1 .\" Copyright (c) 1980, 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
12 .\" 3. Neither the name of the University nor the names of its contributors
13 .\" may be used to endorse or promote products derived from this software
14 .\" without specific prior written permission.
16 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
17 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
20 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 .\" @(#)access.2 8.2 (Berkeley) 4/1/94
31 .Dd September 23, 2020
38 .Nd check accessibility of a file
44 .Fn access "const char *path" "int mode"
46 .Fn eaccess "const char *path" "int mode"
48 .Fn faccessat "int fd" "const char *path" "int mode" "int flag"
54 system calls check the accessibility of the
59 for the access permissions indicated by
65 is either the bitwise-inclusive OR of the access permissions to be
70 for write permission, and
72 for execute/search permission),
76 For additional information, see the
77 .Sx "File Access Permission"
84 the effective user ID and the group access list
85 to authorize the request;
89 the real user ID in place of the effective user ID,
90 the real group ID in place of the effective group ID,
91 and the rest of the group access list.
95 system call is equivalent to
97 except in the case where
99 specifies a relative path.
100 In this case the file whose accessibility is to be determined is
101 located relative to the directory associated with the file descriptor
103 instead of the current working directory.
106 is passed the special value
110 parameter, the current working directory is used and the behavior is
111 identical to a call to
115 are constructed by a bitwise-inclusive OR of flags from the following
118 .Bl -tag -width indent
120 The checks for accessibility are performed using the effective user and group
121 IDs instead of the real user and group ID as required in a call to
124 Only operate on files and directories below the topping directory.
125 See the description of the
130 .It Dv AT_RESOLVE_BENEATH
131 Only walks paths below the topping directory.
132 See the description of the
133 .Dv O_RESOLVE_BENEATH
139 Even if a process's real or effective user has appropriate privileges
140 and indicates success for
142 the file may not actually have execute permission bits set.
161 A component of the path prefix is not a directory.
162 .It Bq Er ENAMETOOLONG
163 A component of a pathname exceeded 255 characters,
164 or an entire path name exceeded 1023 characters.
166 The named file does not exist.
168 Too many symbolic links were encountered in translating the pathname.
170 Write access is requested for a file on a read-only file system.
172 Write access is requested for a pure procedure (shared text)
173 file presently being executed.
175 Permission bits of the file mode do not permit the requested
176 access, or search permission is denied on a component of the
182 points outside the process's allocated address space.
184 An I/O error occurred while reading from or writing to the file system.
186 Corrupted data was detected while reading from the file system.
191 system call may fail if:
196 argument does not specify an absolute path and the
201 nor a valid file descriptor.
205 argument is not valid.
209 argument is not an absolute path and
213 nor a file descriptor associated with a directory.
214 .It Bq Er ENOTCAPABLE
217 or contained a ".." component leading to a
218 directory outside of the directory hierarchy specified by
220 and the process is in capability mode.
221 .It Bq Er ENOTCAPABLE
228 does not have its tail fully contained under the topping directory,
240 system call is expected to conform to
244 system call follows The Open Group Extended API Set 2 specification.
252 system call appeared in
254 .Sh SECURITY CONSIDERATIONS
258 is a potential security hole due to race conditions and
259 should never be used.
260 Set-user-ID and set-group-ID applications should restore the
261 effective user or group ID,
262 and perform actions directly rather than use
264 to simulate access checks for the real user or group ID.
268 likewise may be subject to races if used inappropriately.
271 remains useful for providing clues to users as to whether operations
272 make sense for particular filesystem objects (e.g. 'delete' menu
273 item only highlighted in a writable folder ... avoiding interpretation
274 of the st_mode bits that the application might not understand --
275 e.g. in the case of AFS).
276 It also allows a cheaper file existence test than