access.2freebsd

Langue: en

Autres versions - même langue

Version: 266008 (debian - 07/07/09)

Section: 2 (Appels système)


BSD mandoc

NAME

access , eaccess - check accessibility of a file

LIBRARY

Lb libc

SYNOPSIS

In unistd.h Ft int Fn access const char *path int mode Ft int Fn eaccess const char *path int mode

DESCRIPTION

The Fn access and Fn eaccess system calls check the accessibility of the file named by the Fa path argument for the access permissions indicated by the Fa mode argument. The value of Fa mode is either 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 execute/search permission), or the existence test (F_OK )

For additional information, see the Sx File Access Permission section of intro(2).

The Fn eaccess system call uses the effective user ID and the group access list to authorize the request; the Fn access system call uses the real user ID in place of the effective user ID, the real group ID in place of the effective group ID, and the rest of the group access list.

Even if a process's real or effective user has appropriate privileges and indicates success for X_OK the file may not actually have execute permission bits set. Likewise for R_OK and W_OK

RETURN VALUES

Rv -std

ERRORS

Access to the file is denied if:
Bq Er ENOTDIR
A component of the path prefix is not a directory.
Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
Bq Er ENOENT
The named file does not exist.
Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
Bq Er EROFS
Write access is requested for a file on a read-only file system.
Bq Er ETXTBSY
Write access is requested for a pure procedure (shared text) file presently being executed.
Bq Er 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.
Bq Er EFAULT
The Fa path argument points outside the process's allocated address space.
Bq Er EIO
An I/O error occurred while reading from or writing to the file system.

SECURITY CONSIDERATIONS

The Fn access system call is a potential security hole due to race conditions and should never be used. Set-user-ID and set-group-ID applications should restore the effective user or group ID, and perform actions directly rather than use Fn access to simulate access checks for the real user or group ID. The Fn eaccess system call likewise may be subject to races if used inappropriately.

Fn access remains useful for providing clues to users as to whether operations make sense for particular filesystem objects (e.g. 'delete' menu item only highlighted in a writable folder ... avoiding interpretation of the st_mode bits that the application might not understand -- e.g. in the case of AFS). It also allows a cheaper file existence test than stat(2).

SEE ALSO

chmod(2), intro(2), stat(2)

STANDARDS

The Fn access system call is expected to conform to St -p1003.1-90 .

HISTORY

The Fn access function appeared in AT&T System v7 .