1.\" $NetBSD: chmod.2,v 1.38 2011/10/12 22:46:36 christos 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 October 11, 2011 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 a regular file by the super-user, but has no effect. 112.Pp 113If mode 114.Dv ISVTX 115(the 116.Sq sticky bit ) 117is set on a directory, 118an unprivileged user may not delete or rename 119files of other users in that directory. 120The sticky bit may be set by any user on a directory which the user 121owns or has appropriate permissions. 122.Pp 123For more information about the history and properties of the sticky bit, see 124.Xr sticky 7 . 125.Pp 126Changing the owner of a file 127turns off the set-user-id and set-group-id bits; 128writing to a file 129turns off the set-user-id and set-group-id bits 130unless the user is the super-user. 131This makes the system somewhat more secure 132by protecting set-user-id (set-group-id) files 133from remaining set-user-id (set-group-id) if they are modified, 134at the expense of a degree of compatibility. 135.Sh RETURN VALUES 136Upon successful completion, a value of 0 is returned. 137Otherwise, a value of \-1 is returned and 138.Va errno 139is set to indicate the error. 140.Sh ERRORS 141.Fn chmod 142and 143.Fn lchmod 144will fail and the file mode will be unchanged if: 145.Bl -tag -width Er 146.It Bq Er ENOTDIR 147A component of the path prefix is not a directory. 148.It Bq Er ENAMETOOLONG 149A component of a pathname exceeded 150.Brq Dv NAME_MAX 151characters, or an entire path name exceeded 152.Brq Dv PATH_MAX 153characters. 154.It Bq Er ENOENT 155The named file does not exist. 156.It Bq Er EACCES 157Search permission is denied for a component of the path prefix. 158.It Bq Er ELOOP 159Too many symbolic links were encountered in translating the pathname. 160.It Bq Er EPERM 161The effective user ID does not match the owner of the file and 162the effective user ID is not the super-user. 163.It Bq Er EPERM 164The mode includes the setgid bit 165.Pq Dv S_ISGID 166but the file's group is neither the effective group ID nor is it in the 167group access list. 168.It Bq Er EROFS 169The named file resides on a read-only file system. 170.It Bq Er EFAULT 171.Fa path 172points outside the process's allocated address space. 173.It Bq Er EIO 174An I/O error occurred while reading from or writing to the file system. 175.It Bq Er EFTYPE 176The effective user ID is not the super-user, the 177.Fa mode 178includes the sticky bit 179.Pq Dv S_ISVTX , 180and 181.Fa path 182does not refer to a directory. 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 EINVAL 191.Fa fd 192refers to a socket, not to a file. 193.It Bq Er EPERM 194The effective user ID does not match the owner of the file and 195the effective user ID is not the super-user. 196.It Bq Er EPERM 197The mode includes the setgid bit 198.Pq Dv S_ISGID 199but the file's group is neither the effective group ID nor is it in the 200group access list. 201.It Bq Er EROFS 202The file resides on a read-only file system. 203.It Bq Er EIO 204An I/O error occurred while reading from or writing to the file system. 205.It Bq Er EFTYPE 206The effective user ID is not the super-user, the 207.Fa mode 208includes the sticky bit 209.Pq Dv S_ISVTX , 210and 211.Fa fd 212does not refer to a directory. 213.El 214.Sh SEE ALSO 215.Xr chmod 1 , 216.Xr chflags 2 , 217.Xr chown 2 , 218.Xr open 2 , 219.Xr stat 2 , 220.Xr getmode 3 , 221.Xr setmode 3 , 222.Xr sticky 7 , 223.Xr symlink 7 224.Sh STANDARDS 225The 226.Fn chmod 227function conforms to 228.St -p1003.1-90 . 229.Sh HISTORY 230The 231.Fn fchmod 232function call 233appeared in 234.Bx 4.2 . 235The 236.Fn lchmod 237function call appeared in 238.Nx 1.3 . 239