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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-user-ID programs to easily determine the invoking
       user's authority.

       Only access bits are checked, not the file type	or  contents.	There‐
       fore,  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	 indi‐
       cate  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	appro‐
       priately.

ERRORS
       access() shall fail if:

       EACCES The  requested access would be denied to the file or search per‐
	      mission is denied for one of the directories in the path	prefix
	      of pathname.  (See also path_resolution(2).)

       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  exe‐
	      cuted.

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
       SVr4, POSIX.1-2001, 4.3BSD

SEE ALSO
       chmod(2),  chown(2),  faccessat(2),  open(2),  path_resolution(2), set‐
       gid(2), setuid(2), stat(2)

Linux				  2004-06-23			     ACCESS(2)
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