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32 .\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
33 .\" $FreeBSD: src/lib/libc/sys/chmod.2,v 1.16.2.7 2001/12/14 18:34:00 ru Exp $
43 .Nd change mode of file
49 .Fn chmod "const char *path" "mode_t mode"
51 .Fn fchmod "int fd" "mode_t mode"
53 .Fn lchmod "const char *path" "mode_t mode"
55 .Fn fchmodat "int dirfd" "const char *path" "mode_t mode" "int flags"
57 The file permission bits of the file named specified by
59 or referenced by the file descriptor
65 function verifies that the process owner (user) either owns
74 function follows symbolic links to operate on the target of the link
75 rather than the link itself.
79 function is similar to
81 but does not follow symbolic links.
85 function is equivalent to the
89 functions except in the case where the
91 specifies a relative path.
92 In this case the file to be opened is determined relative to the directory
93 associated with the file descriptor
95 instead of the current working directory.
98 is passed the special value
102 parameter, the current working directory is used
103 and the behavior is identical to a call to
108 A mode is created from
114 .Bd -literal -offset indent -compact
115 #define S_IRWXU 0000700 /* RWX mask for owner */
116 #define S_IRUSR 0000400 /* R for owner */
117 #define S_IWUSR 0000200 /* W for owner */
118 #define S_IXUSR 0000100 /* X for owner */
120 #define S_IRWXG 0000070 /* RWX mask for group */
121 #define S_IRGRP 0000040 /* R for group */
122 #define S_IWGRP 0000020 /* W for group */
123 #define S_IXGRP 0000010 /* X for group */
125 #define S_IRWXO 0000007 /* RWX mask for other */
126 #define S_IROTH 0000004 /* R for other */
127 #define S_IWOTH 0000002 /* W for other */
128 #define S_IXOTH 0000001 /* X for other */
130 #define S_ISUID 0004000 /* set user id on execution */
131 #define S_ISGID 0002000 /* set group id on execution */
132 #define S_ISVTX 0001000 /* sticky bit */
133 #ifndef _POSIX_SOURCE
134 #define S_ISTXT 0001000
140 VM system totally ignores the sticky bit
143 On UFS-based filesystems (FFS, MFS, LFS) the sticky
144 bit may only be set upon directories.
148 (the `sticky bit') is set on a directory,
149 an unprivileged user may not delete or rename
150 files of other users in that directory.
151 The sticky bit may be
152 set by any user on a directory which the user owns or has appropriate
154 For more details of the properties of the sticky bit, see
157 If mode ISUID (set UID) is set on a directory,
158 and the MNT_SUIDDIR option was used in the mount of the filesystem,
159 then the owner of any new files and sub-directories
160 created within this directory are set
161 to be the same as the owner of that directory.
162 If this function is enabled, new directories will inherit
163 the bit from their parents. Execute bits are removed from
164 the file, and it will not be given to root.
165 This behavior does not change the
166 requirements for the user to be allowed to write the file, but only the eventual
167 owner after it has been created.
168 Group inheritance is not affected.
170 This feature is designed for use on fileservers serving PC users via
172 It provides security holes for shell users and as
173 such should not be used on shell machines, especially on home directories.
174 This option requires the SUIDDIR
175 option in the kernel to work.
176 Only UFS filesystems support this option.
177 For more details of the suiddir mount option, see
180 Writing or changing the owner of a file
181 turns off the set-user-id and set-group-id bits
182 unless the user is the super-user.
183 This makes the system somewhat more secure
184 by protecting set-user-id (set-group-id) files
185 from remaining set-user-id (set-group-id) if they are modified,
186 at the expense of a degree of compatibility.
190 are constructed by a bitwise-inclusive OR of flags from the following list,
193 .Bl -tag -width indent
194 .It Dv AT_SYMLINK_NOFOLLOW
197 names a symbolic link, the mode of the symbolic link is changed.
206 will fail and the file mode will be unchanged if:
209 A component of the path prefix or
212 .It Bq Er ENAMETOOLONG
213 A component of a pathname exceeded 255 characters,
214 or an entire path name exceeded 1023 characters.
216 The named file does not exist.
218 Search permission is denied for a component of the path prefix.
220 Too many symbolic links were encountered in translating the pathname.
222 The effective user ID does not match the owner of the file and
223 the effective user ID is not the super-user.
225 The named file resides on a read-only file system.
228 points outside the process's allocated address space.
230 An I/O error occurred while reading from or writing to the file system.
232 An attempt was made to set the sticky bit upon an executable.
239 The descriptor is not valid.
242 refers to a socket, not to a file.
244 The file resides on a read-only file system.
246 An I/O error occurred while reading from or writing to the file system.
257 function call is expected to conform to
259 except for the return of
266 function call appeared in
275 function call appeared in
280 system call appeared in