1.\" $OpenBSD: access.2,v 1.15 2008/06/10 16:37:57 otto Exp $ 2.\" $NetBSD: access.2,v 1.7 1995/02/27 12:31:44 cgd Exp $ 3.\" 4.\" Copyright (c) 1980, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)access.2 8.2 (Berkeley) 4/1/94 32.\" 33.Dd $Mdocdate: June 10 2008 $ 34.Dt ACCESS 2 35.Os 36.Sh NAME 37.Nm access 38.Nd check access permissions of a file or pathname 39.Sh SYNOPSIS 40.Fd #include <unistd.h> 41.Ft int 42.Fn access "const char *path" "int mode" 43.Sh DESCRIPTION 44The 45.Fn access 46function checks the accessibility of the file named by 47.Fa path 48for the access permissions indicated by 49.Fa mode . 50The value of 51.Fa mode 52is the bitwise inclusive 53.Tn OR 54of the access permissions to be checked 55.Pf ( Dv R_OK 56for read permission, 57.Dv W_OK 58for write permission, and 59.Dv X_OK 60for execute/search permission) or the existence test, 61.Dv F_OK . 62All components of the pathname 63.Fa path 64are checked for access permissions (including 65.Dv F_OK ) . 66.Pp 67The real user ID is used in place of the effective user ID 68and the real group access list 69(including the real group ID) is 70used in place of the effective ID for verifying permission. 71.Pp 72If the invoking process has superuser privileges, 73.Fn access 74will always indicate success for 75.Dv R_OK 76and 77.Dv W_OK , 78regardless of the actual file permission bits. 79Likewise, for 80.Dv X_OK , 81if the file has any of the execute bits set and 82.Fa path 83is not a directory, 84.Fn access 85will indicate success. 86.Sh RETURN VALUES 87If 88.Fa path 89cannot be found or if any of the desired access modes would not be granted, 90then a \-1 value is returned; otherwise a 0 value is returned. 91.Sh ERRORS 92Access to the file is denied if: 93.Bl -tag -width Er 94.It Bq Er ENOTDIR 95A component of the path prefix is not a directory. 96.It Bq Er ENAMETOOLONG 97A component of a pathname exceeded 98.Dv {NAME_MAX} 99characters, or an entire path name exceeded 100.Dv {PATH_MAX} 101characters. 102.It Bq Er ENOENT 103The named file does not exist. 104.It Bq Er ELOOP 105Too many symbolic links were encountered in translating the pathname. 106.It Bq Er EROFS 107Write access is requested for a file on a read-only file system. 108.It Bq Er ETXTBSY 109Write access is requested for a pure procedure (shared text) 110file presently being executed. 111.It Bq Er EACCES 112Permission bits of the file mode do not permit the requested access, 113or search permission is denied on a component of the path prefix. 114The owner of a file has permission checked with respect to the 115.Dq owner 116read, write, and execute mode bits, members of the file's group other 117than the owner have permission checked with respect to the 118.Dq group 119mode bits, and all others have permissions checked with respect to the 120.Dq other 121mode bits. 122.It Bq Er EPERM 123Write access has been requested and the named file has its immutable 124flag set (see 125.Xr chflags 2 ) . 126.It Bq Er EFAULT 127.Fa path 128points outside the process's allocated address space. 129.It Bq Er EIO 130An I/O error occurred while reading from or writing to the file system. 131.It Bq Er EINVAL 132An invalid value was specified for 133.Ar mode . 134.El 135.Sh SEE ALSO 136.Xr chmod 2 , 137.Xr stat 2 138.Sh STANDARDS 139The 140.Fn access 141function conforms to 142.St -p1003.1-90 . 143.Sh CAVEATS 144.Fn access 145should never be used for actual access control. 146Doing so can result in a time of check vs. time of use security hole. 147