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28 .\" @(#)access.2 8.2 (Berkeley) 4/1/94
29 .\" $FreeBSD: release/9.0.0/lib/libc/sys/access.2 208027 2010-05-13 12:07:55Z uqs $
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.
136 Access to the file is denied if:
139 A component of the path prefix is not a directory.
140 .It Bq Er ENAMETOOLONG
141 A component of a pathname exceeded 255 characters,
142 or an entire path name exceeded 1023 characters.
144 The named file does not exist.
146 Too many symbolic links were encountered in translating the pathname.
148 Write access is requested for a file on a read-only file system.
150 Write access is requested for a pure procedure (shared text)
151 file presently being executed.
153 Permission bits of the file mode do not permit the requested
154 access, or search permission is denied on a component of the
160 points outside the process's allocated address space.
162 An I/O error occurred while reading from or writing to the file system.
167 system call may fail if:
172 argument does not specify an absolute path and the
177 nor a valid file descriptor.
181 argument is not valid.
185 argument is not an absolute path and
189 nor a file descriptor associated with a directory.
198 system call is expected to conform to
202 system call follows The Open Group Extended API Set 2 specification.
210 system call appeared in
212 .Sh SECURITY CONSIDERATIONS
216 is a potential security hole due to race conditions and
217 should never be used.
218 Set-user-ID and set-group-ID applications should restore the
219 effective user or group ID,
220 and perform actions directly rather than use
222 to simulate access checks for the real user or group ID.
226 likewise may be subject to races if used inappropriately.
229 remains useful for providing clues to users as to whether operations
230 make sense for particular filesystem objects (e.g. 'delete' menu
231 item only highlighted in a writable folder ... avoiding interpretation
232 of the st_mode bits that the application might not understand --
233 e.g. in the case of AFS).
234 It also allows a cheaper file existence test than