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RedHat 9 (Linux i386) - man page for access (redhat section 2)

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

       access - check user's permissions for a file

       #include <unistd.h>

       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)

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