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28 .\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
29 .\" $FreeBSD: src/lib/libc/sys/chmod.2,v 1.16.2.7 2001/12/14 18:34:00 ru Exp $
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 dirfd" "const char *path" "mode_t mode" "int flags"
53 The file permission bits of the file named specified by
55 or referenced by the file descriptor
61 function verifies that the process owner (user) either owns
70 function follows symbolic links to operate on the target of the link
71 rather than the link itself.
75 function is similar to
77 but does not follow symbolic links.
81 function is equivalent to the
85 functions except in the case where the
87 specifies a relative path.
88 In this case the file to be opened is determined relative to the directory
89 associated with the file descriptor
91 instead of the current working directory.
94 is passed the special value
98 parameter, the current working directory is used
99 and the behavior is identical to a call to
104 A mode is created from
110 .Bd -literal -offset indent -compact
111 #define S_IRWXU 0000700 /* RWX mask for owner */
112 #define S_IRUSR 0000400 /* R for owner */
113 #define S_IWUSR 0000200 /* W for owner */
114 #define S_IXUSR 0000100 /* X for owner */
116 #define S_IRWXG 0000070 /* RWX mask for group */
117 #define S_IRGRP 0000040 /* R for group */
118 #define S_IWGRP 0000020 /* W for group */
119 #define S_IXGRP 0000010 /* X for group */
121 #define S_IRWXO 0000007 /* RWX mask for other */
122 #define S_IROTH 0000004 /* R for other */
123 #define S_IWOTH 0000002 /* W for other */
124 #define S_IXOTH 0000001 /* X for other */
126 #define S_ISUID 0004000 /* set user id on execution */
127 #define S_ISGID 0002000 /* set group id on execution */
128 #define S_ISVTX 0001000 /* sticky bit */
130 #define S_ISTXT 0001000
136 VM system totally ignores the sticky bit
139 On UFS-based filesystems (FFS, MFS, LFS) the sticky
140 bit may only be set upon directories.
144 (the `sticky bit') is set on a directory,
145 an unprivileged user may not delete or rename
146 files of other users in that directory.
147 The sticky bit may be
148 set by any user on a directory which the user owns or has appropriate
150 For more details of the properties of the sticky bit, see
153 If mode ISUID (set UID) is set on a directory, and the
155 option was used in the mount of the filesystem,
156 then the owner of any new files and sub-directories
157 created within this directory are set
158 to be the same as the owner of that directory.
159 If this function is enabled, new directories will inherit
160 the bit from their parents.
161 Execute bits are removed from the file, and it will not be given to root.
162 This behavior does not change the
163 requirements for the user to be allowed to write the file, but only the eventual
164 owner after it has been created.
165 Group inheritance is not affected.
167 This feature is designed for use on fileservers serving PC users via
169 It provides security holes for shell users and as
170 such should not be used on shell machines, especially on home directories.
171 This option requires the SUIDDIR
172 option in the kernel to work.
173 Only UFS filesystems support this option.
174 For more details of the suiddir mount option, see
177 Writing or changing the owner of a file
178 turns off the set-user-id and set-group-id bits
179 unless the user is the super-user.
180 This makes the system somewhat more secure
181 by protecting set-user-id (set-group-id) files
182 from remaining set-user-id (set-group-id) if they are modified,
183 at the expense of a degree of compatibility.
187 are constructed by a bitwise-inclusive OR of flags from the following list,
190 .Bl -tag -width indent
191 .It Dv AT_SYMLINK_NOFOLLOW
194 names a symbolic link, the mode of the symbolic link is changed.
203 will fail and the file mode will be unchanged if:
206 A component of the path prefix or
209 .It Bq Er ENAMETOOLONG
210 A component of a pathname exceeded 255 characters,
211 or an entire path name exceeded 1023 characters.
213 The named file does not exist.
215 Search permission is denied for a component of the path prefix.
217 Too many symbolic links were encountered in translating the pathname.
219 The effective user ID does not match the owner of the file and
220 the effective user ID is not the super-user.
222 The named file resides on a read-only file system.
225 points outside the process's allocated address space.
227 An I/O error occurred while reading from or writing to the file system.
229 An attempt was made to set the sticky bit upon an executable.
236 The descriptor is not valid.
239 refers to a socket, not to a file.
241 The file resides on a read-only file system.
243 An I/O error occurred while reading from or writing to the file system.
254 function call is expected to conform to
256 except for the return of
263 function call appeared in
272 function call appeared in
277 system call appeared in