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1 .\" $NetBSD: chmod.2,v 1.7 1995/02/27 12:32:06 cgd Exp $
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34 .\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
35 .\"
36 .Dd June 4, 1993
37 .Dt CHMOD 2
38 .Os BSD 4
39 .Sh NAME
40 .Nm chmod ,
41 .Nm fchmod ,
42 .Nm fchmodat
43 .Nd change mode of file
44 .Sh SYNOPSIS
45 .Fd #include <sys/types.h>
46 .Fd #include <sys/stat.h>
47 .Ft int
48 .Fo chmod
49 .Fa "const char *path"
50 .Fa "mode_t mode"
51 .Fc
52 .Ft int
53 .Fo fchmod
54 .Fa "int fildes"
55 .Fa "mode_t mode"
56 .Fc
57 .Ft int
58 .Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag"
59 .Sh DESCRIPTION
60 The function
61 .Fn chmod
62 sets the file permission bits
63 of the file
64 specified by the pathname
65 .Fa path
66 to
67 .Fa mode .
68 .Fn fchmod
69 sets the permission bits of the specified
70 file descriptor
71 .Fa fildes .
72 .Fn chmod
73 verifies that the process owner (user) either owns
74 the file specified by
75 .Fa path
76 (or
77 .Fa fildes ) ,
78 or
79 is the super-user.
80 .Pp
81 The
82 .Fn fchmodat
83 is equivalent to
84 .Fn chmod
85 except in the case where
86 .Fa path
87 specifies a relative path.
88 In this case the file to be changed is determined relative to the directory
89 associated with the file descriptor
90 .Fa fd
91 instead of the current working directory.
92 The values for the
93 .Fa flag
94 are constructed by a bitwise-inclusive OR of flags from the following list, defined
95 in
96 .In fcntl.h :
97 .Bl -tag -width indent
98 .It Dv AT_SYMLINK_NOFOLLOW
99 If
100 .Fa path
101 names a symbolic link, then the mode of the symbolic link is changed.
102 .El
103 .Pp
104 If
105 .Fn fchmodat
106 is passed the special value
107 .Dv AT_FDCWD
108 in the
109 .Fa fd
110 parameter, the current working directory is used.
111 If also
112 .Fa flag
113 is zero, the behavior is identical to a call to
114 .Fn chmod .
115 A mode is created from
116 .Em or'd
117 permission bit masks
118 defined in
119 .Aq Pa sys/stat.h :
120 .Bd -literal -offset indent -compact
121 #define S_IRWXU 0000700 /* RWX mask for owner */
122 #define S_IRUSR 0000400 /* R for owner */
123 #define S_IWUSR 0000200 /* W for owner */
124 #define S_IXUSR 0000100 /* X for owner */
125
126 #define S_IRWXG 0000070 /* RWX mask for group */
127 #define S_IRGRP 0000040 /* R for group */
128 #define S_IWGRP 0000020 /* W for group */
129 #define S_IXGRP 0000010 /* X for group */
130
131 #define S_IRWXO 0000007 /* RWX mask for other */
132 #define S_IROTH 0000004 /* R for other */
133 #define S_IWOTH 0000002 /* W for other */
134 #define S_IXOTH 0000001 /* X for other */
135
136 #define S_ISUID 0004000 /* set user id on execution */
137 #define S_ISGID 0002000 /* set group id on execution */
138 #define S_ISVTX 0001000 /* save swapped text even after use */
139 .Ed
140 .Pp
141 The
142 .Dv ISVTX
143 (the
144 .Em sticky bit )
145 indicates to the system which executable files are shareable (the
146 default) and the system maintains the program text of the files
147 in the swap area. The sticky bit may only be set by the super user
148 on shareable executable files.
149 .Pp
150 If mode
151 .Dv ISVTX
152 (the `sticky bit') is set on a directory,
153 an unprivileged user may not delete or rename
154 files of other users in that directory. The sticky bit may be
155 set by any user on a directory which the user owns or has appropriate
156 permissions.
157 For more details of the properties of the sticky bit, see
158 .Xr sticky 8 .
159 .Pp
160 Writing or changing the owner of a file
161 turns off the set-user-id and set-group-id bits
162 unless the user is the super-user.
163 This makes the system somewhat more secure
164 by protecting set-user-id (set-group-id) files
165 from remaining set-user-id (set-group-id) if they are modified,
166 at the expense of a degree of compatibility.
167 .Sh RETURN VALUES
168 Upon successful completion, a value of 0 is returned.
169 Otherwise, a value of -1 is returned and
170 .Va errno
171 is set to indicate the error.
172 .Sh ERRORS
173 The
174 .Fn chmod
175 system call will fail and the file mode will be unchanged if:
176 .Bl -tag -width Er
177 .\" ==========
178 .It Bq Er EACCES
179 Search permission is denied for a component of the path prefix.
180 .\" ==========
181 .It Bq Er EFAULT
182 .Fa Path
183 points outside the process's allocated address space.
184 .\" ==========
185 .It Bq Er EINTR
186 Its execution was interrupted by a signal.
187 .\" ==========
188 .It Bq Er EIO
189 An I/O error occurred while reading from or writing to the file system.
190 .\" ==========
191 .It Bq Er ELOOP
192 Too many symbolic links were encountered in translating the pathname.
193 This is taken to be indicative of a looping symbolic link.
194 .\" ==========
195 .It Bq Er ENAMETOOLONG
196 A component of a pathname exceeded
197 .Dv {NAME_MAX}
198 characters, or an entire path name exceeded
199 .Dv {PATH_MAX}
200 characters.
201 .\" ==========
202 .It Bq Er ENOENT
203 The named file does not exist.
204 .\" ==========
205 .It Bq Er ENOTDIR
206 A component of the path prefix is not a directory.
207 .\" ==========
208 .It Bq Er EPERM
209 The effective user ID does not match the owner of the file and
210 the effective user ID is not the super-user.
211 .\" ==========
212 .It Bq Er EROFS
213 The named file resides on a read-only file system.
214 .El
215 .Pp
216 .Fn fchmod
217 will fail if:
218 .Bl -tag -width Er
219 .\" ==========
220 .It Bq Er EBADF
221 .Fa fildes
222 is not a valid file descriptor.
223 .\" ==========
224 .It Bq Er EINVAL
225 .Fa fildes
226 refers to a socket, not to a file.
227 .\" ==========
228 .It Bq Er EINVAL
229 .Fa mode
230 is not a valid file mode.
231 .\" ==========
232 .It Bq Er EINTR
233 Its execution was interrupted by a signal.
234 .\" ==========
235 .It Bq Er EIO
236 An I/O error occurred while reading from or writing to the file system.
237 .\" ==========
238 .It Bq Er EPERM
239 The effective user ID does not match the owner of the file and
240 the effective user ID is not the super-user.
241 .\" ==========
242 .It Bq Er EROFS
243 The file resides on a read-only file system.
244 .El
245 .Pp
246 In addition to the
247 .Fn chmod
248 errors,
249 .Fn fchmodat
250 fails if:
251 .Bl -tag -width Er
252 .It Bq Er EBADF
253 The
254 .Fa path
255 argument does not specify an absolute path and the
256 .Fa fd
257 argument is neither
258 .Fa AT_FDCWD
259 nor a valid file descriptor open for searching.
260 .It Bq Er EINVAL
261 The value of the
262 .Fa flag
263 argument is not valid.
264 .It Bq Er ENOTDIR
265 The
266 .Fa path
267 argument is not an absolute path and
268 .Fa fd
269 is neither
270 .Dv AT_FDCWD
271 nor a file descriptor associated with a directory.
272 .El
273 .Sh LEGACY SYNOPSIS
274 .Fd #include <sys/types.h>
275 .Fd #include <sys/stat.h>
276 .Pp
277 The include file
278 .In sys/types.h
279 is necessary.
280 .Sh SEE ALSO
281 .Xr chmod 1 ,
282 .Xr chown 2 ,
283 .Xr open 2 ,
284 .Xr stat 2 ,
285 .Xr compat 5 ,
286 .Xr sticky 8
287 .Sh STANDARDS
288 The
289 .Fn chmod
290 function is expected to conform to
291 .St -p1003.1-88 .
292 The
293 .Fn fchmodat
294 function is expected to conform to POSIX.1-2008 .
295 .Sh HISTORY
296 The
297 .Fn fchmod
298 function call
299 appeared in
300 .Bx 4.2 .
301 The
302 .Fn fchmodat
303 system call appeared in OS X 10.10