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diff --git a/man2/access.2 b/man2/access.2 new file mode 100644 index 000000000..66bbf55be --- /dev/null +++ b/man2/access.2 @@ -0,0 +1,181 @@ +.\" 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 +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date.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 <jsm28@cam.ac.uk> +.\" 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 <rl@hellgate.ch> +.\" 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 <unistd.h> +.sp +.BI "int access(const char *" pathname ", int " mode ); +.fi +.SH DESCRIPTION +.B 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-UID 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 +.B 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 directory component in +.I pathname +would have been accessible but does not exist or was 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 +.B 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 RESTRICTIONS +.B access +returns an error if any of the access types in the requested call +fails, even if other types might be successful. +.PP +.B 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 +.B 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" +SVID, AT&T, POSIX, X/OPEN, BSD 4.3 +.SH "SEE ALSO" +.BR chmod (2), +.BR chown (2), +.BR open (2), +.BR path_resolution (2), +.BR setgid (2), +.BR setuid (2), +.BR stat (2) |