ACCESS(2) AerieBSD 1.0 Refernce Manual ACCESS(2)


access — check access permissions of a file or pathname


#include <unistd.h>

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


The access(); function checks the accessibility of the file named by path for the access permissions indicated by mode. The value of mode is the bitwise inclusive OR of the access permissions to be checked .Pf ( Dv R_OK for read permission, W_OK for write permission, and X_OK for execute/search permission) or the existence test, F_OK. All components of the pathname path are checked for access permissions (including F_OK)).

The real user ID is used in place of the effective user ID and the real group access list (including the real group ID) is used in place of the effective ID for verifying permission.

If the invoking process has superuser privileges, access(); will always indicate success for R_OK and W_OK, regardless of the actual file permission bits. Likewise, for X_OK, if the file has any of the execute bits set and path is not a directory, access(); will indicate success.


If path cannot be found or if any of the desired access modes would not be granted, then a \-1 value is returned; otherwise a 0 value is returned.


Access to the file is denied if:
A component of the path prefix is not a directory.
A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.
The named file does not exist.
Too many symbolic links were encountered in translating the pathname.
Write access is requested for a file on a read-only file system.
Write access is requested for a pure procedure (shared text) file presently being executed.
Permission bits of the file mode do not permit the requested access, or search permission is denied on a component of the path prefix. The owner of a file has permission checked with respect to the “owner” read, write, and execute mode bits, members of the file's group other than the owner have permission checked with respect to the “group” mode bits, and all others have permissions checked with respect to the “other” mode bits.
Write access has been requested and the named file has its immutable flag set (see chflags(2/)).
path points outside the process's allocated address space.
An I/O error occurred while reading from or writing to the file system.
An invalid value was specified for mode.


chmod(2), stat(2)


The access(); function conforms to


access(); should never be used for actual access control. Doing so can result in a time of check vs. time of use security hole.

AerieBSD 1.0 Reference Manual December 26 2008 ACCESS(2)