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ACCESS(2) FreeBSD System Calls Manual ACCESS(2)
NAME
access, eaccess -- check accessibility of a file
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
int
access(const char *path, int mode);
int
eaccess(const char *path, int mode);
DESCRIPTION
The access() and eaccess() system calls check the accessibility of the
file named by the path argument for the access permissions indicated by
the mode argument. The value of 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 File Access Permission section of
intro(2).
The eaccess() system call uses the effective user ID and the group access
list to authorize the request; the 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 per-
mission bits set. Likewise for R_OK and W_OK.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
Access to the file is denied if:
[ENOTDIR] A component of the path prefix is not a directory.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or
an entire path name exceeded 1023 characters.
[ENOENT] The named file does not exist.
[ELOOP] Too many symbolic links were encountered in translat-
ing the pathname.
[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.
[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.
[EFAULT] The path argument points outside the process's allo-
cated address space.
[EIO] An I/O error occurred while reading from or writing to
the file system.
SECURITY CONSIDERATIONS
The access() system call is a potential security hole due to race condi-
tions and should never be used. Set-user-ID and set-group-ID applica-
tions 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 eaccess() system call likewise may be subject to
races if used inappropriately.
SEE ALSO
chmod(2), intro(2), stat(2)
STANDARDS
The access() system call is expected to conform to ISO/IEC 9945-1:1990
(``POSIX.1'').
HISTORY
The access() function appeared in Version 7 AT&T UNIX.
FreeBSD 6.2 September 21, 2001 FreeBSD 6.2
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This page was generated on Wed Sep 19 20:03:14 BST 2007
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