ACCESS(2)						     Linux Programmer's Manual							 ACCESS(2)

NAME

       access - check user's permissions for a file

SYNOPSIS

       #include <unistd.h>

       int access(const char *pathname, int mode);

DESCRIPTION

       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 execute permissions, respectively.	F_OK just requests
       checking for the existence of the file.

       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 symbolic 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 "exe-
       cutable," 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.

RETURN VALUE

       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.

ERRORS

       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.

       ENAMETOOLONG
	      pathname is too long.

       ENOENT A directory component in pathname would have been accessible but does not exist or was a dangling symbolic link.

       ENOTDIR
	      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.

       ETXTBSY
	      Write access was requested to an executable which is being executed.

RESTRICTIONS

       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.

CONFORMING TO

       SVID, AT&T, POSIX, X/OPEN, BSD 4.3

SEE ALSO

       stat(2), open(2), chmod(2), chown(2), setuid(2), setgid(2)

Linux								    2002-04-23								 ACCESS(2)