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28 .\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
39 .Nd change mode of file
45 .Fn chmod "const char *path" "mode_t mode"
47 .Fn fchmod "int fd" "mode_t mode"
49 .Fn lchmod "const char *path" "mode_t mode"
51 .Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag"
53 The file permission bits of the file named specified by
55 or referenced by the file descriptor
61 system call verifies that the process owner (user) either owns
70 system call follows symbolic links to operate on the target of the link
71 rather than the link itself.
75 system call is similar to
77 but does not follow symbolic links.
81 is equivalent to either
87 except in the case where
89 specifies a relative path.
90 In this case the file to be changed is determined relative to the directory
91 associated with the file descriptor
93 instead of the current working directory.
96 are constructed by a bitwise-inclusive OR of flags from the following list, defined
99 .Bl -tag -width indent
100 .It Dv AT_SYMLINK_NOFOLLOW
103 names a symbolic link, then the mode of the symbolic link is changed.
105 Only allow to change permissions of a file which is beneath of
106 the topping directory.
107 See the description of the
116 is passed the special value
120 parameter, the current working directory is used.
123 is zero, the behavior is identical to a call to
126 A mode is created from
132 .Bd -literal -offset indent -compact
133 #define S_IRWXU 0000700 /* RWX mask for owner */
134 #define S_IRUSR 0000400 /* R for owner */
135 #define S_IWUSR 0000200 /* W for owner */
136 #define S_IXUSR 0000100 /* X for owner */
138 #define S_IRWXG 0000070 /* RWX mask for group */
139 #define S_IRGRP 0000040 /* R for group */
140 #define S_IWGRP 0000020 /* W for group */
141 #define S_IXGRP 0000010 /* X for group */
143 #define S_IRWXO 0000007 /* RWX mask for other */
144 #define S_IROTH 0000004 /* R for other */
145 #define S_IWOTH 0000002 /* W for other */
146 #define S_IXOTH 0000001 /* X for other */
148 #define S_ISUID 0004000 /* set user id on execution */
149 #define S_ISGID 0002000 /* set group id on execution */
150 #define S_ISVTX 0001000 /* sticky bit */
160 VM system totally ignores the sticky bit
163 On UFS-based file systems (FFS, LFS) the sticky
164 bit may only be set upon directories.
168 (the `sticky bit') is set on a directory,
169 an unprivileged user may not delete or rename
170 files of other users in that directory.
171 The sticky bit may be
172 set by any user on a directory which the user owns or has appropriate
174 For more details of the properties of the sticky bit, see
177 If mode ISUID (set UID) is set on a directory,
178 and the MNT_SUIDDIR option was used in the mount of the file system,
179 then the owner of any new files and sub-directories
180 created within this directory are set
181 to be the same as the owner of that directory.
182 If this function is enabled, new directories will inherit
183 the bit from their parents.
184 Execute bits are removed from
185 the file, and it will not be given to root.
186 This behavior does not change the
187 requirements for the user to be allowed to write the file, but only the eventual
188 owner after it has been created.
189 Group inheritance is not affected.
191 This feature is designed for use on fileservers serving PC users via
192 ftp, SAMBA, or netatalk.
193 It provides security holes for shell users and as
194 such should not be used on shell machines, especially on home directories.
195 This option requires the SUIDDIR
196 option in the kernel to work.
197 Only UFS file systems support this option.
198 For more details of the suiddir mount option, see
201 Writing or changing the owner of a file
202 turns off the set-user-id and set-group-id bits
203 unless the user is the super-user.
204 This makes the system somewhat more secure
205 by protecting set-user-id (set-group-id) files
206 from remaining set-user-id (set-group-id) if they are modified,
207 at the expense of a degree of compatibility.
214 will fail and the file mode will be unchanged if:
217 A component of the path prefix is not a directory.
218 .It Bq Er ENAMETOOLONG
219 A component of a pathname exceeded 255 characters,
220 or an entire path name exceeded 1023 characters.
222 The named file does not exist.
224 Search permission is denied for a component of the path prefix.
226 Too many symbolic links were encountered in translating the pathname.
228 The effective user ID does not match the owner of the file and
229 the effective user ID is not the super-user.
231 The effective user ID is not the super-user, the effective user ID do match the
232 owner of the file, but the group ID of the file does not match the effective
233 group ID nor one of the supplementary group IDs.
235 The named file has its immutable or append-only flag set, see the
237 manual page for more information.
239 The named file resides on a read-only file system.
244 points outside the process's allocated address space.
246 An I/O error occurred while reading from or writing to the file system.
248 The effective user ID is not the super-user, the mode includes the sticky bit
250 and path does not refer to a directory.
255 system call will fail if:
258 The descriptor is not valid.
263 refers to a socket, not to a file.
265 The file resides on a read-only file system.
267 An I/O error occurred while reading from or writing to the file system.
279 argument does not specify an absolute path and the
283 nor a valid file descriptor open for searching.
287 argument is not valid.
291 argument is not an absolute path and
295 nor a file descriptor associated with a directory.
296 .It Bq Er ENOTCAPABLE
299 or contained a ".." component leading to a
300 directory outside of the directory hierarchy specified by
302 and the process is in capability mode.
303 .It Bq Er ENOTCAPABLE
310 does not have its tail fully contained under the topping directory,
325 system call is expected to conform to
327 except for the return of
331 bit on directories is expected to conform to
335 system call is expected to conform to
344 system call appeared in
348 system call appeared in
352 system call appeared in