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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 January 16, 2006 32.Dt CHMOD 2 33.Os 34.Sh NAME 35.Nm chmod , 36.Nm fchmod , 37.Nm lchmod 38.Nd change mode of file 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/stat.h 43.Ft int 44.Fn chmod "const char *path" "mode_t mode" 45.Ft int 46.Fn fchmod "int fd" "mode_t mode" 47.Ft int 48.Fn lchmod "const char *path" "mode_t mode" 49.Sh DESCRIPTION 50The file permission bits of the file named specified by 51.Fa path 52or referenced by the file descriptor 53.Fa fd 54are changed to 55.Fa mode . 56The 57.Fn chmod 58system call verifies that the process owner (user) either owns 59the file specified by 60.Fa path 61(or 62.Fa fd ) , 63or 64is the super-user. 65The 66.Fn chmod 67system call follows symbolic links to operate on the target of the link 68rather than the link itself. 69.Pp 70The 71.Fn lchmod 72system call is similar to 73.Fn chmod 74but does not follow symbolic links. 75.Pp 76A mode is created from 77.Em or'd 78permission bit masks 79defined in 80.In sys/stat.h : 81.Pp 82.Bd -literal -offset indent -compact 83#define S_IRWXU 0000700 /* RWX mask for owner */ 84#define S_IRUSR 0000400 /* R for owner */ 85#define S_IWUSR 0000200 /* W for owner */ 86#define S_IXUSR 0000100 /* X for owner */ 87 88#define S_IRWXG 0000070 /* RWX mask for group */ 89#define S_IRGRP 0000040 /* R for group */ 90#define S_IWGRP 0000020 /* W for group */ 91#define S_IXGRP 0000010 /* X for group */ 92 93#define S_IRWXO 0000007 /* RWX mask for other */ 94#define S_IROTH 0000004 /* R for other */ 95#define S_IWOTH 0000002 /* W for other */ 96#define S_IXOTH 0000001 /* X for other */ 97 98#define S_ISUID 0004000 /* set user id on execution */ 99#define S_ISGID 0002000 /* set group id on execution */ 100#ifndef __BSD_VISIBLE 101#define S_ISTXT 0001000 /* sticky bit */ 102#endif 103.Ed 104.Pp 105The 106.Fx 107VM system totally ignores the sticky bit 108.Pq Dv ISTXT 109for executables. 110On UFS-based file systems (FFS, LFS) the sticky 111bit may only be set upon directories. 112.Pp 113If mode 114.Dv ISTXT 115(the `sticky bit') is set on a directory, 116an unprivileged user may not delete or rename 117files of other users in that directory. 118The sticky bit may be 119set by any user on a directory which the user owns or has appropriate 120permissions. 121For more details of the properties of the sticky bit, see 122.Xr sticky 8 . 123.Pp 124If mode ISUID (set UID) is set on a directory, 125and the MNT_SUIDDIR option was used in the mount of the file system, 126then the owner of any new files and sub-directories 127created within this directory are set 128to be the same as the owner of that directory. 129If this function is enabled, new directories will inherit 130the bit from their parents. 131Execute bits are removed from 132the file, and it will not be given to root. 133This behavior does not change the 134requirements for the user to be allowed to write the file, but only the eventual 135owner after it has been created. 136Group inheritance is not affected. 137.Pp 138This feature is designed for use on fileservers serving PC users via 139ftp, SAMBA, or netatalk. 140It provides security holes for shell users and as 141such should not be used on shell machines, especially on home directories. 142This option requires the SUIDDIR 143option in the kernel to work. 144Only UFS file systems support this option. 145For more details of the suiddir mount option, see 146.Xr mount 8 . 147.Pp 148Writing or changing the owner of a file 149turns off the set-user-id and set-group-id bits 150unless the user is the super-user. 151This makes the system somewhat more secure 152by protecting set-user-id (set-group-id) files 153from remaining set-user-id (set-group-id) if they are modified, 154at the expense of a degree of compatibility. 155.Sh RETURN VALUES 156.Rv -std 157.Sh ERRORS 158The 159.Fn chmod 160system call 161will fail and the file mode will be unchanged if: 162.Bl -tag -width Er 163.It Bq Er ENOTDIR 164A component of the path prefix is not a directory. 165.It Bq Er ENAMETOOLONG 166A component of a pathname exceeded 255 characters, 167or an entire path name exceeded 1023 characters. 168.It Bq Er ENOENT 169The named file does not exist. 170.It Bq Er EACCES 171Search permission is denied for a component of the path prefix. 172.It Bq Er ELOOP 173Too many symbolic links were encountered in translating the pathname. 174.It Bq Er EPERM 175The effective user ID does not match the owner of the file and 176the effective user ID is not the super-user. 177.It Bq Er EPERM 178The effective user ID is not the super-user, the effective user ID do match the 179owner of the file, but the group ID of the file does not match the effective 180group ID nor one of the supplementary group IDs. 181.It Bq Er EPERM 182The named file has its immutable or append-only flag set, see the 183.Xr chflags 2 184manual page for more information. 185.It Bq Er EROFS 186The named file resides on a read-only file system. 187.It Bq Er EFAULT 188The 189.Fa path 190argument 191points outside the process's allocated address space. 192.It Bq Er EIO 193An I/O error occurred while reading from or writing to the file system. 194.It Bq Er EFTYPE 195The effective user ID is not the super-user, the mode includes the sticky bit 196.Dv ( S_ISVTX ) , 197and path does not refer to a directory. 198.El 199.Pp 200The 201.Fn fchmod 202system call will fail if: 203.Bl -tag -width Er 204.It Bq Er EBADF 205The descriptor is not valid. 206.It Bq Er EINVAL 207The 208.Fa fd 209argument 210refers to a socket, not to a file. 211.It Bq Er EROFS 212The file resides on a read-only file system. 213.It Bq Er EIO 214An I/O error occurred while reading from or writing to the file system. 215.El 216.Sh SEE ALSO 217.Xr chmod 1 , 218.Xr chflags 2 , 219.Xr chown 2 , 220.Xr open 2 , 221.Xr stat 2 , 222.Xr sticky 8 223.Sh STANDARDS 224The 225.Fn chmod 226system call is expected to conform to 227.St -p1003.1-90 , 228except for the return of 229.Er EFTYPE 230and the use of 231.Dv S_ISTXT . 232.Sh HISTORY 233The 234.Fn chmod 235function appeared in 236.At v7 . 237The 238.Fn fchmod 239system call appeared in 240.Bx 4.2 . 241The 242.Fn lchmod 243system call appeared in 244.Fx 3.0 . 245