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28 .\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
31 .Dd September 23, 2020
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
112 .It Dv AT_RESOLVE_BENEATH
113 Only walks paths below the topping directory.
114 See the description of the
115 .Dv O_RESOLVE_BENEATH
123 is passed the special value
127 parameter, the current working directory is used.
130 is zero, the behavior is identical to a call to
133 A mode is created from
139 .Bd -literal -offset indent -compact
140 #define S_IRWXU 0000700 /* RWX mask for owner */
141 #define S_IRUSR 0000400 /* R for owner */
142 #define S_IWUSR 0000200 /* W for owner */
143 #define S_IXUSR 0000100 /* X for owner */
145 #define S_IRWXG 0000070 /* RWX mask for group */
146 #define S_IRGRP 0000040 /* R for group */
147 #define S_IWGRP 0000020 /* W for group */
148 #define S_IXGRP 0000010 /* X for group */
150 #define S_IRWXO 0000007 /* RWX mask for other */
151 #define S_IROTH 0000004 /* R for other */
152 #define S_IWOTH 0000002 /* W for other */
153 #define S_IXOTH 0000001 /* X for other */
155 #define S_ISUID 0004000 /* set user id on execution */
156 #define S_ISGID 0002000 /* set group id on execution */
157 #define S_ISVTX 0001000 /* sticky bit */
167 VM system totally ignores the sticky bit
170 On UFS-based file systems (FFS, LFS) the sticky
171 bit may only be set upon directories.
175 (the `sticky bit') is set on a directory,
176 an unprivileged user may not delete or rename
177 files of other users in that directory.
178 The sticky bit may be
179 set by any user on a directory which the user owns or has appropriate
181 For more details of the properties of the sticky bit, see
184 If mode ISUID (set UID) is set on a directory,
185 and the MNT_SUIDDIR option was used in the mount of the file system,
186 then the owner of any new files and sub-directories
187 created within this directory are set
188 to be the same as the owner of that directory.
189 If this function is enabled, new directories will inherit
190 the bit from their parents.
191 Execute bits are removed from
192 the file, and it will not be given to root.
193 This behavior does not change the
194 requirements for the user to be allowed to write the file, but only the eventual
195 owner after it has been created.
196 Group inheritance is not affected.
198 This feature is designed for use on fileservers serving PC users via
199 ftp, SAMBA, or netatalk.
200 It provides security holes for shell users and as
201 such should not be used on shell machines, especially on home directories.
202 This option requires the SUIDDIR
203 option in the kernel to work.
204 Only UFS file systems support this option.
205 For more details of the suiddir mount option, see
208 Writing or changing the owner of a file
209 turns off the set-user-id and set-group-id bits
210 unless the user is the super-user.
211 This makes the system somewhat more secure
212 by protecting set-user-id (set-group-id) files
213 from remaining set-user-id (set-group-id) if they are modified,
214 at the expense of a degree of compatibility.
221 will fail and the file mode will be unchanged if:
224 A component of the path prefix is not a directory.
225 .It Bq Er ENAMETOOLONG
226 A component of a pathname exceeded 255 characters,
227 or an entire path name exceeded 1023 characters.
229 The named file does not exist.
231 Search permission is denied for a component of the path prefix.
233 Too many symbolic links were encountered in translating the pathname.
235 The effective user ID does not match the owner of the file and
236 the effective user ID is not the super-user.
238 The effective user ID is not the super-user, the effective user ID do match the
239 owner of the file, but the group ID of the file does not match the effective
240 group ID nor one of the supplementary group IDs.
242 The named file has its immutable or append-only flag set, see the
244 manual page for more information.
246 The named file resides on a read-only file system.
251 points outside the process's allocated address space.
253 An I/O error occurred while reading from or writing to the file system.
255 Corrupted data was detected while reading from the file system.
257 The effective user ID is not the super-user, the mode includes the sticky bit
259 and path does not refer to a directory.
264 system call will fail if:
267 The descriptor is not valid.
272 refers to a socket, not to a file.
274 The file resides on a read-only file system.
276 An I/O error occurred while reading from or writing to the file system.
278 Corrupted data was detected while reading from the file system.
290 argument does not specify an absolute path and the
294 nor a valid file descriptor open for searching.
298 argument is not valid.
302 argument is not an absolute path and
306 nor a file descriptor associated with a directory.
307 .It Bq Er ENOTCAPABLE
310 or contained a ".." component leading to a
311 directory outside of the directory hierarchy specified by
313 and the process is in capability mode.
314 .It Bq Er ENOTCAPABLE
321 does not have its tail fully contained under the topping directory,
336 system call is expected to conform to
338 except for the return of
342 bit on directories is expected to conform to
346 system call is expected to conform to
355 system call appeared in
359 system call appeared in
363 system call appeared in