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28 .\" @(#)access.2 8.2 (Berkeley) 4/1/94
31 .Dd September 15, 2014
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
125 Even if a process's real or effective user has appropriate privileges
126 and indicates success for
128 the file may not actually have execute permission bits set.
147 A component of the path prefix is not a directory.
148 .It Bq Er ENAMETOOLONG
149 A component of a pathname exceeded 255 characters,
150 or an entire path name exceeded 1023 characters.
152 The named file does not exist.
154 Too many symbolic links were encountered in translating the pathname.
156 Write access is requested for a file on a read-only file system.
158 Write access is requested for a pure procedure (shared text)
159 file presently being executed.
161 Permission bits of the file mode do not permit the requested
162 access, or search permission is denied on a component of the
168 points outside the process's allocated address space.
170 An I/O error occurred while reading from or writing to the file system.
175 system call may fail if:
180 argument does not specify an absolute path and the
185 nor a valid file descriptor.
189 argument is not valid.
193 argument is not an absolute path and
197 nor a file descriptor associated with a directory.
206 system call is expected to conform to
210 system call follows The Open Group Extended API Set 2 specification.
218 system call appeared in
220 .Sh SECURITY CONSIDERATIONS
224 is a potential security hole due to race conditions and
225 should never be used.
226 Set-user-ID and set-group-ID applications should restore the
227 effective user or group ID,
228 and perform actions directly rather than use
230 to simulate access checks for the real user or group ID.
234 likewise may be subject to races if used inappropriately.
237 remains useful for providing clues to users as to whether operations
238 make sense for particular filesystem objects (e.g. 'delete' menu
239 item only highlighted in a writable folder ... avoiding interpretation
240 of the st_mode bits that the application might not understand --
241 e.g. in the case of AFS).
242 It also allows a cheaper file existence test than