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Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 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.\" 35.Dd August 9, 2009 36.Dt CHMOD 2 37.Os 38.Sh NAME 39.Nm chmod , 40.Nm fchmod , 41.Nm lchmod , 42.Nm fchmodat 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.Ft int 55.Fn fchmodat "int dirfd" "const char *path" "mode_t mode" "int flags" 56.Sh DESCRIPTION 57The file permission bits of the file named specified by 58.Fa path 59or referenced by the file descriptor 60.Fa fd 61are changed to 62.Fa mode . 63The 64.Fn chmod 65function verifies that the process owner (user) either owns 66the file specified by 67.Fa path 68(or 69.Fa fd ) , 70or 71is the super-user. 72The 73.Fn chmod 74function follows symbolic links to operate on the target of the link 75rather than the link itself. 76.Pp 77The 78.Fa lchmod 79function is similar to 80.Fn chmod 81but does not follow symbolic links. 82.Pp 83The 84.Fn fchmodat 85function is equivalent to the 86.Fn chmod 87or 88.Fn lchmod 89functions except in the case where the 90.Fa path 91specifies a relative path. 92In this case the file to be opened is determined relative to the directory 93associated with the file descriptor 94.Fa dirfd 95instead of the current working directory. 96If 97.Fn fchmodat 98is passed the special value 99.Dv AT_FDCWD 100in the 101.Fa dirfd 102parameter, the current working directory is used 103and the behavior is identical to a call to 104.Fn chmod 105or 106.Fn lchmod . 107.Pp 108A mode is created from 109.Em or'd 110permission bit masks 111defined in 112.In sys/stat.h : 113.Pp 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 */ 119 120#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 */ 124 125#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 */ 129 130#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 135#endif 136.Ed 137.Pp 138The 139.Dx 140VM system totally ignores the sticky bit 141.Pq Dv ISVTX 142for executables. 143On UFS-based filesystems (FFS, MFS, LFS) the sticky 144bit may only be set upon directories. 145.Pp 146If mode 147.Dv ISVTX 148(the `sticky bit') is set on a directory, 149an unprivileged user may not delete or rename 150files of other users in that directory. 151The sticky bit may be 152set by any user on a directory which the user owns or has appropriate 153permissions. 154For more details of the properties of the sticky bit, see 155.Xr sticky 8 . 156.Pp 157If mode ISUID (set UID) is set on a directory, 158and the MNT_SUIDDIR option was used in the mount of the filesystem, 159then the owner of any new files and sub-directories 160created within this directory are set 161to be the same as the owner of that directory. 162If this function is enabled, new directories will inherit 163the bit from their parents. Execute bits are removed from 164the file, and it will not be given to root. 165This behavior does not change the 166requirements for the user to be allowed to write the file, but only the eventual 167owner after it has been created. 168Group inheritance is not affected. 169.Pp 170This feature is designed for use on fileservers serving PC users via 171ftp or SAMBA. 172It provides security holes for shell users and as 173such should not be used on shell machines, especially on home directories. 174This option requires the SUIDDIR 175option in the kernel to work. 176Only UFS filesystems support this option. 177For more details of the suiddir mount option, see 178.Xr mount 8 . 179.Pp 180Writing or changing the owner of a file 181turns off the set-user-id and set-group-id bits 182unless the user is the super-user. 183This makes the system somewhat more secure 184by protecting set-user-id (set-group-id) files 185from remaining set-user-id (set-group-id) if they are modified, 186at the expense of a degree of compatibility. 187.Pp 188The values for the 189.Fa flags 190are constructed by a bitwise-inclusive OR of flags from the following list, 191defined in 192.In fcntl.h : 193.Bl -tag -width indent 194.It Dv AT_SYMLINK_NOFOLLOW 195If 196.Fa path 197names a symbolic link, the mode of the symbolic link is changed. 198.El 199.Sh RETURN VALUES 200.Rv -std 201.Sh ERRORS 202.Fn Chmod , 203.Fn lchmod 204and 205.Fn fchmodat 206will fail and the file mode will be unchanged if: 207.Bl -tag -width Er 208.It Bq Er ENOTDIR 209A component of the path prefix or 210.Fa dirfd 211is not a directory. 212.It Bq Er ENAMETOOLONG 213A component of a pathname exceeded 255 characters, 214or an entire path name exceeded 1023 characters. 215.It Bq Er ENOENT 216The named file does not exist. 217.It Bq Er EACCES 218Search permission is denied for a component of the path prefix. 219.It Bq Er ELOOP 220Too many symbolic links were encountered in translating the pathname. 221.It Bq Er EPERM 222The effective user ID does not match the owner of the file and 223the effective user ID is not the super-user. 224.It Bq Er EROFS 225The named file resides on a read-only file system. 226.It Bq Er EFAULT 227.Fa Path 228points outside the process's allocated address space. 229.It Bq Er EIO 230An I/O error occurred while reading from or writing to the file system. 231.It Bq Er EFTYPE 232An attempt was made to set the sticky bit upon an executable. 233.El 234.Pp 235.Fn Fchmod 236will fail if: 237.Bl -tag -width Er 238.It Bq Er EBADF 239The descriptor is not valid. 240.It Bq Er EINVAL 241.Fa fd 242refers to a socket, not to a file. 243.It Bq Er EROFS 244The file resides on a read-only file system. 245.It Bq Er EIO 246An I/O error occurred while reading from or writing to the file system. 247.El 248.Sh SEE ALSO 249.Xr chmod 1 , 250.Xr chown 2 , 251.Xr open 2 , 252.Xr stat 2 , 253.Xr sticky 8 254.Sh STANDARDS 255The 256.Fn chmod 257function call is expected to conform to 258.St -p1003.1-90 , 259except for the return of 260.Er EFTYPE 261and the use of 262.Dv S_ISTXT . 263.Sh HISTORY 264A 265.Fn chmod 266function call appeared in 267.At v7 . 268The 269.Fn fchmod 270function call 271appeared in 272.Bx 4.2 . 273The 274.Fn lchmod 275function call appeared in 276.Fx 3.0 . 277.Pp 278The 279.Fn fchmodat 280system call appeared in 281.Dx 2.3 . 282