ACCESS(2) System Calls Manual ACCESS(2)NAME
access - determine accessibility of file
SYNOPSIS
access(name, mode)
char *name;
DESCRIPTION
Access checks the given file name for accessibility according to mode, which is 4 (read), 2 (write) or 1 (execute) or a combination
thereof. Specifying mode 0 tests whether the directories leading to the file can be searched and the file exists.
An appropriate error indication is returned if name cannot be found or if any of the desired access modes would not be granted. On disal-
lowed accesses -1 is returned and the error code is in errno. 0 is returned from successful tests.
The user and group IDs with respect to which permission is checked are the real UID and GID of the process, so this call is useful to set-
UID programs.
Notice that it is only access bits that are checked. A directory may be announced as writable by access, but an attempt to open it for
writing will fail (although files may be created there); a file may look executable, but exec will fail unless it is in proper format.
SEE ALSO stat(2)ASSEMBLER
(access = 33.)
sys access; name; mode
ACCESS(2)
Check Out this Related Man Page
ACCESS(2) BSD System Calls Manual ACCESS(2)NAME
access -- check access permissions of a file or pathname
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
int
access(const char *path, int mode);
DESCRIPTION
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 (R_OK for read permission, W_OK for write permission and X_OK for exe-
cute/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) are used in place of
the effective ID for verifying permission.
If a process has super-user privileges and indicates success for R_OK or W_OK, the file may not actually have read or write permission bits
set. If a process has super-user privileges and indicates success for X_OK, at least one of the user, group, or other execute bits is set.
(However, the file may still not be executable. See execve(2).)
RETURN VALUES
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.
ERRORS
Access to the file is denied 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. 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.
[EFAULT] path points outside the process's allocated address space.
[EIO] An I/O error occurred while reading from or writing to the file system.
[ELOOP] Too many symbolic links were encountered in translating the pathname.
[ENAMETOOLONG] A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.
[ENOENT] The named file does not exist.
[ENOTDIR] A component of the path prefix is not a directory.
[EROFS] Write access is requested for a file on a read-only file system.
[ETXTBSY] Write access is requested for a pure procedure (shared text) file presently being executed.
SEE ALSO chmod(2), execve(2), stat(2), secure_path(3)STANDARDS
The access() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').
SECURITY CONSIDERATIONS
The access() system call is a potential security hole due to race conditions. It should never be used. Set-user-ID and set-group-ID appli-
cations should restore the effective user or group ID, and perform actions directly rather than use access() to simulate access checks for
the real user or group ID.
The access() system call may however have some value in providing clues to users as to whether certain operations make sense for a particular
filesystem object. Arguably it also allows a cheaper file existence test than stat(2).
BSD May 3, 2010 BSD