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ACCESS(3P)		   POSIX Programmer's Manual		    ACCESS(3P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       access - determine accessibility of a file

       #include <unistd.h>

       int access(const char *path, int amode);

       The access() function shall  check  the	file  named  by	 the  pathname
       pointed	to by the path argument for accessibility according to the bit
       pattern contained in amode, using the real user	ID  in	place  of  the
       effective user ID and the real group ID in place of the effective group

       The value of amode is either the bitwise-inclusive  OR  of  the	access
       permissions  to	be  checked  (R_OK,  W_OK, X_OK) or the existence test

       If any access permissions are checked, each shall be checked  individu‐
       ally,	as    described	   in	the   Base   Definitions   volume   of
       IEEE Std 1003.1-2001, Chapter 3, Definitions. If the process has appro‐
       priate privileges, an implementation may indicate success for X_OK even
       if none of the execute file permission bits are set.

       If the requested access	is  permitted,	access()  succeeds  and	 shall
       return  0;  otherwise,  -1  shall be returned and errno shall be set to
       indicate the error.

       The access() function shall fail if:

       EACCES Permission bits of the file mode do  not	permit	the  requested
	      access,  or  search  permission  is denied on a component of the
	      path prefix.

       ELOOP  A loop exists in symbolic links encountered during resolution of
	      the path argument.

	      The length of the path argument exceeds {PATH_MAX} or a pathname
	      component is longer than {NAME_MAX}.

       ENOENT A component of path does not name an existing file or path is an
	      empty string.

	      A component of the path prefix is not a directory.

       EROFS  Write access is requested for a file on a read-only file system.

       The access() function may fail if:

       EINVAL The value of the amode argument is invalid.

       ELOOP  More  than  {SYMLOOP_MAX} symbolic links were encountered during
	      resolution of the path argument.

	      As a result of encountering a symbolic link in resolution of the
	      path  argument,  the  length  of the substituted pathname string
	      exceeded {PATH_MAX}.

	      Write access is requested for a  pure  procedure	(shared	 text)
	      file that is being executed.

       The following sections are informative.

   Testing for the Existence of a File
       The  following  example tests whether a file named myfile exists in the
       /tmp directory.

	      #include <unistd.h>
	      int result;
	      const char *filename = "/tmp/myfile";

	      result = access (filename, F_OK);

       Additional values of amode other than the set defined in	 the  descrip‐
       tion  may  be  valid; for example, if a system has extended access con‐

       In early proposals, some inadequacies in the access() function  led  to
       the creation of an eaccess() function because:

	1. Historical implementations of access() do not test file access cor‐
	   rectly when the process' real user ID is superuser. In  particular,
	   they	 always	 return	 zero when testing execute permissions without
	   regard to whether the file is executable.

	2. The superuser has complete access to all files on a	system.	 As  a
	   consequence,	 programs started by the superuser and switched to the
	   effective user ID with lesser privileges  cannot  use  access()  to
	   test their file access permissions.

       However,	 the  historical  model	 of eaccess() does not resolve problem
       (1), so this volume of  IEEE Std 1003.1-2001  now  allows  access()  to
       behave  in  the	desired	 way because several implementations have cor‐
       rected the problem. It was also argued that problem (2) is more	easily
       solved by using open(), chdir(), or one of the exec functions as appro‐
       priate and responding to the error, rather than creating a new function
       that  would not be as reliable. Therefore, eaccess() is not included in
       this volume of IEEE Std 1003.1-2001.

       The sentence concerning appropriate privileges and  execute  permission
       bits reflects the two possibilities implemented by historical implemen‐
       tations when checking superuser access for X_OK.

       New implementations are discouraged from returning X_OK unless at least
       one execution permission bit is set.


       chmod(),	 stat(),  the Base Definitions volume of IEEE Std 1003.1-2001,

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at .

IEEE/The Open Group		     2003			    ACCESS(3P)

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