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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 #ifndef __BSD_VISIBLE
143 #define S_ISTXT 0001000 /* sticky bit */
149 VM system totally ignores the sticky bit
152 On UFS-based file systems (FFS, LFS) the sticky
153 bit may only be set upon directories.
157 (the `sticky bit') is set on a directory,
158 an unprivileged user may not delete or rename
159 files of other users in that directory.
160 The sticky bit may be
161 set by any user on a directory which the user owns or has appropriate
163 For more details of the properties of the sticky bit, see
166 If mode ISUID (set UID) is set on a directory,
167 and the MNT_SUIDDIR option was used in the mount of the file system,
168 then the owner of any new files and sub-directories
169 created within this directory are set
170 to be the same as the owner of that directory.
171 If this function is enabled, new directories will inherit
172 the bit from their parents.
173 Execute bits are removed from
174 the file, and it will not be given to root.
175 This behavior does not change the
176 requirements for the user to be allowed to write the file, but only the eventual
177 owner after it has been created.
178 Group inheritance is not affected.
180 This feature is designed for use on fileservers serving PC users via
181 ftp, SAMBA, or netatalk.
182 It provides security holes for shell users and as
183 such should not be used on shell machines, especially on home directories.
184 This option requires the SUIDDIR
185 option in the kernel to work.
186 Only UFS file systems support this option.
187 For more details of the suiddir mount option, see
190 Writing or changing the owner of a file
191 turns off the set-user-id and set-group-id bits
192 unless the user is the super-user.
193 This makes the system somewhat more secure
194 by protecting set-user-id (set-group-id) files
195 from remaining set-user-id (set-group-id) if they are modified,
196 at the expense of a degree of compatibility.
203 will fail and the file mode will be unchanged if:
206 A component of the path prefix is not a directory.
207 .It Bq Er ENAMETOOLONG
208 A component of a pathname exceeded 255 characters,
209 or an entire path name exceeded 1023 characters.
211 The named file does not exist.
213 Search permission is denied for a component of the path prefix.
215 Too many symbolic links were encountered in translating the pathname.
217 The effective user ID does not match the owner of the file and
218 the effective user ID is not the super-user.
220 The effective user ID is not the super-user, the effective user ID do match the
221 owner of the file, but the group ID of the file does not match the effective
222 group ID nor one of the supplementary group IDs.
224 The named file has its immutable or append-only flag set, see the
226 manual page for more information.
228 The named file resides on a read-only file system.
233 points outside the process's allocated address space.
235 An I/O error occurred while reading from or writing to the file system.
237 The effective user ID is not the super-user, the mode includes the sticky bit
239 and path does not refer to a directory.
244 system call will fail if:
247 The descriptor is not valid.
252 refers to a socket, not to a file.
254 The file resides on a read-only file system.
256 An I/O error occurred while reading from or writing to the file system.
268 argument does not specify an absolute path and the
272 nor a valid file descriptor open for searching.
276 argument is not valid.
280 argument is not an absolute path and
284 nor a file descriptor associated with a directory.
296 system call is expected to conform to
298 except for the return of
304 system call follows The Open Group Extended API Set 2 specification.
312 system call appeared in
316 system call appeared in
320 system call appeared in