.\" Hey Emacs! This file is -*- nroff -*- source. .\" .\" This manpage is Copyright (C) 1992 Drew Eckhardt; .\" 1993 Michael Haardt, Ian Jackson. .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .\" Modified 1993-07-21 Rik Faith (faith@cs.unc.edu) .\" Modified 1994-08-21 by Michael Chastain (mec@shell.portal.com): .\" Removed note about old kernel (pre-1.1.44) using wrong id on path. .\" Modified 1996-03-18 by Martin Schulze (joey@infodrom.north.de): .\" Stated more clearly how it behaves with symbolic links. .\" Added correction due to Nick Duffek (nsd@bbc.com), aeb, 960426 .\" Modified 1996-09-07 by Michael Haardt: .\" Restrictions for NFS .\" Modified 1997-09-09 by Joseph S. Myers .\" Modified 1998-01-13 by Michael Haardt: .\" Using access is often insecure .\" Modified 2001-10-16 by aeb .\" Modified 2002-04-23 by Roger Luethi .\" Modified 2004-06-23 by Michael Kerrisk .\" .TH ACCESS 2 2004-06-23 "Linux" "Linux Programmer's Manual" .SH NAME access \- check user's permissions for a file .SH SYNOPSIS .nf .B #include .sp .BI "int access(const char *" pathname ", int " mode ); .fi .SH DESCRIPTION .BR access () checks whether the process would be allowed to read, write or test for existence of the file (or other file system object) whose name is .IR pathname . If .I pathname is a symbolic link permissions of the file referred to by this symbolic link are tested. .I mode is a mask consisting of one or more of .BR R_OK ", " W_OK ", " X_OK " and " F_OK . .BR R_OK ", " W_OK " and " X_OK request checking whether the file exists and has read, write and execute permissions, respectively. .B F_OK just requests checking for the existence of the file. The tests depend on the permissions of the directories occurring in the path to the file, as given in .IR pathname , and on the permissions of directories and files referred to by symbolic links encountered on the way. The check is done with the process's .I real UID and GID, rather than with the effective IDs as is done when actually attempting an operation. This is to allow set-user-ID programs to easily determine the invoking user's authority. Only access bits are checked, not the file type or contents. Therefore, if a directory is found to be "writable," it probably means that files can be created in the directory, and not that the directory can be written as a file. Similarly, a DOS file may be found to be "executable," but the .BR execve (2) call will still fail. If the process has appropriate privileges, an implementation may indicate success for .B X_OK even if none of the execute file permission bits are set. .SH "RETURN VALUE" On success (all requested permissions granted), zero is returned. On error (at least one bit in .I mode asked for a permission that is denied, or some other error occurred), \-1 is returned, and .I errno is set appropriately. .SH ERRORS .BR access () shall fail if: .TP .B EACCES The requested access would be denied to the file or search permission is denied for one of the directories in the path prefix of .IR pathname . (See also .BR path_resolution (2).) .TP .B ELOOP Too many symbolic links were encountered in resolving .IR pathname . .TP .B ENAMETOOLONG .I pathname is too long. .TP .B ENOENT A component of .I pathname does not exist or is a dangling symbolic link. .TP .B ENOTDIR A component used as a directory in .I pathname is not, in fact, a directory. .TP .B EROFS Write permission was requested for a file on a read-only filesystem. .PP .BR access () may fail if: .TP .B EFAULT .I pathname points outside your accessible address space. .TP .B EINVAL .I mode was incorrectly specified. .TP .B EIO An I/O error occurred. .TP .B ENOMEM Insufficient kernel memory was available. .TP .B ETXTBSY Write access was requested to an executable which is being executed. .SH "LINUX NOTES" In kernels before 2.6.20, .BR access () ignored the effect of the .B MS_NOEXEC flag if it was used to .BR mount (2) the underlying file system. Since kernel 2.6.20, .BR access () honours this flag. .SH RESTRICTIONS .BR access () returns an error if any of the access types in the requested call fails, even if other types might be successful. .PP .BR access () may not work correctly on NFS file systems with UID mapping enabled, because UID mapping is done on the server and hidden from the client, which checks permissions. .PP Using .BR access () to check if a user is authorized to e.g. open a file before actually doing so using .BR open (2) creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it. .SH "CONFORMING TO" SVr4, 4.3BSD, POSIX.1-2001. .SH "SEE ALSO" .BR chmod (2), .BR chown (2), .BR faccessat (2), .BR open (2), .BR path_resolution (2), .BR setgid (2), .BR setuid (2), .BR stat (2)