The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


access - determine accessibility of a file


#include <unistd.h>

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


The access() function checks 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 to be checked, each will be checked individually, as described in the XBD specification, Chapter 2, Definitions. 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.


If the requested access is permitted, access() succeeds and returns 0. Otherwise, -1 is returned and errno is set to indicate the error.


The access() function will fail if:
Permission bits of the file mode do not permit the requested access, or search permission is denied on a component of the path prefix.
Too many symbolic links were encountered in resolving path.
The length of the path argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
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.
Write access is requested for a file on a read-only file system.

The access() function may fail if:

The value of the amode argument is invalid.
Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.
Write access is requested for a pure procedure (shared text) file that is being executed.




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




chmod(), stat(), <unistd.h>.


Derived from Issue 1 of the SVID.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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