.\" Hey Emacs! This file is -*- nroff -*- source.
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.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
.\"                               1993 Michael Haardt, Ian Jackson.
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.\" 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.\" manual page may be incorrect or out-of-date.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
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.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
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.\" Modified Wed Jul 21 19:36:29 1993, Rik Faith (faith@cs.unc.edu)
.\" Modified 21 Aug 1994 by Michael Chastain (mec@shell.portal.com):
.\"   Removed note about old kernel (pre-1.1.44) using wrong id on path.
.\" Modified 18 Mar 1996 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 Sat Sep 07 18:17:26 MET DST 1996 by Michael Haardt:
.\"   Restrictions for NFS
.\" Modified by Joseph S. Myers <jsm28@cam.ac.uk>, 970909
.\" Modified Tue Jan 13 21:21:03 MET 1998 by Michael Haardt:
.\"   Using access is often insecure
.\"
.\" Japanese Version Copyright (c) 1997-1998 HANATAKA Shinya
.\"         all rights reserved.
.\" Translated Wed Dec 17 00:05:13 JST 1997
.\"         by HANATAKA Shinya <hanataka@abyss.rim.or.jp>
.\" Modified Mon May 11 14:47:31 JST 1998
.\"         by HANATAKA Shinya <hanataka@abyss.rim.or.jp>
.\"
.\"WORD:	user			桼
.\"WORD:	file system		ե롦ƥ
.\"WORD:	object			֥
.\"WORD:	symbolic link		ܥå
.\"WORD:	refer			Ȥ
.\"WORD:	mask			ޥ
.\"WORD:	path			ѥ
.\"WORD:	effective user-ID	¸桼ID
.\"WORD:	real user-ID		¥桼ID
.\"WORD:	uid			桼ID
.\"WORD:	gid			롼ID
.\"WORD:	directory		ǥ쥯ȥ
.\"WORD:	call			
.\"WORD:	kernel			ͥ
.\"WORD:	memory			
.\"WORD:	dangling symbolic link	줿ܥå
.\"
.TH ACCESS 2 "January 13, 1998" "Linux" "System calls"
.SH ̾
access \- 桼ΥեФ븢å򤹤
.SH 
.nf
.B #include <unistd.h>
.sp
.BI "int access(const char *" pathname ", int " mode );
.fi
.SH 
.B access

.IR pathname 
Ȥ̾ĥե(ޤ¾Υե롦ƥΥ֥)
Фƥץɤ߹ߡ񤭹ߤƤ뤫
ե뤬¸ߤƤ뤫ʤɤΥåԤʤ
.I pathname
ܥå󥯤ʤФΥܥå󥯤λȤե
Ф븢롣

.I mode

.BR R_OK ", " W_OK ", " X_OK ", " F_OK 
ΰİʾ夫鹽ޥǤ롣

.BR R_OK ", " W_OK ", " X_OK
Ϥ줾ե뤬¸ߤɤ߹ߵġ񤭹ߵġ¹ԵĤ
뤫å褦׵᤹롣
.B F_OK
ϥե뤬¸ߤ뤫ɤΤߤå褦׵᤹롣


.IR pathname 
Ϳ줿եؤΥѥ˸ǥ쥯ȥεĤ˰¸Ƥ롣
ޤܥå󥯤ˤäƻȤեؤΥǥ쥯ȥ
¸Ƥ롣

åϼºݤǻѤץμ¸(effective)ID Ǥʤ
.I (real)
桼ID  
.I (real)
롼ID ǹԤʤ롣
 set-UID ץǵư桼θ¤ꤹ뤳Ȥ
ưפˤ롣

ӥåȤΤߤå졢եμƤϥåʤ
ǡǥ쥯ȥֽ꤬񤭹߲ǽפȤʤäϡ֤ǥ쥯ȥ
ե뤳ȤǽʤȤ̣ǥ쥯ȥեȤ
񤭹ळȤǽʤ櫓ǤϤʤƱͤ DOS Υեϡּ¹Բǽפ
ȽǤ뤬
.BR execve (2)
ϼԤ
.SH ֤
(Ƥ׵ᤵ줿Ĥ줿)֤롣
顼ξ(ʤȤĤ
.I mode
׵ᤵ줿Ĥʤä䡢¾Υ顼)
\-1 ֤졢
.I errno
Ŭڤꤵ롣
.SH 顼
.TP
.B EACCES
׵ᤵ줿
Υե뼫Ȥǧ줿
.IR pathname
ؤΥǥ쥯ȥΤɤ줫˸(search permission)ʤä
.TP
.B EROFS
ɤ߹(read-only)Υե롦ƥФƽ񤭹ߵĤ
׵ᤷ
.TP
.B EFAULT
.I pathname
ǽʥɥ쥹֤γؤƤ롣
.TP
.B EINVAL
.I mode
ͤꤵ줿
.TP
.B ENAMETOOLONG
.I pathname
Ĺ᤮롣
.TP
.B ENOENT
.I pathname
Υǥ쥯ȥʬǽ¸ߤʤ줿(dangling)
ܥå󥯤Ǥ롣
.TP
.B ENOTDIR
.I pathname
Υǥ쥯ȥʬºݤˤϡǥ쥯ȥǤʤ
.TP
.B ENOMEM
ͥ˽ʬʥ꤬ʤ
.TP
.B ELOOP
.IR pathname
褹ݤ륷ܥå󥯤¿᤮롣
.TP
.B EIO
I/O 顼ȯ
.SH 
.B access
׵ᤵ줿Τɤ줫˼ԤˤϡȤ¾Τɤ줫
ȤƤ⥨顼֤
.PP
.B access
ϥ桼ID ޥåԥ󥰤Ѥ NFS ե롦ƥǤ˵ǽ
ʤ⤷ʤʤʤХ桼ID Υޥåԥ󥰤ϥСǹԤ
츢Υå򤹤륯饤ȤˤϸʤǤ롣
.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.

ºݤ
.BR open (2)
Ѥ˥ե򥪡ץ󤹤븢ǧ뤿
.B access
Ѥ뤳Ȥϥƥۡˤʤ롣ʤʤå򤷤Ƥ
ºݤ˥եΥץ򤹤֤ûֳ֤ѤǤ뤫顣
.SH 
SVID, AT&T, POSIX, X/OPEN, BSD 4.3
.SH Ϣ
.BR stat (2),
.BR open (2),
.BR chmod (2),
.BR chown (2),
.BR setuid (2),
.BR setgid (2)