access(S)

access -- determine accessibility of a file

Synopsis

   #include <unistd.h>
   
   int access(const char path, int amode);

Description

access checks the accessibility of a file. path points to a pathname naming a file. access checks the named file 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 bit pattern contained in amode is constructed by an OR of the following constants (defined in unistd.h):

R_OK: test for read permission
W_OK: test for write permission
X_OK: test for execute (search) permission
F_OK: test for existence of file
EX_OK: test for regular, executable file
EFF_ONLY_OK: test using effective IDs

Note that successful checking of the EXEC_OK file does not imply that the exec(S) system call will succeed on the file named by path, since the check succeeds if at least one execute bit is set; there are also additional checks made for execute permission by exec.

Return values

If the requested access is permitted, access returns 0. Otherwise, access returns -1 and sets errno to identify the reason.

In the following conditions, access sets errno to:

EACCES: Search permission is denied on a component of the path prefix.
EACCES: Access permission is denied.
EACCES: The file is not a regular file.
EFAULT: path points outside the allocated address space for the process.
EINTR: A signal was caught during the access system call.
EINVAL: amode is invalid.
ELOOP: Too many symbolic links were encountered in translating path.
EMULTIHOP: Components of path require hopping to multiple remote machines.
ENAMETOOLONG: The length of the path argument exceeds {PATH_MAX}, or the length of a path component exceeds {NAME_MAX} while _POSIX_NO_TRUNC is in effect.
ENOTDIR: A component of the path prefix is not a directory.
ENOENT: Read, write, or execute (search) permission is requested for a null pathname.
ENOENT: The named file does not exist.
ENOLINK: path points to a remote machine and the link to that machine is no longer active.
EROFS: Write access is requested for a file on a read-only file system.

References

chmod(S), intro(S), stat(S)

Notices

Privileges

The P_DACREAD and P_DACWRITE privileges allow the calling process to override mode bit and ACL (i.e., discretionary) access checks. See ``Privileges''.

Considerations for threads programming

Access rights are an attribute of the containing process and are shared by sibling threads.