1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. 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: src/lib/libc/sys/chmod.2,v 1.16.2.7 2001/12/14 18:34:00 ru Exp $ 30.\" 31.Dd August 9, 2009 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 dirfd" "const char *path" "mode_t mode" "int flags" 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 61function 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 70function follows symbolic links to operate on the target of the link 71rather than the link itself. 72.Pp 73The 74.Fa lchmod 75function is similar to 76.Fn chmod 77but does not follow symbolic links. 78.Pp 79The 80.Fn fchmodat 81function is equivalent to the 82.Fn chmod 83or 84.Fn lchmod 85functions except in the case where the 86.Fa path 87specifies a relative path. 88In this case the file to be opened is determined relative to the directory 89associated with the file descriptor 90.Fa dirfd 91instead of the current working directory. 92If 93.Fn fchmodat 94is passed the special value 95.Dv AT_FDCWD 96in the 97.Fa dirfd 98parameter, the current working directory is used 99and the behavior is identical to a call to 100.Fn chmod 101or 102.Fn lchmod . 103.Pp 104A mode is created from 105.Em or'd 106permission bit masks 107defined in 108.In sys/stat.h : 109.Pp 110.Bd -literal -offset indent -compact 111#define S_IRWXU 0000700 /* RWX mask for owner */ 112#define S_IRUSR 0000400 /* R for owner */ 113#define S_IWUSR 0000200 /* W for owner */ 114#define S_IXUSR 0000100 /* X for owner */ 115 116#define S_IRWXG 0000070 /* RWX mask for group */ 117#define S_IRGRP 0000040 /* R for group */ 118#define S_IWGRP 0000020 /* W for group */ 119#define S_IXGRP 0000010 /* X for group */ 120 121#define S_IRWXO 0000007 /* RWX mask for other */ 122#define S_IROTH 0000004 /* R for other */ 123#define S_IWOTH 0000002 /* W for other */ 124#define S_IXOTH 0000001 /* X for other */ 125 126#define S_ISUID 0004000 /* set user id on execution */ 127#define S_ISGID 0002000 /* set group id on execution */ 128#define S_ISVTX 0001000 /* sticky bit */ 129#ifndef _POSIX_SOURCE 130#define S_ISTXT 0001000 131#endif 132.Ed 133.Pp 134The 135.Dx 136VM system totally ignores the sticky bit 137.Pq Dv ISVTX 138for executables. 139On UFS-based filesystems (FFS, MFS, LFS) the sticky 140bit may only be set upon directories. 141.Pp 142If mode 143.Dv ISVTX 144(the `sticky bit') is set on a directory, 145an unprivileged user may not delete or rename 146files of other users in that directory. 147The sticky bit may be 148set by any user on a directory which the user owns or has appropriate 149permissions. 150For more details of the properties of the sticky bit, see 151.Xr sticky 8 . 152.Pp 153If mode ISUID (set UID) is set on a directory, 154and the MNT_SUIDDIR option was used in the mount of the filesystem, 155then the owner of any new files and sub-directories 156created within this directory are set 157to be the same as the owner of that directory. 158If this function is enabled, new directories will inherit 159the bit from their parents. Execute bits are removed from 160the file, and it will not be given to root. 161This behavior does not change the 162requirements for the user to be allowed to write the file, but only the eventual 163owner after it has been created. 164Group inheritance is not affected. 165.Pp 166This feature is designed for use on fileservers serving PC users via 167ftp or SAMBA. 168It provides security holes for shell users and as 169such should not be used on shell machines, especially on home directories. 170This option requires the SUIDDIR 171option in the kernel to work. 172Only UFS filesystems support this option. 173For more details of the suiddir mount option, see 174.Xr mount 8 . 175.Pp 176Writing or changing the owner of a file 177turns off the set-user-id and set-group-id bits 178unless the user is the super-user. 179This makes the system somewhat more secure 180by protecting set-user-id (set-group-id) files 181from remaining set-user-id (set-group-id) if they are modified, 182at the expense of a degree of compatibility. 183.Pp 184The values for the 185.Fa flags 186are constructed by a bitwise-inclusive OR of flags from the following list, 187defined in 188.In fcntl.h : 189.Bl -tag -width indent 190.It Dv AT_SYMLINK_NOFOLLOW 191If 192.Fa path 193names a symbolic link, the mode of the symbolic link is changed. 194.El 195.Sh RETURN VALUES 196.Rv -std 197.Sh ERRORS 198.Fn Chmod , 199.Fn lchmod 200and 201.Fn fchmodat 202will fail and the file mode will be unchanged if: 203.Bl -tag -width Er 204.It Bq Er ENOTDIR 205A component of the path prefix or 206.Fa dirfd 207is not a directory. 208.It Bq Er ENAMETOOLONG 209A component of a pathname exceeded 255 characters, 210or an entire path name exceeded 1023 characters. 211.It Bq Er ENOENT 212The named file does not exist. 213.It Bq Er EACCES 214Search permission is denied for a component of the path prefix. 215.It Bq Er ELOOP 216Too many symbolic links were encountered in translating the pathname. 217.It Bq Er EPERM 218The effective user ID does not match the owner of the file and 219the effective user ID is not the super-user. 220.It Bq Er EROFS 221The named file resides on a read-only file system. 222.It Bq Er EFAULT 223.Fa Path 224points outside the process's allocated address space. 225.It Bq Er EIO 226An I/O error occurred while reading from or writing to the file system. 227.It Bq Er EFTYPE 228An attempt was made to set the sticky bit upon an executable. 229.El 230.Pp 231.Fn Fchmod 232will fail if: 233.Bl -tag -width Er 234.It Bq Er EBADF 235The descriptor is not valid. 236.It Bq Er EINVAL 237.Fa fd 238refers to a socket, not to a file. 239.It Bq Er EROFS 240The file resides on a read-only file system. 241.It Bq Er EIO 242An I/O error occurred while reading from or writing to the file system. 243.El 244.Sh SEE ALSO 245.Xr chmod 1 , 246.Xr chown 2 , 247.Xr open 2 , 248.Xr stat 2 , 249.Xr sticky 8 250.Sh STANDARDS 251The 252.Fn chmod 253function call is expected to conform to 254.St -p1003.1-90 , 255except for the return of 256.Er EFTYPE 257and the use of 258.Dv S_ISTXT . 259.Sh HISTORY 260A 261.Fn chmod 262function call appeared in 263.At v7 . 264The 265.Fn fchmod 266function call 267appeared in 268.Bx 4.2 . 269The 270.Fn lchmod 271function call appeared in 272.Fx 3.0 . 273.Pp 274The 275.Fn fchmodat 276system call appeared in 277.Dx 2.3 . 278