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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)chmod.2 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD$ 30.\" 31.Dd April 10, 2008 32.Dt CHMOD 2 33.Os 34.Sh NAME 35.Nm chmod , 36.Nm fchmod , 37.Nm lchmod , 38.Nm fchmodat 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 fchmod "int fd" "mode_t mode" 48.Ft int 49.Fn lchmod "const char *path" "mode_t mode" 50.Ft int 51.Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag" 52.Sh DESCRIPTION 53The file permission bits of the file named specified by 54.Fa path 55or referenced by the file descriptor 56.Fa fd 57are changed to 58.Fa mode . 59The 60.Fn chmod 61system call verifies that the process owner (user) either owns 62the file specified by 63.Fa path 64(or 65.Fa fd ) , 66or 67is the super-user. 68The 69.Fn chmod 70system call follows symbolic links to operate on the target of the link 71rather than the link itself. 72.Pp 73The 74.Fn lchmod 75system call is similar to 76.Fn chmod 77but does not follow symbolic links. 78.Pp 79The 80.Fn fchmodat 81is equivalent to either 82.Fn chmod 83or 84.Fn lchmod 85depending on the 86.Fa flag 87except in the case where 88.Fa path 89specifies a relative path. 90In this case the file to be changed is determined relative to the directory 91associated with the file descriptor 92.Fa fd 93instead of the current working directory. 94The values for the 95.Fa flag 96are constructed by a bitwise-inclusive OR of flags from the following list, defined 97in 98.In fcntl.h : 99.Bl -tag -width indent 100.It Dv AT_SYMLINK_NOFOLLOW 101If 102.Fa path 103names a symbolic link, then the mode of the symbolic link is changed. 104.El 105.Pp 106If 107.Fn fchmodat 108is passed the special value 109.Dv AT_FDCWD 110in the 111.Fa fd 112parameter, the current working directory is used. 113If also 114.Fa flag 115is zero, the behavior is identical to a call to 116.Fn chmod . 117.Pp 118A mode is created from 119.Em or'd 120permission bit masks 121defined in 122.In sys/stat.h : 123.Pp 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 */ 129 130#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 */ 134 135#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 */ 139 140#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 */ 144#endif 145.Ed 146.Pp 147The 148.Fx 149VM system totally ignores the sticky bit 150.Pq Dv ISTXT 151for executables. 152On UFS-based file systems (FFS, LFS) the sticky 153bit may only be set upon directories. 154.Pp 155If mode 156.Dv ISTXT 157(the `sticky bit') is set on a directory, 158an unprivileged user may not delete or rename 159files of other users in that directory. 160The sticky bit may be 161set by any user on a directory which the user owns or has appropriate 162permissions. 163For more details of the properties of the sticky bit, see 164.Xr sticky 8 . 165.Pp 166If mode ISUID (set UID) is set on a directory, 167and the MNT_SUIDDIR option was used in the mount of the file system, 168then the owner of any new files and sub-directories 169created within this directory are set 170to be the same as the owner of that directory. 171If this function is enabled, new directories will inherit 172the bit from their parents. 173Execute bits are removed from 174the file, and it will not be given to root. 175This behavior does not change the 176requirements for the user to be allowed to write the file, but only the eventual 177owner after it has been created. 178Group inheritance is not affected. 179.Pp 180This feature is designed for use on fileservers serving PC users via 181ftp, SAMBA, or netatalk. 182It provides security holes for shell users and as 183such should not be used on shell machines, especially on home directories. 184This option requires the SUIDDIR 185option in the kernel to work. 186Only UFS file systems support this option. 187For more details of the suiddir mount option, see 188.Xr mount 8 . 189.Pp 190Writing or changing the owner of a file 191turns off the set-user-id and set-group-id bits 192unless the user is the super-user. 193This makes the system somewhat more secure 194by protecting set-user-id (set-group-id) files 195from remaining set-user-id (set-group-id) if they are modified, 196at the expense of a degree of compatibility. 197.Sh RETURN VALUES 198.Rv -std 199.Sh ERRORS 200The 201.Fn chmod 202system call 203will fail and the file mode will be unchanged if: 204.Bl -tag -width Er 205.It Bq Er ENOTDIR 206A component of the path prefix is not a directory. 207.It Bq Er ENAMETOOLONG 208A component of a pathname exceeded 255 characters, 209or an entire path name exceeded 1023 characters. 210.It Bq Er ENOENT 211The named file does not exist. 212.It Bq Er EACCES 213Search permission is denied for a component of the path prefix. 214.It Bq Er ELOOP 215Too many symbolic links were encountered in translating the pathname. 216.It Bq Er EPERM 217The effective user ID does not match the owner of the file and 218the effective user ID is not the super-user. 219.It Bq Er EPERM 220The effective user ID is not the super-user, the effective user ID do match the 221owner of the file, but the group ID of the file does not match the effective 222group ID nor one of the supplementary group IDs. 223.It Bq Er EPERM 224The named file has its immutable or append-only flag set, see the 225.Xr chflags 2 226manual page for more information. 227.It Bq Er EROFS 228The named file resides on a read-only file system. 229.It Bq Er EFAULT 230The 231.Fa path 232argument 233points outside the process's allocated address space. 234.It Bq Er EIO 235An I/O error occurred while reading from or writing to the file system. 236.It Bq Er EFTYPE 237The effective user ID is not the super-user, the mode includes the sticky bit 238.Dv ( S_ISVTX ) , 239and path does not refer to a directory. 240.El 241.Pp 242The 243.Fn fchmod 244system call will fail if: 245.Bl -tag -width Er 246.It Bq Er EBADF 247The descriptor is not valid. 248.It Bq Er EINVAL 249The 250.Fa fd 251argument 252refers to a socket, not to a file. 253.It Bq Er EROFS 254The file resides on a read-only file system. 255.It Bq Er EIO 256An I/O error occurred while reading from or writing to the file system. 257.El 258.Pp 259In addition to the 260.Fn chmod 261errors, 262.Fn fchmodat 263fails if: 264.Bl -tag -width Er 265.It Bq Er EBADF 266The 267.Fa path 268argument does not specify an absolute path and the 269.Fa fd 270argument is neither 271.Fa AT_FDCWD 272nor a valid file descriptor open for searching. 273.It Bq Er EINVAL 274The value of the 275.Fa flag 276argument is not valid. 277.It Bq Er ENOTDIR 278The 279.Fa path 280argument is not an absolute path and 281.Fa fd 282is neither 283.Dv AT_FDCWD 284nor a file descriptor associated with a directory. 285.El 286.Sh SEE ALSO 287.Xr chmod 1 , 288.Xr chflags 2 , 289.Xr chown 2 , 290.Xr open 2 , 291.Xr stat 2 , 292.Xr sticky 8 293.Sh STANDARDS 294The 295.Fn chmod 296system call is expected to conform to 297.St -p1003.1-90 , 298except for the return of 299.Er EFTYPE 300and the use of 301.Dv S_ISTXT . 302The 303.Fn fchmodat 304system call follows The Open Group Extended API Set 2 specification. 305.Sh HISTORY 306The 307.Fn chmod 308function appeared in 309.At v7 . 310The 311.Fn fchmod 312system call appeared in 313.Bx 4.2 . 314The 315.Fn lchmod 316system call appeared in 317.Fx 3.0 . 318The 319.Fn fchmodat 320system call appeared in 321.Fx 8.0 . 322