access(2) [netbsd 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

Check Out this Related Man Page

access(2) System Calls Manual access(2)

Name
access - determine the accessibility of file

Syntax
#include <unistd.h>
accessible = access(path, mode)
int accessible;
char *path;
int mode;

Description
The system call, checks the given file path for accessibility according to mode. The argument mode is an inclusive OR of the bits R_OK,
W_OK, and X_OK. Specifying the argument mode as F_OK tests whether the directories leading to the file can be searched and whether the
file exists.

The real user ID and the group access list (including the real group ID) are used to verify permissions. This call is useful to set-UID
programs.

Note that only access bits are checked. The call may indicate that a directory is writeable, but an attempt to open the directory fails,
although files are present in the directory. Additionally, a file may appear to be executable, but fails unless the file is in proper for-
mat.

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

Diagnostics
Access to the file is denied if any of the following is true:

[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's read, write, and execute mode bits.
Members of the file's group, other than the owner, have permission checked with respect to the group's mode bits. All oth-
ers have permissions checked with respect to the other mode bits.

[EFAULT] The 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 path component length exceeds 255 characters or the length of path exceeds 1023 characters.

[ENOENT] The file referred to by path does not exist or the path points to an empty string and the environment defined is POSIX or
SYSTEM_FIVE.

[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.

[ESTALE] The file handle given in the argument was invalid. The file referred to by that file handle no longer exists or has been
revoked.

[ETIMEDOUT] A connect request or remote file operation fails because the connected party did not respond after a period of time deter-
mined by the communications protocol.

[ETXTBSY] Write access is requested for a pure procedure (shared text) file that is being executed.

Linux and UNIX Man Pages

access(2) [netbsd man page]

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