denied to
one of the directories in pathname.
ELOOP Too many symbolic links were encountered in resolving pathname.
pathname is too long.
ENOENT A directory component in pathname would have been accessible but does not exist or
was a dangling symbolic link.
A component used as a directory in pathname is not, in fact, a directory.
EROFS Write permission was requested for a file on a read-only filesystem.
access may fail if:
EFAULT pathname points outside your accessible address space.
EINVAL mode was incorrectly specified.
EIO An I/O error occurred.
ENOMEM Insufficient kernel memory was available.
Write access was requested to an executable which is being executed.
access returns an error if any of the access types in the requested call fails, even if
other types might be successful.
access may not work correctly on NFS file systems with UID mapping enabled, because UID
mapping is done on the server and hidden from the client, which checks permissions.
Using access to check if a user is authorized to e.g. open a file before actually doing so
using open(2) creates a security hole, because the user might exploit the short time
interval between checking and opening the file to manipulate it.
SVID, AT&T, POSIX, X/OPEN, BSD 4.3
stat(2), open(2), chmod(2), chown(2), setuid(2), setgid(2)
Linux 2002-04-23 ACCESS(2)