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NAME    [Toc]    [Back]

       access - check user's permissions for a file

SYNOPSIS    [Toc]    [Back]

       #include <unistd.h>

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

DESCRIPTION    [Toc]    [Back]

       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

       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.

RETURN VALUE    [Toc]    [Back]

       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    [Toc]    [Back]

       EACCES The requested access would be denied to the file or search  permission
 is denied to one of the directories in pathname.

       EROFS  Write  permission  was  requested  for  a  file  on  a read-only

       EFAULT pathname points outside your accessible address space.

       EINVAL mode was incorrectly specified.

       ENAMETOOLONG    [Toc]    [Back]
	      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    [Toc]    [Back]
	      A  component  used as a directory in pathname is not, in fact, a

       ENOMEM Insufficient kernel memory was available.

       ELOOP  Too many symbolic links were encountered in resolving  pathname.

       EIO    An I/O error occurred.

RESTRICTIONS    [Toc]    [Back]

       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    [Toc]    [Back]

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

SEE ALSO    [Toc]    [Back]

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

Linux				  1998-01-13			     ACCESS(2)
[ Back ]
 Similar pages
Name OS Title
access NetBSD check access permissions of a file or pathname
uucheck IRIX check the uucp directories and permissions file
access OpenBSD check access permissions of a file or pathname
uucheck HP-UX check the uucp directories and permissions file
VOP_ACCESS FreeBSD check access permissions of a file or Unix domain socket
cd_defs Tru64 sets or gets default values for the User or Group ID, or for file or directory permissions
vaccess OpenBSD check access permissions based on vnode parameters
permissions IRIX Change Permissions - Modify Permissions and Ownership of Files
acl_delete_perm Tru64 Delete permissions from a set of permissions belonging to an ACL entry
chmod Linux change permissions of a file
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