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30 .\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
31 .\"
32 .Dd January 4, 2009
33 .Dt CHMOD 2
34 .Os
35 .Sh NAME
36 .Nm chmod ,
37 .Nm lchmod ,
38 .Nm fchmod
39 .Nd change mode of file
40 .Sh LIBRARY
41 .Lb libc
42 .Sh SYNOPSIS
43 .In sys/stat.h
44 .Ft int
45 .Fn chmod "const char *path" "mode_t mode"
46 .Ft int
47 .Fn lchmod "const char *path" "mode_t mode"
48 .Ft int
49 .Fn fchmod "int fd" "mode_t mode"
50 .Sh DESCRIPTION
51 The function
52 .Fn chmod
53 sets the file permission bits
54 of the file
55 specified by the pathname
56 .Fa path
57 to
58 .Fa mode .
59 .Fn fchmod
60 sets the permission bits of the specified
61 file descriptor
62 .Fa fd .
63 .Fn lchmod
64 is like
65 .Fn chmod
66 except in the case where the named file is a symbolic link,
67 in which case
68 .Fn lchmod
69 sets the permission bits of the link,
70 while
71 .Fn chmod
72 sets the bits of the file the link references.
73 .Fn chmod
74 verifies that the process owner (user) either owns
75 the file specified by
76 .Fa path
77 (or
78 .Fa fd ) ,
79 or
80 is the super-user.
81 A mode is created from
82 .Em or'd
83 permission bit masks
84 defined in
85 .In sys/stat.h :
86 .Bd -literal -offset indent -compact
87 #define S_IRWXU 0000700 /* RWX mask for owner */
88 #define S_IRUSR 0000400 /* R for owner */
89 #define S_IWUSR 0000200 /* W for owner */
90 #define S_IXUSR 0000100 /* X for owner */
92 #define S_IRWXG 0000070 /* RWX mask for group */
93 #define S_IRGRP 0000040 /* R for group */
94 #define S_IWGRP 0000020 /* W for group */
95 #define S_IXGRP 0000010 /* X for group */
97 #define S_IRWXO 0000007 /* RWX mask for other */
98 #define S_IROTH 0000004 /* R for other */
99 #define S_IWOTH 0000002 /* W for other */
100 #define S_IXOTH 0000001 /* X for other */
102 #define S_ISUID 0004000 /* set user id on execution */
103 #define S_ISGID 0002000 /* set group id on execution */
104 #define S_ISVTX 0001000 /* save swapped text even after use */
105 .Ed
106 .Pp
107 If mode
108 .Dv ISVTX
109 (the
110 .Sq sticky bit )
111 is set on a regular file, it historically meant that the system should
112 save a shareable copy of the program text in the swap area.
113 When applied to commonly used programs like the shell or editor, this
114 would decrease memory usage and startup time.
115 In
116 .Nx ,
117 the sticky bit may still be set on regular files by the super-user,
118 but has no effect.
119 The historical meaning became obsolete in the 1980s with the advent of
120 memory-mapped executables, and is only documented as a matter of
121 historical interest.
122 .Pp
123 If mode
124 .Dv ISVTX
125 (the
126 .Sq sticky bit )
127 is set on a directory,
128 an unprivileged user may not delete or rename
129 files of other users in that directory.
130 The sticky bit may be set by any user on a directory which the user
131 owns or has appropriate permissions.
132 .Pp
133 For more information about the properties of the sticky bit, see
134 .Xr sticky 7 .
135 .Pp
136 Changing the owner of a file
137 turns off the set-user-id and set-group-id bits;
138 writing to a file
139 turns off the set-user-id and set-group-id bits
140 unless the user is the super-user.
141 This makes the system somewhat more secure
142 by protecting set-user-id (set-group-id) files
143 from remaining set-user-id (set-group-id) if they are modified,
144 at the expense of a degree of compatibility.
145 .Sh RETURN VALUES
146 Upon successful completion, a value of 0 is returned.
147 Otherwise, a value of \-1 is returned and
148 .Va errno
149 is set to indicate the error.
150 .Sh ERRORS
151 .Fn chmod
152 and
153 .Fn lchmod
154 will fail and the file mode will be unchanged if:
155 .Bl -tag -width Er
156 .It Bq Er ENOTDIR
157 A component of the path prefix is not a directory.
158 .It Bq Er ENAMETOOLONG
159 A component of a pathname exceeded
160 .Brq Dv NAME_MAX
161 characters, or an entire path name exceeded
162 .Brq Dv PATH_MAX
163 characters.
164 .It Bq Er ENOENT
165 The named file does not exist.
166 .It Bq Er EACCES
167 Search permission is denied for a component of the path prefix.
168 .It Bq Er ELOOP
169 Too many symbolic links were encountered in translating the pathname.
170 .It Bq Er EPERM
171 The effective user ID does not match the owner of the file and
172 the effective user ID is not the super-user.
173 .It Bq Er EPERM
174 The mode includes the setgid bit
175 .Pq Dv S_ISGID
176 but the file's group is neither the effective group ID nor is it in the
177 group access list.
178 .It Bq Er EROFS
179 The named file resides on a read-only file system.
180 .It Bq Er EFAULT
181 .Fa path
182 points outside the process's allocated address space.
183 .It Bq Er EIO
184 An I/O error occurred while reading from or writing to the file system.
185 .It Bq Er EFTYPE
186 The effective user ID is not the super-user, the
187 .Fa mode
188 includes the sticky bit
189 .Pq Dv S_ISVTX ,
190 and
191 .Fa path
192 does not refer to a directory.
193 .El
194 .Pp
195 .Fn fchmod
196 will fail if:
197 .Bl -tag -width Er
198 .It Bq Er EBADF
199 The descriptor is not valid.
200 .It Bq Er EINVAL
201 .Fa fd
202 refers to a socket, not to a file.
203 .It Bq Er EPERM
204 The effective user ID does not match the owner of the file and
205 the effective user ID is not the super-user.
206 .It Bq Er EPERM
207 The mode includes the setgid bit
208 .Pq Dv S_ISGID
209 but the file's group is neither the effective group ID nor is it in the
210 group access list.
211 .It Bq Er EROFS
212 The file resides on a read-only file system.
213 .It Bq Er EIO
214 An I/O error occurred while reading from or writing to the file system.
215 .It Bq Er EFTYPE
216 The effective user ID is not the super-user, the
217 .Fa mode
218 includes the sticky bit
219 .Pq Dv S_ISVTX ,
220 and
221 .Fa fd
222 does not refer to a directory.
223 .El
224 .Sh SEE ALSO
225 .Xr chmod 1 ,
226 .Xr chflags 2 ,
227 .Xr chown 2 ,
228 .Xr open 2 ,
229 .Xr stat 2 ,
230 .Xr getmode 3 ,
231 .Xr setmode 3 ,
232 .Xr sticky 7 ,
233 .Xr symlink 7
234 .Sh STANDARDS
235 The
236 .Fn chmod
237 function conforms to
238 .St -p1003.1-90 .
239 .Sh HISTORY
240 The
241 .Fn fchmod
242 function call
243 appeared in
244 .Bx 4.2 .
245 The
246 .Fn lchmod
247 function call appeared in
248 .Nx 1.3 .