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       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,  faccessat  —  determine  accessibility  of  a  file  relative  to  directory file


       #include <unistd.h>

       int access(const char *path, int amode);
       int faccessat(int fd, const char *path, int amode, int flag);


       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 ID.

       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 (F_OK).

       If any access permissions are checked, each shall be checked individually, as described in
       the  Base Definitions volume of POSIX.1‐2008, Section 4.4, File Access Permissions, except
       that where that description refers to execute permission for a  process  with  appropriate
       privileges,  an implementation may indicate success for X_OK even if execute permission is
       not granted to any user.

       The faccessat() function shall be equivalent to the access() function, except in the  case
       where  path  specifies a relative path. In this case the file whose accessibility is to be
       determined shall be located relative to the directory associated with the file  descriptor
       fd  instead  of  the  current working directory. If the file descriptor was opened without
       O_SEARCH, the function shall check whether directory  searches  are  permitted  using  the
       current  permissions  of  the  directory  underlying  the  file  descriptor.  If  the file
       descriptor was opened with O_SEARCH, the function shall not perform the check.

       If faccessat() is passed the special value AT_FDCWD  in  the  fd  parameter,  the  current
       working directory shall be used and the behavior shall be identical to a call to access().

       Values  for  flag  are  constructed  by a bitwise-inclusive OR of flags from the following
       list, defined in <fcntl.h>:

       AT_EACCESS  The checks for accessibility are performed using the effective user and  group
                   IDs instead of the real user and group ID as required in a call to access().


       Upon  successful  completion,  these  functions shall return 0. Otherwise, these functions
       shall return −1 and set errno to indicate the error.


       These functions 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 a component of a pathname 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 names an existing file that is neither a directory
              nor a symbolic link to a directory, or the path  argument  contains  at  least  one
              non-<slash> character and ends with one or more trailing <slash> characters and the
              last pathname component names an existing file that is neither a  directory  nor  a
              symbolic link to a directory.

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

       The faccessat() function shall fail if:

       EACCES fd  was not opened with O_SEARCH and the permissions of the directory underlying fd
              do not permit directory searches.

       EBADF  The path argument does not specify an absolute path and the fd argument is  neither
              AT_FDCWD nor a valid file descriptor open for reading or searching.

              The  path  argument  is not an absolute path and fd is a file descriptor associated
              with a non-directory file.

       These functions 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.

              The  length  of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic
              link produced an intermediate result with a length that exceeds {PATH_MAX}.

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

       The faccessat() function may fail if:

       EINVAL The value of the flag argument is not valid.

       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 *pathname = "/tmp/myfile";

           result = access (pathname, F_OK);


       Additional values of amode other than the set defined in the description may be valid; for
       example, if a system has extended access controls.

       The use of the AT_EACCESS value for flag enables functionality not available in access().


       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 correctly 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
       POSIX.1‐2008  now  allows  access()  to  behave  in  the  desired  way   because   several
       implementations  have  corrected  the problem. It was also argued that problem (2) is more
       easily solved by using open(), chdir(), or one of the exec functions  as  appropriate  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 POSIX.1‐2008.

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

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

       The  purpose of the faccessat() function is to enable the checking of the accessibility of
       files in directories other than the current working directory  without  exposure  to  race
       conditions.  Any  part  of  the  path  of a file could be changed in parallel to a call to
       access(), resulting in unspecified behavior. By opening a file descriptor for  the  target
       directory and using the faccessat() function it can be guaranteed that the file tested for
       accessibility is located relative to the desired directory.




       chmod(), fstatat()

       The Base Definitions  volume  of  POSIX.1‐2008,  Section  4.4,  File  Access  Permissions,
       <fcntl.h>, <unistd.h>


       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  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 .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
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