1.\" $OpenBSD: chmod.2,v 1.14 2007/05/31 19:19:32 jmc Exp $ 2.\" $NetBSD: chmod.2,v 1.7 1995/02/27 12:32:06 cgd Exp $ 3.\" 4.\" Copyright (c) 1980, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)chmod.2 8.1 (Berkeley) 6/4/93 32.\" 33.Dd $Mdocdate: May 31 2007 $ 34.Dt CHMOD 2 35.Os 36.Sh NAME 37.Nm chmod , 38.Nm fchmod 39.Nd change mode of file 40.Sh SYNOPSIS 41.Fd #include <sys/types.h> 42.Fd #include <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.Sh DESCRIPTION 48The function 49.Fn chmod 50sets the file permission bits of the file specified by the pathname 51.Fa path 52to 53.Fa mode . 54.Fn fchmod 55sets the permission bits of the specified file descriptor 56.Fa fd . 57.Fn chmod 58verifies that the process owner (user) either owns the file specified by 59.Fa path 60(or 61.Fa fd ) , 62or is the superuser. 63A mode is created from 64.Em or'd 65permission bit masks defined in 66.Aq Pa sys/stat.h : 67.Bd -literal -offset indent 68#define S_IRWXU 0000700 /* RWX mask for owner */ 69#define S_IRUSR 0000400 /* R for owner */ 70#define S_IWUSR 0000200 /* W for owner */ 71#define S_IXUSR 0000100 /* X for owner */ 72 73#define S_IRWXG 0000070 /* RWX mask for group */ 74#define S_IRGRP 0000040 /* R for group */ 75#define S_IWGRP 0000020 /* W for group */ 76#define S_IXGRP 0000010 /* X for group */ 77 78#define S_IRWXO 0000007 /* RWX mask for other */ 79#define S_IROTH 0000004 /* R for other */ 80#define S_IWOTH 0000002 /* W for other */ 81#define S_IXOTH 0000001 /* X for other */ 82 83#define S_ISUID 0004000 /* set user id on execution */ 84#define S_ISGID 0002000 /* set group id on execution */ 85#define S_ISVTX 0001000 /* save swapped text even after use */ 86.Ed 87.Pp 88If mode 89.Dv ISVTX 90(the 91.Em sticky bit ) 92is set on a file, it is ignored. 93.Pp 94If mode 95.Dv ISVTX 96(the 97.Em sticky bit ) 98is set on a directory, an unprivileged user may not delete or rename 99files of other users in that directory. 100The sticky bit may be set by any user on a directory which the user owns 101or has appropriate permissions. 102For more details of the properties of the sticky bit, see 103.Xr sticky 8 . 104.Pp 105Writing or changing the owner of a file turns off the set-user-ID and 106set-group-ID bits unless the user is the superuser. 107This makes the system somewhat more secure by protecting 108set-user-ID (set-group-ID) files from remaining set-user-ID (set-group-ID) 109if they are modified, at the expense of a degree of compatibility. 110.Sh RETURN VALUES 111Upon successful completion, a value of 0 is returned. 112Otherwise, a value of \-1 is returned and 113.Va errno 114is set to indicate the error. 115.Sh ERRORS 116.Fn chmod 117will fail and the file mode will be unchanged if: 118.Bl -tag -width Er 119.It Bq Er ENOTDIR 120A component of the path prefix is not a directory. 121.It Bq Er ENAMETOOLONG 122A component of a pathname exceeded 123.Dv {NAME_MAX} 124characters, or an entire path name exceeded 125.Dv {PATH_MAX} 126characters. 127.It Bq Er ENOENT 128The named file does not exist. 129.It Bq Er EACCES 130Search permission is denied for a component of the path prefix. 131.It Bq Er EINVAL 132.Fa mode 133contains bits other than the file type and those described above. 134.It Bq Er ELOOP 135Too many symbolic links were encountered in translating the pathname. 136.It Bq Er EPERM 137The effective user ID does not match the owner of the file and 138the effective user ID is not the superuser. 139.It Bq Er EROFS 140The named file resides on a read-only file system. 141.It Bq Er EFAULT 142.Fa path 143points outside the process's allocated address space. 144.It Bq Er EIO 145An I/O error occurred while reading from or writing to the file system. 146.El 147.Pp 148.Fn fchmod 149will fail and the file mode will be unchanged if: 150.Bl -tag -width Er 151.It Bq Er EBADF 152The descriptor is not valid. 153.It Bq Er EINVAL 154.Fa fd 155refers to a socket, not to a file. 156.It Bq Er EINVAL 157.Fa mode 158contains bits other than the file type and those described above. 159.It Bq Er EROFS 160The file resides on a read-only file system. 161.It Bq Er EIO 162An I/O error occurred while reading from or writing to the file system. 163.El 164.Sh SEE ALSO 165.Xr chmod 1 , 166.Xr chown 2 , 167.Xr open 2 , 168.Xr stat 2 , 169.Xr sticky 8 170.Sh STANDARDS 171The 172.Fn chmod 173function is expected to conform to 174.St -p1003.1-88 . 175.Sh HISTORY 176The 177.Fn fchmod 178function call appeared in 179.Bx 4.2 . 180