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28 .\" @(#)access.2 8.2 (Berkeley) 4/1/94
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
123 .It Dv AT_RESOLVE_BENEATH
124 Only walk paths below the directory specified by the
127 See the description of the
128 .Dv O_RESOLVE_BENEATH
134 Even if a process's real or effective user has appropriate privileges
135 and indicates success for
137 the file may not actually have execute permission bits set.
156 A component of the path prefix is not a directory.
157 .It Bq Er ENAMETOOLONG
158 A component of a pathname exceeded 255 characters,
159 or an entire path name exceeded 1023 characters.
161 The named file does not exist.
163 Too many symbolic links were encountered in translating the pathname.
165 Write access is requested for a file on a read-only file system.
167 Write access is requested for a pure procedure (shared text)
168 file presently being executed.
170 Permission bits of the file mode do not permit the requested
171 access, or search permission is denied on a component of the
177 points outside the process's allocated address space.
179 An I/O error occurred while reading from or writing to the file system.
181 Corrupted data was detected while reading from the file system.
186 system call may fail if:
191 argument does not specify an absolute path and the
196 nor a valid file descriptor.
200 argument is not valid.
204 argument is not an absolute path and
208 nor a file descriptor associated with a directory.
209 .It Bq Er ENOTCAPABLE
212 or contained a ".." component leading to a
213 directory outside of the directory hierarchy specified by
215 and the process is in capability mode.
224 system call is expected to conform to
228 system call follows The Open Group Extended API Set 2 specification.
236 system call appeared in
238 .Sh SECURITY CONSIDERATIONS
242 is a potential security hole due to race conditions and
243 should never be used.
244 Set-user-ID and set-group-ID applications should restore the
245 effective user or group ID,
246 and perform actions directly rather than use
248 to simulate access checks for the real user or group ID.
252 likewise may be subject to races if used inappropriately.
255 remains useful for providing clues to users as to whether operations
256 make sense for particular filesystem objects (e.g. 'delete' menu
257 item only highlighted in a writable folder ... avoiding interpretation
258 of the st_mode bits that the application might not understand --
259 e.g. in the case of AFS).
260 It also allows a cheaper file existence test than