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1 .\" $NetBSD: chmod.2,v 1.47 2013/10/15 11:43:21 njoly Exp $
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30 .\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
31 .\"
32 .Dd July 29, 2013
33 .Dt CHMOD 2
34 .Os
35 .Sh NAME
36 .Nm chmod ,
37 .Nm lchmod ,
38 .Nm fchmod ,
39 .Nm fchmodat
40 .Nd change mode of file
41 .Sh LIBRARY
42 .Lb libc
43 .Sh SYNOPSIS
44 .In sys/stat.h
45 .Ft int
46 .Fn chmod "const char *path" "mode_t mode"
47 .Ft int
48 .Fn lchmod "const char *path" "mode_t mode"
49 .Ft int
50 .Fn fchmod "int fd" "mode_t mode"
51 .In sys/stat.h
52 .In fcntl.h
53 .Ft int
54 .Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag"
55 .Sh DESCRIPTION
56 The function
57 .Fn chmod
58 sets the file permission bits
59 of the file
60 specified by the pathname
61 .Fa path
62 to
63 .Fa mode .
64 .Fn fchmod
65 sets the permission bits of the specified
66 file descriptor
67 .Fa fd .
68 .Fn lchmod
69 is like
70 .Fn chmod
71 except in the case where the named file is a symbolic link,
72 in which case
73 .Fn lchmod
74 sets the permission bits of the link,
75 while
76 .Fn chmod
77 sets the bits of the file the link references.
78 .Pp
79 .Fn fchmodat
80 works the same way as
81 .Fn chmod
82 (or
83 .Fn lchmod
84 if
85 .Dv AT_SYMLINK_NOFOLLOW
86 is set in
87 .Fa flag )
88 except if
89 .Fa path
90 is relative.
91 In that case, it is looked up from a directory whose file
92 descriptor was passed as
93 .Fa fd .
94 Search permission is required on this directory.
95 .\" (These alternatives await a decision about the semantics of O_SEARCH)
96 .\" Search permission is required on this directory
97 .\" except if
98 .\" .Fa fd
99 .\" was opened with the
100 .\" .Dv O_SEARCH
101 .\" flag.
102 .\" - or -
103 .\" This file descriptor must have been opened with the
104 .\" .Dv O_SEARCH
105 .\" flag.
106 .Fa fd
107 except if that file descriptor was opened with the
108 .Dv O_SEARCH
109 flag.
110 .Fa fd
111 can be set to
112 .Dv AT_FDCWD
113 in order to specify the current directory.
114 .Pp
115 .Fn chmod
116 verifies that the process owner (user) either owns
117 the file specified by
118 .Fa path
119 (or
120 .Fa fd ) ,
121 or
122 is the super-user.
123 A mode is created from
124 .Em or'd
125 permission bit masks
126 defined in
127 .In sys/stat.h :
128 .Bd -literal -offset indent -compact
129 #define S_IRWXU 0000700 /* RWX mask for owner */
130 #define S_IRUSR 0000400 /* R for owner */
131 #define S_IWUSR 0000200 /* W for owner */
132 #define S_IXUSR 0000100 /* X for owner */
134 #define S_IRWXG 0000070 /* RWX mask for group */
135 #define S_IRGRP 0000040 /* R for group */
136 #define S_IWGRP 0000020 /* W for group */
137 #define S_IXGRP 0000010 /* X for group */
139 #define S_IRWXO 0000007 /* RWX mask for other */
140 #define S_IROTH 0000004 /* R for other */
141 #define S_IWOTH 0000002 /* W for other */
142 #define S_IXOTH 0000001 /* X for other */
144 #define S_ISUID 0004000 /* set user id on execution */
145 #define S_ISGID 0002000 /* set group id on execution */
146 #define S_ISVTX 0001000 /* sticky bit */
147 .Ed
148 .Pp
149 The mode
150 .Dv ISVTX
151 (the
152 .Sq sticky bit )
153 can be set on regular files, but has no effect.
154 For historical reasons this can be done only by the super-user.
155 .Pp
156 If mode
157 .Dv ISVTX
158 (the
159 .Sq sticky bit )
160 is set on a directory,
161 an unprivileged user may not delete or rename
162 files of other users in that directory.
163 The sticky bit may be set by any user on a directory which the user
164 owns or has appropriate permissions.
165 .Pp
166 For more information about the history and properties of the sticky bit, see
167 .Xr sticky 7 .
168 .Pp
169 Changing the owner of a file
170 turns off the set-user-id and set-group-id bits;
171 writing to a file
172 turns off the set-user-id and set-group-id bits
173 unless the user is the super-user.
174 This makes the system somewhat more secure
175 by protecting set-user-id (set-group-id) files
176 from remaining set-user-id (set-group-id) if they are modified,
177 at the expense of a degree of compatibility.
178 .Sh RETURN VALUES
179 .Rv -std chmod lchmod fchmod fchmodat
180 .Sh ERRORS
181 .Fn chmod ,
182 .Fn lchmod
183 and
184 .Fn fchmodat
185 will fail and the file mode will be unchanged if:
186 .Bl -tag -width Er
187 .It Bq Er EACCES
188 Search permission is denied for a component of the path prefix.
189 .It Bq Er EFAULT
190 .Fa path
191 points outside the process's allocated address space.
192 .It Bq Er EFTYPE
193 The effective user ID is not the super-user, the
194 .Fa mode
195 includes the sticky bit
196 .Pq Dv S_ISVTX ,
197 and
198 .Fa path
199 does not refer to a directory.
200 .It Bq Er EIO
201 An I/O error occurred while reading from or writing to the file system.
202 .It Bq Er ELOOP
203 Too many symbolic links were encountered in translating the pathname.
204 .It Bq Er ENAMETOOLONG
205 A component of a pathname exceeded
206 .Brq Dv NAME_MAX
207 characters, or an entire path name exceeded
208 .Brq Dv PATH_MAX
209 characters.
210 .It Bq Er ENOENT
211 The named file does not exist.
212 .It Bq Er ENOTDIR
213 A component of the path prefix is not a directory.
214 .It Bq Er EPERM
215 The effective user ID does not match the owner of the file and
216 the effective user ID is not the super-user; or
217 the mode includes the setgid bit
218 .Pq Dv S_ISGID
219 but the file's group is neither the effective group ID nor is it in the
220 group access list.
221 .It Bq Er EROFS
222 The named file resides on a read-only file system.
223 .El
224 .Pp
225 In addition,
226 .Fn fchmodat
227 will fail if:
228 .Bl -tag -width Er
229 .It Bq Er EBADF
230 .Fa path
231 does not specify an absolute path and
232 .Fa fd
233 is neither
234 .Dv AT_FDCWD
235 nor a valid file descriptor open for reading or searching.
236 .It Bq Er ENOTDIR
237 .Fa path
238 is not an absolute path and
239 .Fa fd
240 is a file descriptor associated with a non-directory file.
241 .El
242 .Pp
243 .Fn fchmod
244 will fail if:
245 .Bl -tag -width Er
246 .It Bq Er EBADF
247 The descriptor is not valid.
248 .It Bq Er EFTYPE
249 The effective user ID is not the super-user, the
250 .Fa mode
251 includes the sticky bit
252 .Pq Dv S_ISVTX ,
253 and
254 .Fa fd
255 does not refer to a directory.
256 .It Bq Er EINVAL
257 .Fa fd
258 refers to a socket, not to a file.
259 .It Bq Er EIO
260 An I/O error occurred while reading from or writing to the file system.
261 .It Bq Er EPERM
262 The effective user ID does not match the owner of the file and
263 the effective user ID is not the super-user; or
264 the mode includes the setgid bit
265 .Pq Dv S_ISGID
266 but the file's group is neither the effective group ID nor is it in the
267 group access list.
268 .It Bq Er EROFS
269 The file resides on a read-only file system.
270 .El
271 .Sh SEE ALSO
272 .Xr chmod 1 ,
273 .Xr chflags 2 ,
274 .Xr chown 2 ,
275 .Xr open 2 ,
276 .Xr stat 2 ,
277 .Xr getmode 3 ,
278 .Xr setmode 3 ,
279 .Xr sticky 7 ,
280 .Xr symlink 7
281 .Sh STANDARDS
282 The
283 .Fn chmod
284 function conforms to
285 .St -p1003.1-90 .
286 .Fn fchmodat
287 function conforms to
288 .St -p1003.1-2008 .
289 .Sh HISTORY
290 The
291 .Fn fchmod
292 function call
293 appeared in
294 .Bx 4.2 .
295 The
296 .Fn lchmod
297 function call appeared in
298 .Nx 1.3 .