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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 $
34 .\" $DragonFly: src/lib/libc/sys/chmod.2,v 1.4 2006/05/26 19:39:37 swildner Exp $
35 .\"
36 .Dd June 4, 1993
37 .Dt CHMOD 2
38 .Os
39 .Sh NAME
40 .Nm chmod ,
41 .Nm fchmod ,
42 .Nm lchmod
43 .Nd change mode of file
44 .Sh LIBRARY
45 .Lb libc
46 .Sh SYNOPSIS
47 .In sys/stat.h
48 .Ft int
49 .Fn chmod "const char *path" "mode_t mode"
50 .Ft int
51 .Fn fchmod "int fd" "mode_t mode"
52 .Ft int
53 .Fn lchmod "const char *path" "mode_t mode"
54 .Sh DESCRIPTION
55 The file permission bits of the file named specified by
56 .Fa path
57 or referenced by the file descriptor
58 .Fa fd
59 are changed to
60 .Fa mode .
61 The
62 .Fn chmod
63 function verifies that the process owner (user) either owns
64 the file specified by
65 .Fa path
66 (or
67 .Fa fd ) ,
68 or
69 is the super-user.
70 The
71 .Fn chmod
72 function follows symbolic links to operate on the target of the link
73 rather than the link itself.
74 .Pp
75 The
76 .Fa lchmod
77 function is similar to
78 .Fn chmod
79 but does not follow symbolic links.
80 .Pp
81 A mode is created from
82 .Em or'd
83 permission bit masks
84 defined in
85 .In sys/stat.h :
86 .Pp
87 .Bd -literal -offset indent -compact
88 #define S_IRWXU 0000700 /* RWX mask for owner */
89 #define S_IRUSR 0000400 /* R for owner */
90 #define S_IWUSR 0000200 /* W for owner */
91 #define S_IXUSR 0000100 /* X for owner */
93 #define S_IRWXG 0000070 /* RWX mask for group */
94 #define S_IRGRP 0000040 /* R for group */
95 #define S_IWGRP 0000020 /* W for group */
96 #define S_IXGRP 0000010 /* X for group */
98 #define S_IRWXO 0000007 /* RWX mask for other */
99 #define S_IROTH 0000004 /* R for other */
100 #define S_IWOTH 0000002 /* W for other */
101 #define S_IXOTH 0000001 /* X for other */
103 #define S_ISUID 0004000 /* set user id on execution */
104 #define S_ISGID 0002000 /* set group id on execution */
105 #define S_ISVTX 0001000 /* sticky bit */
106 #ifndef _POSIX_SOURCE
107 #define S_ISTXT 0001000
108 #endif
109 .Ed
110 .Pp
111 The
112 .Dx
113 VM system totally ignores the sticky bit
114 .Pq Dv ISVTX
115 for executables.
116 On UFS-based filesystems (FFS, MFS, LFS) the sticky
117 bit may only be set upon directories.
118 .Pp
119 If mode
120 .Dv ISVTX
121 (the `sticky bit') is set on a directory,
122 an unprivileged user may not delete or rename
123 files of other users in that directory.
124 The sticky bit may be
125 set by any user on a directory which the user owns or has appropriate
126 permissions.
127 For more details of the properties of the sticky bit, see
128 .Xr sticky 8 .
129 .Pp
130 If mode ISUID (set UID) is set on a directory,
131 and the MNT_SUIDDIR option was used in the mount of the filesystem,
132 then the owner of any new files and sub-directories
133 created within this directory are set
134 to be the same as the owner of that directory.
135 If this function is enabled, new directories will inherit
136 the bit from their parents. Execute bits are removed from
137 the file, and it will not be given to root.
138 This behavior does not change the
139 requirements for the user to be allowed to write the file, but only the eventual
140 owner after it has been created.
141 Group inheritance is not affected.
142 .Pp
143 This feature is designed for use on fileservers serving PC users via
144 ftp, SAMBA, or netatalk.
145 It provides security holes for shell users and as
146 such should not be used on shell machines, especially on home directories.
147 This option requires the SUIDDIR
148 option in the kernel to work.
149 Only UFS filesystems support this option.
150 For more details of the suiddir mount option, see
151 .Xr mount 8 .
152 .Pp
153 Writing or changing the owner of a file
154 turns off the set-user-id and set-group-id bits
155 unless the user is the super-user.
156 This makes the system somewhat more secure
157 by protecting set-user-id (set-group-id) files
158 from remaining set-user-id (set-group-id) if they are modified,
159 at the expense of a degree of compatibility.
160 .Sh RETURN VALUES
161 .Rv -std
162 .Sh ERRORS
163 .Fn Chmod
164 will fail and the file mode will be unchanged if:
165 .Bl -tag -width Er
166 .It Bq Er ENOTDIR
167 A component of the path prefix is not a directory.
168 .It Bq Er ENAMETOOLONG
169 A component of a pathname exceeded 255 characters,
170 or an entire path name exceeded 1023 characters.
171 .It Bq Er ENOENT
172 The named file does not exist.
173 .It Bq Er EACCES
174 Search permission is denied for a component of the path prefix.
175 .It Bq Er ELOOP
176 Too many symbolic links were encountered in translating the pathname.
177 .It Bq Er EPERM
178 The effective user ID does not match the owner of the file and
179 the effective user ID is not the super-user.
180 .It Bq Er EROFS
181 The named file resides on a read-only file system.
182 .It Bq Er EFAULT
183 .Fa Path
184 points outside the process's allocated address space.
185 .It Bq Er EIO
186 An I/O error occurred while reading from or writing to the file system.
187 .It Bq Er EFTYPE
188 An attempt was made to set the sticky bit upon an executable.
189 .El
190 .Pp
191 .Fn Fchmod
192 will fail if:
193 .Bl -tag -width Er
194 .It Bq Er EBADF
195 The descriptor is not valid.
196 .It Bq Er EINVAL
197 .Fa fd
198 refers to a socket, not to a file.
199 .It Bq Er EROFS
200 The file resides on a read-only file system.
201 .It Bq Er EIO
202 An I/O error occurred while reading from or writing to the file system.
203 .El
204 .Sh SEE ALSO
205 .Xr chmod 1 ,
206 .Xr chown 2 ,
207 .Xr open 2 ,
208 .Xr stat 2 ,
209 .Xr sticky 8
210 .Sh STANDARDS
211 The
212 .Fn chmod
213 function call is expected to conform to
214 .St -p1003.1-90 ,
215 except for the return of
216 .Er EFTYPE
217 and the use of
218 .Dv S_ISTXT .
219 .Sh HISTORY
220 A
221 .Fn chmod
222 function call appeared in
223 .At v7 .
224 The
225 .Fn fchmod
226 function call
227 appeared in
228 .Bx 4.2 .
229 The
230 .Fn lchmod
231 function call appeared in
232 .Fx 3.0 .