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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.
108 is passed the special value
112 parameter, the current working directory is used.
115 is zero, the behavior is identical to a call to
118 A mode is created from
124 .Bd -literal -offset indent -compact
125 #define S_IRWXU 0000700 /* RWX mask for owner */
126 #define S_IRUSR 0000400 /* R for owner */
127 #define S_IWUSR 0000200 /* W for owner */
128 #define S_IXUSR 0000100 /* X for owner */
130 #define S_IRWXG 0000070 /* RWX mask for group */
131 #define S_IRGRP 0000040 /* R for group */
132 #define S_IWGRP 0000020 /* W for group */
133 #define S_IXGRP 0000010 /* X for group */
135 #define S_IRWXO 0000007 /* RWX mask for other */
136 #define S_IROTH 0000004 /* R for other */
137 #define S_IWOTH 0000002 /* W for other */
138 #define S_IXOTH 0000001 /* X for other */
140 #define S_ISUID 0004000 /* set user id on execution */
141 #define S_ISGID 0002000 /* set group id on execution */
142 #define S_ISVTX 0001000 /* sticky bit */
152 VM system totally ignores the sticky bit
155 On UFS-based file systems (FFS, LFS) the sticky
156 bit may only be set upon directories.
160 (the `sticky bit') 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
164 set by any user on a directory which the user owns or has appropriate
166 For more details of the properties of the sticky bit, see
169 If mode ISUID (set UID) is set on a directory,
170 and the MNT_SUIDDIR option was used in the mount of the file system,
171 then the owner of any new files and sub-directories
172 created within this directory are set
173 to be the same as the owner of that directory.
174 If this function is enabled, new directories will inherit
175 the bit from their parents.
176 Execute bits are removed from
177 the file, and it will not be given to root.
178 This behavior does not change the
179 requirements for the user to be allowed to write the file, but only the eventual
180 owner after it has been created.
181 Group inheritance is not affected.
183 This feature is designed for use on fileservers serving PC users via
184 ftp, SAMBA, or netatalk.
185 It provides security holes for shell users and as
186 such should not be used on shell machines, especially on home directories.
187 This option requires the SUIDDIR
188 option in the kernel to work.
189 Only UFS file systems support this option.
190 For more details of the suiddir mount option, see
193 Writing or changing the owner of a file
194 turns off the set-user-id and set-group-id bits
195 unless the user is the super-user.
196 This makes the system somewhat more secure
197 by protecting set-user-id (set-group-id) files
198 from remaining set-user-id (set-group-id) if they are modified,
199 at the expense of a degree of compatibility.
206 will fail and the file mode will be unchanged if:
209 A component of the path prefix is not a directory.
210 .It Bq Er ENAMETOOLONG
211 A component of a pathname exceeded 255 characters,
212 or an entire path name exceeded 1023 characters.
214 The named file does not exist.
216 Search permission is denied for a component of the path prefix.
218 Too many symbolic links were encountered in translating the pathname.
220 The effective user ID does not match the owner of the file and
221 the effective user ID is not the super-user.
223 The effective user ID is not the super-user, the effective user ID do match the
224 owner of the file, but the group ID of the file does not match the effective
225 group ID nor one of the supplementary group IDs.
227 The named file has its immutable or append-only flag set, see the
229 manual page for more information.
231 The named file resides on a read-only file system.
236 points outside the process's allocated address space.
238 An I/O error occurred while reading from or writing to the file system.
240 The effective user ID is not the super-user, the mode includes the sticky bit
242 and path does not refer to a directory.
247 system call will fail if:
250 The descriptor is not valid.
255 refers to a socket, not to a file.
257 The file resides on a read-only file system.
259 An I/O error occurred while reading from or writing to the file system.
271 argument does not specify an absolute path and the
275 nor a valid file descriptor open for searching.
279 argument is not valid.
283 argument is not an absolute path and
287 nor a file descriptor associated with a directory.
299 system call is expected to conform to
301 except for the return of
305 bit on directories is expected to conform to
309 system call is expected to conform to
318 system call appeared in
322 system call appeared in
326 system call appeared in