1.\" $NetBSD: chmod.2,v 1.40 2012/03/04 11:58:31 wiz Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)chmod.2 8.1 (Berkeley) 6/4/93 31.\" 32.Dd March 3, 2012 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 51The function 52.Fn chmod 53sets the file permission bits 54of the file 55specified by the pathname 56.Fa path 57to 58.Fa mode . 59.Fn fchmod 60sets the permission bits of the specified 61file descriptor 62.Fa fd . 63.Fn lchmod 64is like 65.Fn chmod 66except in the case where the named file is a symbolic link, 67in which case 68.Fn lchmod 69sets the permission bits of the link, 70while 71.Fn chmod 72sets the bits of the file the link references. 73.Fn chmod 74verifies that the process owner (user) either owns 75the file specified by 76.Fa path 77(or 78.Fa fd ) , 79or 80is the super-user. 81A mode is created from 82.Em or'd 83permission bit masks 84defined 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 */ 91 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 */ 96 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 */ 101 102#define S_ISUID 0004000 /* set user id on execution */ 103#define S_ISGID 0002000 /* set group id on execution */ 104#define S_ISVTX 0001000 /* sticky bit */ 105.Ed 106.Pp 107The mode 108.Dv ISVTX 109(the 110.Sq sticky bit ) 111can be set on regular files, but has no effect. 112For historical reasons this can be done only by the super-user. 113.Pp 114If mode 115.Dv ISVTX 116(the 117.Sq sticky bit ) 118is set on a directory, 119an unprivileged user may not delete or rename 120files of other users in that directory. 121The sticky bit may be set by any user on a directory which the user 122owns or has appropriate permissions. 123.Pp 124For more information about the history and properties of the sticky bit, see 125.Xr sticky 7 . 126.Pp 127Changing the owner of a file 128turns off the set-user-id and set-group-id bits; 129writing to a file 130turns off the set-user-id and set-group-id bits 131unless the user is the super-user. 132This makes the system somewhat more secure 133by protecting set-user-id (set-group-id) files 134from remaining set-user-id (set-group-id) if they are modified, 135at the expense of a degree of compatibility. 136.Sh RETURN VALUES 137Upon successful completion, a value of 0 is returned. 138Otherwise, a value of \-1 is returned and 139.Va errno 140is set to indicate the error. 141.Sh ERRORS 142.Fn chmod 143and 144.Fn lchmod 145will fail and the file mode will be unchanged if: 146.Bl -tag -width Er 147.It Bq Er EACCES 148Search permission is denied for a component of the path prefix. 149.It Bq Er EFAULT 150.Fa path 151points outside the process's allocated address space. 152.It Bq Er EFTYPE 153The effective user ID is not the super-user, the 154.Fa mode 155includes the sticky bit 156.Pq Dv S_ISVTX , 157and 158.Fa path 159does not refer to a directory. 160.It Bq Er EIO 161An I/O error occurred while reading from or writing to the file system. 162.It Bq Er ELOOP 163Too many symbolic links were encountered in translating the pathname. 164.It Bq Er ENAMETOOLONG 165A component of a pathname exceeded 166.Brq Dv NAME_MAX 167characters, or an entire path name exceeded 168.Brq Dv PATH_MAX 169characters. 170.It Bq Er ENOENT 171The named file does not exist. 172.It Bq Er ENOTDIR 173A component of the path prefix is not a directory. 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; or 177the mode includes the setgid bit 178.Pq Dv S_ISGID 179but the file's group is neither the effective group ID nor is it in the 180group access list. 181.It Bq Er EROFS 182The named file resides on a read-only file system. 183.El 184.Pp 185.Fn fchmod 186will fail if: 187.Bl -tag -width Er 188.It Bq Er EBADF 189The descriptor is not valid. 190.It Bq Er EFTYPE 191The effective user ID is not the super-user, the 192.Fa mode 193includes the sticky bit 194.Pq Dv S_ISVTX , 195and 196.Fa fd 197does not refer to a directory. 198.It Bq Er EINVAL 199.Fa fd 200refers to a socket, not to a file. 201.It Bq Er EIO 202An I/O error occurred while reading from or writing to the file system. 203.It Bq Er EPERM 204The effective user ID does not match the owner of the file and 205the effective user ID is not the super-user; or 206the mode includes the setgid bit 207.Pq Dv S_ISGID 208but the file's group is neither the effective group ID nor is it in the 209group access list. 210.It Bq Er EROFS 211The file resides on a read-only file system. 212.El 213.Sh SEE ALSO 214.Xr chmod 1 , 215.Xr chflags 2 , 216.Xr chown 2 , 217.Xr open 2 , 218.Xr stat 2 , 219.Xr getmode 3 , 220.Xr setmode 3 , 221.Xr sticky 7 , 222.Xr symlink 7 223.Sh STANDARDS 224The 225.Fn chmod 226function conforms to 227.St -p1003.1-90 . 228.Sh HISTORY 229The 230.Fn fchmod 231function call 232appeared in 233.Bx 4.2 . 234The 235.Fn lchmod 236function call appeared in 237.Nx 1.3 . 238